JP2001016042A - Local oscillator-mixer circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small and inexpensive local oscillator-mixer circuit by inputting an RF reception signal from an input terminal during the phase synchronous state between the signal of a main oscillator and the signal of a local oscillator. SOLUTION: When a main oscillator 1 is operated as a pulse radar, a radio frequency(RF) signal is inputted to the port A of a first microstrip line 14 in terms of pulse, and a phase synchronous state with a local oscillation signal is kept for definite time by the capacity of a resonator 17. When the RF reception signal reflected from a target is inputted from the port A through an antenna 4, a circulator 3, an RF amplifier 22 and a coupler 21 at time until the phase synchronous state of the local oscillation signal is removed after the termination of the pulse oscillation of the main oscillator 1, an amplifier 16 operates as a mixer mixing the RF reception signal and the local oscillation signal by nonlinear characteristics. Thus, an intermediate frequency signal as a Doppler signal is outputted from the port B of a second microstrip line 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a local oscillator / mixer circuit used for converting a main frequency into an intermediate frequency in a Doppler radar device.

[0002]

2. Description of the Related Art A conventional Doppler radar apparatus generally uses a "double conversion system" as shown in FIG.

In FIG. 3, a main oscillator 1 as an oscillation source is shown.
RF (Ra) oscillated from a magnetron or TWT
The dio frequency signal is split by the coupler 2 (coupler), and emitted from the antenna 4 to the space via the circulator 3. The signal hits the target, is reflected, and is captured again by the antenna 4. On the other hand, a part of the RF signal oscillated from the main oscillator 1 and branched by the coupler 2 is combined with the 1st LOCAL frequency in the first-stage local oscillator 6 through the mixer 5 and converted into an intermediate frequency signal. After conversion, I
Using the intermediate frequency signal passed through an F (Intermediate Frequency) amplifier 7, the second-stage local oscillator 8 performs 2nd
Local frequency is configured.

An RF reception signal reflected by a target and captured by an antenna 4 is transmitted to a circulator 3 and an RF amplifier 9.
, Is mixed with the 1st Local frequency by the mixer 10 and dropped to the intermediate frequency. Further, the signal is mixed with the second local frequency by the mixer 12 through the IF amplifier 11 to obtain an intermediate frequency signal as a Doppler signal. In the above circuit, in order to obtain a Doppler signal, all the local oscillators used for them need to be synchronized in phase.

[0005]

In the above-described circuit configuration, the circuit is complicated and a phase-locked local oscillator in the tens of MHz band is required. However, there is a problem that the external dimensions are considerably large. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a small-sized, low-cost local oscillator / mixer circuit used in a Doppler radar device.

[0006]

In order to achieve the above object, the present invention provides a first microstrip line having one end connected to an input terminal and the other end connected to an oscillating element which is a non-linear element, and one end connected to an output terminal. And the other end connected to the oscillation element.
And a resonator formed by a microstrip line which is disposed close to and coupled between lines in which the distance between the first microstrip line and the second microstrip line is partially reduced. A local oscillator comprising a varactor diode connected to the resonator, wherein after partially injecting a signal of a main oscillator as an oscillation source from the outside into the input terminal, the signal of the main oscillator and the local oscillator During the phase synchronization with the signal of
By inputting the F reception signal, the oscillating element also operates as a mixer to extract an intermediate frequency signal from the output terminal.

[0007]

With this configuration, a Doppler signal, which is an intermediate frequency signal, can be obtained directly from the local oscillator, so that the radar itself can be reduced in size and simplified.

[0008]

FIG. 1 shows an embodiment of the present invention.
Reference numeral 3 denotes a local oscillator (local oscillator / mixer circuit).
Reference numeral 14 denotes a first microstrip line, and one end (port A) serves as an input terminal for the RF signal and the RF reception signal of the main oscillator 1 (magnetron). 15 is the second
Microstrip line, one end (port B)
Are the output terminals of the intermediate frequency signal. Reference numeral 16 denotes a non-linear element that operates as an oscillation element, such as an FET or an MMIC.
In the case of the present embodiment (FET), the first microstrip line 14 is connected to the gate of the amplifier 16, the second microstrip line 15 is connected to the drain of the amplifier 16, and the source is grounded. Have been.

