JP2003004839A - Radar - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute a radar wherein the level of a spurious mode radiated from an antenna is suppressed by suppressing the generation of the spurious mode by a magnetron. SOLUTION: The radar is equipped with a transmission-reception part including the magnetron 1 of an oscillator, a circulator 2, the antenna 3 and a limiter 4. The route length L1 between the transmission signal input port of the circulator 2 and the magnetron, the route length L3 between the receiving signal outlet port of the circulator 2 and the limiter 4, and the route length L2 between the antenna port of the circulator 2 and the antenna 3, are respectively set to predetermined lengths to adjust the phase of the return signal of the reflected signal to the magnetron 1 and, by this constitution, the spurious level of a π-1 mode is suppresed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar provided with a magnetron in a transmitting / receiving section.

[0002]

2. Description of the Related Art Conventionally, radars in the microwave band are
A magnetron is used as the oscillator, and radio waves are transmitted and received using a slot antenna or the like.

[0003]

However, in general, although the magnetron has high oscillation efficiency, it has low frequency stability and many spurs (unnecessary oscillation modes) other than the frequency to be used.

The magnetron comprises an anode composed of an even number of vanes and a cathode concentrically provided with the anode. The space of the anode partitioned by the vanes constitutes a resonator. Considering a microwave electric field having a phase difference of π between adjacent resonators, when the frequency of the microwave electric field is f and the number of vanes is N, the microwave electric field is
It rotates around the cathode at an angular velocity of ω = 2πf / (N / 2). Therefore, the DC electric field between the cathode and the anode,
If the magnitude of the DC magnetic field parallel to the tube axis is set appropriately, the electrons orbit the cathode while synchronizing at the same angular velocity as the microwave electric field, and the electron group is accelerated and decelerated by the microwave electric field. And the accelerated electrons are strongly affected by the DC magnetic field, and the orbiting radius around the cathode becomes small, and then collides with the cathode. On the other hand, the decelerated electrons have a larger orbital radius and move toward the anode. In this process, instability occurs in the anode current, and electronic vibration called π mode is excited.

That is, in the magnetron, the frequencies at which the electronic vibration is excited by the space of the anode partitioned by the vanes are π-1, π-2, π-3 in addition to the π mode.
The spurious mode of ... occurs. This is a higher-order resonance mode determined by the number of vanes.

[0006] When such spurious is generated, spurious components are emitted from the antenna, and useless radio waves that do not contribute to the detection capability are radiated. Moreover, depending on the frequency, there is a risk that the surrounding radio wave environment may be adversely affected.

An object of the present invention is to provide a radar that solves the above spurious problem.

[0008]

SUMMARY OF THE INVENTION The present invention is a transmitter / receiver comprising a magnetron connected to a transmission signal input port of a circulator, a limiter connected to a reception signal output port of the circulator, and an antenna connected to an antenna port of the circulator. In the radar provided with, the path between the transmission signal input port of the circulator and the magnetron so that the phase and intensity of the return signal to the magnetron suppress the spurious level of the π-1 mode by the magnetron. A length, a path length between the reception signal output port of the circulator and the limiter, and a path length between the antenna port of the circulator and the antenna are respectively defined.

As a result, the occurrence of the π-1 mode, which has the highest level among the other spurious modes, which uses the π mode as the basic mode, is suppressed.

Further, according to the present invention, the antenna is an array antenna in which a plurality of element antennas are arranged in a substantially straight line, and power is fed in series from the center of the arrangement range of the element antennas in the left-right direction. As a result, the fundamental mode frequency to be used is radiated forward from the array antenna, and the spurious mode radio waves are radiated in directions deviated in the left and right directions from the center, thus suppressing the intensity of spurious mode radiation. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of a transmitting / receiving section of a radar according to the first embodiment. In FIG. 1, 1 is a magnetron as an oscillator. Reference numeral 3 is an antenna for transmitting and receiving radio waves. Reference numeral 4 is a limiter for preventing the transmission signal from propagating to the subsequent stage. Reference numeral 2 is a circulator that propagates the transmission signal from the magnetron 1 to the antenna 3 side and propagates the reception signal from the antenna 3 to the limiter 4.
A down converter 5 converts the received signal into an intermediate frequency signal IF.

