JPH08105955A - Radar device - Google Patents

Abstract

PURPOSE: To provide a radar device having the capability of giving a high resolution by using a relatively small antenna for reducing beam width equivalently. CONSTITUTION: Regarding a radar to be installed on a moon-orbital observation satellite 1 or the like, a phased array antenna 4 is used as an antenna for transmission and receiving in common, and a feeding phase for each antenna element is adjusted for maintaining a difference in each beam axis between a transmission beam 6 at the time of transmission and a receiving beam 7 at the time of receiving, so as to superpose only a part of a transmission beam pattern and a receiving beam pattern on an observation object zone. Constitution is thereby made, so as to form a composite transmission and receiving beam 15 having equivalently narrow breadth.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar apparatus equivalent to narrowing a beam width to obtain high resolution.

[0002]

2. Description of the Related Art Generally, a radar device is designed to perform transmission and reception with a single antenna via a transmission / reception switching unit, and its azimuth direction resolution is that of radio waves emitted from the antenna toward an observation target. In order to obtain a high resolution (ability to discriminate small objects) related to the beam width, a narrow beam width is required. It is well known that a large aperture antenna is required to form a narrow beam width. However, there is a limit to the size of an antenna used as a part of a radar system, not only to be mounted on a flying object such as a spacecraft but also to be installed on the ground.
There is also a limit on the transmission frequency from the viewpoint of the properties of the object (object) to be observed and the effective use of the frequency. Due to such restrictions, the beam width of the antenna is generally equal to these two.
Since it is determined by two parameters, the degree of freedom is small and a compromise is made to some extent at present.

[0003]

By the way, particularly in a radar device mounted on a spacecraft or the like, it is desired that the size of the antenna be as small as possible and the beam width be made small to have a high resolution. However, under the above constraint, there is a problem that an antenna with a large aperture is inevitably required to obtain a high resolution for an object, and thus it is extremely difficult to realize a high resolution.

The present invention has been made in order to solve the above-mentioned problems in the conventional radar device, and a radar in which a beam width is substantially narrowed while a relatively small antenna is used to obtain high resolution. The purpose is to provide a device.

[0005]

In order to solve the above problems, the present invention provides a phased array antenna as a transmitting / receiving antenna in a radar device for ground installation or mounted on a flying vehicle such as a spacecraft. , Adjusting the feeding phase for each antenna element to make each beam axis of the transmission beam at transmission and the reception beam at reception different, so that only a part of the beam pattern at transmission and the beam pattern at reception is observed in the observation area. The beam widths are configured so as to overlap with each other, and an equivalent narrow beam width is formed.

As described above, the phased array antenna is used as a transmitting / receiving antenna, the feeding phase is adjusted, and the beam axes of the transmission beam and the reception beam are made different, and a part of the transmission beam pattern and the reception beam pattern is observed in the observation area. By configuring so that only the overlapping areas overlap each other, only the reflected beam of the transmitted beam irradiated on the narrow overlapping area will be received as the received beam, so it is equivalent to irradiating radio waves with an antenna having a substantially narrow beam width. The effect of is obtained. In this case, the power loss increases, but this can be easily dealt with by increasing the transmission power.

[0007]

EXAMPLES Next, examples will be described. FIG. 1 is a conceptual diagram of an embodiment in which the radar device according to the present invention is applied to a lunar underground exploration radar system mounted on a lunar orbit observation satellite.
3 is a schematic view of the embodiment shown in FIG. 1 as seen from the lateral direction, and FIG. 3 is a schematic view of the embodiment shown in FIG. 1 as seen from above. In the figure, reference numeral 1 denotes a lunar orbiting satellite,
It orbits the moon at an altitude of 70-100 km above,
The satellite 1 is equipped with a radar device 5 including a transmission / reception device 3, a phased array antenna 4, and the like. Reference numeral 6 is a transmission beam formed by adjusting the feeding phase to each antenna element in the phased array antenna 4, and reference numeral 7 is a reception beam similarly formed by being shifted in time from the transmission beam 6. Reference numerals 8 and 9 denote beam axes of the transmission beam 6 and the reception beam 7, respectively. The beam axes 8 and 9 are offset angles θ _t and θ with respect to a vertical axis 10 with respect to the lunar surface 2, respectively.
_{At r} , the phase of each antenna element of the phased array antenna is adjusted such that the beam pattern deviates in the opposite direction from the vertical axis and a part of each beam pattern overlaps on the lunar surface 2. In FIG. 1, 2-1 to 2-2 and 2-3
Indicates the first surface, the second surface, and the third surface of the lunar surface 2, and the arrow attached to the satellite 1 indicates the traveling direction of the satellite 1.

When the transmission beam 6 is radiated from the phased array antenna 4 of the radar apparatus 5 having the above-described configuration toward the moon 2 with a beam width β as shown in FIG. The circular area 11 shown in FIG. 3 is irradiated with the transmission beam. On the other hand, the beam width of the reception beam 7 formed at a time offset by the phased array antenna 4 is also β, and the region 12 of the moon 2 on the basis of the reception beam pattern depends on the beam pattern of the transmission beam 6. This is an area having an overlapping portion 13 that partially overlaps with the area 11.

Thus, the phased array antenna 4
Is configured so that only a part of the transmission beam pattern and the reception beam pattern overlap with each other on the lunar surface 2 that is the observation target area, so that the reception beam 7 receives only the reflected beam from the overlap portion 13. Therefore, the phased array antenna 4 is equivalent to forming the combined transmission / reception beam 15 having a narrow equivalent beam width ω corresponding to the overlapping portion of the transmission beam pattern and the reception beam pattern, and the resolution can be improved. It becomes possible.

