JPH04255681A - Filter built-in type terminal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal for an ultra-high frequency circuit having a filter function. In recent years, in the field of circuits that handle ultra-high frequencies such as microwaves, with the development of MIC (microwave integrated circuit) technology, circuit components are also required to be smaller and lighter. The bias input terminal of a high-frequency amplifier that amplifies ultra-high frequencies such as microwaves must pass only DC components and block high frequencies. In addition, a microwave mixer mixes the input microwave frequency and the oscillation frequency of the local oscillator and outputs an intermediate frequency. At this time, on the output side, the input microwave frequency and local oscillation frequency are need to be prevented.

0002

2. Description of the Related Art FIG. 3 shows the structure of a conventional terminal. 11 is a central conductor made of metal with a circular cross section, 12 is an insulator with a predetermined dielectric constant, and 13 is an outer conductor (grounded conductor) made of metal.
It is. The center conductor 11 is also called a lead, the insulator 12 is also called an insulator, and the outer conductor 13 is also called a shell, and these have the same structure as a coaxial cable. By appropriately selecting the diameter d of the lead 11, the inner diameter D of the shell 13, and the dielectric constant Er of the insulator 12, a predetermined coaxial impedance is maintained. FIG. 3(a) is a longitudinal cross-sectional view, and FIG. 3(b) is a cross-sectional view or an end view. FIG. 3(c) shows an example of use. Reference numeral 20 denotes a housing in which a microwave circuit 21 is housed, and its input and output terminals are connected to an RF (high frequency) input terminal 23 and an output terminal 24 provided on the housing 20. If the terminal 10 shown in FIG. 3(a) is used for these input and output terminals, and the characteristic impedance of the signal input and output cable is 50Ω, the characteristic impedance of the terminal 10 used for the input and output terminals 23 and 24 is also 50Ω. be made into 25 is also a terminal attached to the housing 20, and is connected to the output side of the microwave circuit 21 through the filter 22. This terminal 25 is also shown in Figure 3 (
If the terminal 10 in a) is used (this is also called a feedthrough capacitor) and this terminal 25 is used for the power supply, it is necessary to prevent high frequency output from leaking to the power supply side.
The filter 22 is provided for this purpose, and in this example is a low-pass filter.

0003

[Problem to be Solved by the Invention] A terminal with a coaxial structure is generally attached to a part of a high-frequency device that connects the outside of the housing and the internal circuit, and supplies input signals or power input to the circuit inside the housing. The purpose is to If the terminal is for power input, a filter 22 such as an LPF is inserted to prevent high frequency signals from leaking into the power supply side. However, this increases the number of parts and impedes miniaturization of the device.

[0004] The present invention has been made in view of the above points, and an object thereof is to improve the terminal structure, eliminate the need for a separate filter, and achieve miniaturization.

[0005]

As shown in FIG. 1, in the present invention, a center conductor 11 of a coaxial terminal 10 has large diameter portions 11a, 11c and a small diameter portion 11b. In this example, the small diameter portion 11b is located at the center of the portion of the center conductor 11 surrounded by the outer conductor 13, and the large diameter portions 11a and 11c are located on both sides thereof. In this figure, the lengths of the large-diameter portions 11a and 11c are W1 and W3, and both diameters are d2, and the length of the small-diameter portion 11b is W2, and the diameter is d1. Center conductor 1 as in Figure 3
The diameter of the outer conductor 13 (here, the upper part of 11a and the lower part of 11c) is d, and the inner diameter of the outer conductor 13 is D. These diameters are d2 > d > d1, and the sum of each length W1 +
W2 +W3 is shorter than the length of the outer conductor, that is, the large diameter part,
The reduced diameter portion is within the insulator 12.

[0006]

[Operation] In the ultra-high frequency band, the large diameter portion 11a of the center conductor 11,
11c acts as a capacitor (C component), and the small diameter portion 11b acts as a dielectric, so the equivalent circuit becomes as shown in FIG. 1(b). Capacitors C1 and C2 are large diameter portions 11a,
11c, the inductance L corresponds to the small diameter portion 11b. Obviously, Fig. 1(b) is a π-type LPF, and therefore Fig. 1(b) is a π-type LPF.
The terminal 10 in (a) has a built-in LPF function. Therefore, in Figure 1 (
Determining the dimensions of each part and the dielectric constant of the insulator 12 in a),
Advantages such as the ability to set the cutoff frequency of the LPF to a desired value and the ability to omit the filter 22 in FIG. 3(c) when used as a power supply terminal are obtained.

