JP3334079B2 - Built-in balun loop antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a balun-incorporated loop which is formed on a printed circuit board (PCB) incorporated in a device and incorporates a balun for connecting a coaxial cable and supplying power. Regarding the antenna,
In particular, the present invention relates to a balun-incorporated loop antenna which is advantageous in terms of manufacturing and cost.

[0002]

2. Description of the Related Art In recent years, a PHS (Personal Handy Phone System) master unit, which has been widely spread, employs a built-in loop antenna in order to differentiate itself from other models in terms of external design. This loop antenna is directly connected by soldering to a high-frequency coaxial cable connecting to a radio unit.

[0003] For example, as shown in FIG.
In the case where the loop antenna 111 which is a balanced line formed in a rectangular pattern and the coaxial cable 20 which is an unbalanced line are directly connected to each other and supplied with power from the multi-frequency power supply 30, the coaxial cable 20 is used at the power supply connection point P. Outer sheath conductor 21
Leakage current Ib is generated outside the device. This leakage current Ib affects the gain and the polarization plane of the antenna, causing a reduction in the communication distance, and as a result, a reduction in the communication quality. What prevents such a leakage current is a balun (hereinafter referred to as a balun).

FIG. 5 shows a well-known shovel top 123 attached to an antenna junction as a balun of a coaxial cable 120 having an outer sheath conductor 121 and an inner center conductor 122. Shovel top 123
Has a cylindrical shape formed concentrically from the end face of the antenna junction portion of the coaxial cable 120 to a length of a quarter wavelength from the end face of the antenna junction portion of the coaxial cable 120 while maintaining a predetermined gap around the coaxial cable 120; On the opposite side, the bottom surface is formed by an annular surface that fills the gap with the outer covering conductor 121 and is electrically connected.

Next, the operation principle of the conventional balun built-in type loop antenna will be described with reference to FIG.

As shown in FIG. 6, a rectangular loop antenna 111 formed on a substrate 110
The high frequency oscillator 30 is connected to the outer sheathing conductor 121 and the inner center conductor 122 of the first and second conductors, and a high frequency is supplied between the outer sheathing conductor 121 and the inner center conductor 122 from the high frequency oscillator 30. With this power supply, the outer covering conductor 121 is provided at the power supply junction point P between the loop antenna 111 and the coaxial cable 120.
Current Ib leaks out of the device. This leaking current Ib is
It returns at the bottom surface, which is the joint surface between the outer covering conductor 121 and the shovel top 123, reciprocates on the inner surface of the shovel top 123, passes by half a wavelength, and returns to the feed junction point P. As a result, the leakage current Ib is
The current reciprocates on the inner surface and is offset at the power supply junction P by a current shifted by a half wavelength. Therefore, it is possible to prevent the adverse effect of the leakage current Ib.

[0007]

In the above-mentioned conventional balun-incorporated loop antenna, a shovel top is provided as a balun at a power supply connection point which is an antenna connection point of a power supply coaxial cable. When a shovel top having a size to accommodate the coaxial cable is provided in such a small device, there is no problem in that it is disadvantageous in terms of manufacturing and cost.

An object of the present invention is to solve such a problem and to provide a balun-incorporated loop antenna which can incorporate a balun at the same size as the conventional one and at a reduced manufacturing cost. .

[0009]

A balun-incorporated loop antenna according to the present invention is a balanced loop antenna in which a loop conductor formed on a substrate as a loop antenna is formed on the same substrate at one end connected to a feeding point. It has an unbalanced transformer (balun). As a result, the step of forming the substrate is added, but it is not necessary to attach the balun to the coaxial cable.

[0010] Specifically, the balun (balun) is formed on the substrate, have a one from the tip a predetermined length of the feed junctions said loop conductor is subjected to feed
On both sides of the loop conductor and the center of, as well as positioned in parallel at a predetermined interval, the end opposite to the feeding junction position I the parallel range near, electrically connected to said loop conductor Conductor. Preferably, a portion between an electrical connection position with the balun loop conductor and a power supply junction position of the loop conductor has a length of a quarter wavelength with respect to a high frequency to be supplied. That is being done.

In the loop antenna having such a structure, one end, that is, the end on which the conductor serving as the balun is provided, is connected to the outer covering conductor of the coaxial cable which is at the ground potential. The tip of the other loop antenna is connected to the inner central conductor of the coaxial cable.
Therefore, by forming a balun so that the conductor provided in addition to the loop antenna becomes a balun and becomes a half wavelength at a feeding junction between the loop antenna and the outer coating conductor of the coaxial cable. The effect of canceling out the leakage current can be exhibited. By forming the conductor of the balun portion in parallel with the antenna conductor, the length can be easily determined. If these conductors are formed in a straight line, it is more effective in terms of manufacturing.

[0012]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

The illustrated balun-incorporated loop antenna includes a printed circuit board (hereinafter abbreviated as a board) 10.
A rectangular loop antenna (hereinafter, simply referred to as an antenna) 11 is formed of a conductor thereon, and a balun 12 is formed on the substrate 10 by the conductor. Further, a high-frequency power supply 30 is connected to the antenna 11 by a power supply line. The balun 12 is a quarter wavelength (λ / λ) from a power supply junction of the high frequency power supply 30 which is one end of the antenna 11.
4) formed over a length.

