JPH0591013U - Antenna for small radio - Google Patents

Abstract

(57) [Abstract] [Purpose] By installing an antenna in the housing or in the vicinity of the housing, dimensional restrictions can be solved, the effective gain of the antenna is not reduced, and the size of the receiving frequency band is small. An antenna for a thin wireless device is provided. To do. [Structure] A frame 2 made of an insulator is sandwiched and fixed by a top plate 1 and a bottom plate 3 made of a rectangular plate-shaped conductor, and each side of the top plate 1 and the bottom plate 3 facing each other is conducted by a loading coil 4. An antenna for a small radio having a tuning and matching function by providing an antenna feeding terminal 5 capable of matching with the antenna element. It

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an antenna for a small portable radio such as a personal radio or pager.

[0002]

[Prior Art]

 Conventionally, portable radios have been miniaturized so that users can easily carry them like pagers, and the antennas used in these radios are often loop antennas that can be built into the housing. .. This type of loop antenna generally has a fixed or variable capacitor for tuning and impedance matching connected to the feeding terminal of the antenna element as shown in Fig. 6, and these capacitors and the antenna element form a loop. It then functions as an antenna.

[0003]

[Problems to be solved by the device]

 In recent years, portable radios have become smaller and thinner as seen in card-type pagers, and the need for efficient small antennas has increased accordingly. It is generally known that the radiation efficiency of an antenna remarkably decreases with the miniaturization of the antenna. In addition to this, if a reactance element for impedance matching is added for matching as in the loop antenna described above, The radiation efficiency of the antenna further decreases due to the loss held by this reactance element, and the antenna function is no longer fulfilled. Further, as the portable wireless device becomes smaller and thinner, if the loop antenna as described above is built-in, the reception area formed by the loop becomes smaller and reception becomes difficult.

Further, this type of antenna has a problem that the reception frequency bandwidth is narrow. The purpose of the present invention is to solve the conventional problems as described above, by solving the dimensional constraint by installing the antenna in the housing or in the vicinity of the housing, and without lowering the effective gain as the antenna. , It is to provide an antenna for a small and thin wireless device with a wide reception frequency band.

[0005]

[Means for Solving the Problems]

 In order to achieve the above object, in the present invention, a frame made of an insulating material is sandwiched and fixed by an upper plate and a bottom plate made of a rectangular plate-shaped conductor, and each side of the upper plate and the bottom plate facing each other is loaded with a loading coil. It is characterized in that the antenna element is constituted by conducting with the antenna element, and the antenna element is provided with an antenna feeding terminal capable of matching.

[0006]

[Action]

 Since the antenna for a small radio device of the present invention forms a housing by sandwiching a frame made of an insulating material between a top plate and a bottom plate formed by print vapor deposition or a rectangular plate-shaped conductor on the housing surface, The antenna can be constructed without impairing the mechanical strength of the body. Moreover, since the loading coil and the feed terminal are integrally attached to the antenna radiating element, the antenna element itself operates as an antenna having tuning and matching functions.

[0007]

【Example】

 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a card-type small radio device according to the present invention, and FIG. 2 is an exploded explanatory view excluding the loading coil and the power supply terminal portion in FIG. 1 and 2, 1 is an upper plate made of a rectangular conductor plate, 2 is a frame made of a resinous insulator, 3 is a bottom plate made of a rectangular conductor plate, and the upper plate 1 and the bottom plate 3 are As shown in FIG. 1 or FIG. 2, the upper plate 1 and the bottom plate 3 are arranged one above the other with a frame 2 interposed therebetween, and the upper plate 1 and the bottom plate 3 serve as an antenna radiating element or an antenna receiving element of the antenna for a small radio of the present invention. A wireless circuit unit is housed in the frame 2. Reference numeral 4 is a loading coil for tuning together with the top plate 1 and the bottom plate 3. As shown in FIGS. 1 and 2, the loading coil is arranged and installed between the opposite sides of the top plate and the bottom plate, and the position for the placement is between the top plate and the bottom plate. Any place is acceptable. Reference numeral 5 is an antenna power supply terminal.

Next, the operation of the antenna thus configured will be described. The operation of the antenna when transmitting radio waves from the antenna and when receiving the radio waves from the antenna is reversible, so here we will explain the receiving antenna used for receivers such as pagers. Radio waves from the outside are received by the radiating (receiving) element composed of the upper plate 1 and the lower plate 3, and only the frequencies selected for tuning by the loading coil and the antenna receiving element are received. That is, as shown in FIGS. 1 and 2, the radiating elements 1 and 3 form a dipole type antenna element with a certain distance between the upper plate and the bottom plate.

A comparison between the loop antenna and the dipole antenna used in the thin wireless device will be described below. The radiation efficiency of the loop antenna is determined by the radiation resistance Rr and the loss resistance RL of the loop antenna, and is defined by η = Rr / (Rr + RL). Further, the radiation resistance Rr and the loss resistance RL are expressed as follows, where the vertical and horizontal lengths of the rectangular loop antenna are La and the radius of the Lb loop wire is a.

