JPH06204733A - Small sized antenna - Google Patents

Abstract

PURPOSE:To eliminate the need for a matching circuit with a feeder, to make the antenna small and highly efficient by exciting a radiating element without contacting of a coupling line. CONSTITUTION:A radiation element 1 and a coupling line 2 are arranged without contacting. The coupling line 2 has the same characteristic impedance as that of a feeder 3. Furthermore, the length L of the radiation element 1 in the direction of an electric field of a major polarized wave is shorter than the length of a linear half wavelength dipole element used in the resonance state, and the element 1 is self-resonated at an operating center frequency and excited through electromagnetic coupling with the coupling line 2. Through the constitution of the small sized as above, since the operating frequency depends only on the shape of the radiation element 1, the coupling line 2 of the same shape is used even for an antenna for a different band. Thus, it is not required to make the design of the coupling line 2 in matching with each characteristic of different radiation elements. Thus, the size is made small and the antenna is made highly efficient.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small antenna suitable for use in a base station antenna system for personal communication, a basic antenna module of a highly directional array antenna, and the like.

[0002]

2. Description of the Related Art In recent years, personal communication including communication from mobile bodies such as automobiles, aircrafts, ships, etc. has been widely spread. For this reason, the communication band in the high frequency region has begun to run short, and the communication frequency is being increased. On the other hand, from the viewpoint of effective use of the frequency band, miniaturization of the personal communication base station area is being promoted, and as the number of base station antennas increases, miniaturization and higher directivity of the antennas are required. That is, there is a demand for an antenna that is a more compact version of the half-wavelength antenna that has been conventionally used.

[0003]

Generally, when the length of the radiating element of the antenna is made shorter than the length of 1/2 of the wavelength of the frequency band to be used to make the antenna small, the radiated power is proportional to the square of the element length. Becomes smaller. For this reason, the gain of the antenna is reduced due to the resistance loss of the signal line forming the antenna. Also, along with this, the resistance component of the input impedance of the radiating element, that is, the input resistance becomes extremely small,
Impedance matching with the power supply line becomes difficult. further,
In a non-resonant radiating element such as a micro dipole or a micro loop, the reactance component of the input impedance is tens of thousands to hundreds of thousands times that of the resistance component, which makes impedance matching even more difficult. Therefore, when creating a small antenna, impedance matching with the feed line, which was not necessary with a half-wavelength dipole antenna, etc., is indispensable.For a non-resonant antenna such as a small dipole, a stub with a distributed constant line is used. Will need to be connected in parallel. However, in this case, due to the loss in the matching circuit and the like, the efficiency of the entire antenna becomes extremely low, about 10% or less, together with the low efficiency of the radiating element. As means for solving these problems of efficiency reduction and impedance matching, a small antenna using a self-resonant radiating element using a superconductor, which has a surface resistance lower than that of a normal metal in a high frequency region, is disclosed in, for example, JP-A-4-216203. It is disclosed in the publication. However, even when a superconductor is used for the radiating element, the input resistance of the radiating element is much smaller than that of the feeding line, and an impedance matching circuit with the feeding line is indispensable. However, there is a problem that the size of the superconducting radiating element cannot be fully utilized due to resistance loss at the connection point between the matching circuit itself and the radiating element and the matching circuit. As described above, in a small antenna with a small radiation power, impedance matching with the feed line is indispensable due to the small input resistance of the radiation element, but since loss occurs in the matching circuit, a radiation element with a low efficiency is originally used. Combined with this, there arises a problem that the radiation efficiency becomes very small. Moreover, even if a radiating element made of a superconductor with less loss than ordinary metal is used, the loss at the connection point between the radiating element and the matching circuit and the size of the matching circuit pose problems, realizing a compact and highly efficient antenna. Can not do it.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a highly efficient small antenna which does not require a matching circuit with a feeder line.

[0005]

In order to achieve such an object, the present invention provides a radiating element having a length in the main polarization electric field direction shorter than that of a linear half-wavelength dipole element used in a resonance state. In addition, a structure that self-resonates at the used center frequency is adopted, and this radiating element is excited without contact with the coupling line.

[0006]

Therefore, according to the present invention, the radiating element is excited by electromagnetic coupling between the coupling line and the radiating element without using an impedance matching circuit.

[0007]

EXAMPLES The present invention will now be described in detail based on examples.

