JPH0340526B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a wideband extremely short wave antenna used as a transmitting/receiving antenna for a car-mounted telephone, and in particular, the present invention relates to a wideband extremely short wave antenna used as a transmitting/receiving antenna for a car-mounted telephone. This invention relates to an improvement means for an antenna structure that enables shortening.

[Conventional technology]

Automotive wireless telephone communication, which has recently become popular, connects the telephone set installed in the car and a telephone exchange via wireless communication, providing communication services similar to normal wired telephone communication. As a car phone, it can be thought of as a normal handset (telephone) with a wireless transmitter/receiver installed side by side.

In addition, some car telephone devices are partially separated and used as portable telephones so that they can be effectively used outside the vehicle. In this case, the shape is a normal handset (telephone).
It is preferable that it be similar to . Therefore, there is a demand for a wireless transmitting/receiving device installed in parallel with a handset to be further miniaturized while still fully satisfying the function of a communication device.

The specific requirements for this type of antenna are as follows.

Since the antenna is for telephone communication, it is necessary to configure it as an ungrounded antenna whose characteristics do not easily change due to the presence of a human body, or one that exhibits similar characteristics.

The length of the antenna needs to be smaller than that of a small antenna, for example, about 160 to 200 mm.

Frequency range used: 800~900MHz, bandwidth 70~80M
Hz, the voltage standing wave ratio (hereinafter referred to as VSWR) needs to be 2.0 or less within the above band, and the gain needs to be close to that of a dipole antenna.

[Problem that the invention seeks to solve]

However, in order to construct an antenna that satisfies the above matters, it is possible to achieve it by taking special technical measures to widen the band by taking the basic form of the antenna, a half-wavelength dipole antenna. The length is approximately half a wavelength, and considering the dimensions of the attached connector, it is, for example, 200 to 220 mm.
Although the diameter could be made thinner in some areas, it had to be made thicker in most parts to achieve a wider band, and the limit was 16 to 12 mm. Furthermore, the weight was 30 to 40 g, which was considered too heavy for use as a portable telephone.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a broadband extremely short wave antenna that is small and lightweight and has sufficient electrical characteristics.

[Means for solving problems]

In order to solve the above-mentioned problems and achieve the purpose, the present invention has been developed based on the feeding point of an antenna having an electrical length of λ/4 to λ/2 (antenna impedance Z _A = R _A +
jX _A , reactance component of the antenna between the wavelength λ ₎ and the coaxial feed line (characteristic impedance Z ₀ )
Insert an impedance converter that has _{a reactance -j} ＝√ ₀・_A and Z ₀ < R _A.

[Effect]

By taking such measures, the inductive reactance jX _A of the antenna element impedance Z _{A
is canceled} by the capacitive reactance _{element of the} impedance _{converter -j} Changes in characteristics due to the human body can be reduced by approaching the characteristics of non-grounded antennas, and the antenna element has an electrical length of 1/1.
By setting the length to two wavelengths or less, miniaturization can be achieved.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention. In Figure 1, 1 is the electrical length of 1/4
Wavelength ~ 1/2 wavelength, specifically 3/8 wavelength, antenna element with impedance Z _A = R _A + _j an insulator that holds the power feeding side end of the element 1;
Reference numeral 3 denotes a conductive outer cylinder connected in the longitudinal direction of the insulator 2, 4 a matching coil electrically connected to the feeding side end of the antenna element 1, and 5 the matching coil 4 and the conductive outer cylinder. This is a dielectric material placed between 3 and 3. Here, the conductive outer cylinder 3, the matching coil 4, and the dielectric 5 constitute an impedance converter 6 having an electrical length of 1/4 wavelength, and is connected to the antenna element 1 via the feeding point ES. The structure is as follows. In addition, the conductive outer cylinder 3, the matching coil 4, and the dielectric 5 create a capacitive reactance.
jX _Q is formed, an impedance converter for matching with the antenna element 1 is formed by the matching coil 4, and when the feed line impedance Z is ₀ , the relationship Z ₀ < R _A , R _Q = √ ₀・_A is established. It is composed of

FIG. 2 is a diagram showing the electrical equivalent circuit of FIG. 1. The antenna element impedance seen from the feeding point of the antenna element 1 is Z _A = R _A + jX _A , and the impedance of the impedance converter 6 is Z _Q = R _Q
-jX _Q , and the input impedance seen from the input side (connector side) of the impedance converter 6 is Z ₀
It is becoming.

Next, the operation of this embodiment configured as described above will be explained.

Figures 3 and 4 are characteristic diagrams showing the relationship between effective resistance and reactance (inductive, capacitive) with respect to antenna length l/diameter d = k, and as is clear from both figures, the antenna length As l/diameter d=k becomes smaller, the effective resistance and reactance of the antenna both change more gradually, indicating a wider band. Therefore,
The antenna element 1 of this embodiment has a length l = 3/8 wavelength and k (l/d) = 30 to 40, so it can be made smaller and lighter, and a sufficiently wide band can be achieved. . Here, the specific basis for setting the length of the antenna element 1 to l=3/8 wavelength will be explained. In other words, the antenna impedance Z ₀ is normally standardized to 50 (Ω), and as shown in Figure 3, the impedance Z 0 at k (l/d) = 30 to 40 (conditions for miniaturization and broadband expansion) The part that satisfies the condition of ₀ < R _A (the condition that approaches the non-grounded type) is
This is the part corresponding to 1/4 wavelength to 1/2 wavelength in terms of electrical length. The optimum length for keeping the antenna short and achieving a large effective resistance R _A is around 3/8 wavelength.

In the antenna element 1 of this embodiment, the antenna element impedance seen from the feeding point is Z _A = R _A +
jX _A , that is, the antenna has inductive reactance + jX _A. This remaining inductive reactance +jX _A is canceled out by the capacitive reactance -jX _Q of the impedance converter 6.

