CN104883195B - Harmonic feedback based terahertz radar signal transmitter and transmitting method - Google Patents

Abstract

The invention discloses a harmonic feedback based terahertz radar signal transmitter and a transmitting method. The transmitter comprises a radar signal generation module, a clock control module, a digital pre-distortion module, a digital up-conversion module, a digital-to-analog conversion module, a frequency mixing module, a terahertz frequency multiplication and power amplification module, a harmonic feedback module and a radar antenna. The transmitting method disclosed by the invention comprises the steps of generating signals, initializing a nonlinear compensation weight coefficient, acquiring nonlinear compensation signals, acquiring digital radar intermediate frequency signals, acquiring radio frequency signals, carrying out frequency multiplication and amplification, acquiring the harmonic signal power, updating the nonlinear compensation weight coefficient and transmitting terahertz signals after power amplification. According to the invention, nonlinear compensation is carried out on base band digital linear frequency-modulated signals by adopting the harmonic feedback module and the digital pre-distortion module, and the performance of the terahertz radar signal transmitter is improved. A digital pre-distortion technology in harmonic feedback is realized by adopting a high-speed field programmable gate array.

Description

Terahertz radar signal transmitter based on harmonic feedback and transmitting method

Technical Field

The invention belongs to the technical field of terahertz radars, and further relates to a terahertz radar signal transmitter and a transmitting method based on harmonic feedback in the technical field of terahertz radars. The invention adopts a high-speed Field Programmable Gate Array (FPGA) to realize a digital predistortion technology of harmonic feedback, and carries out nonlinear distortion compensation on a terahertz radar transmitting signal so as to solve the problem that the linear amplification range of a power amplifier in a terahertz radar signal transmitter is restricted and improve the performance of the terahertz radar signal transmitter.

Background

In a terahertz radar communication system, due to the fact that enough action distance is obtained, the transmission power of a transmitter needs to be increased, the working point of a power amplifier is close to a saturation region, nonlinear distortion is generated on an output signal of the power amplifier, in-band distortion and out-of-band spectrum expansion of a terahertz radar signal are caused, and the performance of the transmitter is reduced.

The power amplifier in the terahertz radar signal transmitter generally adopts a gunn diode, the output power of the gunn diode can reach 50 milliwatts, but the output efficiency can only reach about 15%. The transmitting power of the existing terahertz radar signal transmitter is at least 10 milliwatts, the transmitting power of the transmitter is difficult to achieve after multistage frequency multiplication amplification, nonlinear distortion is easy to generate for a linear frequency modulation signal generated by the transmitter, and certain influence is brought to subsequent signal processing. Under the background, research on the nonlinear compensation technology of the power amplifier in the terahertz radar signal transmitter is also receiving attention, and the nonlinear compensation technology becomes one of the key technologies of the terahertz radar signal transmitter.

A distortion compensation device and a power amplifier device are disclosed in a patent "distortion compensation device and power amplifier device" filed by fuskato corporation (patent application No. 200910002658.5, publication No. CN 101499781A). The main devices of this patent application are: the device comprises an adaptive distortion compensation unit, an adaptive equalizer, a memory and a control unit, wherein the device utilizes an adaptive algorithm to carry out nonlinear compensation on a nonlinear distortion circuit signal. The device and the method disclosed in the patent application have the defects that the range of nonlinear compensation for signals is small, the adaptive equalizer is realized by a digital filter, the terahertz radar signal is a high-frequency and high-bandwidth signal, and the common digital filter is difficult to meet the requirement, so that a digital predistortion system based on a common digital circuit is difficult to be widely applied to occasions of processing high-frequency and high-bandwidth signals of the terahertz radar.

A digital predistortion method and apparatus based on a feedback loop is disclosed in "a predistortion processing method and apparatus" of the university of electronic technology application (patent application No. 201110075953.0, publication No. CN 102271106A). The device comprises a preprocessing unit, a main predistortion unit, a downlink modulation link, a power amplifier, a feedback loop, a main predistortion unit change-over switch, a power amplifier change-over switch and a control unit, wherein the main predistortion unit change-over switch is connected with the main predistortion unit in parallel, the power amplifier change-over switch is connected with the power amplifier in parallel, and the feedback loop is formed by connecting an uplink demodulation link and an auxiliary predistortion unit in series. The method of the patent application enables the feedback signal to be compensated by adding predistortion processing in the feedback loop, and eliminates distortion caused by the feedback loop. The device and the method disclosed by the patent application have the defects that a hardware circuit connected with a power amplifier is relatively complex to realize, the transmission power requirement of a terahertz radar signal transmitter cannot be met, the signal bandwidth capable of being processed is not large enough, the effect of nonlinear compensation on radar linear frequency modulation signals is not obvious, and the nonlinear distortion caused in the terahertz radar signal transmitter is still obvious on subsequent signal processing.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a terahertz radar signal transmitter based on harmonic feedback and a transmitting method thereof, and the invention adopts a high-speed Field Programmable Gate Array (FPGA) to realize the digital predistortion technology of the harmonic feedback, and can realize the nonlinear compensation of a power amplifier in the terahertz radar signal transmitter.

In order to achieve the technical purpose, the invention is realized by adopting the following technical scheme.

