JP2001267835A - Circularly polarized wave microstrip antenna and cross polarization component reducing method to be used for the antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve transmitting and receiving gain by reducing a cross polarization component. SOLUTION: In a circularly polarized wave microstrip antenna provided with a patch element 11, feeders 12A, 12B connected to the patch element 11 on respective feeding points A', B' and a hybrid coupler circuit 13 having ports A, B on one end and connected to the feeders 12A, 12B on the other end, structure for setting up respective input amplitude ratios on the feeding points A', B' by shifting them from the position 1:1 to a position in the direction to cancel the power of the cross polarization component is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circularly polarized microstrip antenna in which a hybrid coupler circuit is connected to a patch element via a feed line, and more particularly to a circularly polarized wave suitable for reducing cross-polarized components. The present invention relates to a microstrip antenna and a cross-polarization component reduction method applied to the antenna.

[0002]

2. Description of the Related Art A conventional circularly polarized microstrip antenna (circularly polarized patch antenna) that radiates circularly polarized waves will be described with reference to FIG. FIG. 1 shows a circularly polarized microstrip antenna according to an embodiment of the present invention as described later. However, since the basic configuration is the same as that of a conventional circularly polarized microstrip antenna, FIG. 1 is referred to for the description of the circularly polarized microstrip antenna.

[0003] Generally, a circularly polarized microstrip antenna is provided on a substrate 10 with a patch element 11 for radiating circularly polarized waves.
A first power supply line 12A connected to the patch element 11 at a first power supply point A ', a second power supply line 12B connected to the patch element 11 at a second power supply point B', One end has a first port A and a second port B, and the other end has a hybrid coupler circuit 13 connected to the power supply lines 12A and 12B.

In the circularly polarized microstrip antenna shown in FIG. 1, when a transmission signal is input from, for example, port A (as a transmission port), the transmission signal is amplified by the hybrid coupler circuit 13 to feed points A 'and B'. Ratio 1:
1, the phase difference is distributed to 0 °: 90 ° to excite the patch element 11, and the transmission radio wave is generally radiated as right-handed circularly polarized wave. Here, when the transmission signal is input from the port B, contrary to the above, the transmission radio wave is radiated as a left-handed circularly polarized wave. In the case of the circularly polarized microstrip antenna shown in FIG. 1, when the radio wave received by the patch element 11 is a circularly polarized wave that rotates in the opposite direction to the transmitted radio wave, the received signal is the input signal of the port A or B which is the input of the transmitted signal. Port (transmission port)
Output from a different port (reception port).

[0005] As described above, in the conventional circularly polarized microstrip antenna, the amplitude ratio and the phase difference at the two feeding points are set to be 1: 1 and 0 °: 90 °. Was common.

However, in such a conventional circularly polarized microstrip antenna configuration, electrical coupling occurs between the two feeding points of the patch element, causing an increase in the cross polarization component. For this reason, transmission and reception gains have been reduced. In addition, when performing polarization sharing using cross polarization for different reception channels, the number of reception signals of unnecessary channels is increased. Further, since the amount of rejection of the filter that blocks this signal is increased, designing the filter is difficult.

[0007]

As described above, in the conventional circularly polarized microstrip antenna, the amplitude ratio and the phase difference at the two feeding points are 1: 1 and 0 °: 90 °. However, there is a problem that the transmission and reception gains are reduced even if the setting is made, and that it is difficult to design a filter that blocks a reception signal of an unnecessary channel when performing polarization sharing.

The present invention has been made in view of the above circumstances, and has as its object to reduce the cross-polarization component only by changing predetermined parameters at two feeding points to improve transmission and reception gains. An object of the present invention is to provide a circularly polarized microstrip antenna which can be achieved and a method for reducing cross polarized components applied to the antenna.

[0009]

According to the present invention, a patch element, a first feed line connected to the patch element at a first feeding point, and a patch element connected to the patch element at a second feeding point. A circularly polarized microstrip comprising: a second feeder line; and a hybrid coupler circuit having first and second ports on one end and connected to the first and second feeders on the other end. The antenna is characterized in that the input amplitude ratio at the first and second feed points is shifted from 1: 1 in a direction to cancel out the power of the cross-polarization component. Here, to shift the input amplitude ratio from 1: 1
What is necessary is just to apply the structure in which the shape of the said 1st and 2nd feeder lines, for example, at least one of a thickness or a length, is asymmetrical by the amount which offsets the electric power of a cross polarization component.

