JPS58631B2 - radar antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna for a radar such as a vehicle-mounted radar.

Radar includes pulse radar, CW radar, and others.
FM-CW radar is considered as a radar mounted on a car and used to detect a vehicle or an obstacle ahead.

In a CW radar that uses the homodyne detection method, local power is obtained from a transmitting wave oscillator.
There are methods shown in Figures a and b.

FIG. 1a shows a shared antenna system for transmitting and receiving, and FIG. 1b shows a system using a power transmitting and receiving antenna.

In Figure 1a, A is an antenna, C is a circulator,
O20 is an oscillator, and MIX is a mixer.

In this method, an FM transmission signal from an oscillator OSC is transmitted to an antenna A through a circulator C, and is radiated from the antenna to a target.

The radiated radio waves hit the target, and the reflected waves are received by antenna A, transmitted to mixer MIX by circulator C, and mixed with local power transmitted from oscillator O8C through circulator C.

As a result, the mixer MIX produces an output indicating the distance to the target.

This circuit is of a duplexer type, that is, the antenna is used for both transmission and reception, and although the configuration is relatively simple, isolation is poor.

This is not a problem when the transmitted and received radio waves can be separated by time, as in a pulse radar, but when the transmitted and received radio waves are continuous, as in a CW radar, the isolation dominates the reception performance.

However, at present, the isolation of the circulator is only about 20 dB.

The power transmitting and receiving antenna system shown in Figure 1 is excellent in this respect.

In this figure, AT is the transmitting antenna and AR. is a receiving antenna, DC is a coupler such as a cloisonné type directional coupler, and M
IX and O20 are a mixer and an oscillator, respectively, as in FIG. 1a.

In this method, the output of the oscillator O8C is transmitted to the transmitting antenna AT.
while a part of it is also transmitted to the receiving side by the directional coupler DC.

The oscillator output sent to the receiving side is mixed as a local signal with the received signal from the antenna AR by a mixer MIX, and the mixer outputs a signal indicating the distance to the target.

This method provides an isolation level of 50 to 60 dB or more, giving good results, but it requires a large number of components such as directional couplers, making it cumbersome and expensive, which poses problems for automotive use. .

A possible way to obtain local power is to use mutual coupling of antennas.

However, it is extremely difficult to eliminate mutual coupling between transmitting and receiving antennas without changing antenna specifications such as antenna gain, beam width, and side lobes.

For example, to obtain a maximum local power of -15 dBm from an oscillator with a transmission output of 17 dBm, the mutual coupling of the antennas must be 32 dB, but cylindrical parabolic antennas for transmitting and receiving each have good isolation, so
It is very difficult to obtain mutual coupling on the order of 2 dB.

The present invention uses separate antennas for transmitting and receiving, and allows for the necessary amount of mutual coupling without affecting the antenna pattern, thus providing good isolation, the necessary amount of coupling, and a small number of components. This paper proposes a radar system that can be miniaturized.

Next, this will be explained in detail with reference to examples.

Figure 2 shows an outline of a parabolic antenna used in radar.

In the figure, F is a primary radiator and P is a parabolic reflector.

The radiator F emits radio waves from the side facing the reflector P so as to irradiate only the reflector, and the emitted radio waves are reflected by the reflector P, the beam shape is adjusted, and the radio waves are projected toward the target. Ru.

At this time, the radio waves radiated to the reflector portion directly behind the radiator F will hit the radiator F again after being reflected, and will not be radiated to the target.

The shaded area in FIG. 2 indicates this invalid area.

The energy in this blocking region does not contribute to the formation of the antenna pattern, and moreover, it hits directly below the primary radiator F, so the electric field strength is extremely large.

The present invention focused on this blocking region, provided a small reflector in the region, caused the receiving antenna to radiate radio waves, and mutually coupled the transmitting and receiving antennas with a desired degree of coupling.

