JP2545875Y2 - Radar transponder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a frequency sweep circuit of a search / rescue radar / transponder.

[Conventional technology]

In recent years, search and rescue radars and transponders for ships and lifeboats mounted on ships and life-rafts have been put into practical use, targeting 9GHz band radars mounted on ships and aircraft. Has been approved as a floating transponder as a commercialization test station ahead of the world, and is equipped on some fishing boats.

This utility was recognized by the IMO (International Maritime Organization)
Already IMO Performance standard (Reso-lution A. *
**) MSC 53/24, Annex 8, COM 31 / WP.1, Annex 5 determine the performance requirements of radar transponders for surviving boats (hereinafter abbreviated as SART). .

This is a recommendation of the CCIR (International Advisory Committee on Radio Communications) [62
8) [TECHNICAL CHARACTER-ISTICS FOR S EARCH
A ND RESCUE R ADAR T RANSPONDERS], with additional requirements for operation.

Here, in order to facilitate understanding of the present invention, a document describing the contents of the SART of the practical use test station will be introduced, and an embodiment of the SART system will be described. Recently, the monthly magazine “Shipbuilding Technology”, '85 / 11,
Vol.18 no.11 P44-P51 has the description.

Currently, P48-P
Of the 51, the former are functionally equivalent and will be approved after some revision.

First, an example of the SART system will be described with reference to the system diagram of FIG. 3 and the waveform diagrams of main parts in FIG.

In FIGS. 3 and 4, when the radar pulse radio wave (a) is emitted, it is delayed by the time of its relative distance and attenuates as shown in (b) before reaching the SART. This pulse radio wave (a) is emitted hundreds to thousands of times per second,
FIG. 3 shows only two shots.

SART is independent of the pulse width of the pulse radio wave (a),
Amplification for obtaining the system trigger (c) is performed based on the leading edge.

Since SAST targets horizontal polarization such as marine radar, all antenna systems transmit and receive with the same polarization. The directivity is omnidirectional in a horizontal plane, and a characteristic of 25 degrees or more in a vertical plane is required. That is, it is determined that the SART itself or a life raft or a lifeboat equipped with the SART must always be pointed at the radar even when exposed to waves.

There is no special tuning circuit in the receiving part of the SART until the system trigger (c) is obtained, and it has a flat broadband characteristic from about 9300 to 9500 MHz.

Therefore, if the arrival level of the radar wave (b) exceeds a certain value, all radar waves within this frequency band can be received. Note that there is concern about a time delay mainly due to the frequency bandwidth of the video intensifier from the reception of the radar wave (b) to the derivation of the system trigger (c). Is used.

The system trigger (c) is a transmission / reception switching circuit (2-input NAND, A
ND gate, etc.), and is added to a pulse train generation circuit for creating a time reference for frequency sweeping.

The comb-shaped pulse (d) created here is divided by a counter to create a response transmission basic pulse (e) having a pulse width of 100 μs.

This value of 100 μs is constant and does not change even when irradiated with radar waves with different pulse repetition frequencies, and the upper limit is limited by this width, but if there are multiple radars in the same direction, the remaining time will be An interrupt can be made about every 110 μs. Also, about one radar
Compatible with radars of about 8700pps (pulse repetition cycle of 115μs or more).

However, the pulse repetition frequency of the target radar is
It exists in 300 to 3000 pps, which is almost equal to the audible frequency bandwidth of the telephone class, and there are few coincidences in direction even if many radars are seen from the SART, and there is no synchronization problem, so there is no practical inconvenience .

This basic pulse is also applied to the low-frequency power amplifier to drive a round speaker for sound monitoring.Sounds such as life-saving rafts and life-saving boats are equipped with SART in advance and can be used by those who can get on The monitor works effectively.

That is, each time the radar wave is irradiated, the approaching state of the ship or the aircraft can be recognized by the sound of the pulse repetition frequency each time. (For example, in the case of irradiation from two types of radars, two sounds are heard every few seconds because the radar antenna is rotating, and simultaneously emits response radio waves as described later.) If it is high, it means that the pulse repetition frequency is high, so you will be searching for a short distance.If the sound continues for a long time, it will be radiated from side lobes, minor lobes, etc. other than the beam width of the radar antenna. It indicates that you are in a close range, and this signal is a chance to launch a signal red flame.

This information will also help to encourage victims.

The response transmission basic pulse (e) is slightly delayed by a pulse delay circuit and is replaced with a response transmission pulse (g). The reason for this is that, as can be seen from the time relationship between the output (f) of the pulse trailing edge extension circuit and the response radio wave (j) of the SART in FIG. The reason is to surely interrupt the loop with respect to time.