In this embodiment, the transmission beam width and the reception beam width β are set to 16 degrees, and each beam axis is shifted by about 6 degrees in the opposite direction with respect to the vertical axis, so that the equivalent beam width ω becomes about 4 degrees. can do. FIG. 4 shows a transmission beam when transmitting from a single phased array antenna with a beam width β = 16 ° and an offset angle θ _t = 6 °, and a transmitting beam when transmitting with a beam width β = 16 ° and an offset angle θ _r = 6 °. FIG. 8 is a diagram showing a calculation example of each beam pattern in the case where the reception beams are formed and the respective beams are superimposed to form a combined beam having an equivalent beam width of ω = 3.8 °; The reception beam pattern, c, indicates a combined beam pattern.

Further, in the radar device of the above embodiment, it is possible to measure the thickness of the topsoil on the moon surface and high resolution. That is, in order to measure the thickness of the lunar surface soil, the transmitted beam 6 formed by the phased array antenna 4 is reflected from the first surface 2-1 of the lunar surface 2 and returns, It must be physically distinguishable at the receiver from the reflected beam returning from the surface 2-2. In the above embodiment, the transmission beam pattern and the reception beam pattern are partially overlapped to form a combined transmission / reception beam 15 having a narrow equivalent beam width ω. In the following description, it is assumed that the combined transmission / reception beam 15 is formed from the phased array antenna 4. In FIG. After the reflected beam from one intersection A with the first surface 2-1 has reached the receiver, the intersection of the perpendicular dropped from the phased array antenna 4 to the moon 2 and the second surface 2-2 The reflected beam from B (the shortest part between the phased array antenna 4 and the second surface 2-2) must reach so as to distinguish between the two.

Since the power of the reflected beam from point A on the first surface 2-1 of the lunar surface 2 is much larger than the power of the reflected beam from point B on the second surface 2-2, points A and B In order to clearly distinguish the reflected beam from the point, it can be seen that when the pulse width is ignored and the phased array antenna position is O, the following equation (1) is satisfied: OA length <OB length It is ... (1)

If the above equation (1) is established, the thickness HB (depth resolution) of the first layer can be measured. In order to improve this depth resolution, the length of OA is increased. Should be shortened, that is, the length of AH should be shortened.
Note that point H is the intersection of the perpendicular drawn from the phased array antenna 4 to the moon surface 2 and the first surface 2-1. In order to shorten the length of the AH, a large aperture antenna which generally forms a very narrow beam width is required. In the present invention, however, a single phased array antenna 4 is used as described above. , The length of AH can be shortened, the length of OA can be shortened, and therefore the distance of short HB can be measured. Resolution can be improved.

Considering the pulse width τ (s), the equation (1) is expressed as the following equation (2). Length of OA <length of OB-cτ / 2 (2) Here, c is the speed of light. As can be seen from equation (2), in order to increase the depth resolution, it is necessary not only to narrow the beam width but also to shorten the pulse width τ. In a conventional normal radar, the azimuth resolution determined by the beam width and the range resolution determined by the pulse width are independent,
In the radar apparatus according to the present invention, the depth resolution corresponding to the distance resolution is represented by the minimum value of BH satisfying the condition of the above equation (2), and the equation (2) involves the term of AH representing the azimuth resolution. Therefore, unlike ordinary radar, it can be seen that depth resolution (distance resolution) is related to azimuth resolution.

In the above embodiments, the present invention is applied to the lunar underground exploration radar mounted on the lunar orbit observation satellite. However, the present invention is not limited to this, and the present invention is not limited to this. It is applicable to a wide range such as body radar, and in the present embodiment, a single phased array antenna is used, but a parabolic antenna or the like is used, and the phased array antenna is arranged in the primary radiator arrangement portion. It is also possible to provide a mirror and use a reflecting mirror.

[0016]

As described above on the basis of the embodiments,
According to the present invention, since a single phased array antenna is used to form a combined transmission / reception beam having an equivalently narrow beam width, the beam width can be equivalently narrowed with a small antenna. , A spacecraft or the like can be easily mounted.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an embodiment of a radar device according to the present invention.

FIG. 2 is a schematic view of the embodiment shown in FIG. 1 as seen from the lateral direction.

FIG. 3 is a diagram showing a spread state of a beam pattern on the moon surface in the embodiment shown in FIG. 1;

FIG. 4 is a diagram showing an example of calculation of each beam pattern of a transmission beam, a reception beam, and a combined transmission / reception beam in the embodiment shown in FIG.

[Explanation of symbols]

 1 Orbiting satellite 2 Lunar surface 3 Transmitter / receiver 4 Phased array antenna 5 Radar device 6 Transmit beam 7 Receive beam 8 Transmit beam axis 9 Receive beam axis 10 Vertical axis 11 Transmit beam pattern area 12 Receive beam pattern area 13 Overlap part 15 Composite Transmit / receive beam

Claims (1)

[Claims] 1. A radar device for ground installation or mounted on a spacecraft or other such flying vehicle, comprising a phased array antenna as an antenna for both transmission and reception, and adjusting the feeding phase for each antenna element to transmit and receive a transmission beam at the time of transmission. Each beam axis of the reception beam at the time is made different so that only part of the beam pattern at the time of transmission and the beam pattern at the time of reception overlap each other in the observation area, so that an equivalent narrow beam width is formed. A radar device characterized by the above.