JPH0785521B2 - Low-pass filter Waveguide type diode-limiter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a waveguide type diode limiter used in radar devices and the like.

[Prior art]

For example, as shown in FIG. 4, the radar device sends the microwave oscillated by the magnetron 1 toward the antenna 3 by the circulator 2 and receives the reflected wave reflected by the target object by the antenna 3 and the limiter 2 by the circulator 2. 4 and further transfers to the receiver 5 for analysis processing.

The limiter 4 is for protecting the receiver 5 from the microwave directly reflected by the antenna 3 and the microwave of large energy which directly leaks through the circulator 2 and is input, and normally a PIN diode is used. , The impedance is changed by self-bias by microwave power, and the circuit is short-circuited at the time of high power to perform a limiter function.

FIG. 5 is a diagram showing a conventional device in which such a limiter is configured as a waveguide type diode limiter. In this example, in order to couple a low impedance PIN diode 7 to a high impedance waveguide 6 as a microwave transmission line, the waveguide 6 is loaded with branch stubs 8 and 9 of a coaxial circuit and The diode 7 is loaded by the stubs 8 and 9, and a circuit for short-circuiting and releasing at the branch point is configured by the switching action by the self-bias of the diode 7 so that the limiter function is exhibited.

In this branch stub circuit, its characteristic impedance Zs
To be equal to half the capacitive reactance of the diode 7, and its electrical lengths θ ₁ and θ ₂ are 3λ / 8 and
When λ / 8 is set, an optimum circuit for short-circuiting and releasing at the branch point C can be obtained by the change in the impedance of the diode 7 due to the application of microwave power (short-circuiting when high power is applied). Zo is the characteristic impedance of the waveguide 6, A is an input terminal, and B is an output terminal.

Furthermore, in consideration of improvement of isolation (cutoff) characteristics in short-circuit configuration and improvement of withstand power, a diode having each of the characteristics, that is, a PIN diode having a thin I layer is preferable as an isolation characteristic, and the withstand power characteristic is On the contrary, because thick elements are good,
Two diodes having respective characteristics are shown in FIG.
There are also two-stage branch circuits that are used as shown by 7 ". 8 ', 8", 9', 9 "are branch stubs, where the electrical length θ ₃ between the multi-stage branches is A quarter wavelength coupling circuit is constructed by setting an odd multiple of λ / 4.

However, the waveguide type diode limiter configured as described above has a transmission characteristic as shown in FIG. 7 (a) and a separation characteristic as shown in FIG. 7 (b). In particular, the separation characteristic increases the loss amount only in a specific frequency band, but the loss amount becomes small on both sides.

Therefore, when used in a radar device, the magnetron 1
In the oscillation mode higher than the fundamental oscillation mode (frequency range X in FIG. 7), sufficient attenuation cannot be obtained,
If the high-mode component becomes large power and is input, there is a possibility that the receiver 5 may be destroyed.

Therefore, as shown in FIG.
Load a bandpass filter consisting of λ / 4 wavelength coupling,
As shown by the chain double-dashed line in FIG.

However, even with this method, multi-stage loading of branch stubs is often performed at intervals of λ / 4 due to dimensional restrictions, etc., and it is impossible to sufficiently attenuate the higher-order modes generated by the band filter. During the transient period when the diode impedance changes, the λ / 4 coupling is disturbed and an unnecessary resonance mode is generated, which does not result in a completely separated state.

That is, in the conventional waveguide type diode limiter, a branch stub having an electrical length depending on the wavelength is required, and in the case of a multi-stage configuration, a branch stub interval is required, so that the separation and transmission characteristics always have frequency characteristics, The separation band (stop band) cannot be widened, and if a λ / 4 type filter is combined for widening the band, unnecessary resonance and higher-order modes are generated due to transient changes in diode impedance. However, there is a problem that the circuit shape becomes large due to the mounting of the filter.

[Object of the Invention]

An object of the present invention is to solve the above-mentioned problems and to obtain sufficient separation characteristics even in a band above the target separation frequency and to prevent unnecessary resonance and the like.

[Structure of Invention]

To this end, the invention provides for loading a limiter diode in the capacitive gap stage of a comb gear waveguide with low pass characteristics,
The impedance of the limiter diode is changed according to the microwave power propagating through the waveguide to transmit and block the microwave.

