JPH044765B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a small antenna that is built into a small portable radio device and used.

Conventionally, a loop antenna as shown in FIG. 1 is often used as a built-in antenna for small portable radio equipment. However, the small loop antenna is an antenna with extremely low efficiency due to its small radiation resistance. Also, since the gain of a loop antenna depends on its loop cross-sectional area, the loop cross-sectional area is naturally limited by the shape and dimensions of the built-in case.
In order to make the device smaller and lighter, the gain of the built-in loop antenna must be reduced. Further, a loop antenna has a characteristic that when a circuit component approaches the loop plane, the gain decreases due to a decrease in magnetic flux linkage and a change in equivalent damping resistance.

The purpose of the present invention is to be small, thin, and lightweight, to achieve better efficiency than conventional types, to be less susceptible to the effects of circuit elements, and to eliminate the need for any special matching circuit between the transmitter/receiver circuit and the antenna. The present invention provides a compact antenna for a practical portable radio device that is capable of impedance matching.

For the above purpose, the present invention loads a coil electrically connected between two parallel conductor plates having a sufficiently small interval compared to the wavelength as shown in FIG. By operating as a magnetic current forming antenna that receives power from any electrically favorable position on the coil, it is small, thin, and lightweight, with less characteristic deterioration due to circuit elements, and compared to loop antennas. The shape and configuration realizes a small antenna with good efficiency.

(Example) An example of the present invention will be described below with reference to the drawings.
FIG. 2 is a block diagram of an embodiment of the antenna according to the present invention. A is a perspective view, and b is a side view. 1 is a rectangular upper conductor plate, 2 is a rectangular lower conductor plate, 3 is a loading coil, 4 is a tap feed point, 5 is a high frequency connector, L is the length in the vertical direction, W is the length in the horizontal direction, T
is the length of the gap between both conductor plates.

The dimensions of each part and the position of the power feeding point are determined as follows. The dimensions of both the upper and lower conductor plates and the gap length T between the two conductor plates are limited by the shape and dimensions of the case of the radio device in which it is installed. Furthermore, within a range where the value of the gap length T is sufficiently small compared to the wavelength, the gain of the antenna increases as the value increases.

The upper conductor plate 1 and the lower conductor plate 2 are electrically connected by a loading coil 3. coaxial connector 5
is attached from the bottom surface of the lower conductor plate, and its position is at the feed point 4.

The resonant frequency of the antenna is approximately determined by the dimensions L and W of the upper conductor plate, the gap length T, and the inductance value of the loading coil 3, but these values are approximate values, and the exact resonant frequency cannot be determined. Values are determined experimentally. Next, the position of the feeding point 4 is determined at a position where the value of the antenna input impedance is set to an arbitrary value in the resonance state. In this embodiment, the value is set to 50 [Ω].

As described above, the dimensions and positions of each part of the antenna are determined. In this example, at =280MHz,
L=42mm, W=52mm, T=5mm. FIG. 5 shows the directivity of the antenna manufactured with the above dimensions. In the X-Y plane of Fig. 4, vertically polarized waves (Fig. 5 A) show almost omnidirectionality, and horizontally polarized waves (Fig. 5 B) show a figure-of-eight directivity. There is. In the dimensions of the antenna described above,
Its gain is about -12 dB compared to a dipole, and its efficiency is about 6 to 10%.

In order to further reduce the size of the antenna, the length of the upper conductor plate in the vertical direction, ie, the value of L, was shortened to about 60% of the dimension shown in the previous example, and its efficiency was as high as that of the above-mentioned efficiency. It was confirmed that there was almost no change compared to the value.

FIG. 3 is a configuration diagram of a second embodiment in which the antenna and circuit section of the present invention are mounted. As shown in the figure, the antenna section and circuit section are separated, so
The characteristics of the antenna can avoid the influence of circuit elements. As shown above, the shape of the antenna is
Furthermore, since it can be made smaller, the mounting area of the circuit section can be expanded, resulting in a highly practical compact portable radio device.

(Effects of the Invention) As described above, in this antenna, two parallel conductor plates are electrically connected by the loading coil, and the antenna shape is made smaller by the loading coil, This is a magnetic current forming antenna that uses tap feeding to facilitate impedance matching. Its efficiency is better than that of a small loop antenna, and its directional characteristics are relatively good. The shape of the antenna can be made extremely small, thin, and lightweight in the UHF band and quasi-microwave band, so when it is attached to a small radio device, it can be separated from the circuit components, and the characteristics change due to the proximity of the circuit components. This has the advantage that it can be used widely as an antenna for small radio equipment.

[Brief explanation of drawings]

Figure 1 is a perspective view of a conventional small loop antenna.
FIG. 2 is a perspective view a and a side view b showing a configuration diagram of a small antenna according to an embodiment of the present invention, and FIG. 3 is a perspective view c and a side view showing a configuration diagram of a small antenna of the present invention equipped with a circuit section. FIG. d and FIG. 4 are coordinate diagrams for explaining directivity, and FIG. 5 is a directivity diagram in free space. 1... Upper conductor plate, 2... Lower conductor plate, 3...
Loading coil, 4... feeding point, 5... high frequency connector.

Claims (1)

[Claims] 1. Two rectangular conductor plates are arranged in parallel at a sufficiently small interval compared to the wavelength,
A small antenna characterized in that a coil is loaded between both conductive plates, both conductive plates are electrically coupled by the loaded coil, and power is fed at any electrically favorable position on the loaded coil.