Also, if the initial rise time corresponding to the retrace time of the frequency modulation signal (h) is included in the response radio wave (j), unnecessary spectrum is likely to be generated in addition to the occupied frequency bandwidth. The response transmission pulse (g) is subjected to power conversion by an electronic switch (high-speed switch transistor), and drives a microwave FM oscillator.

On the other hand, the comb-shaped pulse train (d) obtains a frequency modulation signal (h) by a saw-tooth wave generation circuit, and the microwave / FM oscillator performs pulse / frequency simultaneous modulation.

The microwave FM oscillator is an electronically tuned oscillator using a micro strip line for the resonance circuit, a varactor diode for frequency modulation, and a GaAs-FET for an oscillation element. The varactor diode's frequency change characteristic is non-linear with respect to the applied voltage, as described later. Therefore, if the frequency sweep is given by a linear saw-tooth wave, the equivalent pulse width τe described later will become narrower depending on the operating frequency of the radar. Thus, it is not possible to provide a desired symbol within a predetermined frequency bandwidth range.

In order to linearize the frequency sweep, it is necessary to apply a predistortion (pre-emphasis) as shown in a waveform (h) of FIG.

(K) and (k ') in FIG. 4 show an ideal frequency sweep pattern after the predistortion is given. Thereafter, response radio waves (j) and (k) are emitted from the transmitting antenna in all directions. (Even if a radar wave of any frequency is irradiated, this radio wave radiates a response frequency of 9300 to 9500 MHz in a predetermined frequency range, as shown in this figure, in a synchronized relationship with each other.) , The video output (m) appears as a pulse train as shown in FIG.
The pulse equivalent pulse width τe is approximately as follows.

τe = B · t / Δf (1) ∴B: Pass band width of the radar receiver (Hz) t: Frequency sweep time per unit (second), 5 in this SART
μs (5 × 10 ⁶ seconds) Δf: Frequency sweep range (Hz), 200 MHz (200
× 10 ⁶ Hz) For example, if the pass band of the radar receiver is 10MHz,
The equivalent pulse width τe is 0.25 μs, and 5 μ
A row of 20 bright spots is displayed every s (about 0.4 nautical miles). In this case, the wider the pass band of the radar receiver, the larger the bright spot becomes and the easier it is to find.

Also, as can be seen from FIG. 4 (k '), the time at which the video output (m) appears varies within the range of 5 .mu.s depending on the operating frequency of the radar.

That is, in the case of a SART in which the frequency is swept from a higher frequency to a lower frequency as shown in FIG. 4, the higher the radar operating frequency, the smaller the distance error of the bright spot appearing first in the pulse train, and the vicinity of 9300 MHz Will see about 0.4 nautical miles behind the SART.

This radar has a receiver pass bandwidth of 3 MHz, and also receives an image frequency described later. This can be done by adding an image rejection filter (or SSB Mi
If xer) is not inserted, two waves can be received at the operating frequency, and an image of a sequence of 40 luminescent spots instead of a sequence of 20 luminescent spots is obtained.

For example, if the transmitting and receiving frequency of the radar is 9375 MHz, the intermediate frequency is 30 MHz, and the local oscillation frequency is 9405 MHz, which is set to the higher one, the image frequency is 9435 MHz, and two bright spot sequences of 9375 MHz and 9435 MHz are obtained. They will appear alternately in the distance direction.

In any case, if such a large number of bright spot sequences are found, it means that a sea disaster has occurred in the direction of the distance and rescue is being sought.

As the radar-equipped ship approaches its target, the PPI image of the multi-spot sequence will spread out in a fan-like fashion for the same reason as described for the acoustic monitor, and will appear almost 360 degrees around short distances. become. (On the SART side, the sound continues for a long time, or in the case of a floating type, the blinking type indicator light is almost continuously lit.) If the direction of the SART tends to be unknown on the radar side as it is, the gain adjustment of the radar receiver must be adjusted. If you check the direction again, you should find SART right in front of you.

In addition, according to the performance requirements of IMO, after starting this device, the receiving condition is continued for 4 consecutive days, then the repetition frequency is 1000PPS.
Radars are required to have a response transmission capability of at least 8 hours in a row.

In view of the low-temperature characteristics and long-term storability, SART dedicated batteries tend to use lithium-based batteries. Lithium batteries are roughly classified into two systems, one of which is a unit voltage of 3.6V.
And a manganese dioxide type with an elementary voltage of 3.0V.

