JPH0653720A - Whip antenna having broad band characteristic for radio communication - Google Patents

Abstract

PURPOSE:To obtain a whip antenna having a broad band VSWR characteristic. CONSTITUTION:An antenna element 1 has fixed size almost within a range of 1/4-1/2lambda. A capacitor C is inserted between an antenna element section 8 and a matching circuit section 7 and they are coupled through capacitive coupling rejecting a direct current. The matching circuit section 7 is short-circuited in terms of DC by an inductor L3 when viewing from an antenna feeding terminal 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a wide band characteristic whip antenna used for wireless communication.

[0002]

2. Description of the Related Art In recent years, portable radios in mobile communication have been downsized, and along with this, antenna performance has been maintained.
Alternatively, it is desired to improve the size and reduce the size of the antenna. Generally, the size reduction of the antenna leads to the decrease of the resistance component and the increase of the reactance component in the antenna impedance. In order to fully demonstrate the high-frequency signal input / output performance, it is necessary to match the characteristic impedance of the radio device input / output end with the antenna input / output end impedance.
It is necessary to add a matching circuit that increases the resistance component and cancels the reactance by adding the reverse reactance component to the antenna feed end between each other, and the effect of this matching circuit inevitably results in antenna gain loss and narrow band characteristics of the frequency band. It was known that it was done.

Due to the increase in various communication systems due to the increase in mobile communication users in recent years, a frequency band required for a transmission / reception antenna is a ratio band, which is more than double the wide band performance of the conventional one. The specific band is defined by the following formula. Ratio band [%] = {(VSWR (voltage standing wave ratio) n or less frequency band [MHz]) / (center frequency of used frequency band [MHz])} x 100

Considering the propagation characteristics in land mobile communication, the arrival of radio waves is further upward from a substantially horizontal direction within a range of 1 [Km] or more from the base station and in which the base station antenna cannot be seen. Hereinafter, it is known that the distribution is concentrated in the range of 20 degrees to 30 degrees (hereinafter referred to as "elevation angle"), and a state in which a mobile wireless station (vehicle, portable wireless device, etc.) and an antenna are combined (hereinafter " In the directional characteristic of the antenna system) as well, it is necessary to satisfy the omnidirectional performance in the horizontal plane due to the elevation angle performance and the unspecified directivity between the mobile radio station and the communication partner (see FIG. 5).

The impedance characteristic of the 1/4 λ type whip antenna shown in FIG. 6 (a) is the impedance of a general high frequency interface component as shown in FIG.
Since it is close to 0 [Ω] and is close to a pure resistance component, it does not require a matching circuit and has wide-band impedance performance, but it is highly dependent on the ground for operation of the antenna.
The ideal condition is that it should be installed vertically on an infinite earth, whereas in reality it is installed on a small area ground, and from the size of the portable radio, the radio element is shorter than the antenna element length (l). Since the effective earth length (H) is larger (l <H), the desired elevation angle performance cannot be obtained. Further, the horizontal plane directional characteristics depend on the earth structure, and the antenna is short because the element is short. It is also susceptible to the system and the surrounding environment, and has the drawback that it is generally not possible to obtain the desired omnidirectionality. On the other hand, FIG.
In the whip antenna having the antenna element length exceeding 1 / 4λ such as the 3 / 8λ type and the 5 / 8λ type shown in (b) and (c), as the resistance component in impedance increases and the reactance component increases, It will not be possible unless a matching circuit is provided directly under the antenna element,
By adding capacitance between the antenna element and the ground with this matching circuit, it is possible to reduce the dependency of the ground, and it becomes an antenna adapted as an antenna system, and it is widely used in recent years. In the form, it has been unreasonable in terms of frequency band performance and elevation angle performance.

At present, MCA (multi-channel access) type wireless systems, automobiles, portable public wireless telephone systems, etc. are widely used as land mobile communication systems using frequencies in the vicinity of 900 [MHz]. For convenience, a compact and lightweight portable wireless device is desired, and a product having a shape with a length in the longitudinal direction of the portable wireless device of about 145 [mm] (during call operation) or less is becoming mainstream.

Here, assuming that the center frequency of the used frequency band of the used system is 900 [MHz], the free space wavelength λ
₀ becomes 333.33 [mm], which is 145 [mm] in the longitudinal direction.
Is 0.435 in terms of free space wavelength. However, the length of the portable radio in the longitudinal direction is the external dimension of the radio, and since the external appearance of the radio is generally made of a resin material for the purpose of weight reduction, its conductivity cannot be expected and it is essential for antenna operation. The ground length must be dependent on the chassis housing inside the radio, the ground conductor surface on the copper clad laminated printed circuit board, etc. The ground length is generally 80% of the external dimensions. ] Or less, the effective ground length of the above dimensions is 116 [m
m] and the free space wavelength is estimated to be 0.348 or less.

[0008]

Conventionally, 900 [MHz]
The portable radio in the frequency utilization system above the band,
A 5/8 λ type whip antenna (the effective radiating part that is involved in the directional characteristics is a ½ λ length from the tip of the antenna element) was often used, but as the portable radio becomes smaller,
In the elevation angle characteristic shown in (1), the relation of 1> H is satisfied, and the desired elevation angle performance cannot be obtained, and the radiation / reception efficiency is reduced. In order to improve this, using a 3/8 λ type whip antenna to make l and H approximately equal and make the elevation angle in the horizontal direction to substantially recover the radiation / reception efficiency, the antenna element length was The shorter the antenna gain, the shorter the operating gain. Further, from the demand for portable wireless devices which are further miniaturized in the future, the tendency of l> H is strong, and it becomes difficult to control the elevation angle with a fixed size of 3 / 8λ.