[0007]

[Example] When a large-diameter part and a small-diameter part are made in the center conductor of a coaxial terminal, the former becomes C and the latter becomes L, and a π-type LPF can be formed with the structure shown in Figure 1(a), but this modification By repeatedly forming large-diameter portions and small-diameter portions, a multi-stage π-type LPF can be obtained, and the amount of attenuation in the stopband can be increased. And vice versa,
If only 11a and 11b are used in FIG. 1(a), it becomes an L-type LPF. The former will be longer, and the latter will be shorter, but it will be difficult in terms of mechanical strength. In this respect, the structure of FIG. 1(a) is appropriate.

The terminal shown in FIG. 1(a) consists of a coaxial cable with a large center conductor diameter and a coaxial cable with a small center conductor diameter (
If we consider that the outer conductors have the same diameter and short length) connected in series, then C1 and C2 are the former,
L indicates the characteristic impedance of the latter. Therefore, although Figure 1(b) is simply illustrated as a lumped constant type π-type LPF, it is actually a distributed constant type, more complicated LPF.
It is.

If the insulator 12 is made of, for example, hard glass, and the gap between the outer conductor 13 and the center conductor 11 placed at the center is filled and sealed, a terminal with a hermetic structure can be obtained, which has a low resistance to high frequencies. The terminal has sufficient mechanical strength while maintaining a constant dielectric constant due to loss. Since the filter formed by this terminal is a distributed constant circuit, lowering the cutoff frequency increases the size. Therefore, it is practical to set the cutoff frequency to an appropriate high frequency in the microwave band, which is several GHz or more.

FIG. 2(a) shows an example in which the terminal of the present invention is used in a microwave amplifier. This amplifier includes an amplification element TR, which is a GaAsFET, in a housing 20, and an input matching circuit 2.
7 and an output matching circuit 28, and the housing 20 has an RF input terminal 23, an RF output terminal 24, and a power supply terminal 25.
, a bias terminal 26 is attached. Matching circuit 27, 2
8 is actually a microstrip line, equipped with C-type/L-type stubs, etc., and is a transistor TR when viewed from the input/output end.
The input/output circuit of the input/output signal line is, for example, 50Ω.

A DC voltage is externally applied to the drain D of the transistor TR through the power supply terminal 25, and a bias voltage is applied to the gate G of the transistor TR through the bias terminal 26. The terminal 10 of the present invention includes these terminals 25,
Used for 26. This will supply the necessary DC voltage to the drain and gate of transistor TR, and will also supply R to the power supply side.
Leakage of the F signal can be prevented. When using a voltage including relatively high frequency components such as a pulse voltage as a bias, it is not possible to use a feed-through capacitor at the bias power supply terminal. However, even in such a case, the terminal 10 of the present invention can easily change the bias voltage waveform. A bias voltage can be stably supplied without deterioration, and leakage of RF signals can be prevented.

FIG. 2(b) shows an embodiment of a microwave mixer, in which a high frequency signal and a local frequency are input, and a diode MD
and outputs an IF (intermediate frequency) signal. In conventional devices, a filter that blocks RF signals and local signals and passes only IF signals is connected after the diode MD, but by using the terminal 24 of the present invention as the output terminal 24, this filter can be omitted. can. Furthermore, diode 1
It is also possible to simultaneously supply the DC bias necessary for 6 from this terminal 24.

[0013]

[Effects of the Invention] As explained above, according to the present invention, it is possible to provide the terminal with a filter function, and the filter circuit provided in the conventional microwave amplifier is eliminated, making it possible to downsize the amplifier. Can be done. Similarly, when extracting intermediate frequency components in a microwave mixer, the filter circuit can be omitted.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the present invention.

FIG. 2 is an explanatory diagram of an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a conventional example.

[Explanation of symbols]

11 Center conductor 12 Insulator 13 Outer conductor 11a, 11c Large diameter part 11b Small diameter part

Claims (2)

[Claims] Claim 1: A central conductor, an outer conductor surrounding the center conductor, and an insulator packed between these, wherein the center conductor (11) is a portion surrounded by the outer conductor (13). in,
A small diameter portion (11b) forming an inductance and a large diameter portion (11a, 11) forming a capacitor.
c) A built-in filter terminal. [Claim 2] The center conductor is characterized in that it has a smaller diameter at the center of the portion surrounded by the outer conductor and larger diameter portions at both ends thereof, forming a π-type low-pass filter. A built-in filter type terminal according to claim 1.