In the circularly polarized microstrip antenna having such a configuration, the input amplitude ratio (that is, the power distribution ratio) at the two feeding points cancels the cross-polarized component power from the conventional 1: 1 ratio. Since it is shifted in the direction, that is, by an amount corresponding to the power of the cross polarization component, it becomes possible to reduce the cross polarization component. This makes it possible to reduce the amount of rejection of the filter that blocks the leaked signal, thereby facilitating filter design.

Further, instead of the structure in which the input amplitude ratio is set to be shifted from 1: 1 in the direction to cancel the power of the cross polarization component, the phase difference between the first and second feed points is changed to the cross polarization. It is also possible to apply a structure that is set so as to be shifted from 0 °: 90 ° in a direction to cancel the power of the wave component. here,
To shift the phase difference from 0 °: 90 °, an angle formed by a line connecting the center of the patch element and the first feeding point and a line connecting the center of the patch element and the second feeding point. Cancels the power of the cross-polarization component, the first and second
At a position where the phase difference at the feeding point of
What is necessary is just to apply the structure in which the said 1st and 2nd feeding point is set.

The present invention relating to the above apparatus (circularly polarized microstrip antenna) is a method (cross polarized component reduction method applied to a circularly polarized microstrip antenna).
The invention also holds as the invention according to the above.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing the appearance of a circularly polarized microstrip antenna according to one embodiment of the present invention.

In FIG. 1, for example, a circular patch element 11 and a first power supply point A 'connected to the patch element 11 are formed on an insulating substrate 10 superposed on a conductive ground plate 10a. , A second power supply line 12B connected to the patch element 11 at a second power supply point B ′, a first port A and a second port B on one end side, and the other end. A hybrid coupler circuit 13 connected to the power supply lines 12A and 12B on the side is formed. Patch element 11,
Power supply lines 12A, 12B and hybrid coupler circuit 1
3 is formed by removing portions other than the corresponding portions of the copper foil laminated on the substrate 10 by a mask technique and an etching technique. Here, in order to improve the corrosion resistance and the conductivity, the above-mentioned portions are plated with gold.

The feature of the circularly polarized microstrip antenna shown in FIG. 1 is that the signal amplitude ratio at the feeding points A 'and B' deviates from 1: 1 as described later.

Here, the principle of circularly polarized wave generation in the circularly polarized microstrip antenna shown in FIG.
The description will be made with reference to FIG. 2 with reference to the description in JP 082 (page 12, left column, line 12 to the same page, right column, line 19).

First, feed points A 'and B' of the patch element 11 of the circularly polarized microstrip antenna shown in FIG.
Are supplied with equal-amplitude (that is, an input amplitude ratio of 1: 1) power having a phase difference of 90 ° (0 °: 90 °) to obtain a circularly polarized wave from the patch element 11 of the antenna. In the figure, C is the antenna center point (the center of the patch element 11), and the angle between the CA ′ line and the CB ′ line is 90 °.

Here, when the lowest-order mode (first-order mode) is set to a desired mode and the feeding point A 'is excited in the lowest-order mode, the surface current distribution of the patch element 11 is shown in FIG.
It becomes as shown in. When excited in the lowest-order mode, the unnecessary mode having the greatest influence, that is, the unnecessary mode having the natural resonance frequency closest to the natural resonance frequency of the lowest-order mode is the second higher-order mode.
1 is also excited by this second higher mode. FIG. 2C shows the surface current distribution of the patch element 11 based on the second higher-order mode. Further, the patch element 11 is excited by the unnecessary higher-order mode (here, the second higher-order mode) to induce a second back electromotive force, and the back electromotive force causes the back electromotive force to be shown in FIG. Such a surface current distribution is generated.

Next, the feeding point B 'in the lowest order mode described above.
(However, a phase difference of + 90 ° is provided for the excitation condition of the feeding point A ′), the surface current distribution of the patch element 11 becomes as shown in FIG. Here, FIG.
FIG. 2F shows the surface current distribution of the second-order higher-order mode (corresponding to FIG. 2C) generated in the patch element 11 based on the excitation of the feed point B ′, and FIG. Induced (secondary induced) by the second higher-order mode (FIG. 2D)
2 shows the surface current distribution of the lowest mode.

