JP3434219B2 - antenna - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna having a structure in which a ground current of an antenna element such as a linear antenna used for mobile communication or the like cannot sufficiently flow, such as a portable device or an automobile antenna. More specifically, the present invention relates to an antenna having a structure in which it is difficult to sufficiently process the ground current, such as a linear antenna, and the antenna performance can be improved as a structure in which the ground current is sufficiently obtained.

[0002]

2. Description of the Related Art Conventionally, a linear antenna has been used as an antenna for FM communication, TV reception or the like, or an antenna for mobile communication or the like. These linear antennas generally have a structure in which a lead wire is connected from the antenna element to the preamplifier of the receiving apparatus. Therefore, in the antenna having such a structure, the ground conductor (ground plane) of the antenna is small, and the performance as the original antenna cannot be sufficiently obtained.

That is, for example, in a coaxial line connected to an antenna element, electromagnetic waves are transmitted by causing currents to flow in opposite directions in an inner conductor and an outer conductor, but a linear antenna is connected to the inner conductor. Only the antenna element is in a stretched state, and the ground conductor is often the casing of the wireless device or the like. However, since the housing itself is small and apart from the antenna element, it does not sufficiently contribute to the length of the antenna element as a ground conductor. Especially,
Recently, the housing has become smaller and made of resin, and it has become impossible to provide a ground conductor such as a ground plane.

[0004]

As described above, particularly in the conventional antenna extending from the housing such as the linear antenna, the ground conductor is not sufficiently provided in the vicinity of the antenna element or the ground conductor is provided. It has a structure that does not allow the current in the opposite direction to be sufficiently induced.
Therefore, there is a problem that the original performance of the antenna cannot be sufficiently obtained, and the performance such as frequency characteristics and antenna gain cannot be sufficiently satisfied.

Particularly, with recent demands for electronic devices, and further for miniaturization and high performance of antennas, an antenna that can obtain a large gain with a small antenna element is required.
Further improvement in gain is required.

On the other hand, if the ground conductor is directly extended in the vicinity of the antenna element, the directions of the electric currents in the antenna element and the ground conductor are opposite to each other, and the electric field direction of the electromagnetic wave in the space near the antenna element does not match. They cancel each other out, weakening the transmitted and received signals and not functioning as an antenna.

The present invention has been made to solve such a problem, and it is not possible to provide a ground conductor (ground plate), or a small structure such as a structure protruding from a housing like a linear antenna. It is an object of the present invention to provide an antenna that can improve its gain.

[0008]

An antenna according to the present invention comprises a hot-side antenna element connected to a feeding portion, and
It is connected to the ground conductor near the power supply and is used for transmission and reception.
Phase control that produces a phase difference of approximately 1/2 wavelength of the frequency band
Control line and the phase control line connected to the front,
Serial consists parallel to the ground antenna element which is provided with a hot side antenna element.

Here, the hot-side antenna element means a portion of a normal antenna element connected to an inner conductor when the antenna is connected to a coaxial cable, and the ground-side antenna element means a part of the coaxial cable. An element connected to an outer conductor and cooperating as an antenna.

With this structure, the hot-side antenna element and the ground-side antenna element are in phase with each other by the phase control line, and the signal radio waves flying in space can be received by both antenna elements, and the reception sensitivity is improved. Can be greatly improved.

[0011]

The hot-side antenna element and the ground-side antenna element are each formed in a semi-cylindrical shape, and are opposed to each other so as to have a substantially cylindrical shape and are fixed by an insulator so that a rod shape (linear shape) is obtained. This is preferable because it serves as an antenna and is a rod antenna similar in shape to the conventional one, and it is possible to improve the receiving sensitivity in the same way as an antenna having a ground conductor even in a case or the like in which a ground conductor is not provided.