FIG. 3 shows an embodiment of the present invention, in which FT is the primary radiator of the transmitting antenna, PT is its main reflector, FR is the primary radiator of the receiving antenna, and PR is its main reflector.

The main reflectors are joined together at adjacent edges, and the edges of this joint are lower than the opposite edges.

PS is a sub-reflector provided in the blocking region of the main reflector PT, and has a wedge-shaped shape so as to project the energy emitted from the radiator FT to the radiator FR.

In order not to interfere with this path L, the height of the connecting portion of the main reflectors PT and PR is made low as described above.

In this method, energy emitted from the primary radiator FT is reflected by the main reflector PT and radiated to the target.

In addition, the energy radiated to the blocking region is reflected by the sub-reflector PS and projected to the radiator FR.
is received and becomes local power.

The radiator FR also receives the reflected waves of the radio waves emitted to the target object from the main reflector PR, and these signals are mixed by a mixer to generate a distance signal to the target object.

This system does not require a directional coupler, so the directional coupler DC shown in FIG. 1 can be omitted, making it possible to reduce the size and cost of the device.

FIG. 4 shows a specific example in which the present invention is applied to a cylindrical parabolic antenna.

In the figure, FT is a primary radiator for transmission, and FR is a primary radiator for reception, both of which are slot array types.

These are formed by forming grooves or slots S in a waveguide, and radio waves are emitted or input from the slots.

PT and PR are main reflectors, Ps is a sub-reflector, and the main reflector is made by combining two cylindrical parabolas for transmission and reception, and the joint part is the transmitting signal reflected by the wedge-shaped sub-reflector Ps. The antenna is shaved off to the extent that a portion of the antenna can reach the receiving radiator FR and its characteristics as an antenna are not impaired.

The antenna is not limited to a cylindrical shape, but may have any other suitable shape.

Further, in order to secure the coupling path L from the transmitting antenna to the receiving antenna, it is convenient to use an offset parabola or the like.

As explained in detail above, in the present invention, the transmitting and receiving antennas are separate in a homodyne detection type radar device, and a wedge-shaped sub-reflector is attached to the blocking region of the reflector of the transmitting side parabolic antenna, and the energy of this region is transferred by spatial coupling. By supplying the signal to the receiving side, it is possible to provide a radar device that has good isolation and can be miniaturized by omitting parts such as a directional coupler.

In addition, since the sub-reflector is located in the blocking area, there is no negative effect on the antenna pattern, and the amount of mutual coupling between both antennas can be adjusted by adjusting the inclination angle and/or width of the sub-reflector. Since it is very small, it has various advantages such as easy attachment of a sub-reflector.

[Brief explanation of the drawing]

Figures 1a and b are block diagrams showing an example of a homodyne detection type radar device, Figure 2 is an explanatory diagram of a parabolic antenna,
FIG. 3 is an explanatory diagram of a main part of an embodiment of the present invention, and FIG. 4 is a schematic perspective view showing a specific example of a separate cylindrical parabolic antenna for transmission and reception according to the present invention. A, AT, AR...Antenna, C...
Circulator, O8C...Oscillator, MIX
...Mixer, DC...Directional coupler, F
, FT, FR, ...radiator, P, PT, PR・
...Main reflector, PS...Sub-reflector.

Claims (1)

[Claims] 1. A parabolic antenna for transmitting and a parabolic antenna for receiving are arranged side by side, and a part of the transmitted radio wave is transmitted to the blocking area of the main reflector of the parabolic transmitting antenna as the primary radiation of the parabolic receiving antenna. A radar antenna characterized in that it is provided with a sub-reflector that reflects light toward a target. 2. The transmitting/receiving parabolic antenna is a cylindrical parabolic antenna in which the main reflectors are coupled at adjacent edges, and the sub-reflector is a wedge-shaped body provided in the blocking area of the transmitting-side main reflector. A radar antenna according to claim 1.