By simultaneously applying the above-described excitation to the feeding points A 'and B', the patch element 11 generates a circularly polarized wave in principle.

However, when focusing on the directionality of each surface current distribution described above, as is apparent from FIGS. 1B to 1G, the surface current distribution in the desired mode (lowest mode) (FIG. 1B ), (E)), the surface current distribution of the desired mode (lowest mode) induced by the rotation direction of the polarization (main polarization) based on the unnecessary mode (second higher mode) (see FIG. 1).
It can be seen that the rotation direction is opposite to the rotation direction of the polarization based on (d) and (g)). The polarization component rotating in the opposite direction is the cross polarization component, and the cross polarization component affects the main polarization component (circular polarization component). Specifically, the polarization is shifted from the circular polarization by the cross-polarization component and becomes the elliptical polarization.

In the present embodiment, only the power corresponding to the cross-polarized component, that is, the back electromotive force induced by the unnecessary mode (second higher-order mode), is input at the feeding points A 'and B'. By shifting the amplitude ratio from 1: 1, the power of the cross-polarization component is canceled, and a circular polarization can be obtained.

FIG. 3B shows that, unlike the circularly polarized microstrip antenna according to the present embodiment, the input amplitude ratio at the feeding points A 'and B' is 1: 1 as in the conventional case. An example of a beam pattern (radiation pattern) of the circularly polarized microstrip antenna in such a case will be described. That is, in FIG. 3B, a transmission signal is input from, for example, a port A, and the input transmission signal is applied to the feeding points A ′ and B ′ by the hybrid coupler circuit 13 and the feeding lines 12A and 12B at an amplitude ratio of 1: 1. , And a beam pattern (radiation pattern) radiated from the patch element 11 when the light beam is distributed at a phase difference of 0 °: 90 °. As is clear from FIG.
There is a cross-polarization component of about −20 dB in the antenna front direction (0 ° direction).

As described above, the conventional circularly polarized microstrip antenna has a relatively large level of cross-polarized component. Therefore, in the present embodiment, the input amplitude ratios at the feeding points A ′ and B ′ are shifted from 1: 1 in a direction to offset the power of the cross polarization component (by an amount corresponding to the power of the cross polarization component). I have to.

FIG. 4 shows the relationship between the input amplitude ratio and the cross polarization component in the antenna front direction (0 ° direction) when the input amplitude ratio at the feeding points A ′ and B ′ is changed. In addition,
The phase difference between the feeding points A 'and B' is set to be 0 °: 90 ° as in the conventional case.

As can be seen from the figure, there is an optimum value for the input amplitude ratio, and when the input amplitude ratio is 1: 0.8, the cross polarization component is reduced most, and is about -40 dB.

Therefore, when the input amplitude ratio at the feeding points A 'and B' is shifted from 1: 1 in the prior art to 1: 0.8 and the phase difference is set to 0 °: 90 ° which is the same as in the prior art, the patch element 11 Fig. 3 (a) shows the beam pattern (radiation pattern) emitted from
Shown in As is clear from comparison with FIG. 3B, the cross-polarization component in the antenna front direction (0 ° direction) is significantly reduced as compared with the conventional input amplitude ratio of 1: 0.8 ( -40 dB or less at the lowest part).

Here, in order to set the input amplitude ratio at the feeding points A 'and B' to an arbitrary value, (1) Change at least one of the width and length of the feeding lines 12A and 12B, that is, the feeding lines (2) One of the power supply lines 12A and 12B (for example, the power supply line 12
A method such as providing an attenuator on the B side) is applicable.

Instead of changing the input amplitude ratio at the feeding points A 'and B' (shifting from 1: 1), the phase difference is changed to 0 °:
Even if the angle is changed from 90 °, the cross polarization component can be reduced. Further, both the input amplitude ratio and the phase difference may be changed. Here, the simplest method of changing the phase difference is to move the position of the feeding point A 'or B' on, for example, the circumference of the patch element 11, and to set a line connecting the center of the patch element 11 and the feeding point A '. Center of patch element 11 and feeding point B '
Is to change the angle between the line and the line connecting.

