JPH03181208A - Compact antenna - Google Patents

Abstract

PURPOSE:To obtain the satisfactory antenna gain by forming a slot at the end of one of both sides of a band part of a watch. CONSTITUTION:The band part of a watch consists of two metallic layers 3 and 4 for formation of a resonance slot antenna 2 which receives the supply of power via a slit 5 (opening part) formed at an end of both sides of the layers 3 and 4 respectively and a capacity 8 loaded at the end of the other side. Then the antenna 2 is connected to a receiver main body 1, and the band part is fixed on a writst. Thus the variable capacity 8 is loaded in parallel to the slit 5 formed between a power supply surface and a ground surface. In such a constitution, the antenna 2 can be resonated. Furthermore a feeding point can be set at an optimum position by shifting the positions of the capacity 8 and a short circuit part 6 when the antenna 2 is connected to the main body 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a small antenna suitable for a wristwatch-type small receiver or the like.

2. Description of the Related Art Conventionally, there are examples of small-sized receivers, such as selective calling receivers, which have a built-in loop antenna and are made small. - In order to make the receiver more layered, it may be possible to use it in the shape of a wristwatch to increase its usability, but in this case, the antenna in this case would be to incorporate the aforementioned loop antenna into the wristwatch-shaped receiver body.
Alternatively, it is possible to attach a short whip antenna and use a wristwatch band as a loop antenna, but it is difficult to obtain practical antenna characteristics in either case.

Problems to be Solved by the Invention However, in a small and thin wristwatch-shaped compact receiver that has the shape of a wristwatch, the conventional micro loop antenna built into the housing is limited by the size and shape of the wristwatch, and the antenna aperture area is small. However, there is a problem that it is difficult to obtain sufficient antenna gain and is not practical.

The present invention solves these conventional problems,
The purpose is to provide a small antenna that can obtain sufficient antenna gain with a simple configuration.

Means for Solving the Problems In order to achieve the above object, the present invention uses a two-layered metal ring as the band portion of a wristwatch, and forms a slot antenna in which the gap on the inner side of both ends of the metal ring is an opening. Then, a capacitor was loaded on the opposite end to form a resonant slot antenna by offset feeding, which was connected to the main body of the GJ receiver and used by wearing the band on the arm.

Function The present invention has the following effects due to the above configuration. That is, by forming a slot at one end of the band portion, limitations due to the size and shape of the wristwatch and electromagnetic adverse effects due to proximity to the receiver circuit are eliminated, and sufficient antenna gain can be obtained.

Embodiment FIG. 1 is a diagram showing the overall configuration of a small antenna device of the present invention, and FIG. 2 is an explanatory diagram of its equivalent circuit.

In these figures, l is the receiver body, 2 is an antenna part that also serves as a watch band, 3 is an inner metal ring made of a cylindrical thin metal plate that surrounds the arm, 4 is also an outer outer metal ring, and 5 is an inner metal ring. In the gap (slit) between the plate 3 and the outer metal plate 4, a plastic core material may be inserted as a flexible, low-loss dielectric. 6 is a short-circuit portion provided at the opening 7 of one gap, 8 is a variable capacitor provided at the opening 9 of the other gap, 10 is a connection portion between the receiver main body 1 and the inner metal ring 3, and 11 is a receiver A connection part 12 between the main body 1 and the outer metal ring 4 is a power feeding point formed between the connection part 10.11. Note that the connecting portion 10 is connected to the ground point of the receiving circuit of the receiver main body 1, and the connecting portion 11 is connected to the input portion (hot side) of the receiver circuit. Further, as shown in FIG. 2, the connecting portion 13 on the opposite side of the receiver body from the connecting portions 10 and 11 is electrically connected to the receiver body in a nearly open state.

Next, the operation of the above configuration will be explained. The antenna part 2 is a kind of slot antenna, and an inner metal ring 3, an outer metal ring 4, and a short circuit part 6 constitute an open-ended slot antenna. Connection I (a feeding point is configured between 110 and 11, and is connected to the receiving circuit of the receiver main body I. The variable capacitor 7 is connected to the opposite side to the short circuit part 6, and equivalently, between the slits This means that the variable capacitor 7 is loaded in parallel. Therefore, by appropriately selecting the positions of the variable capacitor 7 and the short-circuit part 6, the slot antenna 2 can be made to resonate, and the resonant impedance can be divided by offset feeding [to the receiving circuit]. It can be converted to a compatible impedance and connected.

According to the above configuration, the antenna aperture area is not limited by the small loop antenna built into the receiver main body 1, and a twisted slot antenna is used, so the antenna gain decreases when worn on the human body. It has the characteristic that it does not.

Next, the operation of the slot antenna 2 will be explained in detail. In Fig. 2, if the total length 11 of the slot antenna 2, that is, the band dimension, is short compared to the wavelength and the length necessary for the slot antenna to resonate cannot be obtained, the input impedance Z of the slot antenna 2 is expressed by the following formula. expressed.

Z2R-1-jX Here, the radiation resistance R is small, and the reactance X becomes an inductive component.

Therefore, in order to eliminate this inductive component X, a variable capacitor 7 is loaded in parallel to the slit gap 5 to cause the slot antenna 2 to resonate, and the impedance is tuned by the offset of the feeding point 12. Further, when connecting the slot antenna 2 and the receiver main body 1, the position of the feeding point 12 can be set at an optimal position by shifting the short circuit part 6 and the variable capacitor 7. As described above, a slot can be formed at one end of the band portion.

Note that the characteristics of the micro loop antenna in the same figure are those of the aforementioned selective receiver antenna, and of course if the same type of antenna is miniaturized and built into the receiver main body 1, a large gain reduction is expected. . On the other hand, in the case of a small slot antenna, a gain comparable to that of the selective receiver antenna described above can be obtained when worn on the human body, indicating that it is sufficiently practical.

Effects of the Invention As is clear from the above-mentioned embodiment, the present invention has a slot formed at one end of the band portion of the small wristwatch type receiver, and a variable capacitor is connected in parallel between the slit in the power supply plane and the ground plane. Loading allows the slot antenna to resonate. By shifting the positions of the short-circuit part and the variable capacitor when connecting the twisted slot antenna and the receiver main body, there is an advantage that the position of the feeding point can be set at the optimum position. Furthermore, since the wristwatch-type small receiver is not close to the receiver circuit, it is not affected by electromagnetic adverse effects, and since it is a magnetic field type antenna, it has the advantage that sufficient antenna gain can be obtained when worn on the human body. .

[Brief explanation of drawings]

FIG. 1 shows a small antenna according to an embodiment of the present invention: receiver main body, 2: antenna section, 3: inner metal ring,
4... Outer metal ring, 5... Gap, 6... Short circuit plate,
8...Variable capacitance, 0 11...Connection part.

Claims (1)

[Claims] A receiver main body, a double metal ring having a gap in the middle, a short circuit plate that sandwiches the gap at one end of the metal ring and short-circuits it, and a variable capacitor loaded on the end opposite to the short circuit plate. and,
A part of the double metal ring is cut out, and each of the double metal rings is made up of a connecting part connected to a receiving circuit built in the receiver main body, and a slot antenna is formed with the connecting part as a feeding point, and the double metal ring is A small antenna with a metal ring attached to the arm.