The end portion of the hot side antenna element on the side of the power feeding portion is connected to the inner conductor of the coaxial cable , and a part of the hot side antenna element side of the coaxial cable is wound in a coil shape, thereby making it coaxial. It is possible to prevent the outer skin current of the antenna from being excited in the outer skin of the outer conductor of the cable, cancel the antenna current due to the outer skin current, and maintain the antenna performance at a high level.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an antenna of the present invention will be described with reference to the drawings. The antenna of the present invention is provided with a hot-side antenna element 1 and a ground-side antenna element 2 in parallel with the hot-side antenna element 1 as shown in the explanatory view of the embodiment thereof in FIG. ,
The phase control line 3 is provided between the grounding-side antenna element 2 and the grounding conductor (outer conductor 5b of the coaxial cable 5) near the end of the hot-side antenna element 1 on the side of the feeding portion. In the example shown in FIG. 1, the antenna is attached to the tip of the coaxial cable 5, and the hot antenna element 1 is connected to the inner conductor 5a, and the ground antenna element 2 is connected to the outer conductor 5b via the phase control line 3. It is installed.

Each of the hot side antenna element 1 and the ground side antenna element 2 is made of a metal such as copper having a good electric conductivity, and has a length such that the electric length is, for example, a quarter wavelength of a wavelength band for transmission and reception. Are formed respectively. The metal may be a wire-shaped single wire or a plate-shaped body. The two antenna elements 1 and 2 can be provided so as to face each other around an insulator such as a cylindrical or columnar resin rod, or can be arranged side by side on an insulating plate-like body.

The phase control line 3 is provided so that the hot side antenna element 1 and the ground side antenna element 2 have the same phase. That is, in a normal coaxial cable, the electric current is transmitted in the opposite direction between the inner conductor and the outer conductor, but when a radio wave propagating in space is received at the same place, it becomes a current in the same direction, and The cable cannot carry both currents and cannot cancel each other. Therefore, it is provided to correct the phase difference between the inner conductor and the outer conductor in the coaxial cable. For example, since the phase control line 3 is formed to have an electrical length of ½ wavelength, the phase of the ground side antenna element 2 is exactly the same as the phase of the hot side antenna element 1. As a result, while being received by both antenna elements 1 and 2, the coaxial cable propagates with a phase difference of 180 °,
The coaxial cable can be transmitted without loss. The phase control line 3 may be formed of a line having an electric length of ½ wavelength, or may be formed to have the same electric length by combining an inductive element and a capacitive element.

According to the antenna of the present invention, even in a small portable device in which the ground plane cannot be provided, the antenna itself has a ground side antenna element corresponding to the ground plane,
When installed as it is, it operates as a high-performance antenna with excellent sensitivity. That is, since the ground side antenna element is connected to the outer conductor of the coaxial cable via the phase control line capable of making the phase difference approximately half the wavelength, the antenna part is in-air as an in-phase antenna element. With a coaxial cable that can pass a current due to an electromagnetic field and is connected to the power feeding side of the antenna element,
Since it passes through the phase control line, the inner conductor and the outer conductor have opposite phases, and the coaxial cable can be transmitted as a normal coaxial line.

FIG. 2 shows an example in which the antenna of FIG. 1 has a more concrete structure. For example, the hot side antenna element 1 and the ground side antenna element 2 are each formed in a semi-cylindrical shape.
For example, it is formed by winding it around an insulator rod 4 such as a resin rod, and covering it with a vinyl tube (not shown) or the like, and can be attached as it is as a normal rod antenna. With such a structure, even if the semi-cylindrical antenna element is not wound around the insulator rod,
The two antenna elements may be directly fixed to each other with a resin or the like, or the two linear antenna elements may be fixed in a rod shape via an insulator to form a rod antenna shape.

FIG. 3 is an explanatory view showing still another example. That is, when the above antenna elements 1 and 2 are connected to the tip of the coaxial cable 5, the electromagnetic waves transmitted from or received by the antenna elements 1 and 2 are the outer conductors of the coaxial cable 5 close to the antenna elements 1 and 2. When a skin current is excited in the skin and the skin current flows into the coaxial cable 5, the current flowing inside the outer conductor corresponding to the inner conductor in the coaxial cable 5 is offset. In order to avoid this, the coil 5c is formed in the vicinity of the antenna elements 1 and 2 of the coaxial cable 5. This coil 5c is, for example, 90 MH
In the frequency band of about z, the outer diameter of the coil is about 0.7 to 1 cm, the number of turns is about 10 to 15 and the winding is formed into a close winding, and the circumference is covered with vinyl or the like. In FIG. 3, the coil portion 5c is provided at a fixed distance A from the tip of the coaxial cable, for example, at a quarter wavelength of the transmitted / received signal, but it may be provided at the tip.