The first technical scheme is as follows:

a terahertz radar signal transmitter based on harmonic feedback is characterized by comprising: the terahertz frequency doubling power amplifier comprises a radar signal generation module, a clock control module, a digital predistortion module, a digital up-conversion module, a digital-to-analog conversion module, a frequency mixing module, a terahertz frequency doubling power amplification module, a harmonic feedback module and a radar antenna; all modules are connected through a bus; wherein,

the radar signal generation module is used for generating a baseband digital linear frequency modulation signal and carrying out data low-pass filtering on the baseband digital linear frequency modulation signal; and generating a local oscillation signal;

the clock control module is used for generating a fixed clock period and controlling the input and the output of the baseband digital linear frequency modulation signal;

the digital predistortion module is used for carrying out nonlinear compensation on the baseband digital linear frequency modulation signal after the low-pass filtering to obtain a nonlinear compensation signal;

the digital up-conversion module is used for up-regulating the frequency of the nonlinear compensation signal to a signal of a higher frequency band to obtain a digital radar intermediate frequency signal;

the digital-to-analog conversion module is used for converting the digital radar intermediate frequency signal into an analog linear frequency modulation signal;

the frequency mixing module is used for modulating the central frequency of the analog linear frequency modulation signal to obtain a radio frequency signal;

the terahertz frequency doubling power amplification module is used for performing multi-stage frequency doubling and power amplification on the radio frequency signal to obtain a terahertz radar signal after power amplification;

the harmonic feedback module is used for extracting a harmonic signal in the terahertz radar signal after power amplification and feeding the power of the harmonic signal back to the digital predistortion module;

the radar antenna is used for transmitting the terahertz radar signals after power amplification.

The second technical scheme is as follows:

a terahertz radar signal transmitting method based on harmonic feedback is based on the terahertz radar signal transmitter based on harmonic feedback, and is characterized by comprising the following steps:

(1) generating a signal:

1a) performing digital low-pass filtering on the baseband digital linear frequency modulation signal generated by the radar signal generation module to obtain a baseband digital linear frequency modulation signal after low-pass filtering;

1b) under the control of the clock control module, the digital predistortion module receives the baseband digital chirp signals after the low-pass filtering, and performs double extraction on baseband frequency spectrum data of the baseband digital chirp signals after the low-pass filtering, namely baseband orthogonal digital signals, so as to respectively obtain real part signals of the baseband orthogonal digital signals and imaginary part signals of the baseband orthogonal digital signals.

(2) Initializing nonlinear compensation weight coefficients:

2a) calculating an initialized nonlinear compensation weight coefficient and sending the weight coefficient into a weight coefficient updating module;

2b) the weight coefficient updating module transmits the initialized nonlinear compensation weight coefficients to the digital predistortion calculation module.

(3) Obtaining a nonlinear compensation signal:

3a) the data predistortion calculation module takes the received real part signal of the baseband orthogonal digital signal and the imaginary part signal of the baseband orthogonal digital signal as data of a first channel;

3b) under the control of the clock control module, delaying the data of the first channel by one clock cycle to obtain the data of a second channel, delaying the data of the second channel by one clock cycle to obtain the data of a third channel, delaying the data of the third channel by one clock cycle to obtain the data of a fourth channel, and delaying the data of the fourth channel by one clock cycle to obtain the data of a fifth channel;

3c) under the control of the clock control module, 5-channel pre-compensated data are obtained according to the following formula:

wherein x is_m(n) represents data precompensated for the mth of the five channels, n represents the number of sampling points of the baseband digital chirp signal generated by the radar signal generation module, x (n-m +1) represents data for the mth of the five channels,k represents the total number of times of compensating the mth channel data, K is a positive integer greater than or equal to 3, and w_mkRepresenting a weight coefficient for performing K-th compensation on the mth channel in the five channels, wherein the K is a positive integer in the value range of 1-K, | · | represents the modulo operation on data;

3d) under the control of the clock control module, the compensation data of 5 channels are obtained according to the following formula:

y_m(n)＝x(n-m+1)x_m(n)

wherein, y_m(n) represents compensation data of an mth channel of the five channels, n represents the number of sampling points of the baseband digital chirp signal generated by the radar signal generation module, x (n-m +1) represents data of the mth channel of the five channels, and x_m(n) data representing the m-th channel precompensation among the five channels;

3e) under the control of the clock control module, a nonlinear compensation signal is obtained according to the following formula:

wherein y (n) represents a nonlinear compensation signal, n represents the number of sampling points of the baseband digital chirp signal generated by the radar signal generation module, and M represents the total number of channels.

(4) Obtaining a digital radar intermediate frequency signal:

4a) under the control of the clock control module, the digital predistortion module sends the nonlinear compensation signal to the polyphase filtering module; the multi-phase filtering module carries out multi-phase filtering operation on the received nonlinear compensation signal to obtain a high-speed signal; performing double extraction on the high-rate signal to obtain an imaginary part signal and a real part signal of the high-rate signal;

4b) under the control of the clock control module, the half-phase filtering module receives the imaginary part signal of the high-speed signal and performs low-pass filtering on the imaginary part signal to obtain the imaginary part signal of the filtered high-speed signal;

4c) under the control of the clock control module, the shifting module receives the real part signal of the high-rate signal and shifts the real part signal to the right, wherein the bit number of the shifting is the bit number of the imaginary part signal of the high-rate signal, and the real part signal of the shifted high-rate signal is obtained;

4d) under the control of the clock control module, transmitting the imaginary part signal of the filtered high-speed signal and the real part signal of the shifted high-speed signal to the digital orthogonal transformation inverse process module; the digital orthogonal transformation inverse process module multiplies the real part signal of the high-speed signal after the displacement by-1, and adds the real part signal of the high-speed signal after the filtering to obtain a high-speed radar digital linear frequency modulation signal;

4e) and under the control of the clock control module, sending the high-speed radar digital linear frequency modulation signal to the binary code conversion module to obtain a digital radar intermediate frequency signal.

(5) Obtaining a radio frequency signal:

5a) the digital-to-analog conversion module converts the digital radar intermediate frequency signal into an analog linear frequency modulation signal through a D/A converter;

5b) and the frequency mixing module is used for mixing the analog linear frequency modulation signal with the local oscillator signal to obtain a radio frequency signal.

