JPH0129082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microstrip antenna;
In particular, the present invention relates to a microstrip antenna that suppresses the excitation of unnecessary modes that are excited together with a desired mode when arrayed and operated with circularly polarized waves over a wide band.

Generally, the bandwidth of microstrip antennas is extremely narrow.

For this reason, conventional efforts have been made to widen the band of the microstrip antenna by increasing the thickness of the substrate or lowering the dielectric constant of the dielectric material.

By the way, when a microstrip antenna is made to have a wider band, in addition to the dominant mode or the desired higher-order mode, an unnecessary mode having a natural resonance frequency near the natural resonance frequency of the dominant mode or the desired higher-order mode is also excited. This causes problems such as deterioration of the characteristics of the circularly polarized waves generated. This also applies to arrayed microstrip antennas.

However, in the past, almost no countermeasures were taken against the follow-up excitation of the unnecessary mode.

The present invention has been made in view of the above circumstances, and provides a microstrip that suppresses harmful unnecessary modes and obtains stabilized circularly polarized waves when arrayed and circularly polarized waves are operated over a wide band. The purpose is to provide a flexible antenna.

According to the present invention, when forming an array of patch-type microstrip antennas with a wide band, a plurality of second element antennas each radiating a circularly polarized wave are connected to a first element antenna that radiates a circularly polarized wave. are rotated 90 degrees in the same direction, and by combining both the first and second element antennas,
The circularly polarized wave components rotating in the first direction are in phase with each other in the desired direction, and the circularly polarized wave components rotating in the second direction opposite to the first direction are out of phase in the desired direction. The above-mentioned unnecessary mode is suppressed by supplying power to.

EMBODIMENT OF THE INVENTION Hereinafter, a microstrip antenna according to the present invention will be described in detail with reference to embodiments of the accompanying drawings.

First, the principle of the microstrip antenna according to the present invention will be explained with reference to FIGS. 1 and 2.

Now, it is assumed that equal amplitude power having a phase difference of 90° is supplied to feeding points P1 and P2 of the microstrip antenna shown in Fig. 1a to obtain circularly polarized waves from this microstrip antenna. . However, it is the center point of the antenna, and the feeding point P
1 is placed at any position on the A line, and the feeding point P
2 is arranged at a position corresponding to the above-mentioned power feeding point P1 on the B line (a position where P1=P2). Note that the above-mentioned line A and line B are orthogonal to each other.

For example, if the lowest order mode (first mode) is set as the desired mode and the feeding point P1 is excited in the lowest order mode, the surface current distribution of this microstrip antenna will take the form shown in FIG. 1b. Furthermore, when excited in the above-mentioned lowest order mode, the unnecessary mode with the greatest influence, that is, the unnecessary mode having the natural resonance frequency closest to the natural resonance frequency of the above-mentioned lowest order mode, is the second higher-order mode, and the microstrip As the band becomes wider, the antenna is also excited by this second higher-order mode. This second
The surface current distribution based on higher-order modes takes the form shown in FIG. 1c. Furthermore, the microstrip antenna is excited by the unnecessary higher-order mode (in this example, the second higher-order mode), thereby secondarily inducing a back electromotive force at point R1 on line B, and the induced The back electromotive force generated causes a surface current distribution as shown in FIG. 1d.

Next, when feeding point P2 is excited in the lowest-order mode described above (with a phase difference of +90° with respect to the excitation condition of feeding point P1), the surface current distribution of this microstrip antenna is The state shown in FIG. 1e is obtained. Below, Figures 1f and 1g show the surface current distribution of the second higher order mode generated in this microstrip antenna based on the excitation of the feeding point P2, and the surface current distribution due to the second higher order mode, respectively. This figure shows the surface current distribution of the lowest-order mode induced (secondary excitation) by the vibration, and corresponds to FIGS. 1c and 1d, respectively, described above.

Now, in principle, this microstrip antenna generates circularly polarized waves by simultaneously applying the above-mentioned excitation to the feeding points P1 and P2.