Reference numeral 17 denotes a resonator formed of a microstrip line, and a varactor diode 1 for frequency control whose one end is grounded or adjusted to a predetermined bias voltage.
8 is connected. Reference numeral 19 denotes a coupler composed of the first microstrip line 14, the second microstrip line 15, and the resonator 17.

The local oscillator 13 oscillates when the following condition is satisfied. Ga is the gain of the amplifier 16, φa
Is the phase of the amplifier 16, Loss is the loss of the coupler 19, and φb is the phase change of the coupler 19 including the line length. Ga> Loss φa + φb = 2π × N (rad) (N = 0, 1 ,
2 ...) When the above condition is satisfied, the local oscillator 13 oscillates at the frequency fLO determined by the resonator 17.

At this time, the Q of the circuit of the local oscillator 13 is set to 30 or more and 50 or less by adjusting the distance between the first microstrip line 14, the second microstrip line 15 and the resonator 17. If a part of the RF signal of the main oscillator 1 is input to the port A of the first microstrip line 14 via the coupler 20 and the coupler 21, the local oscillation frequency fLO becomes equal to the oscillation of the main oscillator 1. Attracting to the frequency fmag, phase synchronization is performed. That is, fLO = fmag, and the phase of fLO = fmag.

FIG. 2 is a time chart of the present embodiment.
a is the RF signal (fmag) of the main oscillator 1, b is the main oscillator 1
Is a local oscillation signal (fLO) of the local oscillator 13 phase-synchronized with the RF signal, and c is an intermediate frequency signal. When the main oscillator 1 is operated as a pulse radar, the RF signal is pulsed to the port A of the first microstrip line 14.
(FIG. 2a), but due to the capacitance of the resonator 17,
The local oscillation signal and the phase synchronization state are held for a fixed time (FIG. 2B).

Therefore, the RF reception signal reflected from the target during a period from the end of the pulse oscillation of the main oscillator 1 to the time when the phase synchronization state of the local oscillation signal is lost is transmitted to the antenna 4, the circulator 3, and the RF amplifier 22. When input from the port A through the coupler 21, the amplifier 16 operates as a mixer that mixes the RF reception signal and the local oscillation signal due to the non-linear characteristic, so that the Doppler signal is output from the port B of the second microstrip line 15. An intermediate frequency signal is output (FIG. 2c). In addition, L
By adding the ow pass filter 23, it is possible to remove only the intermediate frequency signal without leaking the local oscillation frequency fLo.

[0014]

As described above, according to the present invention, a single direct conversion is possible with a small and simple circuit configuration, and the size of the local oscillator and the mixer is smaller than that of the conventional double conversion method. Can be reduced in size, so that there is an advantage that a small-sized, low-cost Doppler radar can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a time chart of the embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional Doppler radar.

[Explanation of symbols]

 1. Main oscillator 2. Coupler 3. Circulator 4. Antenna 5. Mixer 6. 6. First-stage local oscillator IF amplifier8. 8. Second stage local oscillator RF amplifier 10. Mixer 11. IF amplifier 12. Mixer 13. 13. Local oscillator (local oscillator / mixer circuit) First microstrip line 15. Second microstrip line 16. Amplifier 17. Resonator 18. Varactor diode 19. Coupler 20. Combiner 21. Coupler 22. RF amplifier 23. Low Pass Filter

Claims (1)

[Claims] A first microstrip line having one end as an input end and the other end connected to an oscillation element which is a non-linear element, and a second microstrip line having one end as an output end and the other end connected to the oscillation element.
And a resonator formed by a microstrip line which is disposed close to and coupled between lines in which the distance between the first microstrip line and the second microstrip line is partially reduced. A local oscillator comprising a varactor diode connected to the resonator, wherein after partially injecting a signal of a main oscillator as an oscillation source from the outside into the input terminal, the signal of the main oscillator and the local oscillator During the phase synchronization with the signal of
A local oscillator / mixer circuit, wherein the oscillation element operates as a mixer by inputting an F reception signal to extract an intermediate frequency signal from the output terminal.