FIG. 1 is a diagram showing the basic configuration of the present invention. In the figure, 1 is a meandering self-resonant radiating element (hereinafter simply referred to as radiating element), 2 is a coupling transmission line (hereinafter referred to as coupling line), 3 is a feeder line, and radiating element 1 The coupling line 2 is arranged in a non-contact manner. The characteristic of the coupled line 2 depends only on the characteristic impedance and structure of the feeder line 3, such as a balanced line or an unbalanced line. Therefore, the structure of the coupling line 2 also depends only on the power supply line 3 used, and has no relation to the input resistance or the resonance frequency of the radiating element 1. The coupled line 2 has a structure that is terminated by either a short circuit, an open circuit, or an arbitrary load. In this embodiment, the coupled line 2
Has the same characteristic impedance as the feeder line 3.
The length of the radiating element 1 in the main polarization electric field direction is longer than that of the linear half-wavelength dipole element used in the resonance state.
The structure has a short (radiating element length) and self-resonates at the used center frequency, and is excited by electromagnetic coupling with the coupling line 2.

In the small antenna thus constructed,
Since the frequency to be used is determined only by the shape of the radiating element, it is possible to use the coupling line of the same shape for antennas of different bands. Therefore, when designing the coupling line, it is not necessary to design the radiating elements for different radiating elements according to their characteristics, such as a matching circuit in a conventional small antenna.

FIG. 2 is a cross-sectional view of a coupling portion when a coaxial cable is used for the power feed line 3 and a microstrip line is used for the coupling line 2. FIG. 3 is a cross-sectional view of a coupling portion when a parallel line is used for the power feed line 3 and a parallel plate line is used for the coupling line 2. In these figures, 4 is a radiating element support substrate, 5
Is a central conductor of the microstrip line, 6 is a ground plane of the microstrip line, 7 is a dielectric spacer of the microstrip line, and 8 is a parallel plate line. It goes without saying that the radiating element 1 and the coupling line 2 are also arranged in non-contact with each other in these embodiments.

In FIG. 4, 600M of copper is used as the radiating element 1.
The measured values of the operating gain of the antenna using the meander radiating element in the Hz band are shown. This radiating element is designed so that the reactance component becomes zero at 590 MHz, that is, self-resonating, and the radiating element length corresponds to λ / 20. The operating gain of the antenna is -6MHz at 590MHz, and 1
It has achieved an efficiency of 7%. When a small antenna is made of an ordinary metal such as copper, the conventional small antenna has a large loss in the matching circuit in addition to the resistance loss caused by the radiating element, resulting in a very low antenna efficiency.
On the other hand, in the small antenna according to the present embodiment, since there is no matching circuit, high efficiency can be obtained even when copper, which causes significant loss in the radiating element, is obtained. The size of can also be made small.

In order to maximize the efficiency of the antenna, a superconducting film may be used for the radiating element 1. FIG. 5 shows the actual measurement value of the operating gain of a 900 MHz band antenna with a radiating element length of λ / 42 using a superconducting film. For comparison, the figure also shows the characteristics of an antenna in which the same superconducting radiating element is used and impedance matching is performed with the feeder by a capacitor. The operating gain of the superconducting antenna according to the present embodiment is -1.5 dBi, which realizes an operating gain that is 4 dB higher than that of the superconducting antenna using the matching circuit. This is because in an antenna using a matching circuit, the efficiency of the antenna decreases due to resistance loss in the matching circuit and its connection point.
While the excellent characteristics of the superconducting radiating element have not been fully utilized, the superconducting antenna according to the present embodiment does not have a matching circuit, and therefore the characteristics of the superconducting radiating element can be sufficiently obtained. The radiation efficiency of the superconducting antenna according to the present embodiment is as high as 50%. These results indicate that a highly efficient small antenna can be realized by optimizing the superconducting film as the conductive material.

[0013]

As is apparent from the above description, according to the present invention, since the radiating element is excited without contact with the coupling line, a matching circuit with the feeder line is not required,
In addition to miniaturization, high efficiency can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of the present invention.

FIG. 2 is a cross-sectional view of a coupling portion when a coaxial cable and a microstrip line are used for a power supply line and a coupling line.

FIG. 3 is a cross-sectional view of a coupling portion when a parallel line and a parallel plate line are used as a feeder line and a coupling line.

FIG. 4 is a characteristic diagram showing an actual measurement value of an operating gain of an antenna using a 600 MHz band meander radiating element made of copper as a radiating element.

FIG. 5 is a radiating element using a superconducting film having a length of λ / 42 of 9
It is a characteristic view which shows the measured value of the operating gain of a 00 MHz band antenna.

[Explanation of symbols]

 1 Self-resonant type radiating element (radiating element) 2 Coupling transmission line (coupling line) 3 Feed line 4 Radiating element support substrate 5 Microstrip line center conductor 6 Microstrip line ground plane 7 Microstrip line dielectric spacer 8 Parallel plate track

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Ishii 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. A length in the main polarization electric field direction is shorter than a length of a linear half-wave dipole element used in a resonance state, self-resonates at a used center frequency, and excited without contact with a coupling line. A small antenna equipped with a radiating element.