JP2009281868A - Microwave frequency converter and radar receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microwave frequency converter to be used in a radar receiver capable of receiving a signal continuously from a far position to a close position. <P>SOLUTION: A first microwave signal (an RF signal) which is input to a limiter 20 and is pulse-modulated is input to an FET amplifier 40 so as to be amplified. An output of the FET amplifier 40 is input to a first mixer. A second RF signal obtained in such a manner that a branch circuit 23 is connected to a gate bias channel of the FET amplifier 40 so as to generate a leakage, is applied to a second single mixer 24. An output from a local oscillator 26 is applied to local oscillation terminals of both the mixers 24, 25. An IF output of the first mixer 25 is applied to a first IF amplifier 29. An IF output of the second mixer 24 is directly applied to a second IF amplifier 31. After amplitudes of the IF amplifiers 29, 31 are adequately tuned, the outputs are detected and added by a detection/addition circuit 32 so as to be output therefrom, and an image of the added result is displayed on a radar display device. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a microwave frequency converter used in a radar receiver and a radar receiver using the same.

  The configuration of the pulse radar is shown in FIG. The pulse radar shown in FIG. 1 outputs a pulse signal having an oscillation frequency of, for example, 9.41 GHz from the magnetron 1 (for example, a pulse width of 1 μs and an output of 10 kW), radiates in the air from the antenna 3 via the circulator 2, and is reflected by an object. The received signal is again received by the antenna 3 and guided to the limiter 4. The signal input to the frequency converter 5 via the limiter 4 is mixed with the output of the local oscillator 6 (local signal, for example, 9.47 GHz) and converted to an intermediate frequency (IF signal) of, for example, 60 MHz. The IF signal is amplified by the IF amplifier 7, converted into a video signal by the signal processing circuit 8, and an image is displayed on the radar display device (PPI) 9. Note that the limiter 4 may be used to prevent the frequency converter 5 from being damaged due to the input of a large signal.

  FIG. 2 shows a conventionally known circuit configuration of a microwave frequency converter used in a pulse radar as shown in FIG.

  The microwave frequency converter of this example has two independent mixer circuits 24 and 25. One circuit is a single balance mixer 24, and the other circuit is a double balance mixer 25 including an IF output synthesizer 27, each having a signal terminal, a local oscillator terminal, and an intermediate frequency terminal.

  This conventionally known microwave frequency converter is related to Patent Document 1 and a pulse-modulated microwave signal (RF signal) input to an input terminal 21 of a limiter 20 is amplified by an RF amplifier 22 to be double balanced mixer 25. The signal is mixed with the signal of the local oscillator 26 (local signal), and the two IF outputs are synthesized by the built-in IF output synthesizer 27 to obtain a synthesized output at the IF output terminal 28. On the other hand, the limiter 20 and the RF amplifier 22 are connected to the input terminal of the single balance mixer 24 via the branch circuit 23 to obtain an IF output.

  The output of the local oscillator 26 is applied to the local oscillation terminals of the mixers 24 and 25. The IF output of the double balance mixer 25 is synthesized by an IF output synthesizer 27, outputted to an IF output terminal 28, and applied to an IF amplifier 29. On the other hand, the IF output of the single balance mixer 24 is output to the IF output terminal 30 as it is and applied to the IF amplifier 31.

  The outputs of the IF amplifiers 29 and 31 are detected by a detection and addition circuit 32, added and output as a video signal to an output terminal 33, and an image is displayed on a radar display device (PPI) through a signal processing circuit. A logarithmic amplifier may be used as the IF amplifier.

JP 2001-111447

  By the way, the radar pulse signal emitted from the antenna is received as a smaller signal as the reflecting object is farther, received as a larger signal as the reflecting object is closer, and received as a smaller signal as the reflecting object is smaller. A larger signal is received as a larger signal.

  Along with this, the input signal fluctuates, but when the input power increases, a saturation phenomenon of the double balance mixer 25 appears first. As the input power further increases, the RF amplifier 22 is saturated and the impedance changes. As the input power further increases, the impedance of the limiter 20 changes. That is, the reflection coefficient of the input terminal of the RF amplifier 22 increases, and then the reflection coefficient of the limiter 20 increases.