(6) Frequency doubling amplification:

6a) sending the radio frequency signal to a frequency multiplier module to obtain a terahertz radar signal;

6b) and sending the terahertz radar signal to a power amplifier module in the terahertz frequency doubling power amplification module to obtain a terahertz radar signal z (t) after power amplification.

(7) Obtaining the power of the harmonic signal:

7a) sending the terahertz radar signal z (t) subjected to power amplification to a harmonic filter module to obtain a harmonic signal;

7b) sending the harmonic signal to a power amplifier module in a harmonic feedback module to obtain a harmonic signal after power amplification;

7c) and sending the harmonic signal after power amplification to an integrator module to obtain the harmonic signal power.

(8) Updating the nonlinear compensation weight coefficient:

8a) the harmonic signal power is fed back to a weight coefficient updating module, and an updated nonlinear compensation weight coefficient is calculated according to the harmonic signal power;

8b) the weight coefficient updating module sends the updated nonlinear compensation weight coefficient obtained by calculation to the digital predistortion calculation module.

(9) Transmitting the terahertz radar signal after power amplification:

the terahertz radar signal after power amplification is transmitted by the radar antenna.

Compared with the prior art, the invention has the following advantages:

firstly, the harmonic feedback module is introduced into the terahertz radar signal transmitter, so that the nonlinearity compensation precision of the digital predistortion module on the terahertz radar transmission signal is improved, and the power of the output signal of the terahertz radar signal transmitter is greatly increased.

Thirdly, the method of the invention adopts the high-speed field programmable gate array to realize the digital predistortion technology of harmonic feedback, carries out nonlinear compensation on the baseband digital linear frequency modulation signal, improves the effective bandwidth of the baseband digital linear frequency modulation signal and overcomes the defect of low bandwidth when the baseband digital linear frequency modulation signal is processed in the prior art.

Drawings

The invention is described in further detail below with reference to the following description of the drawings and the detailed description.

FIG. 1 is a block diagram of a terahertz radar signal transmitter of the present invention;

FIG. 2 is a flow chart of a terahertz radar signal transmission method of the present invention;

FIG. 3 is a schematic diagram of a digital pre-distortion step in the terahertz radar signal transmitting method according to the present invention;

fig. 4 is a schematic diagram of a polyphase filtering operation step in the terahertz radar signal transmitting method according to the present invention.

Detailed Description

Referring to fig. 1, the terahertz radar signal transmitter based on harmonic feedback of the present invention includes a radar signal generation module, a clock control module, a digital predistortion module, a digital up-conversion module, a digital-to-analog conversion module, a frequency mixing module, a terahertz frequency doubling power amplification module, a harmonic feedback module, and a radar antenna; wherein,

the radar signal generation module is used for generating a baseband digital chirp signal through the frequency source signal generator and carrying out digital low-pass filtering on the baseband digital chirp signal to obtain a baseband digital chirp signal after low-pass filtering; and performing digital-to-analog conversion and frequency multiplication on the baseband digital linear frequency modulation signal to obtain a local oscillation signal. In the embodiment of the invention, the frequency source signal generator adopts a Direct Digital Synthesizer (DDS); the center frequency of the local oscillator signal is 20 GHz.

And the clock control module is used for designing a clock period and controlling the input and the output of the baseband digital linear frequency modulation signal. In the embodiment of the invention, the clock control module is realized in an FPGA chip.

The digital predistortion module is used for carrying out nonlinear compensation on the baseband digital linear frequency modulation signal after the low-pass filtering; the digital pre-distortion compensation method comprises a weight coefficient updating module and a digital pre-distortion calculation module; the weight coefficient updating module provides a nonlinear compensation weight coefficient for the baseband digital linear frequency modulation signal after low-pass filtering, and is used for dynamically updating the nonlinear compensation weight coefficient in real time; the digital predistortion calculation module is used for receiving and processing the baseband digital linear frequency modulation signal after the low-pass filtering and the data generated by the weight coefficient updating module to obtain a nonlinear compensation signal, so as to realize the nonlinear compensation of the baseband digital linear frequency modulation signal after the low-pass filtering. In the embodiment of the invention, the digital predistortion module is realized in an FRGA chip.

The digital up-conversion module is used for up-regulating the frequency of the nonlinear compensation signal to a signal of a higher frequency band to obtain a digital radar intermediate frequency signal; the device comprises a multiphase filter module, a half-phase filter module, a shift module, a digital orthogonal transformation inverse process module and a binary code conversion module; the multi-phase filtering module is used for carrying out multi-phase filtering operation on the nonlinear compensation signal to obtain a high-rate signal, and carrying out double extraction on the high-rate signal to obtain a real part signal of the high-rate signal and an imaginary part signal of the high-rate signal; the half-phase filtering module is used for carrying out low-pass filtering on the imaginary part signal of the high-speed signal to obtain the imaginary part signal of the filtered high-speed signal; the shifting module is used for shifting the real part signal of the high-rate signal to the right, and the number of the shifted bits is the number of bits of the imaginary part signal of the high-rate signal to obtain the shifted real part signal of the high-rate signal; the digital orthogonal transformation inverse process module is used for multiplying the real part signal of the high-speed signal after the displacement by-1 and adding the real part signal of the high-speed signal after the displacement and the imaginary part signal of the high-speed signal after the filtering to obtain a high-speed radar digital linear frequency modulation signal; the binary code conversion module is used for converting the high-speed radar digital linear frequency modulation signals into unsigned data to obtain digital radar intermediate frequency signals. In the embodiment of the invention, the binary code conversion module is realized by adopting a conversion chip 8192.

And the digital-to-analog conversion module is used for converting the digital radar intermediate frequency signal into an analog linear frequency modulation signal to realize digital-to-analog conversion.

And the frequency mixing module is used for modulating the central frequency of the analog linear frequency modulation signal to obtain a radio frequency signal.