A modulator 6 for applying an input pulse to the cathode thereof is connected to the magnetron 1, and the modulator 6 inputs a trigger signal and applies an input pulse to the magnetron 1. As a result, the magnetron 1 outputs pulsed radio waves.

In FIG. 1, the path length of the propagation path (waveguide) between the output port of the magnetron 1 and the transmission signal input port of the circulator 2 is L1, and the path length from the antenna port of the circulator 2 to the antenna 3 is The path length is L2, and the path length of the propagation path from the reception signal output port of the circulator 2 to the limiter 4 is L3. These path lengths L1, L2, L3 affect the return signal to the magnetron 1. That is, the circulator 2
Since a slight impedance mismatch occurs at the transmission signal input port of, the transmission signal is reflected at that position, and the reflection signal returns to the magnetron 1 back and forth through L1. In addition, since a slight impedance mismatch occurs at the connection between the antenna 3 and the propagation path, the transmission signal is reflected at the connection between the propagation path and the antenna. This reflected signal propagates from the circulator 2 to the limiter 4. Also in the input part of the limiter 4, reflection occurs due to impedance mismatch, and the reflected signal returns to the magnetron 1 via the circulator 2. Eventually, the reflected signal returns to the magnetron 1 following the path of L1 → L2 → L2 → L3 → L3 → L1.

The return signal to the magnetron 1 is a composite of the above two reflected signals. The phase / intensity of the π mode and the phase / intensity of the spurious modes such as the π-1 mode of the return signal to the magnetron 1 are determined by the reflection intensity at each reflection point and the path length indicated by L1, L2, and L3. The path lengths L1, L2 and L3 are determined by these return signals so that the π-1 mode spurious intensity output from the magnetron 1 is most suppressed without reducing the π mode intensity.

Here, the impedance unmatched portion of the waveguide is connected to the output port of the magnetron through a phase shifter,
FIG. 2 shows the spurious level output from the magnetron when the phase shift amount of the phase shifter is changed. As shown in this figure, the π-1 mode fluctuates with the phase change of the reflected signal, and when the return signal has a certain phase, the π-1 mode can be suppressed to the minimum.

As described above, there is a frequency dependence between the phase of the return signal to the magnetron and the spurious level,
It can be seen that the spurious level of the predetermined frequency can be selectively suppressed by adjusting the phase of the return signal.

Next, a radar according to the second embodiment will be described with reference to FIGS. FIG. 3 shows an example of the feeding method for the array antenna and the change in the radiation direction due to the frequency change. FIG. 3A is an end-feed type array antenna in which the element antennas E1 to E7 are fed in series from one side.
Here, the adjacent distance La between the respective element antennas E1 to E7 is La.
Is a wavelength on the propagation path and is set to be equal to one wavelength of the used frequency.

(B) shows a plurality of arrayed element antennas E
This is a so-called center-feed type array antenna in which power is serially fed from the center of the array range of 11 to E15 and E21 to E25 in the left-right direction of the array.

Therefore, the used frequency (for example, 9.41 GH)
When the signal of z) is fed, the wavefront of the radio wave radiated from the array antenna becomes parallel to the surface where the element antennas are arranged, as shown by the solid line in the figure. If a signal higher than the used frequency is fed, the feeding phase is delayed as the element antenna is farther from the feeding point for this array antenna. As a result, in the end-feed type shown in (A), as shown by the broken line in the figure, the wavefront (equal phase surface) of the radiated radio wave is emitted so that the wavefront is inclined from the side closer to the feeding point for the array antenna to the side farther. The beam direction is tilted. In the center-feed type shown in (B), the inclination of the radiation beam due to series feeding in the one end direction from the feeding point to the array antenna and the inclination of the radiation beam due to series feeding in the other termination direction are the entire array antenna. Lean from the front to the left and right. as a result,
For the signal components other than the used frequency in the front direction of the array antenna, the radiation directions are dispersed, and the radiation intensity is reduced. Since the frequency of the π-1 mode is higher than the frequency of the π mode which is the fundamental mode, by using the center feed type array antenna shown in (B),
It is possible to suppress the levels of the π-1 mode and higher-order spurious modes.

