JPS6337527B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a diode limiter circuit that suppresses excessive power of extremely high frequencies such as microwaves and millimeter waves to minute power.

Circuits that receive extremely high frequency signals with high sensitivity generally use semiconductor elements with fine structures, but these are vulnerable to excessive power and are often destroyed. As an example of a device in which a receiving circuit is exposed to excessive power, an example of a transmitting/receiving circuit of a radar device is shown in FIG. Here, high-frequency power 10 output from a high-power transmission source 1 using a magnetron or the like is transmitted to an antenna 3 by a circulator 2, and is radiated into the air as radio waves from there. The radiated radio wave is reflected by an object, enters the antenna 3, and is transmitted to the receiving circuit 4 by the circulator 2, making it possible to detect the reflected wave 20 and, therefore, the presence of the object. A protection circuit 5 is provided between the circulator 2 and the receiving circuit 4, and the reason why it is necessary is as follows.

In a circulator that irreversibly transmits high frequency waves directionally, some high frequency waves 30 also leak in the opposite direction where transmission is not originally expected. The ratio of the forward direction power to the reverse direction leakage power is called isolation, and the larger the number, the less the reverse direction leakage, that is, the better the directionality. A carefully designed and constructed circulator can provide isolation of over 100 times (20dB). However, in the case of high power radar systems, this reverse leakage power is often large enough to degrade or destroy the semiconductor elements of the receiving circuit. For example, if the transmitting power is 10 Kw and a circulator with 20 dB isolation is used, there is a risk that about 100 mW of power will be input to the receiving circuit. This power is more than enough to shorten the lifetime of highly sensitive receiving semiconductor devices. Furthermore, if a reflective object is close to the antenna or a radar device of the same type is nearby, it is expected that large amounts of power will enter the receiving circuit from the outside.

From the above description, it has become clear that the circuit 5 that protects the receiving circuit from excessive power is necessary. By the way, the protection circuit 5 must sufficiently cut off excessive power while not preventing the weak reflected waves 20 from being transmitted to the receiving circuit. A diode limiter circuit is used to satisfy these two extremely different performance requirements. Second
The figure is an example of a conventional diode limiter circuit in the case of a waveguide circuit. Here, diodes 110 and 120 are attached to the waveguide 100. The best diode is usually one with a pin structure, that is, a pin diode. Both diodes are connected to the inner surface of the waveguide, so the anodes and cathodes of the diodes are short-circuited in terms of direct current. In addition, the number of diodes to be used should be determined according to the amount of power to be cut off, but 1/
It is appropriate to have two wavelengths separated by four wavelengths.

Next, the operating principle of the diode limiter circuit will be briefly explained. First, when a small amount of power is input, both diodes 110 and 120 have no detection effect and are in a nearly open state in terms of high frequency. It can pass through waveguide circuits with little to no accompaniment. However, when high power is input, a detection current flows through the input side diode 110, and at the same time, the diode 110 becomes a low impedance state close to a short circuit in terms of high frequency, and the high frequency of the high power is reflected back to the input side. become. The diode 110 is not completely short-circuited (zero impedance state), and a portion of the high frequency is transmitted to the diode 120, where it is reflected again, and the power output from the waveguide is extremely small. Become.

In this conventional diode limiter circuit, both the first stage and next stage (or subsequent stages) diodes detect the high frequency power they receive and reflect the high frequency power using the detected current. ) method. Therefore,
If the first stage diode 110 that receives the entire incident power is assumed to have a large power capacity, the next stage diode 1
20 must have a detection current flowing even at low power and a fast response speed, that is, it must be sensitive and have a low power capacity. Also, the next stage diode 1
Although the incident power of 20 is small, it still acts passively, so it is difficult to obtain a large isolation, and if you try to increase the isolation and make it highly sensitive, it has the disadvantage of being easily broken. Ta. Of course, using three or more stages of diodes improves isolation, but increases insertion loss and increases cost. Furthermore, using different diodes for the first stage and the next stage increases manufacturing costs, and since there is a directionality between the input side and the output side, there is the inconvenience of using the diodes because if they are connected in the wrong direction, the diodes will be destroyed. be.

The purpose of the present invention is to improve isolation without increasing insertion loss or significantly increasing cost, to allow use of diodes with similar characteristics in each stage if necessary, and to increase breakdown power consumption. The purpose of the present invention is to provide a diode limiter circuit that has no directionality.

The configuration of the present invention is such that when a high-power ultra-high frequency wave is received, a detection current flows through a plurality of diodes, and this detection current causes the diodes to have a low impedance, thereby reflecting the high-power ultra-high frequency wave and reducing the passing power. In the diode limiter circuit for reducing the current, a resistor is connected in series between the diodes so that the detection current flowing through one diode also flows into at least one other diode.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 3 is a circuit diagram showing one embodiment of the present invention. Here, unlike the conventional example, one ends of the diodes 210 and 220 are not short-circuited with the waveguide 200 in terms of direct current (short-circuited in terms of high frequency), and both diodes are connected in series via a resistor 230. has been done. Of course, it is also possible to short-circuit the resistor. The high frequency equivalent circuit and DC equivalent circuit of FIG. 3 are shown in FIGS. 4 and 5, respectively. In this case as well, the basic principle of operation is the same as that described in FIG. (Active) Acts like a limiter. Therefore, the isolation of the diode 220 and, by extension, the isolation of the entire limiter circuit is improved. Moreover, the insertion loss in this limiter circuit is the same as in the conventional one. Also,
By adjusting the detection current 240 by changing the resistance value of the resistor 230, the limiter performance of the diode 210 can be maximized.

In this way, in addition to being able to improve the characteristics by allowing the detection current of the previous stage diode to flow into the latter stage diode, it is also possible to use a later stage diode with the same large power capacity as the previous stage, so it can be used as a limiter circuit. It is possible to improve the fracture resistance of the material, and in this way there is no directionality. Furthermore, although the above explanation has been made for the case of two diodes, it goes without saying that the same circuit configuration can be realized even when there are three or more diodes. Furthermore, it is obvious that diodes with detection characteristics other than the Pin diode can be used.

As explained above, according to the present invention, isolation is improved without an increase in insertion loss or a significant increase in cost, and diodes with similar characteristics can be used in each stage if necessary, and breakdown resistance is improved. It is possible to obtain a diode limiter circuit which has a large amount of electric power and has no directionality.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a transmission/reception system of a radar device, Fig. 2 is a circuit diagram showing a conventional diode limiter circuit, Fig. 3 is a circuit diagram showing an embodiment of the present invention, Figs. The figures are a high frequency equivalent circuit diagram and a DC equivalent circuit diagram of FIG. 3, respectively. DESCRIPTION OF SYMBOLS 1... Transmission source, 2... Circulator, 3... Transmission/reception antenna, 4... Receiving circuit, 5... Protection circuit, 10
0,200...Waveguide, 110,120,210,
220...Diode, 230...Resistor, 240...
Detection current.

Claims (1)

[Claims] 1 When a high-power ultra-high frequency wave is received, a detection current flows through multiple diodes, and this detection current causes the diodes to have low impedance, thereby reflecting the high-power ultra-high frequency wave and reducing the passing power. In the Mituta circuit, the detection current flowing through one diode is
1. A diode limiter circuit characterized in that a resistor is connected in series between the diodes so that the flow also flows into the other diodes.