However, when paying attention to the directionality of each surface current distribution mentioned above, as is clear from Fig. 1 b to g, the surface current distribution of the desired mode (lowest order mode) (see Fig. 1 b and e) The rotation direction of polarization based on the surface current distribution of the desired mode (lowest order mode) induced by the unwanted mode (second higher order mode) (see Figure 1 d and g) It turns out that it goes in the opposite direction. That is, this polarized wave component rotating in the opposite direction is a cross-polarized wave, and this cross-polarized wave interferes with the circularly polarized wave component obtained above.

Figure 2a shows the feeding points P1 and P2 of the microstrip antenna shown in Figure 1a above.
Feed points P3 and P4 with a rotational displacement of 90°
In this microstrip antenna, circularly polarized waves are obtained by supplying equal amplitude power having a phase difference of 90° to feed points P3 and P4, respectively. However, the phase of the power supplied to the microstrip antenna shown in Fig. 2a is further advanced by 90 degrees than the phase of the power supplied to the microstrip antenna shown in Fig.
It is assumed that the phase of the power supplied to the point P4 (see FIG. 1a) and the phase of the power supplied to the power supply point P4 (see FIG. 2a) are exactly opposite in phase (phase difference of 180°).

Now, when excitation is applied to each of the feed points P3 and P4 of this microstrip antenna, the surface current distribution of the lowest order mode, the surface current distribution of the second higher order mode, and this second order The surface current distribution of the lowest order mode induced by the higher order mode (secondary excitation) is shown in Figures 2 b to d, respectively.
And the embodiments shown in FIGS. 2e to 2g are obtained. however,
These FIGS. 2b to 2g correspond to FIGS. 1b to 1g shown above, respectively, and detailed description thereof will be omitted.

In other words, in this microstrip antenna as well, a predetermined circularly polarized wave is generated by simultaneously applying the above-mentioned excitation to the feed points P3 and P4, but an unnecessary mode (second higher order mode) is generated. Along with excitation, cross-polarized waves that are harmful to the generated circularly polarized waves are also generated at the same time.

Next, suppose that the microstrip antenna shown in FIG. 1 and the microstrip antenna shown in FIG. 2 are simultaneously excited as a pair array element.

In this case, as is clear from Fig. 1 b to g and Fig. 2 b to g, the circularly polarized wave component due to the surface current distribution of the lowest mode (see Fig. 1 b, e and Fig. 2 b, e) are in phase and strengthen each other, and the surface current distribution of the lowest mode induced (secondary excitation) by the second higher order mode (see Figure 1 d, g and Figure 2 d, g) The cross-polarized components due to this will have opposite phases and cancel each other out.

In this way, damage caused by unnecessary modes can be suppressed by using a pair array element in which a microstrip antenna that operates with circularly polarized waves over a wide band is rotated by 90 degrees.

It goes without saying that the above-described principle is also applicable to suppressing other unnecessary modes.

Furthermore, even if multiple feeding points are provided on line A and line B in Figure 1a, similar surface current distributions will be shown; in this case, Figure 2a
In the microstrip antenna shown in FIG. 1, a plurality of feed points may be provided on the B line and the C line, and the above-mentioned feed conditions may be applied to each of these feed points at once.

In addition, in the above description, for convenience, each power feeding point P1, P2 and P3 shown in FIG. 1a and FIG.
Although the arrangement positions of P4 are set to be equidistant from each center point, the arrangement positions of these feeding points P1 and P2 do not necessarily have to be equidistant from each center point. That is, as long as at least one of these feeding points P1, P2 and P3, P4 is biased in opposite directions, a sufficient effect can be obtained by appropriately considering the feeding conditions. This also applies to the case where there are a plurality of feeding points.

Now, FIG. 3 shows a configuration example in which the above-described principle is applied to an arrayed microstrip antenna for obtaining circularly polarized waves.

