KR950002748B1 - Waveguide-type diode limiter for low-pass filtering - Google Patents

Abstract

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Description

Waveguide Diode Limiters for Lowpass Filters

1A is a front view of an embodiment of a cloud wave guide for a low pass filter.

1b is a longitudinal sectional view of FIG. 1a,

Figure 1c is an equivalent circuit diagram of Figure 1a.

2 is a characteristic diagram of the waveguide of FIG.

3A is a front view of one embodiment of the diode limiter of the present invention.

FIG. 3B is a longitudinal sectional view of FIG. 3A.

3C is a circuit diagram of FIG. 3A.

3d is an equivalent circuit diagram of FIG. 3a PIN-diode.

4a and 4b are characteristic diagrams of the diode limiter of FIG. 3a under the previous day and glass conditions, respectively.

5A is a front view of another embodiment of two (2) diode limiters of the present invention.

FIG. 5B is a longitudinal sectional view of FIG. 5A.

6 is a longitudinal cross-sectional view of another embodiment of the diode limiter of the present invention.

7 is a general block diagram of a radar device.

8A is a front view of a conventional diode limiter.

FIG. 8B is a longitudinal sectional view of FIG. 8A. FIG.

8C is an equivalent circuit diagram of FIG. 8A.

9A is a front view of another conventional diode limiter.

FIG. 9B is a longitudinal sectional view of FIG. 9A. FIG.

FIG. 9C is an equivalent circuit diagram of FIG. 9A. FIG.

10A and 10B are characteristic charts of conventional diode limiters under transfer and separation conditions, respectively.

11A is a front view of a conventional diode limiter having a band pass filter.

FIG. 11B is a longitudinal sectional view of FIG. 11A. FIG.

11C is an equivalent circuit diagram of FIG. 11A.

12A, 12B and 12C are characteristic charts of the diode limiter of the present invention, the conventional two (2) diode limiter and the conventional two (2) diode limiter each having a band pass filter.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to waveguide type diode limiters for low pass filters used in radar devices and the like. Generally, the radar device is composed of a magnetron 1, a circuit 2, an antenna 3, a limiter 4 and a receiver 5 as shown in FIG.

The magnetron 1 generates microwaves, and the microwaves are transmitted to the antenna 3 by the circulation circuit 2. The antenna 3 emits microwaves towards the object and receives the microwaves reflected back from the object. The received microwave is again passed by the circuit 2 to the receiver 5 for analysis past the limiter.

The limiter 4 protects the receiver from damage by high energy microwaves returning directly from the antenna and / or high energy microwaves leaking from the circuit. This limiting function is performed by an IPN-diode (a diode of p-type, 1-type and N-type layers) in the limiter, where the impedance of the diode is controlled by the magnetic bias generated by the microwave energy and the PIN-diode The circuit including the is in a short circuit when the high-energy microwave enters the limiter. Normally the bias is supplied from an external power source, but in this case the PIN-diode is called "self-bias" because it changes the microwave energy to the bias alone.

8A and 8B show a conventional limiter formed into the waveguide (waveguide) 6.

In this type of limiter, coaxial branching stubs 8, 9 are used to connect the low-impedance PIN-diode 7 to the waveguide with high impedance applicable to the microwave supply. The coaxial branch stub 8, 9 acts as a transformer and achieves impedance matching between the waveguide 6 and the PIN-diode 7. This PIN-diode 7 acts as a switch by its own bias, so the branch circuit can be changed from an open circuit to a short circuit.

Branch circuits controlled by impedance magnetic bias (which becomes low impedance in high energy microwaves) have a characteristic impedance Zs of coaxial branch stub (8) (9) equal to half of the capacitive reactance of the PIN-diode (7). 2), when the electric lengths θ ₁ and θ ₂ are adjusted to 2λ / 8 and λ / 8, respectively, they are in a short circuit or an open circuit state at the branch point C as appropriate.

In Fig. 8C, the symbol Zo represents the characteristic impedance of the waveguide 6 and the symbols A and B represent the input terminal and the output terminal of the waveguide 6, respectively.

The reason why the characteristic impedance Zs of the coaxial branch stub 8 and 9 and the electric field θ ₁ and θ ₂ are adjusted in this manner is as follows:

When the wavelength of the microwaves becomes close to the length of the circuit elements, the circuit becomes a distributed regular circuit. In circuits where it is necessary to connect elements (components) according to the wavelength of the microwave, for example, it is necessary to adopt a quarter-wave connection.

Furthermore, in order to improve the glass (separation) characteristics and power handling capability, it is desirable to select a PIN-diode each having a suitable characteristic, that is, to improve the glass characteristics, a PIN-diode having a thin 1-type layer is selected. In order to improve the power handling capability, select a PIN-diode with a thick 1-type layer.

9a and 9b show specific examples of such limiters. In FIGS. 9A and 9B, reference numerals 7a and 7b denote PIN-diodes, and reference numerals 8a, 8b, 9a (and 9b) denote branch stubs.

The overall length (θ ₃₎ between the quarter-wave connection to the fork in the embodiments both an odd number times of the 1/4 wave control, for example, can be made with λ / 4,3λ / 4,5λ / 4.

However, since the waveguide diode limiter has transfer and separation characteristics as shown in FIGS. 10A and 10B, the loss in the separation condition is small except for the fundamental frequency band.

Due to the above characteristics, when using an ordinary waveguide diode limiter for a radar device, the receiver (5) has a limiter sufficient for the higher frequency mode than the fundamental frequency mode (denoted by X in Figs. 10a and 10b). Since no loss can be obtained, there is a possibility of damage and the next high frequency mode enters the receiver while maintaining high energy power. Therefore, in order to remedy the above drawback, as shown in Fig. 11B, a band pass filter is provided in the resonant window of the reducer inserted at both ends of the waveguide 6 in a quarter wave connection. Present a diode limiter. The characteristics of this limiter are improved as shown in FIG. 10B by the two-point chain line.

