Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects of the prior art, and provide a photon assisted Doppler radar detection method, which does not need an electric signal generator to generate electric intermediate frequency and electric radio frequency signals, can flexibly shift the frequency of the demodulated signals and has a compact structure.
The invention specifically adopts the following technical scheme to solve the technical problems:
a photon-assisted Doppler radar detection method comprises the steps of performing photoelectric oscillation on single-wavelength laser, leading out one path of modulated light signals generated in the photoelectric oscillation process, filtering the modulated light signals to obtain reference light signals only retaining a single-side first-order sideband, dividing photo-generated microwave signals generated by the photoelectric oscillation into two paths, dividing one path into intermediate-frequency electric signals, and transmitting the other path as radar transmitting signals; performing frequency shift modulation on one path of optical signal led out from the photoelectric oscillation process by using the intermediate frequency electric signal, then modulating the frequency shift optical signal obtained by frequency shift modulation by using a received radar echo signal, performing filtering processing to obtain a modulated optical signal only retaining a first-order sideband at the same side as a reference optical signal, performing orthogonal frequency mixing on the modulated optical signal and the reference optical signal, and performing balanced photoelectric detection to obtain two paths of intermediate frequency signals with the same amplitude and orthogonal phase; and performing digital signal processing on the two paths of intermediate frequency signals to obtain two paths of low-frequency orthogonal signals carrying target Doppler information, and further extracting the target Doppler information.
Preferably, the one path of optical signal led out from the photoelectric oscillation process is a beam splitting signal of the single-wavelength laser.
Based on the same inventive concept, the following technical scheme can be obtained:
a photon assisted doppler radar detection apparatus comprising:
the photoelectric oscillation module is used for carrying out photoelectric oscillation on the single-wavelength laser and dividing a photoproduction microwave signal generated by the photoelectric oscillation into two paths, wherein one path is divided into intermediate-frequency electric signals, and the other path is used as a radar transmitting signal to be transmitted;
the reference light generation module is used for leading out a path of modulated light signals generated in the photoelectric oscillation process, and filtering the modulated light signals to obtain reference light signals only retaining a single-side first-order sideband;
the frequency shift modulation module is used for performing frequency shift modulation on one path of optical signal led out from the photoelectric oscillation process by using the intermediate-frequency electric signal;
the receiving signal modulation module is used for modulating a frequency shift optical signal obtained by frequency shift modulation by using a received radar echo signal and filtering the frequency shift optical signal to obtain a modulated optical signal only retaining a first-order sideband on the same side as the reference optical signal; the orthogonal frequency mixing module is used for carrying out orthogonal frequency mixing on the modulated optical signal output by the received signal modulation module and the reference optical signal and then carrying out balanced photoelectric detection to obtain two paths of intermediate frequency signals with the same amplitude and orthogonal phases;
and the signal acquisition and processing module is used for carrying out digital signal processing on the two paths of intermediate frequency signals to obtain two paths of low-frequency orthogonal signals carrying target Doppler information, and further extracting the target Doppler information.
Preferably, the one path of optical signal led out from the photoelectric oscillation process is a beam splitting signal of the single-wavelength laser.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1) the invention utilizes the photoelectric oscillation technology to generate pure optical microwave signals and radio frequency electric signals, improves the signal quality, and has lower phase noise at the frequency deviation of Doppler frequency magnitude (thousands of hertz), thereby improving the detection sensitivity of the Doppler radar, avoiding using an electric signal generator and having more flexible structure;
2) the invention realizes the frequency shift of the optical signal in the receiver by utilizing the acousto-optic modulator in the optical domain, avoids the problems of noise, nonlinear effect and the like caused by adopting an electric mixer, has larger frequency shift range, and can flexibly adjust the frequency of two paths of intermediate frequency signals obtained after orthogonal frequency mixing so as to avoid direct current interference; meanwhile, the intermediate frequency signal for driving acousto-optic modulation is generated by a radar emission signal, an additional electric signal source is not needed, and the structure is more compact.
3) The invention realizes microwave quadrature mixing in the optical domain, restrains image frequency signals, overcomes the problem of fuzzy speed measurement, and simultaneously avoids the problems of the limit of working bandwidth, electromagnetic interference and the like caused by using an electric quadrature mixing device.
Detailed Description
Aiming at the defects of the conventional photon assisted Doppler radar technology, the invention adopts the solution that a pure radar signal is generated by using an Optoelectronic oscillator (OEO) method, flexible down-conversion is realized by combining frequency shift in an optical domain with microwave photon orthogonal frequency mixing to obtain a pair of orthogonal intermediate frequency signals, and finally two paths of low-frequency orthogonal signals carrying target Doppler information are obtained by digital signal processing.