The terahertz frequency doubling power amplification module is used for performing multi-stage frequency doubling and power amplification on the radio frequency signal to obtain a terahertz radar signal after power amplification; the frequency multiplier comprises a frequency multiplier module and a power amplifier module; the frequency multiplier module is used for amplifying the frequency of the radio frequency signal by six times to obtain a terahertz radar signal; and the power amplifier module of the terahertz frequency doubling power amplification module is used for increasing the power of the terahertz radar signal to obtain the terahertz radar signal after power amplification.

The harmonic feedback module is used for extracting a harmonic signal from the terahertz radar signal after power amplification and feeding the power of the harmonic signal back to the digital predistortion module; the harmonic filter module, the power amplifier module and the integrator module are included; the harmonic filter module is used for extracting a harmonic signal from the terahertz radar signal; the power amplifier module of the harmonic feedback module is used for increasing the power of the harmonic signal to obtain a harmonic signal after power amplification; the integrator module is used for obtaining the power of the harmonic signal. In the embodiment of the invention, the harmonic feedback module is realized in an FRGA chip.

And the radar antenna is used for transmitting the terahertz radar signals after power amplification.

Referring to the attached figure 2, the terahertz radar signal transmitting method based on harmonic feedback comprises the following specific steps:

step 1, generating a signal.

And the radar signal generation module modulates and generates a baseband digital linear frequency modulation signal through the frequency source signal generator, and performs digital low-pass filtering on the baseband digital linear frequency modulation signal to obtain the baseband digital linear frequency modulation signal after low-pass filtering. In the embodiment of the invention, the frequency of the baseband digital chirp signal is 360 MHz.

The digital predistortion module receives the baseband digital chirp signals after the low-pass filtering, and performs double extraction on baseband frequency spectrum data of the baseband digital chirp signals after the low-pass filtering under the control of the clock control module to respectively obtain real part signals of the baseband orthogonal digital signals and imaginary part signals of the baseband orthogonal digital signals.

And 2, initializing a nonlinear compensation weight coefficient.

Calculating to obtain initialized nonlinear compensation weight coefficients matched with the baseband orthogonal digital signals by an optimization method, transmitting the initialized nonlinear compensation weight coefficients to a weight coefficient updating module, and initializing data in the weight coefficient updating module; the weight coefficient updating module transmits the initialized nonlinear compensation weight coefficients to the digital predistortion calculation module through a data bus.

And 3, obtaining a nonlinear compensation signal.

Referring to FIG. 3, of FIG. 3The sign indicates that the non-linear compensation weight coefficient is multiplied by the channel data,the symbols represent different channel data additions. The specific steps for obtaining the nonlinear compensation signal are as follows:

in the first step, the data predistortion calculation module takes the received real part signal of the baseband quadrature digital signal and the imaginary part signal of the baseband quadrature digital signal as data x (n) of a first channel.

And secondly, under the control of the clock control module, delaying the data of the first channel by one clock cycle to obtain the data x (n-1) of the second channel, delaying the data of the second channel by one clock cycle to obtain the data x (n-2) of the third channel, delaying the data of the third channel by one clock cycle to obtain the data x (n-3) of the fourth channel, and delaying the data of the fourth channel by one clock cycle to obtain the data x (n-4) of the fifth channel.

Thirdly, under the control of the clock control module, obtaining data of 5 channel precompensation according to the following formula:

wherein x is_m(n) represents data precompensated by the mth channel of the five channels, n represents the number of sampling points of the baseband digital chirp signal generated by the radar signal generation module, and x (n-m +1) represents data of the mth channel of the five channels; k represents the total number of times of compensating the mth channel data, is a positive integer greater than or equal to 3, and takes the value of K as 5 in the embodiment of the invention; w is a_mkThe weight coefficient for performing K-th compensation on the mth channel in the five channels is represented, wherein the K is a positive integer between 1 and K, and in the embodiment of the invention, K is a positive integer between 1 and 5; | · | represents the modulo operation on the data.

Fourthly, under the control of the clock control module, obtaining the compensation data of 5 channels according to the following formula:

y_m(n)＝x(n-m+1)x_m(n)

wherein, y_m(n) represents compensation data of an mth channel of the five channels, n represents the number of sampling points of the baseband digital chirp signal generated by the radar signal generation module, x (n-m +1) represents data of the mth channel of the five channels, and x_m(n) represents data pre-compensated for the mth channel of the five channels.

Specifically, in the embodiment of the present invention, taking the data x (n) of the first channel as an example, the weight coefficient w for the first compensation of the data x (n) of the first channel and the channel data₁₁Multiplying to obtain data of a first unit of a first channel; modulo and squaring data of the first channel to obtain | x (n) |²Weight coefficient w for second compensation with the channel data₁₂Multiplying to obtain data of a second unit of the first channel; modulo the data of the first channel and quadratically solving | x (n) luminance⁴Weight coefficient w for third compensation with the channel data₁₃Multiplying to obtain data of a third unit of the first channel; taking the modulus of the data of the first channel and solving for six times(ii) obtaining | x (n) & gtnon-⁶Weight coefficient w for fourth compensation with the channel data₁₄Multiplying to obtain the data of the fourth unit of the first channel; modulo the data of the first channel and solving the octave to obtain | x (n) |⁸Weight coefficient w for fourth compensation with the channel data₁₅Multiplying to obtain the data of the fifth unit of the first channel; summing the data of the five units of the first channel to obtain the pre-compensated data y of the first channel₁(n) of (a). And respectively carrying out the corresponding operation on the data of the other four channels to obtain the data of the precompensation of the other four channels.

Fifthly, under the control of the clock control module, obtaining a nonlinear compensation signal according to the following formula:

wherein y (n) represents the non-linear compensation signal, and in the embodiment of the invention, the frequency of y (n) is 360 MHz; n represents the number of sampling points of the baseband digital chirp signals generated by the radar signal generation module, and M represents the total number of channels.