However, even with a limiter with a bandpass filter, branch stubs are usually mounted at quarter-wavelength spacing for reasons of dimensional limitations, making it impossible to obtain sufficient losses for high mode.

In addition, a quarter-wave connection is unreliable during the instant of the PIN-diode's impedance change, resulting in unnecessarily resonant diodes and thus no sufficient loss (see also Section 12c).

However, the conventional waveguide diode limiter has the following drawbacks due to the distributed constant circuit.

1) The diode limiter requires a stub with a wavelength-dependent electric field, and the separation and propagation characteristics are frequency dependent since an additional electric field between branch stubs is required when multiple PIN-diodes are used. As a result, the separator cannot be widened.

2) When the limiter has a quarter-waveband filter to widen the separator during the instantaneous period of PIN-diode impedance, unwanted resonance or higher modes occur.

3) The size of the limiter with band filter is large because of the attachment of the filter.

It is an object of the present invention to provide a waveguide diode limiter which has sufficient loss over the desired frequency without unnecessary resonance mode.

The present invention relates to a diode limiter consisting of a pleated waveguide for a low pass filter in which a limiter diode is mounted into a capacitive gap of the waveguide.

Figures 8a, 8b, 9a and 9b in the drawings to illustrate the present invention in more detail illustrate the waveguide diode limiter for the low pass filter of the present invention with the same numerals representing the same components.

Cloudy waveguides are used for the low pass filter in the present invention. The microwave's guide wavelength is longer than the dimensions of the corrugated waveguide member and the equivalent circuit can be treated as a batch of regular circuits. The corrugated waveguide 11 has a concave portion 11a formed in the upper and lower inner walls along the direction of microwave transmission at regular intervals, as shown in FIG. 1B (FIG. 1B represents a double-ridge-type waveguide). It has a cross section 11b.

In the waveguide 11, the concave portion 11a acts as an inductive reactance L1, and the concave portion 11b acts as a capacitive reactance C1. Thus, the equivalent circuit of the waveguide is shown in Fig. 1c. This circuit is known as a low pass filter for any frequency (see also Figure 2).

3A and 3B are specific examples of diode limiters having corrugated waveguide 11. In this example, the coaxial choke 12 is attached to the convex portion 11b, i.e. the capacitive gap, and the PIN-diode 7 is connected to the waveguide 11 by the coaxial choke 12. The coaxial choke 12 is composed of a disk 12a having a threaded periphery for connection with the waveguide 11 and a stud bolt 12b passing through the center thereof.

3c is an equivalent circuit diagram of a diode limiter.

In FIG. 3C the choke 12 acts as an inductive reactance L2 parallel to the capacitive reactance of the waveguide 11. The PIN-diode 7 is connected in series with the choke 12. 3d shows an equivalent circuit diagram of a PIN-diode.

In the circuit, the symbol S means a switch controlled by a bias. The switch S indicates the normal position by the solid line and when the high energy microwave is applied thereto, the switch S indicates the change to the other position by the dotted line.

Impedance matching at the diode limiter is performed by adjusting the inductive reactance of the choke by raising or lowering the disk 12a.

In the diode limiter of the present invention, the corrugated waveguide acts as a low pass filter with the above, and when the characteristic frequency is designed to be slightly higher than the filtered frequency, the diode limiter is a short circuit state which reduces the impedance of the PIN-diode 7. The magnetic bias, which makes the branch circuit, separates the high energy microwave corresponding to the filtering frequency.

As a result, the cutoff frequency of the limiter's filter is lower than the frequency of the microwave to be filtered, thus widening the filtering band of the limiter downward.

4a and 4b show characteristic charts of the limiter under the transfer conditions and the blocking conditions, respectively. Characteristic charts show that the limiter can achieve sufficient power loss or complete interruption of the microwave for a high mode, allowing the limiter to switch off the microwave without any unnecessary resonance mode.

5a and 5b show another embodiment of a diode limiter having two PIN-diodes 7a and 7b, where the characteristics of the PIN-diode 7a are poor in power handling capability.

In this embodiment coaxial choke 12 is used to facilitate impedance matching between the PIN-diode and the corrugated waveguide. However, impedance matching between them is not meant to be limited to coaxial chokes.

Furthermore, as in FIG. 6, the impedance matching can be done by adjusting the width of the concave portion operating as an inductive reactance without the choke 12.

According to the present invention as described above, it is possible to obtain a limiter that does not have an unnecessary resonance mode and has sufficient separation characteristics even at a high mode as well as a basic mode. Can widen the filter table. For example, the special filter band of the limiter of the present invention is about 3, 4 as shown in FIG. 12a, or about 1.7 of the conventional diode limiter as shown in FIG. 12b and 12c.

In addition, this limiter can be reduced in size because the equivalent circuit of the limiter can be treated as a batch of regular circuits.

Claims (2)

A waveguide in which irregularities are formed in the tube axial direction on the opposite wall surface of the long periphery of the rectangular waveguide, and the gap between the long peripheral wall surfaces is alternately narrowed to form a gap having low pass filter characteristics. A waveguide diode limiter for a low pass filter, consisting of a limiter diode attached to a gender gap and capable of controlling microwave flow by changing the impedance of the limiter diode. A waveguide diode limiter for a low pass filter according to claim 1, wherein the impedance of the limiter diode is controlled by magnetic bias.

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