The balun 12 is formed of a conductor printed in parallel with a constant gap along both sides of the substrate 10 from the vicinity of the power supply junction point P of the high-frequency power supply 30 and on both sides of the antenna 11 in a linear portion. At a quarter wavelength from the power supply junction P of the high-frequency power supply 30 (balun junction Q)
Are electrically connected to the antenna 11.

Next, the operation principle of the balun-incorporated loop antenna shown in FIG. 1 will be described with reference to FIG.

The illustrated balun-incorporated loop antenna is an antenna 11 formed of a conductor together with a balun 12 on a substrate 10 shown in FIG.
1 is connected to a high frequency power supply 30 via a coaxial cable 20. The tip of the antenna 11 on the side having the balun 12 is joined to the outer covering conductor 21 of the coaxial cable 20, and the other tip of the antenna 11 is joined to the inner center conductor 22 of the coaxial cable 20.

The distance between the balun junction Q with the balun 12 portion of the antenna 11 and the feeding junction P with the outer sheathing conductor 21 of the coaxial cable 20 is a quarter wavelength (λ / 4) of the received high frequency. is there. Therefore, the outer coated conductor 2
A current having a half wavelength (λ / 2) from the balun junction Q returns to the tip of the conductor of the balun 12 located near the one feeding junction P. As a result, the current Ib that is about to leak from the outer sheathed conductor 21 to the outside of the coaxial cable 20 at the feeding junction P is a half wavelength (λ / 2) returning from the balun junction Q to the conductor in the balun 12 portion.
, And the current leaks from the coaxial cable 20 at the feeding junction point P.

Next, with reference to FIG. 3, an application example in which the balun-incorporated loop antenna according to the present invention is employed in the PHS base unit 1 will be described.

The PHS base unit 1 employs a diversity system using two antennas from the viewpoint of stable communication quality, and employs a structure in which one of the two antennas is housed in the housing from the viewpoint of design. I have. That is, one external antenna 2 uses a polarization diversity system in which vertical polarization is used, and the other built-in antenna 3 uses horizontal polarization. Here, the built-in antenna 3 is an antenna 11 having a balun 12 formed on the substrate 10 shown in FIG.
It is. Therefore, the built-in antenna 3 has no gain loss due to the built-in balun, and its polarization plane is horizontal and stable. Therefore, the polarization diversity used in combination with the vertically polarized antenna as the external antenna 2 is used. Thus, a higher diversity gain can be obtained.

In the above description, the antenna on the substrate is described and illustrated as the best rectangle, but may be another shape such as a circle. The conductor of the balun portion is preferably parallel to the antenna conductor, but if the tip portion is near the feeding junction, and the distance from the feeding junction to the tip portion is half the wavelength of the feeding high frequency, the antenna and the balun are not used. Each conductor shape is free.

[0022]

As described above, according to the present invention, a balanced-unbalanced transformer (balun) is formed with one feed connection point in a loop antenna on a printed circuit board connected to a coaxial cable and receiving high-frequency power supplied as a tip. ) Is formed on the same substrate by a conductor to obtain a balun-incorporated loop antenna.

According to this configuration, the balun can be incorporated in the built-in antenna, so that the inherent gain and polarization plane of the antenna can be secured. Therefore, the effect that the call quality can be improved can be obtained. On the other hand, a step of forming the conductor of the balun portion on the substrate is added, but the attachment of the balun to the coaxial cable is unnecessary. Therefore, it is possible to reduce the burden in terms of manufacturing and cost for incorporating the balun.

Furthermore, by forming the balun conductor in a position parallel to the antenna conductor, the required length of the balun conductor can be easily set.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram illustrating an operation principle according to the embodiment shown in FIG. 1;

FIG. 3 is an external view illustrating an example to which an embodiment of the present invention is applied.

FIG. 4 is a block diagram showing an example of a conventional configuration.

FIG. 5 is an explanatory perspective view showing an example of a balun in a conventional coaxial cable.

FIG. 6 is a block diagram illustrating an operation principle in an example using the balun of FIG. 5;

[Explanation of symbols]

 Reference Signs List 1 PHS base unit 2 External antenna 3 Built-in antenna 10 Printed circuit board (substrate) 11 Loop antenna (antenna) 12 Balun (balanced / unbalanced transformer) 20 Coaxial cable 21 Outer sheath conductor 22 Inner center conductor 30 High frequency power supply

Continuation of front page (56) References JP-A-58-134505 (JP, A) JP-A-62-200802 (JP, A) JP-A-6-188610 (JP, A) JP-A-62-102604 (JP, A) JP-A-10-261911 (JP, A) JP-A-6-237109 (JP, A) JP-A-7-46108 (JP, A) JP-A-62-26909 (JP, U) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01Q 5/00-11/20 H01Q 1/00-1/52

Claims (3)

(57) [Claims] 1. A balun-incorporated type wherein a loop conductor formed on a substrate as a loop antenna has a balun transformer formed on the same substrate at one end connected to a feeding point. Loop antenna. 2. The balun according to claim 1, wherein the balun is formed on the substrate and has a predetermined length from one end of a power supply junction to which the loop conductor receives power. on both sides of the loop conductor and the center, as well as positioned in parallel at a predetermined interval, the end opposite to the feeding junction position I the parallel range near and electrically connected to said loop conductor A balun built-in type loop antenna characterized by being a conductor. 3. The high-frequency power supply according to claim 2, wherein a position between an electrical connection position of the balun transformer with the loop conductor and a power supply junction position of the loop conductor is one-fourth of a high frequency to be supplied. A balun-incorporated loop antenna formed to have a wavelength length.