And 4, acquiring a digital radar intermediate frequency signal.

Under the control of the clock control module, the digital predistortion module transmits the nonlinear compensation signal to the multiphase filter module to carry out multiphase filter operation, so as to obtain a high-speed signal. Referring to FIG. 4, FIG. 4Sign indicates data addition, a ↓2sign indicates 2-times data extraction, a ↓3sign indicates 3-times data interpolation, and a Finite Impulse Response (FIR) indicates low-pass filtering of the nonlinear compensation signal. The specific steps of the polyphase filtering operation are as follows:

the method comprises the following steps that firstly, nonlinear compensation signals are evenly divided into six groups of sub-signals with the same number of sampling points;

and secondly, performing the following operations under the control of the clock control module:

delaying the first, fourth and sixth groups of non-linear compensation sub-signals by one clock period, z^-12 times of data extraction, FIR low-pass filtering and 3 times of data interpolation operation are carried out to obtain a first group, a fourth group and a sixth group of high-speed signals;

sequentially performing 2 times of data extraction, FIR low-pass filtering and 3 times of data interpolation on the second group of nonlinear compensation sub-signals and the third group of nonlinear compensation sub-signals to obtain second group of high-speed signals and third group of high-speed signals;

sequentially performing 2 times of data extraction, FIR low-pass filtering, 3 times of data interpolation and time delay on a fifth group of nonlinear compensation sub-signals^-3To obtain a fifth set of high rate signals.

Third, the first and second sets of high rate signals are summed and the summed signal is delayed by one clock period, z^-1Obtaining a first path of high-speed linear frequency modulation signal;

the fourth step, sum the third group of high speed signals and the fourth group of high speed signals, delay the summed signal by two clock cycles, namely z^-2Obtaining a second path of high-speed linear frequency modulation signal;

step five, summing the fifth group of high-speed signals and the sixth group of high-speed signals to obtain a third path of high-speed linear frequency modulation signals;

and sixthly, summing the obtained three paths of high-speed linear frequency modulation signals to obtain a high-speed signal, wherein in the embodiment of the invention, the frequency of the high-speed signal is 540 MHz.

And performing double extraction on the high-rate signal to obtain an imaginary part signal of the high-rate signal and a real part signal of the high-rate signal.

Under the control of the clock control module, the half-phase filtering module receives the imaginary part signal of the high-speed signal, and performs low-pass filtering on the imaginary part signal to obtain the imaginary part signal of the filtered high-speed signal. And the shifting module receives the real part signal of the high-rate signal and shifts the real part signal to the right, wherein the bit number of the shifting is the bit number of the imaginary part signal of the high-rate signal, and the real part signal of the shifted high-rate signal is obtained.

Under the control of a clock control module, transmitting an imaginary part signal of the filtered high-speed signal and a real part signal of the shifted high-speed signal to a digital orthogonal transformation inverse process module, multiplying the real part signal of the shifted high-speed signal by-1 by the module, and adding the multiplied real part signal of the shifted high-speed signal and the imaginary part signal of the filtered high-speed signal to obtain a high-speed radar digital linear frequency modulation signal, wherein in the embodiment of the invention, the frequency of the high-speed radar digital linear frequency modulation signal is 1080 MHz; the binary code conversion module converts the high-rate radar digital chirp signals into unsigned data to obtain digital radar intermediate frequency signals, and in the embodiment of the invention, the binary code conversion module is realized by adopting a conversion chip 8192.

And 5, obtaining the radio frequency signal.

The digital-to-analog conversion module converts the digital radar intermediate frequency signal into an analog linear frequency modulation signal through a D/A converter; and the frequency mixing module is used for mixing the frequency with the local oscillator signal generated by the radar signal generation module to obtain a radio frequency signal.

And 6, frequency doubling amplification.

Sequentially sending the radio frequency signals to a triple frequency multiplier module in the terahertz frequency doubling power amplification module and a Gunn diode of the power amplifier module to obtain intermediate frequency radar signals; and sequentially sending the intermediate frequency radar signal to a double frequency multiplier module in the terahertz frequency doubling power amplification module and a gunn diode of the power amplifier module, and amplifying the frequency of the radio frequency signal by six times to obtain a terahertz radar signal z (t) after power amplification.

And 7, obtaining the power of the harmonic signal.

Sending the terahertz radar signal z (t) subjected to power amplification to a harmonic filter module to obtain a harmonic signal; because the harmonic signal power is weaker, the harmonic signal is sent to a power amplifier module in the harmonic feedback module to obtain a harmonic signal after power amplification; and then the harmonic signal after power amplification is sent to an integrator module to obtain the harmonic signal power.

And 8, updating the nonlinear compensation weight coefficient.

The harmonic signal power is fed back to a weight coefficient updating module, and an updated nonlinear compensation weight coefficient is calculated according to the harmonic signal power; the weight coefficient updating module sends the updated nonlinear compensation weight coefficient obtained by calculation to the digital predistortion calculation module.