In the embodiment described above, the case where the patch element 11 is circular has been described. However, the present invention relates to a circularly polarized microstrip having a configuration using a patch element having another shape (for example, a square). The same applies to antennas. Further, the present invention is not limited to the case where the number of the patch elements 11 is one, and is also applicable to a circularly polarized microstrip antenna having a structure in which a second patch element is stacked. However,
The optimum input amplitude ratio for reducing the cross-polarization component is not always 1: 0.8 in the above embodiment, and it is necessary to set the optimum input amplitude ratio for each circularly polarized microstrip antenna of each shape. There is. This is the same for the optimum phase difference.

[0031]

As described above in detail, according to the present invention, a predetermined parameter such as an input amplitude ratio or a phase difference at two feeding points in a circularly polarized microstrip antenna is used to control the power of the cross polarization component. The cross-polarization component can be reduced only by applying the configuration changed and set by a corresponding amount.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the appearance of a circularly polarized microstrip antenna according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of generation of circularly polarized waves and cross-polarized components in the circularly polarized microstrip antenna of FIG. 1;

FIG. 3 is a view showing a radiation pattern of the circularly polarized microstrip antenna according to the embodiment in comparison with a radiation pattern of a conventional circularly polarized microstrip antenna.

FIG. 4 shows the relationship between the input amplitude ratio and the cross polarization component in the antenna front direction (0 ° direction) when the input amplitude ratio at the feeding points A ′ and B ′ of the circularly polarized microstrip antenna is changed. The figure which shows a relationship.

[Explanation of symbols]

 11: patch element 12A, 12B: power supply line 13: hybrid coupler circuit A, B: port A ', B': power supply point

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J021 AA01 AB06 FA34 GA08 HA05 HA07 JA06 5J045 AA14 CA04 DA10 EA07 HA03 JA12 NA01

Claims (6)

[Claims] A first power supply line connected to the patch element at a first power supply point; a second power supply line connected to the patch element at a second power supply point; Side has first and second ports, and the other end has the first and second ports.
In the circularly polarized microstrip antenna provided with the hybrid coupler circuit connected to the feed line of (1), the input amplitude ratio at the first and second feed points is set to 1: A circularly polarized microstrip antenna having a structure set to be shifted from 1. 2. A patch element, a first feed line connected to the patch element at a first feed point, a second feed line connected to the patch element at a second feed point, and one end. Side has first and second ports, and the other end has the first and second ports.
In the circularly-polarized microstrip antenna provided with the hybrid coupler circuit connected to the feed line of (1), the phase difference at the first and second feed points is 0 ° in a direction in which the power of the cross-polarized component cancels out. A circularly polarized microstrip antenna having a structure set to be shifted from 90 °. 3. The structure according to claim 1, wherein the shapes of the first and second feeder lines are set asymmetrically by an amount that cancels out the power of the cross polarization component.
A circularly polarized microstrip antenna as described. 4. The structure according to claim 1, wherein an angle between a line connecting the center of the patch element and the first feeding point and a line connecting the center of the patch element and the second feeding point is the cross bias. The first and second power supply points are offset by a phase difference of 0 °: 90 ° by an amount corresponding to the offset of the power of the wave component.
3. The circularly polarized microstrip antenna according to claim 2, wherein the second feeding point is set. 5. A patch element, a first feed line connected to the patch element at a first feed point, a second feed line connected to the patch element at a second feed point, and one end. Side has first and second ports, and the other end has the first and second ports.
A cross-polarization component reduction method applied to a circularly polarized microstrip antenna including a hybrid coupler circuit connected to a feed line of the first and second feed lines, wherein an input amplitude ratio at the first and second feed points is 1: 1. A cross-polarization component reduction method applied to a circularly-polarized microstrip antenna, wherein the power of the cross-polarization component is offset by shifting the power from the cross-polarization component. 6. A patch element, a first feed line connected to the patch element at a first feed point, a second feed line connected to the patch element at a second feed point, and one end. Side has first and second ports, and the other end has the first and second ports.
A cross-polarization component reduction method applied to a circularly polarized microstrip antenna including a hybrid coupler circuit connected to a feed line of the first and second feed lines, wherein a phase difference between the first and second feed points is 0 °: 90. A cross-polarization component reduction method applied to a circularly-polarized microstrip antenna, wherein the power of the cross-polarization component is offset by shifting from ゜.