JPH0213841B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable null point type antenna device.

As shown in FIG. 1, such a conventional antenna device is configured as a phase difference feeding type antenna by placing a plurality of antennas such as antennas a and b in the same plane. Therefore, it is necessary that the phase difference between the antennas changes greatly depending on the angle. Since this phase difference is proportional to the difference d in distance from the transmission point X to each antenna, in order to increase this d, the distance l between the antennas is set to about one wavelength. For this reason, the structure becomes large and cannot be used indoors. The above spacing is as large as 1.5 m in the case of 200 MHz.

In addition, in conventional antenna devices, each antenna uses a directional antenna element, and the range of directions in which maximum sensitivity can be obtained is limited to about ±30°, so when trying to receive multiple stations, Then, there were cases where it was necessary to change the direction of the antenna device.

The present invention has been made in view of the above points, and
The purpose is to provide a compact antenna device that can change the null point direction and the direction where maximum sensitivity is obtained by 360° without mechanically changing the direction.

In the antenna device constructed for this purpose, the feed points are positioned opposite to each other and are arranged in parallel, and the relationship between the radius r of each loop and the received wave wavelength λ is 2πr<λ. a pair of loop antenna elements, a variable phase shifter connected to the output of at least one of the loop antenna elements, and an adder for adding the output of the phase shifter and the output of the other loop antenna. Features.

Hereinafter, the present invention will be explained in detail with reference to FIG. 2 and subsequent figures.

FIG. 2 is a block diagram showing an embodiment of the antenna device according to the present invention, in which feeding points 10a and 10a' are positioned opposite to each other and parallel to each other. They are a pair of loop antenna elements that are both arranged horizontally.

Now considering the level directivity and phase directivity of a loop antenna element with radius r, when the radius r has a relationship with the received wave wavelength λ such that λ = 2πr,
The level directivity in the horizontal plane is a figure-8 directivity as shown in FIG. 3a, and the phase directivity is in the shape shown by A in FIG. This characteristic is equivalent to that of a dipole antenna element. Then the perimeter of the loop
When 2πr becomes smaller than λ, a cocoon-shaped directivity as shown in FIG. 3b is obtained, and the phase directivity becomes as shown in FIG. 4 by b. Furthermore, when the loop length 2πr becomes even shorter and becomes less than λ/5, the directivity approaches omnidirectionality as shown in Figure 3c, and the phase directivity also changes to the fourth direction.
As shown by C in the figure, the amount of change decreases.

By the way, in order to configure an antenna device that rotates the null point by 360 degrees, antenna element 1
0,10' must be non-directional. Also,
To avoid sensitivity loss after synthesis, antenna element 1
0 and 10' preferably have a large change in mutual phase difference with respect to the horizontal angle.

Therefore, the pair of loop antenna elements 10,
10' is a loop antenna with a radius of 2πr<λ, so as to have a level directivity characteristic close to omnidirectional as shown in Fig. 3b, and a phase directivity as shown by b in Fig. 4. element is suitable. When such a loop antenna element is used, the phase directivity of the loop antenna elements 10 and 10', which is standardized with the direction of the arrow shown as 0° (the phase to be received by the antenna element 10 is 0°), is as shown in Fig. 5. It becomes like this.

Loop antenna element 1 arranged as described above
The respective feeding points 10a and 10a' of 0 and 10' are as follows:
They are respectively connected to converters 11 and 11' that perform impedance conversion and balanced/unbalanced conversion. The outputs of the converters 11 and 11' are radio frequency (RF)
The signal is amplified by amplifiers 12 and 12'. The output of one of the converters 11, 11' is connected to one input of the adder 13 via the variable phase shifter 13, while the output of the other converter 11' is directly connected to the other input of the adder 14. connected to the input.
The variable phase shifter 13 is configured such that the amount of phase shift can be changed by a control voltage applied from the control circuit 15. The output of the adder 14 is the sum of the RF signal whose phase has been changed and the output of the amplifier 12', and this is sent to the front end of a receiver (not shown).

In the above configuration, if the output of the loop antenna element 10 is now phase shifted by 180 degrees with a phase shift difference 13, the sixth
The phase directivity shown in Figure a is obtained, and the output of the RF amplifier 12' and the output of the variable phase shifter 13 are at 90° and
Since it has a phase difference of 180° in the 270° direction,
No output appears at the output of adder 14. As a result, directivity having null points in the 90° and 270° directions is obtained as shown in FIG. 6b.