Wherein, the process of calculating the updated nonlinear compensation weight coefficient according to the harmonic signal power comprises the following steps: according to an ideal input and output signal power curve of a power amplifier in the terahertz frequency doubling power amplification module, if the harmonic signal power is smaller than a rated value, the terahertz radar signal z (t) after power amplification has nonlinear distortion, the following operations are performed:

firstly, discretizing a terahertz radar signal z (t) after power amplification to obtain a terahertz radar digital signal z (n);

secondly, defining a nonlinear compensation weight coefficient vector W of the weight coefficient updating module and a training vector thereofAre respectively as

W＝[w₁₁,w₁₂,…w_1K,w₂₁,…w_MK]

Wherein M represents the total number of channels, K represents the total number of times of compensating the mth channel data, and K is a positive integer greater than or equal to 3;

thirdly, defining the matrix formed by the data X (n) of the first channel and the delay signal thereof as X_nDefining the matrix formed by the digital signal Z (n) and the delay signal of the terahertz radar as Z_n，

The fourth step, defining the error signal e (n) as

Wherein, the non-linear compensation signal y (n) and its training signalAre respectively as

y(n)＝WX_n

Fifthly, iteration is carried out through a recursive least square adaptive algorithm, and a training vector of the weight coefficient updating module is calculatedThe iteration is terminated when the error signal e (n) meets the requirement, and willAssigning to W to obtain updated nonlinear compensation weight coefficient；

P (n) is the inverse of the autocorrelation matrix of the data x (n) of the first channel, and its initial value is set to P⁰(n); training nonlinear weight coefficient vector of set weight coefficient updating moduleIs initially of

Let l be the number of iterations, willIs assigned to W^lThe iterative formula is

Wherein K (n) represents a gain vector (.)^HExpressing the evaluation of the Hermite matrix, (.)^*The conjugate matrix is obtained, the constant lambda is a forgetting factor, and 0 < lambda < 1.

And 9, transmitting the power amplified terahertz signal.

The terahertz radar signal after power amplification is transmitted by the radar antenna.

According to the terahertz radar signal transmitter and the transmitting method based on harmonic feedback, a digital predistortion technology of harmonic feedback is realized by adopting a high-speed Field Programmable Gate Array (FPGA), and nonlinear compensation of a power amplifier in the terahertz radar signal transmitter can be realized.

Claims (6)

1. A terahertz radar signal transmitter based on harmonic feedback comprises a radar signal generation module, a clock control module, a digital predistortion module, a digital up-conversion module, a digital-to-analog conversion module, a frequency mixing module, a terahertz frequency doubling power amplification module, a harmonic feedback module and a radar antenna; all modules are connected through a bus;

the radar signal generation module is used for generating a baseband digital linear frequency modulation signal and carrying out data low-pass filtering on the baseband digital linear frequency modulation signal; and generating a local oscillation signal;

the clock control module is used for generating a fixed clock period and controlling the input and the output of the baseband digital linear frequency modulation signal;

the digital predistortion module is used for carrying out nonlinear compensation on the baseband digital linear frequency modulation signal after the low-pass filtering to obtain a nonlinear compensation signal; the digital predistortion module comprises a weight coefficient updating module and a digital predistortion calculation module; the weight coefficient updating module is used for receiving the harmonic signal power fed back by the harmonic feedback module, updating the nonlinear compensation weight coefficient in real time according to the harmonic signal power and providing an optimal nonlinear compensation weight coefficient for the baseband digital linear frequency modulation signal after low-pass filtering; the digital predistortion calculation module is used for receiving and processing the baseband digital linear frequency modulation signal after the low-pass filtering and the data generated by the weight coefficient updating module to obtain a nonlinear compensation signal and realize the nonlinear compensation of the baseband digital linear frequency modulation signal;

the digital up-conversion module is used for up-regulating the frequency of the nonlinear compensation signal to a signal of a higher frequency band to obtain a digital radar intermediate frequency signal;

the digital-to-analog conversion module is used for converting the digital radar intermediate frequency signal into an analog linear frequency modulation signal;

the frequency mixing module is used for modulating the central frequency of the analog linear frequency modulation signal to obtain a radio frequency signal;

the terahertz frequency doubling power amplification module is used for performing multi-stage frequency doubling and power amplification on the radio frequency signal to obtain a terahertz radar signal after power amplification;

the harmonic feedback module is used for extracting a harmonic signal in the terahertz radar signal after power amplification and feeding the power of the harmonic signal back to the digital predistortion module; the harmonic feedback module specifically comprises a harmonic filter module, a power amplifier module and an integrator module; the harmonic filter module is used for extracting a harmonic signal from the power amplified terahertz radar signal; the power amplifier module is used for increasing the power of the harmonic signal to obtain a harmonic signal after power amplification; the integrator module is used for obtaining harmonic signal power;

the radar antenna is used for transmitting the terahertz radar signals after power amplification.

2. The harmonic feedback-based terahertz radar signal transmitter of claim 1, wherein the digital up-conversion module comprises a polyphase filtering module, a half-phase filtering module, a shifting module, a digital orthogonal transformation inverse process module, and a binary code conversion module; wherein,

the multi-phase filtering module is used for carrying out multi-phase filtering operation on the nonlinear compensation signal to obtain a high-rate signal, and carrying out double extraction on the high-rate signal to obtain a real part signal of the high-rate signal and an imaginary part signal of the high-rate signal;

the half-phase filtering module is used for carrying out low-pass filtering on the imaginary part signal of the high-speed signal to obtain the imaginary part signal of the filtered high-speed signal;

the shifting module is used for shifting the real part signal of the high-rate signal to the right, wherein the number of the shifted bits is the number of bits of the imaginary part signal of the high-rate signal, and the shifted real part signal of the high-rate signal is obtained;

the digital orthogonal transformation inverse process module is used for multiplying the real part signal of the high-speed signal after the displacement by-1 and adding the real part signal of the high-speed signal after the displacement and the imaginary part signal of the high-speed signal after the filtering to obtain a high-speed radar digital linear frequency modulation signal;

and the binary code conversion module is used for converting the high-speed radar digital linear frequency modulation signal into unsigned data to obtain a digital radar intermediate frequency signal.

3. The harmonic feedback-based terahertz radar signal transmitter of claim 1, wherein the terahertz frequency doubling power amplification module comprises a frequency multiplier module and a power amplifier module; wherein,

the frequency multiplier module is used for amplifying the frequency of the radio frequency signal by six times to obtain a terahertz radar signal;

the power amplifier module is used for increasing the power of the terahertz radar signal to obtain the terahertz radar signal after power amplification.