The former excels in all aspects such as power density, low-temperature characteristics, and long-term storage characteristics. However, if the container is torn, there is a concern that a lethal amount of toxic gas will be generated. For those SARTs that do not meet the above criteria, lithium manganese dioxide batteries are recommended.

As a power switch, a reed switch is often used for a life raft or lifeboat, and a mercury switch is often used for a floating type. A mercury switch attempts to open and close an electrode sealed in a container by moving mercury particles.

The flashing indicator lamp for the floating type shown in FIG. 3 is placed in a transparent lens and blinks an incandescent lamp having a horizontal luminous intensity of about 1 candela. Therefore, in the daytime, the sunlight is detected and turned off, and the light is automatically turned on and off with sunset. However, when the radar radio wave is emitted, it interrupts according to the pulse regardless of day or night, and approaches the continuous lighting. The container that wraps them is a completely waterproof type that also serves as a radome, but it also has a moisture absorption indicator that warns when the relative humidity inside rises abnormally as a guide for periodic inspections.

[Problems to be Solved by the Invention] As described above, since the microwave FM oscillator shown in FIG. 3 uses a varactor diode, when a frequency sweep is given by a linearly changing sawtooth wave, a predetermined frequency sweep range is obtained. In particular, in the reduction, the pulse width becomes narrower than the equivalent pulse width obtained by the equation (1), and the bright spot on the PPI of the radar becomes smaller.

That is, for the varactor diode, FIG. 2 (a) shows the applied voltage vs. capacitance change characteristics, and FIG. 2 (b) shows the applied voltage vs. frequency change characteristics when used as an oscillator. With respect to the varactor diode having such characteristics, the frequency is swept by the varactor diode with respect to a linear sawtooth voltage (horizontal axis is time T, vertical axis is voltage V) as shown in FIG. If the horizontal axis is represented by time T and the vertical axis is represented by frequency F, the result is as shown in FIG. 2 (b). In FIG. 5 (b), the equivalent pulse width becomes narrower in the reduction with respect to the predetermined reception bandwidth by the radar (FIG. 5 (c)).

[Means for Solving the Problems] A radar transponder according to the present invention includes an antenna for receiving a pulse radar radio wave from a radar, a detector for detecting a microwave received by the antenna, and a detector for detecting the microwave. A video amplifier that amplifies the output of the video amplifier, a pulse generation circuit that generates a pulse train signal for determining the transmission time of the transmission signal based on the output from the video amplifier, and a pulse train obtained by dividing the pulse train signal from the pulse generation circuit A frequency divider that generates a signal, an electronic switch circuit that generates a drive pulse when a pulse signal is input from the frequency divider, and a pulse train signal that is supplied from the pulse generation circuit to generate a sawtooth voltage And a drive pulse from the electronic switch circuit is input,
An oscillator using a varactor diode that performs a frequency sweep in a predetermined frequency range based on the sawtooth voltage, and an antenna that radiates a transmission signal swept by the oscillator into space, the sawtooth generator includes: A pulse transformer for boosting the pulse voltage from the pulse generator, and performing impedance conversion, a charge / discharge circuit for charging / discharging the output of the pulse transformer, and setting a pedestal voltage connected to the charge / discharge circuit, and A temperature compensating circuit for compensating a temperature characteristic of the varactor diode, the temperature compensating circuit varying the pedestal voltage, supplying a charge / discharge signal from the charge / discharge circuit to the oscillator, and setting the radar in the predetermined frequency range; , The equivalent pulse width with respect to the reception bandwidth is equalized.

[Operation] The pulse transformer in the radar transponder according to the present invention boosts the voltage to a desired sweep voltage, the temperature compensation circuit can arbitrarily adjust the sawtooth voltage, and the current consumption can be reduced.

Embodiment An embodiment of the present invention will be described below in detail with reference to FIGS. 1 and 5.

In FIG. 1, (1) is an input terminal to which the comb-shaped pulse train (d) of FIG. 3 is applied, and (2) is an input terminal of a circuit current, both of which are applied with a positive polarity. (3) is a base bias resistor of the NPN transistor (10), (4) is a resistor for limiting the emitter current, (5) is a resistor for discharging, (6)
Is a resistor for maintaining the pedestal voltage of the sawtooth wave voltage with predistortion together with the resistor (7), the resistor (8) and the thermistor (9). It constitutes the temperature compensation circuit of the FM oscillator.

(11) is a pulse transformer, which performs both impedance conversion and pulse voltage boosting.

If the pulse transformer (11) is used here, a relatively high degree of freedom can be obtained even when the frequency sweep voltage to be applied to the varactor diode (17) needs to be higher than the power supply voltage.