〔Example〕

Examples of the present invention will be described below. First, in this embodiment, a low pass comb-teeth type waveguide is used as the waveguide. As shown in FIG. 9 (an example of a double ridge in FIG. 9), this waveguide 11 has a shape in which concave portions 11a and convex portions 11b are continuously provided above and below the inner wall along the propagation direction of radio waves. Since it is a waveguide, the concave portion 11a acts as an inductive (coil) component L1 and the convex portion 11b acts as a capacitive component C1, the equivalent circuit is as shown in FIG. It is a low-pass filter that blocks the band components.

FIG. 1 is a diagram showing a waveguide type diode limiter of the present embodiment using such a waveguide 11. In this embodiment, the coaxial choke 12 is attached to the convex portion 11b of the inner wall of the waveguide 11, that is, the capacitive gap portion, and the PI
The N diode 7 is configured to be loaded. FIG. 1 (c) is a diagram showing an equivalent circuit thereof, in which the choke 12 acts as an inductive component L2 connected in parallel, and the diode 7 is connected in series to this. FIG. 1 (d) is a diagram showing an equivalent circuit of the diode 7, S is a switch which is switched by bias, and is normally switched to the side shown by a solid line, and when a microwave of high power is applied, it is shown by a broken line. The operation to switch to the side shown is performed.

As a result, in the diode limiter of this embodiment, the waveguide
Since 11 itself basically has the characteristic of cutting high-frequency components, setting it to a frequency slightly higher than the microwave frequency at which the cutoff frequency should pass allows the diode to be used when high-power microwaves are applied. Since the impedance of 7 is reduced and the microwave is cut off due to a short-circuited state, it is equivalent to that the entire cut-off frequency is below the frequency of the microwave, and the characteristic is that the cut-off frequency has moved to the lower frequency side. Becomes The characteristics are shown in FIG. (A) is a transmission characteristic and (b) is a separation characteristic. Therefore, high-order modes are sufficiently attenuated or blocked, and microwave transmission can be switched without having unnecessary resonance modes.

FIG. 3 is a diagram showing an example of a limiter in which a diode 7'having a good isolation characteristic and a diode 7 "having a sufficient electric power resistance are used as the diodes to form a multistage structure.

〔The invention's effect〕

From the above, according to the present invention, the characteristic is that only the cutoff frequency changes due to the change in the diode impedance.
It does not have an unnecessary resonance mode, and can sufficiently attenuate or cut off modes other than the fundamental transmission mode. Since there is no branching stub or interstage that depends on wavelength as in the conventional case, it is possible to widen the band of the separation characteristic.

In addition, a lumped constant filter is used as the low-pass filter, so that the filter can be realized with a size smaller than the wavelength of the used band, and the size can be reduced.

Furthermore, it is possible to sufficiently effectively attenuate the frequency components above the cutoff frequency, and to completely eliminate the high-order unnecessary oscillation components generated from the microwave oscillator.

[Brief description of drawings]

1A is a front view of a diode limiter according to an embodiment of the present invention, FIG. 1B is a sectional view, FIG. 1C is a circuit diagram of an equivalent circuit, and FIG. 1D is a circuit diagram of an equivalent circuit of a PIN diode. Second
FIG. 3 is a diagram showing the transmission characteristics and isolation characteristics of the diode limiter of this embodiment, FIG. 3 (a) is a front view of a diode limiter of another embodiment, (b) is a sectional view, and (c) is an equivalent circuit. Circuit diagram, FIG. 4 is a block diagram of a schematic configuration of a radar device,
FIG. 5 (a) is a front view of a conventional diode limiter,
6B is a sectional view, FIG. 6C is an equivalent circuit diagram, FIG. 6A is a front view of another conventional diode limiter, FIG. 6B is a sectional view, and FIG. 6C is an equivalent circuit diagram. Is a diagram showing transmission characteristics and isolation characteristics of a conventional diode limiter, FIG. 8 (a) is a front view of still another conventional diode limiter, (b) is a sectional view, (c) is an equivalent circuit diagram, and FIG. FIG. 1A is a front view of a low-pass comb tooth-shaped waveguide used in this embodiment,
(B) is a cross section and (c) is a circuit diagram of an equivalent circuit. 1 ... Magnetron, 2 ... Circulator, 3 ... Antenna, 4 ... Limiter, 5 ... Receiver, 6 ... Waveguide, 7 ... PIN diode, 8, 9 ... Branch stub, 10
…… Shibori, 11 …… Low-pass waveguide, 12 …… Coaxial choke.

Claims (1)

[Claims] 1. A limiter diode is mounted in a capacitive gap stage of a comb-teeth type waveguide having a low-pass characteristic, and an impedance of the limiter diode is changed according to microwave power propagating through the waveguide. Transmission of the microwave,
A low-pass filter waveguide-type diode limiter characterized by being configured to cut off.