Next, if the amount of phase shift by the phase shifter 13 is set to 180°-θ, the phase directivity shown in FIG. 7a is obtained,
The output of the RF amplifier 12' and the output of the variable phase shifter 13 are
Since it has a phase difference of 180° in the 0° direction,
At this point, no output appears at the output of adder 14. As a result, a directivity having a null point in the 0° direction is obtained as shown in FIG. 7b.

Finally, if the phase shift amount by the phase shifter 13 is set to 180° + θ°, the phase directivity shown in FIG. 8a is obtained, and the output of the RF amplifier 12' and the output of the phase shifter 13 are
Since there is a phase difference of 180° in the 180° direction, no output appears in the output of the adder 14 at this point, and the directivity at this time is as shown in Figure 8b.
It has a null point in the 180° direction.

As is clear from the above, the phase shifter 13
If the amount of phase shift is continuously changed, the direction of the null point will also be continuously changed. By arranging the loop antennas as shown in FIG. 2 in this way, a small directional variable antenna device having at least one null point can be realized.

In addition, as mentioned above, since a loop is used in which the phase directivity in the used band changes by more than 90 degrees between the 0 degree direction and the 180 degree direction, the phase difference between both antennas is at most 180 degrees or more. If a null point is created at one location, the sensitivity in the maximum radiation direction in the horizontal plane will not be lower than the sensitivity of one antenna by more than 3 dB.

As described above, the present invention arranges a pair of loop antenna elements such that their feed points are positioned opposite to each other and are parallel to each other, and a variable phase shifter is connected to the output of at least one of the loop antenna elements. The output of this phase shifter and the output of the other loop antenna are added by an adder and output.

Therefore, by continuously changing the amount of phase shift of the variable phase shifter and shifting the output of one loop antenna element, the output of the adder will contain information about the received radio waves from the angular direction according to the amount of phase shift. An output with weakened signal components can be obtained, and the use of a loop antenna element makes it more compact as shown in the perspective view in Figure 9, making it possible to create a variable null point antenna device that can be used indoors. realizable.

In addition, by electrically changing the phase shift amount of the phase shifter, the null point direction and maximum sensitivity direction can be changed by 360 degrees, so there is no need to mechanically change the direction of the antenna device, and the receiver Combining this with the above makes it easy to automate changes in directivity.

Furthermore, when a loop antenna element with a diameter within a specific range is used as in the example, at least one null point is created, which prevents interfering radio waves that cause multipath interference in FM and ghost interference in TV. can be effectively eliminated.

In addition, when the loop antenna is activated, the S/N of received waves can be improved, and
Stabilization of antenna impedance (e.g. 75
Ω), and by stabilizing the impedance, it has become easier to create phase shifters, adders, etc.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of a conventional variable null point type antenna device, FIG. 2 is a block diagram showing an example of an antenna device according to the present invention, and FIG.
Figures a to c are diagrams showing the directivity of loop antenna elements with different diameters, and Figure 4 is the same as Figures 3 a to c.
Figure 5 shows the phase directivity corresponding to the directivity characteristic of
The figure shows an example of the phase directivity of the antenna device of the present invention constructed using a loop antenna element having the characteristics shown in FIG. 3b, and FIGS. 6a, 7a, and 8a are different. Figures 6b, 7b, and 8b, which show the phase directivity with respect to the amount of phase shift, show the directivity when the characteristics are as shown in Figures 6a, 7a, and 8a, respectively. FIG. 9 is a perspective view showing an embodiment of the antenna device of the present invention. 10, 10'...Loop antenna element, 10a,
10a'...Feeding point, 13...Variable phase shifter, 14...
...Adder.

Claims (1)

[Claims] 1 A pair of loop antenna elements whose feeding points are positioned opposite to each other and are both arranged in parallel, and the relationship between the radius r of each loop and the received wave wavelength λ is 2πr<λ; An antenna device comprising: a variable phase shifter connected to the output of one loop antenna element; and an adder that adds the output of the phase shifter and the output of the other loop antenna element.