The invention provides a photon assisted Doppler radar detection method, which comprises the following specific steps:
performing photoelectric oscillation on single-wavelength laser, leading out one path of modulated optical signals generated in the photoelectric oscillation process, filtering the modulated optical signals into reference optical signals only retaining a single-side first-order sideband, and dividing photo-generated microwave signals generated by the photoelectric oscillation into two paths, wherein one path is divided into intermediate-frequency electric signals, and the other path is used as radar transmitting signals for transmission; performing frequency shift modulation on one path of optical signal led out from the photoelectric oscillation process by using the intermediate frequency electric signal, then modulating the frequency shift optical signal obtained by frequency shift modulation by using a received radar echo signal, performing filtering processing to obtain a modulated optical signal only retaining a first-order sideband at the same side as a reference optical signal, performing orthogonal frequency mixing on the modulated optical signal and the reference optical signal, and performing balanced photoelectric detection to obtain two paths of intermediate frequency signals with the same amplitude and orthogonal phase; and performing digital signal processing on the two paths of intermediate frequency signals to obtain two paths of low-frequency orthogonal signals carrying target Doppler information, and further extracting the target Doppler information.
The invention provides a photon assisted Doppler radar detection device, which comprises:
the photoelectric oscillation module is used for carrying out photoelectric oscillation on the single-wavelength laser and dividing a photoproduction microwave signal generated by the photoelectric oscillation into two paths, wherein one path is divided into intermediate-frequency electric signals, and the other path is used as a radar transmitting signal to be transmitted;
the reference light generation module is used for leading out a path of modulated light signals generated in the photoelectric oscillation process, and filtering the modulated light signals to obtain reference light signals only retaining a single-side first-order sideband;
the frequency shift modulation module is used for performing frequency shift modulation on one path of optical signal led out from the photoelectric oscillation process by using the intermediate-frequency electric signal;
the receiving signal modulation module is used for modulating a frequency shift optical signal obtained by frequency shift modulation by using a received radar echo signal and filtering the frequency shift optical signal to obtain a modulated optical signal only retaining a first-order sideband on the same side as the reference optical signal; the orthogonal frequency mixing module is used for carrying out orthogonal frequency mixing on the modulated optical signal output by the received signal modulation module and the reference optical signal and then carrying out balanced photoelectric detection to obtain two paths of intermediate frequency signals with the same amplitude and orthogonal phases;
and the signal acquisition and processing module is used for carrying out digital signal processing on the two paths of intermediate frequency signals to obtain two paths of low-frequency orthogonal signals carrying target Doppler information, and further extracting the target Doppler information.
The photoelectric oscillation module can adopt the existing single-ring structure, double-ring structure or various other improved structures; the path of optical signal led out from the photoelectric oscillation process may be a beam splitting signal of a modulated optical signal generated in the photoelectric oscillation process (i.e., a modulated optical signal output by an electro-optical modulator in the photoelectric oscillation module), or a beam splitting signal of the single-wavelength laser, if the modulated optical signal is adopted, an optical bandpass filter needs to be added outside a forehead of the frequency shift modulation module to extract an optical carrier, and it is ensured that a modulated optical signal of only a negative/positive (specifically, the same side as a first-order sideband reserved in a reference optical signal) first-order sideband obtained after the optical carrier is modulated is obtained by adjusting a passband range of the optical bandpass filter in the received signal modulation module; preferably, a split signal of the single wavelength laser is used.