With this structure, a skin current is excited in the outer surface of the outer conductor by a radio wave radiated from the antenna element or a radio wave propagating in the air, and the skin current is the coil portion formed in the coaxial cable. Since it flows through 5c, reactance of 2πfL (f is the frequency of the radio wave to be transmitted and received) is generated by the inductance L of the coil, is attenuated and almost no skin current flows, and affects the radio wave propagating between the inner conductor and the outer conductor. It can be almost eliminated. On the other hand, the current flowing through the inner surfaces of the inner conductor and the outer conductor due to the radio wave propagating between the inner conductor and the outer conductor is shielded by the outer conductor, and is not substantially attenuated by the coil portion 5c. As a result, the radio waves radiated or received are hardly attenuated, and the skin current that may be generated by the coupling between the antenna elements 1 and 2 and the outer conductor of the coaxial cable 5 is attenuated, and the antenna does not deteriorate in performance.

As described above, the coil current alone can attenuate the outer skin current by the inductance of the coil. However, as shown by the broken line in FIG. 3, the outer surface of the outer conductor of the coil portion 5c is electrically connected to the outer surface of the outer conductor. Connect to C
The capacitance of the capacitor can be set to a value that causes parallel resonance with the inductance L of the coil portion 5c of the coaxial cable 5 with respect to the frequency of the radio wave to be transmitted and received. it can. By forming the trap circuit so as to resonate in parallel, the impedance of the coil portion 5c becomes infinite with respect to the frequency, and the skin current excited by the antenna elements 1 and 2 hardly flows.
Also in this case, the antenna current flowing through the inner surface of the inner conductor and the outer surface of the outer conductor of the coaxial cable is not affected by the electromagnetic field from the outside, and thus is hardly attenuated.

[0022]

According to the present invention, since a ground side antenna element corresponding to the ground plane is built in the antenna itself, it can be used in a small mobile phone such as a resin casing or a portable device such as a cassette radio. Even when the ground plane cannot be provided, the antenna can exhibit the same or higher function as the antenna having the ground conductor.

Further, when power is supplied by the coaxial cable, a coil is formed on the side of the connection portion of the coaxial cable with the antenna element, so that even if an outer skin current is directly excited in the coaxial cable by the electromagnetic field, its influence is exerted. It is possible to improve the sensitivity by eliminating.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of an antenna of the present invention.

FIG. 2 is a diagram showing another structural example of the antenna element of FIG.

FIG. 3 is an explanatory diagram showing an improved example in which the antenna of FIG. 1 is fed by a coaxial cable.

[Explanation of symbols] 1 Hot side antenna element 2 Ground side antenna element 3 Phase control line 5 coaxial cable

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-46028 (JP, A) JP-A-8-204433 (JP, A) JP-A-10-70409 (JP, A) JP-A-5- 160631 (JP, A) JP 8-125421 (JP, A) JP 7-273688 (JP, A) US Pat. No. 5184143 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB) Name) H01Q 9/04-9/30 H01Q 21/12

Claims (3)

(57) [Claims] 1. A hot-side antenna element connected to a power supply section, and a grounding conductor provided in the vicinity of the power supply section.
A phase difference of about half the wavelength of the transmitted and received frequency band is generated.
Phase control line and the connection to the phase control line
Vignetting, antenna comprising a ground side antenna element which is provided in parallel with the hot antenna element. Wherein said hot antenna element and ground antenna element is respectively formed in a semi-cylindrical shape, and substantially in opposition so that a cylindrical shape formed by fixing an insulator claim 1 Symbol placement Antenna. 3. The hot side antenna element has an end portion on the side of a power feeding portion connected to an inner conductor of a coaxial cable, and a part of the coaxial cable on the hot side antenna element side is wound in a coil shape. The antenna according to 1 or 2 .