JPS62165403A - Slot antenna - Google Patents

Abstract

PURPOSE:To shorten equivalent slot length and to obtain the characteristics of a comparatively wide band by executing 2-point feeding by forming an impedance compensating circuit. CONSTITUTION:A slot antenna 4 is formed on the back of a dielectric base 6, a feeding microstrip line 5 is formed on the surface of the dielectric base 6 and a cavity resonator 7 has the function of a ground plate. Crossing points A, B between the antenna 4 and the line 5 are located on positions separately from the center O of the slot by an equal distance and used as feeding points. Thus, electromagnetic waves are radiated from the antenna 4 by oscillating the points A, B with the same phase and amplitude.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a slot antenna having a slot length of one wavelength or less.

(Prior art and its problems) Slot antennas have a low profile, and especially hollow throat antennas with a cavity resonator cannot withstand vibrations, wind pressure, etc., so they are suitable for use in aircraft, automobiles, etc. Widely used as a built-in antenna.

The power feeding of such a slot antenna is generally configured such that power is fed from one point at the center of the slot.

Furthermore, from the viewpoint of input impedance characteristics, a slot antenna having a slot length of about one wavelength at the operating frequency has been conventionally used.

For example, when configuring an array antenna using slot antennas as element antennas, the minimum element spacing is determined by the slot length, and in order to reduce the element spacing, the slot length must be shortened accordingly. In addition, it is also desirable to reduce the size of the slot antenna itself by shortening the slot length when mounting it on an automobile or the like. However, when the slot length is shortened, the input resistance component at the center of the slot has a sharp peak near the design frequency.
The input reactance component has a frequency characteristic that drops sharply, has a very narrow band, and impedance matching becomes difficult. In order to widen the band of such a slot antenna with a short slot length and facilitate impedance matching, a configuration has been proposed in which a load called a top load is attached to both ends of the slot. FIG. 1 shows an example of the configuration of a top-loaded slot antenna. The figure shows the main plate. Although the slot length is short in the configuration shown in Figure 1, the slot length is longer due to constraints such as the length of the top loads at both ends, and in an array antenna that uses this antenna as an element, the mutual feed between the top loads is large. This has the disadvantage that the characteristics of the array antenna deteriorate.

(Object of the Invention) The present invention solves the above-mentioned problems and provides a slot antenna having a short equivalent slot length and relatively wide band characteristics.

(Structure and operation of the invention) The present invention will be described in detail below using the drawings.

First, FIG. 2 shows an example of the configuration of a slot antenna with a two-point feeding cavity, which is the first feature of the present invention. In the figure, 4 is a slot antenna provided on the back surface of the dielectric substrate;
5 is a power feeding microstrip line provided on a dielectric substrate, 6 is an M8 board, 7 is a cavity resonator (which also functions as a ground plate), and the point where the slot antenna 4 and the microstrip line 5 intersect. A and B are the feeding points, and A and B are at equal distances from the center O of the slot.

Points A and B of microstrip line 5 are in phase.

By exciting with the same amplitude, radio waves are radiated from the slot antenna 4.

Here, FIG. 3 shows an example of the frequency characteristic of the input impedance at the feed points A and B when the ratio (Or; offset rate) of the length L2 of the line segment OA to the slot length is used as a parameter. In the figure, the design frequency is 1.6 GHz, and the slot length is half the wavelength at the above frequency (=9.4 am
) This is an example of the characteristics when the antenna is 11.2 cm, which is slightly longer than the antenna, and assumes a slot antenna with a cavity. From the same figure, the offset rate O,.

The larger the value, the smaller the peak of the resistance component, and the gentler the slope of the reactance component. Therefore, the two-point feeding system of the present invention has better matching than the central feeding system (0, = O, O). It can be seen that it is easy to obtain and a wide frequency characteristic can be obtained.

Furthermore, as is clear from FIG. 3, the reactance component has negative frequency characteristics near the design frequency.

Therefore, it is possible to improve the frequency characteristics of the two-point feeding system by providing a circuit having positive frequency characteristics (hereinafter referred to as an impedance compensation circuit) so as to compensate for the reactance component. This is the second feature of the present invention, and an embodiment thereof is shown in FIG. This figure shows a configuration example using an open stub or a capacitor and a short-circuit stub as an impedance compensation circuit, where 8 is an open stub, 9 is a capacitor, and 10 is a short-circuit stub. The open stub 8 can be obtained by opening the terminal end of the microstrip line 5, and the short-circuit stub 10 can be realized by short-circuiting the terminal end.