 In addition, the mark indicates the polarity of the pulse transformer.

(12) and (13) are silicon diodes, (12) acts as an isolator, and (13) acts as a clipper. (1
4) and (15) are bypass capacitors, and (16) is a charging capacitor, which constitutes a charging / discharging circuit together with the discharging resistor (5).

The varactor diode (17) constitutes an electronically tuned oscillator together with a micro strip line, GaAs-FET, etc., as described in the description of the conventional microwave FM oscillator in FIG.

A comb-shaped pulse train signal (d) as shown in FIG. 4 is input to the input terminal (1) shown in FIG. This comb-shaped pulse train signal (d) is, for example, as shown in FIG.
This is 20 pulse train signals in μs. When such a pulse train signal (d) is applied to the input terminal, the voltage is boosted by the pulse transformer (11) through the transistor (10), and the discharging resistor (5) and the charging capacitor (16) are passed through the diode (12). ). At this time, the output of the charge / discharge circuit has a discharge characteristic as shown in FIG. Such a discharge characteristic has a time constant RC
Varies by. A signal as shown in FIG. 6 is applied to the varactor diode (17). Here, the characteristics of the varactor diode (17) are shown in FIGS.
Since the characteristics shown in FIG. 6 are exhibited, by adding the characteristic waveform shown in FIG. 6 to the varactor diode (17), the varactor diode (17) can function as an equalizer. Frequency change characteristics (k) of
It can be linearized as in (k '). The linearity can be obtained by appropriately selecting the time constant of the photodischarge circuit in accordance with the characteristics of the varactor diode (17). In FIG. 4, the lowest voltage (the pedestal voltage) portion of the continuous sawtooth waveform of the waveform (n) can be compared by changing the above-mentioned specification values of the temperature compensation circuit section, particularly, by changing the resistor (8). The current diverted to this portion can be reduced to a negligible level by increasing the value of the resistor group as a whole.

This is because the varactor diode (17) requires only the voltage and consumes no current, so that the impedance can be considered to be close to infinity in the frequency band of the frequency sweep signal. Further, since the transistor (10) is automatically biased by the pulse of the comb-shaped pulse train (d), there is an advantage that no current flows during a time period other than this pulse.

[Effects of the Invention] As described above, the radar transponder according to the present invention supplies the charge / discharge signal to the varactor diode. , It is possible to obtain a uniform equivalent pulse width over the entire frequency band. In addition, the practical value is large, for example, energy saving can be achieved with a simple circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
(B) is a static characteristic diagram of the frequency-swept varactor diode of FIG. 1 and a frequency change characteristic diagram of an oscillator using the same, FIG. 3 is a system diagram of a conventional radar transponder, and FIG. 4 is a diagram of FIG. 5 (b) and 5 (c) illustrate a frequency characteristic diagram by a varactor diode and an equivalent pulse width with respect to the waveform diagram of FIG. 5 (a) for explaining the operation of each portion of the system diagram. FIG. 6 is an output waveform diagram of the charge / discharge circuit according to the present invention. In FIG. 1, (3) to (8) are resistors, (9) is a thermistor, (10) is an NPN transistor, (11) is a pulse transformer, (12) and (13) are silicon diodes,
(14) to (16) are capacitors. In these drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Scope of request for utility model registration] 1. An antenna for receiving radio waves of a pulse radar from a radar, a detector for detecting microwaves received by the antenna, a video amplifier for amplifying an output of the detector, and a signal from the video amplifier. A pulse generation circuit for generating a pulse train signal for determining the transmission time of the transmission signal based on the output, a frequency divider for dividing the pulse train signal from the pulse generation circuit to generate a pulse signal, and An electronic switch circuit for generating a drive pulse when a pulse signal is input, a sawtooth wave generator receiving a pulse train signal from the pulse generation circuit to generate a sawtooth voltage, and the electronic switch circuit An oscillator using a varactor diode that performs a frequency sweep in a predetermined frequency range based on the sawtooth voltage when the drive pulse is input from the An antenna that radiates a transmission signal swept by an oscillator to a space, wherein the saw-tooth wave generator boosts a pulse voltage from the pulse generator and performs impedance conversion. A charge / discharge circuit for charging / discharging the output of the device and a pedestal voltage connected to the charge / discharge circuit; and
A temperature compensating circuit for compensating a temperature characteristic of the varactor diode, the temperature compensating circuit varying the pedestal voltage, supplying a charge / discharge signal from the charge / discharge circuit to the oscillator, and providing the radar in the predetermined frequency range. A radar transponder for equalizing an equivalent pulse width with respect to a receiving bandwidth of the radar.