JPS6145605A - Antenna system of direction finding system - Google Patents

Abstract

PURPOSE:To increase the direction finding accuracy by arranging two circularly polarized wave antennas of the same structure so that they are made orthogonal mutually to an axis vertical to an aperture face and their outputs are combined thereby eliminating a polarized wave characteristic. CONSTITUTION:The two circularly polarized wave antennas 11, 12 of the same structure are arranged so that each aperture face is made different by 90 deg. around the Z axis. One element antenna 10 is constituted by combining outputs of the two antennas 11, 12 by an adder. The antenna of the direction finding system consists of plural elements antennas 10. Through the constitution above, the polarized wave characteristic of the two circularly polarized wave antennas 11, 12 is cancelled together and the direction finding error to azimuth based on the difference in the polarized face is reduced in this direction finding system.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an antenna device for a direction detection system that detects the arrival direction of radio waves such as radar.

[Prior art]

As a detection method for a direction finding system, one conventionally known method is an amplitude comparison method.

Figure 1 shows the configuration of an amplitude comparison type direction finding system. The device shown in FIG. 1 has a detection coverage area of 360° in all directions. In the figure, numerals 1 to 4 are element antennas, and these four element antennas 1 to 4 constitute an antenna section 5. Further, 6 is a switch section, which connects the two receivers 7 and 8 to any one of the four element antennas 1 to 4 adjacent to each other.
It has the function of connecting to two element antennas. Reference numeral 9 denotes an azimuth calculation unit that compares the output signals of the two receivers 7.8 and determines the azimuth.

Next, the operation will be explained. Element antennas 1 to 4 are the second
As shown in the figure, each has a covering area such as 1a to 4a.

In Fig. 2, when a radio wave arrives from the direction θ, the level of the signal received by element antennas 1 and 2 is determined by the pattern of each element antenna.
is proportional to. These two signals OA and OB are inputted by the switch section 6 to the receiver 7.8, where they are amplified and detected, and then input to the azimuth calculation section 9. Since the direction calculating section 9 is made to store the relationship between the amplitude ratio r of the two signals and the direction as shown in FIG. The direction of arrival of the radio wave can be determined from the relationship between the amplitude ratio r and the azimuth θ. For example, if the patterns of the two element antennas 1.2 are exactly the same, then r-1 when θ=45°.

Generally, the pattern of an element antenna has frequency characteristics, and if it is necessary to detect the direction with high accuracy, a calibration curve of the amplitude ratio r and the direction angle θ shown in Fig. 3 should be memorized for each certain frequency range. It is necessary to keep it. Moreover, at this time, a frequency analysis circuit for obtaining frequency information is required.

Conventional direction finding systems are configured as described above and use circularly polarized antennas that can receive radio waves of arbitrary polarization planes, but generally antennas whose gain is completely constant with respect to the polarization plane are used. It is very difficult to obtain.

FIG. 4 shows an example of the antenna pattern of the element antenna 1.2. la.

2a is the same as FIG. 2 and shows an ideal pattern without polarization characteristics. Here, general antenna patterns are, for example, lb and 2b for vertically polarized waves, and lc and 2c for horizontally polarized waves.

In this case, the radio wave arrival direction θ must be given by the amplitude ratio r=oτ/1000, but in reality, when a vertically polarized wave arrives, the amplitude ratio rb=OAb10Bb, and when a horizontally polarized wave arrives, the amplitude ratio rc=OAc10Bc, and radio wave arrival direction θb, θC obtained from these amplitude ratios
Since rb<r<rC, from the calibration curve in Fig. 3, θ
b>θ>θC, and the correct orientation cannot be obtained with any antenna.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional antennas as described above. Two circularly polarized antennas having the same structure are arranged so as to be orthogonal to each other with respect to an axis perpendicular to the aperture surface. To provide an antenna device for an azimuth finding system that can reduce azimuth detection errors caused by differences in polarization planes by using an antenna configured to combine the outputs of these two antennas as one element antenna. It is.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 5 shows the aperture of a spiral antenna, which is a typical circularly polarized antenna. Figure 6 shows the polarization characteristics of the spiral antenna shown in Figure 5. It's a gain. In FIG. 6, if the gain is constant for radio waves of any plane of polarization without polarization characteristics, the polarization characteristics of the circularly polarized antenna are expressed as a circle, as shown by E. However, in general, circularly polarized antennas, for example,
It has elliptical polarization characteristics, such as high gain for vertically polarized waves (low gain for horizontally polarized waves).