  When the reflection phenomenon occurs at two locations, resonance occurs between them. Since this resonance phenomenon and each impedance change in a complicated manner depending on the input power, the phase and amplitude at the point where the branch circuit 23 is connected change in a complicated manner. That is, the microwave power induced in the branch circuit 23 is complicatedly changed by this resonance.

  For this reason, the conventional microwave frequency converter as described above has the following drawbacks.

  First, since the connection between the limiter 20 and the RF amplifier 22 is connected to the input terminal of the single balance mixer 24 via the branch circuit 23, the loss of the branch circuit 23 enters the input side of the RF amplifier 22, so that the amplification degree Decrease and NF degradation.

  In addition, since power is extracted from two intermediate points where the reflection coefficient increases, the power input to the single balance mixer 24 connected via the branch circuit 23 fluctuates greatly, and the IF output linearity with respect to the input power Sex cannot be obtained.

  That is, when the output of the single balance mixer 24 and the output of the double balance mixer 25 are combined, the input / output characteristics fluctuate. This is because there is a high possibility that the IF output power does not change even if the RF signal power changes. When a phenomenon that does not change in output power appears, the video signal also does not change, and the presence or absence of the target is not displayed on the radar display device.

  In order to solve this problem, there is a method in which a directional coupler is connected to the connection between the limiter 20 and the RF amplifier 22 and only the RF power propagating from the limiter 20 toward the RF amplifier 22 is guided to the branch circuit 23. Since the directional coupler requires a length equal to or longer than λ / 4 of the operating frequency (λ is the wavelength of RF at the operating frequency), there is a drawback that the device becomes large.

  Further, when an RF signal is output from the connection between the limiter 20 and the RF amplifier 22 via the branch circuit 23, the loss corresponding to this coupling coefficient increases, the NF viewed from the input terminal 21 increases, and the double balance mixer 25 Was the cause of the performance degradation that the output of.

  The present invention provides a microwave frequency converter used in a radar receiver that can continuously receive from a long distance to a very short distance. More specifically, the present invention solves the above-described conventional problems. In order to provide a microwave frequency converter characterized by having a structure in which a saturation phenomenon does not appear over a wide input power range by reducing the influence of resonance between the limiter and the RF amplifier. Is.

  The microwave frequency converter according to claim 1 of the present invention branches the output of one oscillator to each local oscillation terminal of two independent mixer circuits having a signal terminal, a local oscillation terminal, and an intermediate frequency terminal. The signal is input as a local oscillation signal, and the output signal of the FET amplifier is directly input to one signal terminal of the mixer circuit, and the other signal terminal of the mixer circuit is provided on the gate bias line of the FET amplifier. In addition to being connected via a branch circuit, an independent intermediate frequency signal can be output to each intermediate frequency terminal of each of the two mixer circuits.

  According to the second aspect of the present invention, the pulse-modulated first microwave signal input to the limiter is input to the FET amplifier for amplification, and the output of the FET amplifier is input to the first mixer circuit, A branch circuit is connected to the gate bias line of the FET amplifier, the second microwave signal obtained by leakage is applied to the second mixer circuit, and the local oscillator terminal of both the mixer circuits is connected to the local oscillator terminal. Apply the output, apply the IF output of the first mixer circuit to the first IF amplifier, apply the IF output of the second mixer circuit as it is to the second IF amplifier, and amplify both IF amplifiers After adjusting the degree, the output is detected and added by a detection / addition circuit, and output, so that an image can be displayed on the radar display device.

  According to the third aspect of the present invention, there is provided the microwave frequency converter according to claim 1 or 2, wherein one mixer circuit of the two mixer circuits inputs after the microwave signal is amplified by the microwave amplifier. And the other mixer circuit is constituted by a mixer that inputs a part of the microwave signal by connecting to a gate bias line of the FET amplifier.

  A radar receiver according to claim 4 is characterized by using the microwave frequency converter according to any one of claims 1 to 3.

  In the present invention, the first mixer circuit is not limited to the double balance type. If the single-ended mixer is the first mixer circuit, there is no IF combiner. In that case, the double balance mixer may include the IF combiner as described above.

  The present invention can receive power substantially proportional to a signal reflected from a short distance compared to a conventional microwave frequency converter, and therefore, not only a long distance but also a ship that is the main purpose of use of recent ship radars. Alternatively, there is an effect that it is possible to recognize a target object up to a very short distance, which is a very important function for preventing a collision with a fixed object.