By setting Z ₀ < R _A , the characteristics of the antenna approach those of a non-grounded type, and changes in characteristics due to the influence of the human body (the caller holding the handset) and the housing of the communication device to which the antenna is installed can be reduced.

Theory of 1/4 wavelength matching circuit (Q match theory)
According to the center frequency f ₀ as shown in FIG.
If the characteristic impedance Q of the matching circuit of the 1/4 wavelength line is set as Q= _√0 ·, matching will be achieved between the antenna and the feeding point.

The impedance converter 6, which has an electrical length of 1/4 wavelength, has a dielectric 5 disposed between its matching coil 4 and the conductive outer cylinder 3. Characteristics can be changed by changing to a material with a different dielectric constant. That is, when the dielectric constant of the impedance converter 6 changes, the equivalent electrical length changes. In this case, of course, the physical length does not change. Therefore,
By changing the dielectric constant and changing the electrical length, it is possible to match the characteristics. Here, the dielectric constant can be changed in various ways, such as by combining a dielectric material such as plastic with air, and setting their wall thicknesses. 6th
The figure is a diagram illustrating changes in the above-mentioned characteristics. In Figure 6, the optimum value f ₀ of VSWR is when the dielectric constant is 1.
In other words, it shows the case of only air, and f ₀ ' shows the change in f ₀ when the dielectric constant is changed. Here, the effective resistance R is approximately constant over a wide band by reducing l/λ.

FIG. 7 is a longitudinal sectional view of a portable wideband extremely short wave antenna device manufactured by embodying the above embodiment. This antenna device is composed of an antenna section 10 and a connector section 20, and also includes an antenna element 1 and an impedance converter 6. In FIG. 7, 11 is an antenna top made of soft vinyl chloride, 12 is a rubber sleeve, 13 is an antenna element (antenna element 1) made of flexible wire, etc., 14 is a cover made of plastic, etc., and holds the antenna element 1; 15 and 16 are joints made of copper alloy, 17 is an insulator, 18 is a matching coil 4, 21 is a connector conductive outer cylinder, 22
23 is an insulator, 23 is a cover, and 24 is a contact pin.

According to this manufactured antenna device, the following things were verified. That is, it is configured to exhibit characteristics close to those of a non-grounded antenna, and its characteristics do not change due to the presence of a human body (transmitter/receiver). In addition, the frequency range used is 800 to 900 MHz, and the bandwidth is 70
At ~80MHz antenna length dimension is 150~160mm
It was possible to achieve a VSWR of less than 2.0 and a gain of 0±1 dBD compared to a dipole antenna.
Furthermore, even though the antenna diameter was around 10 mm in some parts, it was 4 to 6 mm over most of the entire length. This reduced the length and diameter, resulting in a reduction in weight.

8 and 9 show the actually measured VSWR characteristics of the antenna device shown in FIG. 7, FIG. 8 is a characteristic diagram of the antenna device shown in FIG. This is a characteristic diagram of a state in which a person is talking with a person attached to an actual communication device, and shows that there is little change in characteristics between the two.

The present invention is not limited to the above embodiments, but can be implemented with various modifications without departing from the gist of the present invention.

〔Effect of the invention〕

The broadband extremely short wave antenna of the present invention has an electrical length between an antenna feed point (antenna impedance Z _A = R _A + jX _A ) and a coaxial feed line (characteristic impedance Z ₀ ) having an electrical length of λ/4 to λ/2. The reactance component that cancels the reactance component jX _A of the antenna between −
_{j _ _ _ _} It is characterized by being configured to have the relationship Z ₀ < _RA .

Therefore, according to the present invention, the inductive reactance jX _A of the antenna element impedance Z _A is canceled by the capacitive reactance element −jX _Q of the impedance converter, and by setting R _Q =√ ₀ · _A , the antenna element becomes By matching the feed line impedance Z ₀ and setting Z ₀ < R _A , changes in characteristics due to the human body can be reduced by approaching the characteristics of an ungrounded antenna, and the antenna element has an electrical length of 1/2 wavelength or less. By setting the length to , miniaturization is achieved.

In this way, it is possible to provide a broadband extremely short wave antenna that is small and lightweight and has sufficient electrical characteristics.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure is an electrical schematic diagram of Figure 1, Figures 3 and 4 are characteristic diagrams showing the relationship between effective resistance and reactance,
Figure 5 is a circuit diagram showing the theory of Q-match, Figure 6 is a characteristic diagram showing changes in center frequency due to changes in dielectric constant, and Figure 7 is a longitudinal cross-section of the antenna device manufactured based on the example shown in Figure 1. The top view, FIGS. 8 and 9 are characteristic diagrams of the antenna device of FIG. 7, respectively. DESCRIPTION OF SYMBOLS 1... Antenna element, 2... Insulator, 3... Conductive outer cylinder, 4... Matching coil, 5... Dielectric, 6... Impedance converter.

Claims (1)

[Claims] 1. A feed point of an antenna with an electrical length of λ/4 to λ/2 (antenna impedance Z _A = R _A + jX _A , wavelength λ) and a coaxial feed line (characteristic impedance Z _O ). It has _a reactance component −jX _Q that cancels out the reactance component jX _A of the antenna between A broadband extremely short wave antenna characterized by inserting an impedance converter and configuring the relationship such that R _Q = √ _O・_A and Z _O < R _A. 2. The impedance converter has a coaxial configuration, and is characterized in that a dielectric material is arranged between the central impedance conversion element and the conductive outer cylinder, and the characteristics are changed by forming different dielectric constants. A broadband extremely short wave antenna according to claim 1.