JPH052871Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a radar front end with a stabilized local oscillation frequency.

[Prior art]

The principle of pulse radar is as shown in Figure 3.
Pulsed microwaves emitted by a microwave oscillator 1 such as a magnetron are transmitted to an antenna 3 by a circulator 2 and radiated from the antenna 3 to a target object, and the reflected waves reflected from the target object are transmitted to the antenna 3. The signal is received by the circulator 2 and transmitted to the radar front end 5 via the limiter 4, where the IF signal obtained by frequency conversion is processed appropriately to measure the size of the target and the distance to it. It is composed of

For example, the distance to this target is A in Figure 4.
This is done by using the time difference T between the pulsed emitted microwave as shown in Figure B and the reflected received wave as shown in Figure B.

By the way, the limiter 4 is closed when the microwave is emitted from the microwave transmitter 1.
At other times, it is controlled to be open.
Microwaves from the microwave oscillator 1 leaking through the circulator 2 during operation are designed not to adversely affect the front end 5.

However, there is a considerable order of magnitude difference between the level of the microwave oscillated by the microwave oscillator 1 and the level of the reflected wave reflected by the target object, and the microwave that has also leaked through the limiter 4 is input to the front end 5.

This front end 5 includes a high-performance RF amplifier 6 and a local oscillator 7 consisting of a self-excited oscillator, PLL, etc.
and a mixer 8 such as a down converter or an up converter that outputs the beat frequency component of the frequency signal from the RF amplifier 6 and the oscillation frequency signal from the local oscillator 7, and processes the IF signal obtained from the mixer 8. It detects the size and distance of the target object.

The frequency of the local oscillator 7 is adjusted in advance so that the frequency of this IF signal becomes a predetermined frequency, but the adjustment of the local oscillator 7 is performed by using leaked microwaves input to the front end 5. There is.

However, the power of the leaked microwave is larger than the power of the local oscillator 7 (for example, the former
10mW, whereas the latter is about 10mW). Therefore, a phenomenon occurs in which the frequency of the local oscillator 7 fluctuates toward the frequency of the microwave oscillator 1.

This is a phenomenon called injection locking, in which when two oscillators oscillate simultaneously, the frequency of the other oscillator shifts to the frequency of the oscillator with larger oscillation power and Q value. If there is an extreme difference, the oscillation frequency of the other oscillator will match the oscillation frequency of the larger one.

Therefore, the frequency adjustment of the local oscillator 7 is performed while the oscillation frequency of the local oscillator 7 is varied from the original frequency as described above.

However, the frequency fluctuation of the local oscillator 7 occurs only when the leaked microwave is input to the front end 5. Therefore, when receiving reflected waves, that is, when oscillation from the microwave oscillator 1 is stopped, the local oscillator 7 is not affected and oscillates at its original frequency. This frequency is a different frequency from the frequency at the time of the adjustment.

Therefore, the oscillation frequency of the local oscillator 7 during the above adjustment and during actual operation (when receiving reflected waves) is different.
Since the oscillation frequency of the local oscillator 7 during actual operation is a frequency that fluctuates from the adjusted frequency, at this time, it becomes impossible to obtain an IF signal of a predetermined frequency that has been adjusted in advance.

Therefore, when adjusting the local oscillator 7, in order to prevent frequency fluctuations due to injection locking of the local oscillator 7, conventionally, an attenuator is installed in the path between the local oscillator 7 and the mixer 8 in the front end 5.
Inserting a type filter or a T-type filter is practiced.

However, this filter circuit is complicated and expensive because it has a configuration in which elements are connected in parallel between the signal line and the ground, and if it is constructed using striplines or microstriplines, it requires a large area. However, there was a problem in that it became an obstacle to miniaturization.

[Purpose of invention]

An object of the present invention is to provide a radar front end that can prevent fluctuations in the oscillation frequency of a local oscillator in response to strong microwave input with a simple configuration, and that solves the above-mentioned problems.

[Structure of the idea]

To this end, the radar front end of the present invention is constructed by inserting a resistor for attenuating the emitted microwave and an impedance conversion circuit for impedance matching in series between the local oscillator and the mixer.

〔Example〕

Examples of the present invention will be described below. 1st
The figure shows an example thereof. In this embodiment, an attenuation resistor 9 (for example, several hundred ohms) and a 1/4 wavelength impedance conversion circuit 10 are configured on the strip line between the mixer 8 and the local oscillator 7, and these are connected in series. . The impedance conversion circuit 10 has a U-shaped microstrip line.

Therefore, the emitted microwave component of the circulator 2 that leaks through the limiter 4 and is input to the front end 5 is attenuated by the resistor 9, thereby preventing an adverse effect on the local oscillator 7 and preventing its frequency fluctuation. can. In addition, due to the impedance conversion circuit 10 inserted in series,
The impedance of the transmission path between the mixer 8 and the local oscillator 7 can be made the same when viewed from the mixer 8 side and when viewed from the local oscillator 7 side,
Impedance matching between the two can also be maintained.

The resistor 9 attenuates the output power from the local oscillator 7 and the leakage microwave power input from the mixer 8 side. At this time, since the output power is small compared to the output power from the local oscillator 7, the amount of attenuation is small. On the other hand, the leakage microwave input from the mixer 8 side has a large amount of attenuation because its micro power is large.

As a result, the output power of the local oscillator 7 is not significantly affected, so the conversion loss of the mixer 8 that outputs the beat frequency component of the frequency signal from the RF amplifier 6 and the oscillation frequency signal from the local oscillator 7 is reduced. Since the leakage microwave power can be greatly attenuated without having a large influence, the frequency fluctuation of the local oscillator 7 due to injection locking can be reduced.

FIG. 2 is a diagram showing an equivalent circuit of the transmission path between the mixer 8 and the local oscillator 7 in FIG.
In order to make the impedance Z seen from the side the same as the impedance seen from the local oscillator 7 side, the impedance Za of the impedance conversion circuit 10 may be set to Za=[Z+(Z+R)] ^1/2 . R is the resistance value of the resistor 9.

[Effect of idea]

From the above, according to the front end of the present invention, the oscillation frequency of the local oscillator can be stabilized against the input of a strong emitted microwave component, and the circuit for attenuating the emitted microwave component can be connected in parallel with the ground. Since no connected elements are required, the circuit configuration is simplified and miniaturization is possible. In addition, when the microwave strip line is used, a relatively small area is required and it is suitable for miniaturization. Furthermore, since the configuration can be simplified, variations in the amount of attenuation are small and reliability is high.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the circuit section between the mixer and local oscillator in the front end of an embodiment of the present invention, Fig. 2 is an equivalent circuit diagram of the same part, and Fig. 3 is a circuit diagram of a general pulse radar. The configuration diagram and FIG. 4 are explanatory views of the operation of the pulse radar. 1...Microwave oscillator, 2...Circulator, 3...Antenna, 4...Limiter, 5...Front end, 6...RF amplifier, 7...Local oscillator, 8...Mixer, 9...For attenuation Resistance, 10...
...Impedance conversion circuit.

Claims (1)

[Claims for Utility Model Registration] In a radar front end that includes a local oscillator and a mixer that mixes a frequency signal from the local oscillator with a radar received wave and converts the frequency, between the local oscillator and the mixer. A radar front end characterized by inserting a resistor and an impedance conversion circuit in series.