Rr = 320π ⁴ (La × Lb) ² / λ ⁴ RL = (La + Lb) (πfμ / σ) ^0.5 / 2πa (where λ: wavelength, f: frequency, σ: conductivity) The radiation efficiency is also determined by the radiation resistance Rr and the loss resistance RL of the dipole antenna, and is defined by η = Rr / (Rr + RL). The radiation resistance Rr and the loss resistance RL are expressed as follows, where L is the length of the rod-shaped dipole antenna and a is the radius of the antenna rod.

Rr = 80π ² (L / λ) ² RL = L (πfμ / σ) ^0.5 / 2πa (where λ: wavelength, f: frequency, σ: conductivity) Details are described in "Antenna Engineering". For example, when the reception frequency is 280 MHz in a box type thin radio with a thickness of 5 mm and a length of 80 mm, the radiation efficiency of the loop antenna is -16 dB and the radiation efficiency of the dipole antenna is -0.5 dB. When the machine becomes thinner, the dipole type antenna is more efficient. When the thickness is further reduced, for example, if the thickness becomes 2 mm, the radiation efficiency becomes -24 dB, and the radiation efficiency further decreases. In this case, the thickness of the loop wire to be used is also restricted, and if a wire with a radius of 0.1 mm is used, the radiation efficiency will be further deteriorated to -30 dB. This is the reason why the dipole type is used as the antenna system of the present invention.

Next, the tuning frequency of the antenna can be adjusted by changing the number of turns of the loading coil or by changing the line length of the thin line, and by configuring the inductance corresponding to the loading coil and adjusting it. Good. FIG. 3 shows the locus of the input impedance of the antenna feeding terminal 5 shown in the embodiment of the present invention. The circle represents the reflection coefficient surface, but the impedance diagram (Smith chart) is not drawn to avoid complicating the drawing. As shown in the figure, when L is increased, the arc of impedance increases and the resistance of the input impedance at the tuning frequency also increases. On the other hand, when L is made smaller, the arc of the impedance locus becomes smaller and the resistance of the input impedance at the tuning frequency also becomes smaller. Therefore, by appropriately selecting the value of L, the resistance of the input impedance at the tuning frequency can be set to an almost arbitrary value, and matching with the radio circuit section can be performed. As a result, the external matching circuit, which was indispensable in the past, can be omitted, and an extra loss reduction can be eliminated.

Next, FIG. 4 shows an example of receiving sensitivity measured by the antenna for a small radio device of the present invention. Fig. 4 shows the values standardized with the receiving sensitivity at a frequency of 280 MHz as a reference. In this case, it can be seen that almost flat characteristics are obtained in the range of 270 MHz to 290 MHz in 20 MHz. As a result, the antenna for a small radio device of the present invention has a wide band frequency characteristic. This means that when the small radio antenna of the present invention is used in a reception-only radio such as a pager, the tuning reception frequency is slightly detuned due to external influences such as vibration, shock, and changes in operating temperature. In this case, it means that there is little deterioration in reception sensitivity and that it has particularly useful characteristics.

The antenna for a small radio device of the present invention configured as described above is installed near the housing as shown in FIG. It may be installed on the front surface or the back surface of the case by print vapor deposition, and the top and bottom plates are made of a conductive material so that the radiating (receiving) element of the small radio antenna can be used as the case. Needless to say, it may be mounted so that the function of the antenna for a small radio device of the present invention can be utilized.

As described above, according to the present invention, it is possible to realize a thin and compact antenna for a small radio device having a high radiation efficiency and having both a tuning function and a matching function.

[0016]

[Effect of the device]

 As described above, in the present invention, the loading coil and the feeding terminal are integrally attached to the antenna radiating element, and the antenna element itself has the tuning and matching functions, so that the loss due to the external matching element as in the past is reduced. In addition, it is possible to prevent the reduction of the reception area due to the reduction in thickness, and to improve the radiation efficiency.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an embodiment according to the present invention.

FIG. 2 is an exploded perspective view excluding a loading coil and a power supply terminal portion in FIG.

FIG. 3 is an impedance locus diagram for explaining the impedance characteristic of the antenna of the present invention.

FIG. 4 is an explanatory diagram for explaining frequency characteristics of the antenna of the present invention.

[Explanation of symbols]

 1 Upper plate 2 Frame 3 Bottom plate 4 Loading coil 5 Antenna feeding terminal

Claims (2)

[Scope of utility model registration request] 1. A small radio antenna connected to a radio circuit, comprising: a frame made of an insulator, a top plate and a bottom plate made of a rectangular plate-shaped conductor, a load coil, and an antenna feeder terminal. The frame is sandwiched and fixed by the upper plate and the bottom plate to form a casing, and the upper plate and the bottom plate are electrically coupled by the load coil to form an antenna radiating element by the upper plate and the bottom plate. An antenna for a small radio device, characterized in that it is configured to be matched depending on the position of the antenna feeder body terminal. 2. The antenna element according to claim 1, wherein a conductive material is printed and vapor-deposited on a surface of an upper plate and a bottom plate which form a housing, and the printed and vapor-deposited upper and lower plates are electrically coupled by a load coil to radiate the antenna. The antenna for a small radio device according to claim 1, wherein an element is formed.