FIG. 4 shows changes in the intensity of radiation in the front direction when the frequency of the feed signal is changed for the end feed type and the center feed type. Here, the square marks are the characteristics of the end-feed type array antenna, and the triangle marks are the characteristics of the center-feed type array antenna.
As described above, in the end feed type, the gain gradually decreases with distance from the resonance frequency which is the used frequency, whereas in the center feed type, the gain decreases rapidly. With such characteristics, it is possible to sufficiently suppress the radiation intensity of spurious modes such as π-1 mode deviated from the used frequency.

FIGS. 5 and 6 show the radiation pattern directivity when the above center feed type array antenna is used. FIG. 5 shows the case where a signal of 9.41 GHz which is the used frequency is fed, and FIG. 6 shows the case where a signal of 10 GHz whose frequency is deviated from that is fed. In both figures, the horizontal axis is the azimuth angle in the left-right direction where the front direction of the antenna is 0 °.

As shown in FIG. 5, the used frequency is 9.
When a 41 GHz signal is supplied, sharp directivity occurs in the front direction. On the other hand, as shown in FIG. 6, when a signal of 10.0 GHz higher than the used frequency is fed, two peaks occur as a radiation pattern and the directivity width widens.

As described above, since the radio waves other than the used frequency are not focused as a sharp beam, it is possible to suppress the radiation intensity of the spurious mode in the predetermined direction.

[0024]

According to the present invention, the path length between the transmission signal input port of the circulator and the magnetron, the path length between the reception signal output port of the circulator and the limiter, the antenna port of the circulator and the antenna. It is possible to reliably suppress the occurrence of the π-1 mode, which has the highest level among the other spurious modes, which uses the π mode as the basic mode, only by determining the respective path lengths.

Further, according to the present invention, the antenna is an array antenna in which a plurality of element antennas are arranged in a substantially straight line, and the antennas are configured to be fed in series in the left-right direction from the central portion of the arrangement range of the element antennas. Since the spurious mode radio waves are radiated from the center in front of the antenna in a laterally offset direction, the intensity of spurious mode radiation can be reliably suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a transmission / reception unit of a radar according to a first embodiment.

FIG. 2 is a diagram showing an example of spurious levels output from a magnetron used in the radar.

FIG. 3 is a diagram showing a configuration of an array antenna used in a radar according to a second embodiment.

FIG. 4 is a diagram showing an example of changes in radiation intensity with respect to frequency by the array antenna.

FIG. 5 is a diagram showing an example of a radiation pattern in the array antenna.

FIG. 6 is a diagram showing an example of a radiation pattern when the frequency of a power feeding signal in the array antenna is changed.

[Explanation of symbols]

1-magnetron 2-circulator 3-antenna 4-limiter 5-down converter

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5J006 LA12 NA08 PB01                 5J021 AA05 AA07 FA17 FA24 FA26                       FA35 HA04 HA05                 5J070 AB01 AD01 AD08 AK28

Claims (2)

[Claims] 1. A radar comprising a transmitter / receiver comprising a circulator transmitting signal input port connected to a magnetron, a circulator receiving signal output port connected to a limiter, and a circulator antenna port connected to an antenna. The phase length and intensity of the return signal to the so that the π-1 mode spurious level by the magnetron is suppressed, the path length between the transmission signal input port of the circulator and the magnetron, the reception signal output of the circulator. A radar that defines a path length between a port and the limiter and a path length between an antenna port of the circulator and the antenna. 2. The antenna according to claim 1, wherein the antenna is an array antenna in which a plurality of element antennas are arranged in a substantially straight line, and the element antennas are fed in series in the left-right direction from the center of the arrangement range. Radar.