FIG. 5 shows a specific example of a capacitor 9 and a shorting stub 10 using a microstrip line 5, and 11 is a shorting plate. The capacitor 9 can be realized by providing a gap in the microstrip line 5.

FIG. 6 shows the input impedance characteristics of the feed points Δ and B when the structure shown in FIG. Has good frequency characteristics. In particular, the effect of the configuration example using the capacitor 9 and the shorting stub 10 is very large.

Next, a cross-slot antenna for circularly polarized wave excitation using the present invention will be described.

A cross-slot antenna can be considered as two two-point feeding slot antennas shown in Fig. 4 arranged to cross each other, and each slot antenna is placed at a 90° angle to each other.
If it is excited to have a phase difference of , it becomes a circularly polarized antenna.

FIGS. 7 and 8 particularly show an example of the configuration of a feeder circuit as an embodiment of a cross-slot antenna for circularly polarized wave excitation. In the figure, 12 and 12' are a composite circuit, and 13 is a 90° hybrid circuit. In the explanation of FIGS. 7 and 8,
Let's take the case of receiving radio waves as an example.

In FIG. 7, the signal components taken out from the feed points A and B of the slot antenna 4.4' are combined in a combining circuit 12.12', and then combined with the output of the combining circuit 2 and the combining circuit 12. Since there is a phase difference of 90'' in the output of the 90° hybrid circuit 13, by compensating for the phase difference and combining the 90° hybrid circuit 13, it is possible to obtain all the components of the received circularly polarized wave in the output. can.

In FIG. 8, the signal component at the feed point A of the slot antenna 4 and the signal component at the feed point B of the slot antenna 4' are connected to the 90' hybrid circuit 13, and the signal component at the feed point B of the slot antenna 4 and the signal component at the feed point B of the slot antenna 4' are connected to the signal component at the feed point B of the slot antenna 4'. After the signal components of the 4° feed point A are combined by the 90° hybrid circuit 13', the respective outputs of the hybrid circuit 13 and 13° are combined by the combining circuit 12.

As shown in FIGS. 7 and 8, by using the two-point feeding slot antenna according to the present invention, a large degree of freedom can be given to the configuration of the feeding circuit. In particular, in the configuration shown in Figure 8, the feed lines do not physically overlap, so the 90°
Hybrid circuit 13゜13'', feeder line 3, composite circuit 1
2 on the dielectric substrate 6, and the antenna can be integrated.

(Effects of the Invention) As described above, the present invention provides two-point power feeding and provides an impedance compensation circuit, thereby making it easy to achieve impedance matching even when the slot length is one wavelength or less, and providing a slot with good impedance frequency characteristics. It provides an antenna.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a configuration example of a top-loaded slot antenna, FIG. 2 is a perspective view showing an embodiment of the present invention in which a slot antenna with a cavity is fed from two points, and FIG.
In the perspective view showing the embodiment in the figure, a side view of the input impedance characteristics at the feeding point during two-point feeding, Figure 4(a) (
b) is a perspective view showing a configuration example of the two-point feeding slot antenna of the present invention using an impedance compensation circuit, FIG. 5 is a perspective view showing a specific example of the capacitor and short-circuit stub used in the present invention, and FIG. 7 and 8 are perspective views showing an embodiment of the cross slot antenna according to the present invention. 1.4.4'...Slot antenna, 2...Top load, 3...Feeding line, 5...Microstrip line for power feeding, 6...Dielectric substrate, 7...Cavity resonance Device: 8...Open stub, 9...Capacitor, 1
0... Short circuit stub, 11... Short circuit plate, 12.12°
...Synthesizer, 13.13゛...90° hybrid circuit, 20...Main plate. Figure 1 Figure 2 Figure 3 Broom Figure 4 Figure 5 Figure 6

Claims (2)

[Claims] (1) A slot antenna with a slot length of one wavelength or less, configured to excite two feeding points equidistant from the center of the slot with the same phase and amplitude via a microstrip line, and where the microstrip line A slot antenna characterized by having a circuit whose impedance increases with frequency at the terminal end of the antenna. (2) The slot antenna according to claim 1, wherein the slot is configured by intersecting a plurality of slots.