  The best mode for carrying out the present invention will be described below with reference to the embodiment shown in FIG. In the following description, the same blocks and terminals as those in FIG.

First, the configuration and operation of this embodiment will be described.
The pulse-modulated first microwave signal (RF signal) input to the limiter 20 is input to the FET amplifier 40 and amplified. The output of the FET amplifier 40 is input to the first mixer circuit 25. The second RF signal obtained by connecting the branch circuit 23 to the gate bias line of the FET amplifier 40 and leaking is applied to the second mixer circuit 24 which is a single balance mixer.

  The output of the local oscillator 26 is applied to the local oscillator terminals of both mixer circuits 24 and 25. The IF output of the first mixer circuit 25 is synthesized by the built-in IF output synthesizer 27 and applied to the IF amplifier 29. The IF output of the second mixer circuit 24 is applied to the IF amplifier 31 as it is. After the amplification levels of both IF amplifiers 29 and 31 are appropriately adjusted, the output is detected and added by the detection and addition circuit 32 and output, and the image is displayed on the radar display device.

  Next, the operation principle of this embodiment will be described with reference to FIG. The difference of this embodiment from the conventional example is that the branch circuit 41 is connected to the gate bias circuit of the FET amplifier 40 as shown in FIG.

  First, the RF amplifier 40 is composed of an FET (HEMT). The gate impedance of the FET (HEMT) has a property of monotonically decreasing as the input power increases. Therefore, if the branch circuit 41 is connected in the immediate vicinity of the gate bias line of the FET amplifier, the power to the branch circuit 41 increases monotonously without being affected by the resonance between the limiter 20 and the RF amplifier 40. .

  The signal terminal to the mixer circuit 24 is connected to the gate bias line of the FET amplifier 50 through a coupling capacitor. The gate bias line of the FET amplifier is composed of a λ / 4 bias line and a λ / 4 open stub, and a negative gate bias is applied to the connection point between the λ / 4 bias line and the λ / 4 open stub via a fixed resistor. Yes. Since the connection point between the λ / 4 bias line and the λ / 4 open stub is theoretically grounded due to the characteristics of the λ / 4 open stub, no RF signal voltage is generated.

  However, in reality, the length of the λ / 4 open stub deviates from λ / 4, and a slight RF signal voltage is generated due to the parasitic resistance. Conventionally, the RF signal leaking into the λ / 4 bias line has been wasted by a resistor included in the gate bias circuit. An RF signal leaking to the connection point between the λ / 4 bias line and the λ / 4 open stub is taken out by a coupling capacitor, and the RF signal is input to the second mixer circuit 24. That is, the output of one oscillator is branched and input as a local oscillation signal to each local oscillation terminal of two independent mixer circuits, and a microwave signal is amplified by a FET amplifier at the signal terminal of one mixer circuit 25 The other mixer circuit 24 is connected to the gate bias line of the FET amplifier to input a part of the microwave signal, and the intermediate frequency signal is output independently to each intermediate frequency terminal. Thus, the output power saturation is greatly improved by adding the signals after amplification with an IF amplifier, detection and conversion into a video signal.

  In addition, two signals are added together at the input stage of the conventional signal processing circuit, and the subsequent processing can be performed in the conventional manner, and no change in usage is required.

  In order to achieve the above object of the present invention, one mixer circuit 25 of the two mixer circuits described above is an image suppression mixer configured by two mixers that are input after a microwave signal is amplified by a microwave amplifier, The other mixer circuit 24 can be configured with a mixer that inputs a part of the microwave signal by connecting it to the gate bias line of the FET amplifier by adopting the same configuration as the conventional example described above.

  Similarly to the conventional example, the output of the local oscillator 26 is applied to the local oscillation terminals of the mixer circuits 24 and 25. The IF output of the mixer circuit 25 is output synthesized by the built-in IF output synthesizer 27, output to the IF output terminal 28, and applied to the IF amplifier 29. On the other hand, the IF output of the mixer circuit 24 is output to the IF output terminal 30 as it is and applied to the IF amplifier 31.

  Each IF amplifier 29, 31 uses a logarithmic amplifier as in the prior art, but its output is detected by a detection / addition circuit 32 after adjusting the amplification degree of the IF amplifiers 29, 31, and added to a video signal at an output terminal 33. And the image is displayed on the radar display device (PPI) through the signal processing circuit as in the prior art.