In FIG. 3, reference numeral 10 denotes an arrayed microstrip antenna, which includes elements (element antennas) 11 and 12 serving as paired array elements, a substrate 13, and an array interposed between these elements 11, 12 and the substrate 13. It is composed of a dielectric material (not shown). Further, as shown in FIG. 3, this arrayed microstrip antenna 10 has feeding points P111, P112 and feeding points P121, P12, which are rotationally displaced by 90 degrees between the elements 11 and 12.
It has 122. Note that this microstrip antenna 10 is appropriately widened by taking measures such as increasing the thickness of the substrate 13 or lowering the dielectric constant of the dielectric material as necessary.

Moreover, the power divider 20 is connected to the power supply point P111,
This device excites the arrayed microstrip antenna 10 by applying power under predetermined conditions to P112, P121, and P122. It is assumed that four types of power are supplied simultaneously. In other words, a predetermined amplitude power with a phase of 0° is supplied to the feed point P111, a predetermined amplitude power with a phase of +90° is supplied to the feed point P112, and a predetermined amplitude power with a phase of +90° is supplied to the feed point P112.
Similarly, a predetermined amplitude power with a phase of +90° is supplied to the power supply point P121, and a power with a phase of +90° is supplied to the feeding point P122.
Supply a predetermined amplitude power of 180°.

As a result, the microstrip antenna 10
is a feed point pair consisting of the feed points P111 and P112, and the feed points P121 and P12.
The pair of feed points consisting of 2 and 2 not only emphasizes the excitation of the desired mode based on the principle described above, but also suppresses damage caused by unnecessary modes (occurrence of cross-polarized components). For convenience, the above explanation has been given for the case of left-handed circularly polarized waves, but the same thing can be said for right-handed circularly polarized waves by reversing the direction of phase rotation.

Therefore, stable circularly polarized waves are radiated from this arrayed microstrip antenna 10.

In addition, the above-mentioned microstrip antenna 1
4 and 5, using the elements shown in FIG.
They may be arrayed as shown in the figure. In this case, stable circularly polarized waves can be obtained by suppressing unnecessary modes with the configuration of the elements 11 and 12 according to the above-described principle, and therefore stable circularly polarized waves can be easily obtained even when arrayed.

Further, although the configuration shown in FIG. 3 is shown for two-point feeding type elements 11 and 12, it may be of a one-point feeding type or the like as long as it can excite circularly polarized waves. With such an element, the rotational displacement of 90 degrees is given to each other, so that the circularly polarized wave components rotating in the first direction are in phase in the desired direction, and rotate in the second direction opposite to the first direction. By feeding power so that the circularly polarized wave components have opposite phases in a desired direction, it is possible to suppress unnecessary modes and obtain stable circularly polarized waves, and the same effect as described above can be obtained. Furthermore, various power feeding methods can be adopted as long as the feeding conditions can be satisfied, such as using a coaxial line or a microstrip line.

Furthermore, the pattern shape of the elements 11 and 12 need only be symmetrical about an axis perpendicular to the vibration direction, and is not limited to the circular shape shown in FIG. 3 as an example.

In addition, as explained in the previous principle, the number of feeding points, the positional relationship, and each feeding condition are not unique in the microstrip antenna according to the present invention, and if this fact is applied, it is possible to It can also be effectively applied to obtaining polarized waves.

As explained above, according to the microstrip antenna according to the present invention, when operating in a wide band, the adverse effects of unnecessary modes can be suppressed, and good circularly polarized waves can be easily obtained.

[Brief explanation of drawings]

FIGS. 1 to 3 are diagrams showing the principle of the microstrip antenna according to the present invention, and FIGS.
The figure shows an embodiment of a microstrip antenna according to the present invention. 10...Microstrip antenna, 11,
12...Element, 13...Substrate, 20...Power divider.

Claims (1)

[Claims] 1. In a patch-type microstrip antenna that is composed of multiple element antennas and operates with circularly polarized waves, a first element antenna that emits circularly polarized waves is connected to a plurality of antenna elements that each radiate circularly polarized waves. The second element antenna is rotated 90 degrees in the same direction, and the combination of the first and second element antennas allows the circularly polarized wave components rotating in the first direction to be in phase in the desired direction. And, the first
A microstrip antenna characterized in that power is fed so that circularly polarized wave components rotating in a second direction opposite to the direction of the antenna are in opposite phases in the desired direction.