4. A terahertz radar signal transmitting method based on harmonic feedback comprises the following steps:

(1) generating a signal:

1a) performing digital low-pass filtering on the baseband digital linear frequency modulation signal generated by the radar signal generation module to obtain a baseband digital linear frequency modulation signal after low-pass filtering;

1b) under the control of the clock control module, the digital predistortion module receives the baseband digital chirp signals after the low-pass filtering, and performs double extraction on baseband frequency spectrum data of the baseband digital chirp signals after the low-pass filtering, namely baseband orthogonal digital signals, so as to respectively obtain real part signals of the baseband orthogonal digital signals and imaginary part signals of the baseband orthogonal digital signals;

(2) initializing nonlinear compensation weight coefficients:

2a) calculating an initialized nonlinear compensation weight coefficient and sending the weight coefficient into a weight coefficient updating module;

2b) the weight coefficient updating module transmits the initialized nonlinear compensation weight coefficient to the digital predistortion calculation module;

(3) obtaining a nonlinear compensation signal:

3a) the data predistortion calculation module takes the received real part signal of the baseband orthogonal digital signal and the imaginary part signal of the baseband orthogonal digital signal as data of a first channel;

3b) under the control of the clock control module, delaying the data of the first channel by one clock cycle to obtain the data of a second channel, delaying the data of the second channel by one clock cycle to obtain the data of a third channel, delaying the data of the third channel by one clock cycle to obtain the data of a fourth channel, and delaying the data of the fourth channel by one clock cycle to obtain the data of a fifth channel;

3c) under the control of the clock control module, 5-channel pre-compensated data are obtained according to the following formula:

$x_m\left(n\right)=\underset{k=1}{\overset{K}{\&Sigma;}}|x(n-m+1){|}^{2(k-1)}{w}_{mk}$

wherein x is_m(n) represents the precompensation data of the mth channel in the five channels, n represents the number of sampling points of the baseband digital chirp signal generated by the radar signal generation module, x (n-m +1) represents the data of the mth channel in the five channels, K represents the total number of times of compensating the mth channel data, K is a positive integer greater than or equal to 3, w_mkRepresenting a weight coefficient for performing K-th compensation on the mth channel in the five channels, wherein the K is a positive integer in the value range of 1-K, | · | represents the modulo operation on data;

3d) under the control of the clock control module, the compensation data of 5 channels are obtained according to the following formula:

y_m(n)＝x(n-m+1)x_m(n)

wherein, y_m(n) represents compensation data of an mth channel of the five channels, n represents the number of sampling points of the baseband digital chirp signal generated by the radar signal generation module, x (n-m +1) represents data of the mth channel of the five channels, and x_m(n) data representing the m-th channel precompensation among the five channels;

3e) under the control of the clock control module, a nonlinear compensation signal is obtained according to the following formula:

$y\left(n\right)=\underset{m=1}{\overset{M}{\&Sigma;}}{y}_m\left(n\right)$

wherein y (n) represents a nonlinear compensation signal, n represents the number of sampling points of a baseband digital linear frequency modulation signal generated by the radar signal generation module, and M represents the total number of channels;

(4) obtaining a digital radar intermediate frequency signal:

4a) under the control of the clock control module, the digital predistortion module sends the nonlinear compensation signal to the polyphase filtering module; the multi-phase filtering module carries out multi-phase filtering operation on the received nonlinear compensation signal to obtain a high-speed signal; performing double extraction on the high-rate signal to obtain an imaginary part signal and a real part signal of the high-rate signal;

4b) under the control of the clock control module, the half-phase filtering module receives the imaginary part signal of the high-speed signal and performs low-pass filtering on the imaginary part signal to obtain the imaginary part signal of the filtered high-speed signal;

4c) under the control of the clock control module, the shifting module receives the real part signal of the high-rate signal and shifts the real part signal to the right, wherein the bit number of the shifting is the bit number of the imaginary part signal of the high-rate signal, and the real part signal of the shifted high-rate signal is obtained;

4d) under the control of the clock control module, transmitting the imaginary part signal of the filtered high-speed signal and the real part signal of the shifted high-speed signal to the digital orthogonal transformation inverse process module; the digital orthogonal transformation inverse process module multiplies the real part signal of the high-speed signal after the displacement by-1, and adds the real part signal of the high-speed signal after the filtering to obtain a high-speed radar digital linear frequency modulation signal;

4e) under the control of the clock control module, sending the high-speed radar digital linear frequency modulation signal to a binary code conversion module to obtain a digital radar intermediate frequency signal;

(5) obtaining a radio frequency signal:

5a) the digital-to-analog conversion module converts the digital radar intermediate frequency signal into an analog linear frequency modulation signal through a D/A converter;

5b) the frequency mixing module is used for mixing the analog linear frequency modulation signal with a local oscillator signal to obtain a radio frequency signal;

(6) frequency doubling amplification:

6a) sending the radio frequency signal to a frequency multiplier module to obtain a terahertz radar signal;

6b) sending the terahertz radar signal to a power amplifier module in a terahertz frequency doubling power amplification module to obtain a terahertz radar signal z (t) after power amplification;

(7) obtaining the power of the harmonic signal:

7a) sending the terahertz radar signal z (t) subjected to power amplification to a harmonic filter module to obtain a harmonic signal;

7b) sending the harmonic signal to a power amplifier module in a harmonic feedback module to obtain a harmonic signal after power amplification;

7c) transmitting the harmonic signal after power amplification to an integrator module to obtain harmonic signal power;

(8) updating the nonlinear compensation weight coefficient:

8a) the harmonic signal power is fed back to a weight coefficient updating module, and an updated nonlinear compensation weight coefficient is calculated according to the harmonic signal power;

8b) the weight coefficient updating module sends the updated nonlinear compensation weight coefficient obtained by calculation to the digital predistortion calculation module;

(9) transmitting the terahertz radar signal after power amplification:

the terahertz radar signal after power amplification is transmitted by the radar antenna.