  FIG. 5 shows input / output characteristics of each IF output terminal of the microwave frequency converter according to the conventional example (A) and the present embodiment (B).

  The IF output terminal 28 has the same input / output characteristics as those of the conventional microwave frequency converter, but the RF signal branched by the branch circuit 41 at the IF output terminal 30 is 10 dB to 20 dB from the direct RF signal. Since this is an attenuated signal, saturation begins when the RF input power is about +20 dBm.

  A signal having the characteristics shown in FIG. 5 with respect to the RF input power is amplified by IF amplifiers (logarithmic amplifiers) 29 and 31 with an appropriate degree of amplification, detected by the detection and addition circuit 32, and the relationship between the added output voltages ( The input / output characteristics are shown in FIG. As is apparent from FIG. 6, the influence of resonance between the limiter 20 and the RF amplifier 40 is reduced in this embodiment with respect to the input / output characteristics of the conventional microwave frequency converter shown in FIG. Recognize.

  This means that when the microwave frequency converter of the present embodiment is used for a radar, a large signal reflected from a short distance is not saturated over a wide range compared to a radar using a conventional microwave frequency converter. This means that the target object can be recognized continuously from a long distance to a very short distance.

In the above description, a single balance type mixer and a double balance type mixer are used for the mixer circuits 24 and 25, respectively. However, the present invention is not limited to this, and any type of mixer such as a single end type or a triple balance type can be used. can do.

  The microwave frequency converter according to the present invention is suitable for use in a small radar such as a leisure boat.

It is a block circuit diagram which shows the block diagram of a pulse radar. It is a block circuit diagram which shows the circuit structure of the conventional microwave frequency converter. It is a block circuit diagram showing the circuit composition of one embodiment of the microwave frequency converter concerning the present invention. It is a circuit diagram which shows RF amplifier and a branch circuit of the microwave frequency converter which concerns on this invention. It is a graph which shows the input-output characteristic of the mixer circuit output terminal of the microwave frequency converter of the past (A) and this invention Example (B). It is a graph which shows the input-output characteristic of each IF amplifier output terminal of the microwave frequency converter of the past (A) and this invention Example (B).

Explanation of symbols

1: Magnetron 2: Circulator 3: Antenna 4: Limiter 5: Frequency converter 6, 26: Local oscillator 7, 29, 31: IF amplifier 8: Signal processing circuit 9: Radar display device (PPI)
20: limiter 22, 40: RF amplifier 25: double balance mixer 27: IF output synthesizer 28, 30: IF output terminal 23, 41: branch circuit 24: single balance mixer 32: detection addition circuit 33: output terminal

Claims (4)

The output of one oscillator is branched and input as a local oscillation signal to each local oscillation terminal of two independent mixer circuits having a signal terminal, a local oscillation terminal, and an intermediate frequency terminal, and one signal terminal of the mixer circuit The output signal of the FET amplifier is directly input, and the other signal terminal of the mixer circuit is connected via a branch circuit provided in the gate bias line of the FET amplifier, and each of the two mixer circuits A microwave frequency converter capable of outputting an independent intermediate frequency signal to the intermediate frequency terminal. The pulse-modulated first microwave signal input to the limiter is input to the FET amplifier for amplification, and the output of the FET amplifier is input to the first mixer circuit, and is branched to the gate bias line of the FET amplifier. The second microwave signal obtained by leakage is applied to the second mixer circuit, the output of the local oscillator is applied to the local oscillation terminal of both mixer circuits, and the first The IF output of the mixer circuit is applied to the first IF amplifier, the IF output of the second mixer circuit is applied to the second IF amplifier, and the output is detected and added after adjusting the amplification degree of both IF amplifiers. A microwave frequency converter characterized by being able to detect, add and output by means of a signal and display an image on a radar display device. 3. The microwave frequency converter according to claim 1, wherein one mixer circuit of the two mixer circuits includes two mixers and one IF output synthesizer that are input after a microwave signal is amplified by a microwave amplifier. A microwave frequency converter comprising: an image suppression mixer configured, wherein the other mixer circuit is configured by a mixer that inputs a part of a microwave signal by connecting to a gate bias line of an FET amplifier. A radar receiver comprising the microwave frequency converter according to any one of claims 1 to 3.