For the public to understand, the technical scheme of the invention is explained in detail by a specific embodiment and the accompanying drawings:
as shown in fig. 1, the photon assisted doppler radar detection device of the present embodiment includes: the optical fiber laser comprises a laser, an optical coupler 1, an optical coupler 2, a Mach-Zehnder modulator 1, a Mach-Zehnder modulator 2, a single-mode optical fiber section, a photoelectric detector, a low-noise amplifier 1, a low-noise amplifier 2, a narrow-band electric filter 1, a narrow-band electric filter 2, a power divider, a frequency divider, an acousto-optic modulator, an optical amplifier 1, an optical amplifier 2, an optical filter 1, an optical filter 2, a 90-degree optical mixer, a balance detector 1, a balance detector 2, an analog-to-digital converter 1, an analog-to-digital converter 2, a transmitting antenna, a receiving antenna and a personal computer. As shown in fig. 1, the output end of the laser is connected with an optical coupler 1; in the transmitter, the output end 1 of an optical coupler 1 is connected with the optical signal input end of a Mach-Zehnder modulator 1; the optical signal output end of the Mach-Zehnder modulator 1 is connected with the optical coupler 2; the output end 1 of the optical coupler 2 is cascaded with a photoelectric detector, a low-noise amplifier, a narrow-band electric filter and a power divider one by one through a section of single-mode optical fiber; the output end 1 of the power divider is connected with a transmitting antenna to output radar radio frequency signals, the output end 2 of the power divider is connected with the microwave signal input end of the Mach-Zehnder modulator 1, and the output end 3 of the power divider is connected with a frequency divider and then is input to the microwave signal input end of the acousto-optic modulator; in the receiver, the output end 2 of the optical coupler 2 is cascaded with the optical amplifier 1, the optical filter 1, the 90-degree optical mixer input port 1, the balance detector 1 and the analog-to-digital converter 1 one by one to form an upper branch; an antenna receiving signal is cascaded with a low noise amplifier 2 and a narrow band electric filter 2 one by one and then input to a microwave signal input end of a Mach-Zehnder modulator 2, an output end 2 of an optical coupler 1 is cascaded with an acousto-optic modulator, the Mach-Zehnder modulator, an optical amplifier 2, an optical filter 2, an input port 2 of a 90-degree optical mixer, a balance detector 2 and an analog-to-digital converter 2 one by one to form a lower branch, and finally two paths of signals are sent to a personal computer for digital signal processing.
In the transmitter, the photoelectric loop is oscillated by adjusting the length of the single-mode optical fiber and the passband range of the narrow-band electric filter 1, so that a required pure single-frequency radar radio-frequency signal is generated; the optical microwave signal output by the photoelectric oscillation module is amplified by an optical amplifier 1, and a +1 or-1 order sideband is selected as a reference optical signal through an optical band-pass filter 1 and is input into a 90-degree optical mixer. In the receiver, the single-wavelength laser is subjected to proper frequency shift by adjusting a frequency divider, the bias voltage of the Mach-Zehnder modulator 2 is adjusted to enable the Mach-Zehnder modulator to work at the minimum working point, the optical signal output by the Mach-Zehnder modulator 2 is amplified by the optical amplifier 2, and the +1 or-1 order sideband which is the same as the reference optical signal is selected by the optical bandpass filter 2 to serve as a modulation optical signal to be input to the 90-degree optical mixer. The 90-degree optical mixer introduces a 90-degree phase difference to one of the signals and outputs four orthogonal signals, and four output ports of the 90-degree optical mixer are respectively connected with two balanced photoelectric detectors to complete photoelectric conversion so as to obtain a pair of intermediate-frequency signals with the same amplitude and orthogonal phases, namely the function of orthogonal frequency mixing is realized.
Let the single-wavelength laser output by the laser be
Wherein E0Amplitude of light wave, fcThe center frequency of the optical wave.
After the oscillation of the optoelectronic loop is stable, the optical coupler 2 outputs the optical microwave signal, which is amplified and filtered, and the reference optical signal output by the optical filter 1 can be represented as
Wherein f isxThe center frequency of the narrow band electrical filter 1. In the present invention, the negative/positive first-order sidebands are all selectable, and the positive first-order sidebands are selected for illustration.
The transmission signal is
And the intermediate frequency signal obtained after frequency division is loaded on the acousto-optic modulator to shift the frequency of the single-wavelength laser. The frequency-shifted optical signal output by the acousto-optic modulator is represented as
Wherein f isΔAt the intermediate frequency.
Then, the modulated signal output from the optical filter 2 is amplified and filtered by the signal modulated by the mach-zehnder modulator driven by the received signal, and the modulated optical signal can be expressed as
Wherein f isdRepresenting the doppler frequency produced by a moving object.
Then, the reference optical signal output by the optical filter 1 and the modulated optical signal output by the optical filter 2 are simultaneously input into a 90 ° optical mixer, and the obtained four optical signals are respectively
Will I1、I2And Q1、Q2Two by two are respectively input to two balanced photoelectric detectors for balanced photoelectric detection to obtain two paths of intermediate frequency electric signals
Comparing the two intermediate frequency signals shown in the formula (7), it can be seen that the two intermediate frequency signals have a phase difference of 90 degrees and the same amplitude, which indicates that the invention can realize quadrature mixing in the optical domain. Meanwhile, the doppler frequency information brought by the moving target is also contained in the two intermediate frequency signals shown in the formula (7), and the doppler frequency information can be down-converted to the baseband through subsequent digital signal processing, so that the doppler frequency is extracted.