5. The method for transmitting terahertz radar signals based on harmonic feedback according to claim 4, wherein the step of the polyphase filtering operation of step 4a) is as follows:

the method comprises the following steps that firstly, nonlinear compensation signals are evenly divided into six groups of sub-signals with the same number of sampling points;

and secondly, performing the following operations under the control of the clock control module:

delaying the first, fourth and sixth groups of non-linear compensation sub-signals by one clock period, z^-12 times of data extraction, FIR low-pass filtering and 3 times of data interpolation operation are carried out to obtain a first group, a fourth group and a sixth group of high-speed signals;

sequentially performing 2 times of data extraction, FIR low-pass filtering and 3 times of data interpolation on the second group of nonlinear compensation sub-signals and the third group of nonlinear compensation sub-signals to obtain second group of high-speed signals and third group of high-speed signals;

sequentially performing 2 times of data extraction, FIR low-pass filtering, 3 times of data interpolation and time delay on a fifth group of nonlinear compensation sub-signals^-3To obtain a fifth set of high rate signals;

third, the first and second sets of high rate signals are summed and the summed signal is delayed by one clock period, z^-1Obtaining a first path of high-speed linear frequency modulation signal;

the fourth step, sum the third group of high speed signals and the fourth group of high speed signals, delay the summed signal by two clock cycles, namely z^-2Obtaining a second path of high-speed linear frequency modulation signal;

step five, summing the fifth group of high-speed signals and the sixth group of high-speed signals to obtain a third path of high-speed linear frequency modulation signals;

and sixthly, summing the obtained three paths of high-speed linear frequency modulation signals to obtain a high-speed signal z (n).

6. The method for transmitting terahertz radar signals based on harmonic feedback according to claim 4, wherein the step 8a) of calculating updated nonlinear compensation weight coefficients according to harmonic signal power comprises the following steps:

the process of calculating the updated nonlinear compensation weight coefficient according to the harmonic signal power is as follows: according to an ideal input and output signal power curve of a power amplifier in the terahertz frequency doubling power amplification module, if the harmonic signal power is smaller than a rated value, the terahertz radar signal z (t) after power amplification has nonlinear distortion, the following operations are performed:

firstly, discretizing a terahertz radar signal z (t) after power amplification to obtain a terahertz radar digital signal z (n);

secondly, defining a nonlinear compensation weight coefficient vector W of the weight coefficient updating module and a training vector thereofAre respectively as

W＝[w₁₁，w₁₂，…w_1K，w2₁，…w_MK]

$\tilde{W}=\&lsqb;{\tilde{w}}_{11},{\tilde{w}}_{12},...{\tilde{w}}_{1K},{\tilde{w}}_{21},...{\tilde{w}}_{MK}\&rsqb;$

Wherein M represents the total number of channels, K represents the total number of times of compensating the mth channel data, and K is a positive integer greater than or equal to 3;

thirdly, defining the matrix formed by the data X (n) of the first channel and the delay signal thereof as X_nDefining the matrix formed by the digital signal Z (n) and the delay signal of the terahertz radar as Z_n，

$X_n=\left(\begin{array}{c}x\left(n\right)\\ x(n-1)\\ .\\ .\\ .\\ x(n-M+1)\\ x\left(n\right)\left|x\left(n\right)\right|\\ .\\ .\\ .\\ x(n-M+1)|x(n-M+1){|}^{2(K-1)}\end{array}\right)$

$Z_n=\left(\begin{array}{c}z\left(n\right)\\ z(n-1)\\ .\\ .\\ .\\ z(n-M+1)\\ z\left(n\right)\left|z\left(n\right)\right|\\ .\\ .\\ .\\ z(n-M+1)|z(n-M+1){|}^{2(K-1)}\end{array}\right);$

The fourth step, defining the error signal e (n) as

$e\left(n\right)=y\left(n\right)-\tilde{y}\left(n\right)={\mathrm{WX}}_n-\tilde{W}{Z}_n$

Wherein, the non-linear compensation signal y (n) and its training signalAre respectively as

y(n)＝WX_n

$\tilde{y}\left(n\right)=\tilde{W}{Z}_n;$

Fifthly, iteration is carried out through a recursive least square adaptive algorithm, and a training vector of the weight coefficient updating module is calculatedThe iteration is terminated when the error signal e (n) meets the requirement, and willAssigning to W to obtain updateThe non-linear compensation weight coefficient of (2);

p (n) is the inverse of the autocorrelation matrix of the data x (n) of the first channel, and its initial value is set to P⁰(n); training nonlinear weight coefficient vector of set weight coefficient updating moduleIs initially of

Let l be the number of iterations, willIs assigned to W^lThe iterative formula is

$e^l\left(n\right)={\tilde{W}}^l(X_n-Z_n)$

$K^{l+1}\left(n\right)=\frac{P^l\left(n\right)Z_n}{\mathrm{\&lambda;}+Z_n^H{P}^l\left(n\right)Z_n}$

$P^{l+1}\left(n\right)=\frac{P^l\left(n\right)-K^{l+1}\left(n\right)Z_n^H{P}^l\left(n\right)}{\mathrm{\&lambda;}}$

${\tilde{W}}^{l+1}\left(n\right)={\tilde{W}}^l\left(n\right)+K^{l+1}\left(n\right){\left(e^l\right(n\left)\right)}^{*}$

Wherein K (n) represents a gain vector (.)^HExpressing the evaluation of the Hermite matrix, (.)^*The conjugate matrix is obtained, the constant lambda is a forgetting factor, and 0 < lambda < 1.