In an antenna device for a direction finding system according to an embodiment of the present invention, two circularly polarized antennas 11 and 12 having the same structure as shown in FIG. The antenna elements 11 and 12 are arranged to differ by 90 degrees around two axes, and the outputs of these two antennas 11 and 12 are combined by an adder to form one element antenna 10. Therefore, the antenna section 5 includes a plurality of element antennas 10.
Consisted of.

Here, the operation of the element antenna 10 will be explained. 7th
Assuming that the polarization characteristic of the antenna 11 in the figure is the same as that of the antenna in FIG. 5, and is expressed as Ev in FIG. 6,
As mentioned above, the polarization characteristics of the antenna 12 in FIG. 7 are Ev
is rotated by 90 degrees on two axes, so when it is superimposed on FIG. 6, it looks like Rh. EV and Eh can each be expressed as ellipses as shown in the following equation.

Now, when a radio wave with an arbitrary polarization plane φ arrives, antenna 1
The levels of the signals received at nodes 1 and 12 are as shown in FIG.
It is expressed as the intersection of Ev and Rh with a straight line indicating the ψ direction, and is expressed as a value proportional to OP and OQ, respectively. Since lv and Eh are ellipses as shown in the above formula, OP
, OQ can be expressed as follows.

OF2 = (n cos φ) 2 + (ms
in φ)2−σQ2 = (mcos φ) 2
+ (nsin φ)2 Therefore, the signal obtained by adding the powers of the signals received by antennas 11 and 12 is 2 + 100 2 - (n2 + m2) (cos2)
φ+sin 2φ) 1"n2+ff12, which is a constant value independent of φ. From this, the signals obtained by arranging two identical antennas with polarization characteristics as shown in Figure 7 and adding their respective signals are equivalent. It can be seen that the polarization characteristics disappear.

As described above, according to the configuration of this embodiment, the element antenna is configured such that two circularly polarized antennas of the same structure are connected at 90° with respect to the two axes.
° Since the configuration is such that they are arranged and combined so that they intersect, and their antenna outputs are combined using an adder, the polarization characteristics of the two circularly polarized antennas cancel each other out, and the polarization plane differs in the direction finding system. This has the effect of reducing the error in detecting direction based on .

In the above embodiment, a spiral antenna is used as the circularly polarized antenna, but it goes without saying that the same effect can be obtained using a circularly polarized antenna.

Furthermore, in the above embodiment, an antenna device for a direction finding system was described in which a conventional element antenna was replaced with an element antenna according to the present invention.
Antenna devices for direction finding systems include those that use four element antennas to cover all directions as shown in the antenna section 5 in Figure 1, as well as those that use six element antennas, or those that use even more element antennas. However, it goes without saying that in any case, the same effect can be obtained by using the element antenna according to the present invention.

〔Effect of the invention〕

As described above, according to the antenna device of the direction finding system according to the present invention, two circularly polarized antennas having the same structure are arranged so as to be orthogonal to each other with respect to an axis perpendicular to the aperture plane. By configuring the antenna to combine the outputs of the antenna, an element antenna with no polarization characteristics is obtained, and this is used to configure the antenna device, making it possible to provide a system with high azimuth finding accuracy. This has the effect of

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the direction finding system, FIGS. 2 and 3 are diagrams showing the operating principle of the direction finding system, and FIG. 4 is a diagram explaining the drawbacks of the antenna device of the conventional direction finding system. FIG. 5 is a diagram showing an example of a conventional element antenna constituting the antenna device shown in FIG. The explanatory diagram, FIG. 7, is a diagram showing the configuration of the element antenna of the device of this embodiment. In the figure, 1 to 4 are element antennas, 5 is an antenna section, 1
0 is an element antenna, and 11.12 is a circularly polarized antenna forming the element antenna IO.

Claims (1)

[Claims] (1) In an antenna device for an amplitude comparison type direction finding system, its element antennas include two circularly polarized antennas of the same structure arranged so as to be orthogonal to each other with respect to an axis perpendicular to the aperture plane, and An antenna device for a direction finding system characterized by using an element antenna consisting of an adder that combines the outputs of circularly polarized antennas.