The vertical in-plane directional elevation angle characteristics due to the relationship between l and H can be understood by analyzing the unbalanced and balanced dipole antennas in the dipole antenna equivalent circuit shown in FIG. It is generally known that the relationship between the whip antenna element length 1 and the antenna operation gain when the maximum value is obtained in the horizontal direction under the condition of 1 = H = 1 / 2λ (see FIG. 9). However, these 3 / 8λ type and 5/8 type
The bandwidth performance of the λ-type whip antenna is about 8 [%] at VSWR (voltage standing wave ratio) 2.0, which could be supported by the old system, but more than double in the recent new system. It is difficult to use because it is required.

Further, the 3 / 8λ type and 5 / 8λ type whip antennas are connected to the antenna element through the coil portion constituting the matching portion from the feeding point center conductor.
Since the center conductor and the outer conductor are insulated from the feeding point, if an unavoidable surge voltage or the like is applied to the antenna element, it will be directly transmitted to the internal circuit of the wireless device, causing a failure or damage to the wireless device. Could occur.

An object of the present invention is to provide a whip antenna having wide band characteristics, which solves the above-mentioned drawbacks of the conventional whip antenna.

[0012]

In order to achieve the above object, the whip antenna of the present invention has a wavelength of about 1/4 wavelength to 1 wavelength.
The feeding direction end of the antenna element having a fixed dimension within the range of / 2 wavelength and the matching circuit are connected by a capacitive coupling means that is not DC-connected, and the matching circuit is DC-like when viewed from the wireless device connection direction end. The gist is that it is configured to be in a short-circuited state.

[0013]

Since the antenna element has a length substantially equal to the effective earth length or an image equivalent length, it has vertical in-plane directional elevation angle characteristics in the horizontal direction. The capacitive reactance of the capacitive coupling approximately cancels the inductive reactance of the antenna element, and the matching circuit widens the impedance performance to increase the specific bandwidth.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a whip antenna used in a transceiver T according to the present invention. In the figure, 1 is a retractable antenna element, 2 is a metal power supply terminal for the antenna element, 3 is an insulator, 4 is a matching box, 5 is a matching substrate, and 6 is a power supply cable.

2A and 2B are an equivalent structure diagram and an equivalent circuit diagram of the whip antenna. In the figure,
The matching circuit section 7 is composed of a capacitor C ₃ , an inductance L _{3 and the} like formed on the matching substrate 5, and the antenna element section 8 is an equivalent resistance R of the antenna element 1.
The capacitor C provided on the matching substrate 5 is inserted between the matching circuit section 7 including a and the equivalent inductance L and the antenna element section 8.

The fixed size of the antenna element 1 is about 1.
From / 4λ to about 1 / 2λ, λ = λ ₀ × Δ. Δ is a constant of 1 or less determined by the thickness, material, surface treatment, etc. of the antenna element 1, and λ ₀ is a free space wavelength. Incidentally, Z is a characteristic impedance at the input / output end of the transceiver T, and AC is a transmitter.

The whip antenna shown in FIG. 1 exceeds the antenna element 1 by about 1 / 4λ, as described above.
Vertical in-plane directional elevation angle characteristics by providing a fixed antenna element length that is approximately equal to the effective earth length determined by the antenna system structure of the portable radio T or the like within a range of / 2λ or less, or an image (image) equivalent length. 2 in the horizontal direction, and the inductive reactance (+ j) due to the inductance L of the antenna element 1 due to the capacitive reactance (−jX _c ) due to the capacitor C inserted between the antenna element portion 8 and the matching circuit portion 7 in FIG.
X _L ), and the matching portion transformation coil L ₃
By matching the impedance resistance component Ra with the characteristic impedance Z at the input / output terminal of the wireless device,
The ratio band is increased to broaden the impedance performance band. Furthermore, the insertion capacitance reactance (−jX _c )
Also acts as a shortening capacitor for the antenna element,
The antenna element diameter is equivalently increased, and the antenna characteristic impedance (Z _0a ) is lowered,
The change in the antenna element length vs. impedance characteristic will be made gradual, synergistic with the above-mentioned effect, and the ratio bandwidth will be increased as the impedance characteristic is widened to a wider range.
At R2.0, a result of 17% or more was also obtained from the experiment, and the wide band characteristic effect of the whip antenna by the capacitive reactance insertion was confirmed. That is, the inserted capacitive reactance −jX _c has the effects of both the matching circuit section 7 and the antenna element section 8.

The matching circuit section 7 in the antenna of the present invention constitutes a transformer circuit using an inductance (L ₃ ), and the center conductor and the outer conductor are short-circuited in direct current as seen from the antenna feeding point 2 side. It is in a state.

Since the inserted capacitive reactance -jX _c has the effects of both the matching circuit section 7 and the antenna element section 8, the physical element length and the electrical element length are arbitrary to some extent. Therefore, it becomes easy to obtain a balance between the effective ground length of the portable radio and the antenna element length in consideration of the elevation angle performance.

The 3 / 8λ type whip antenna is 900 [MHz] in recent years if only focusing on the elevation angle performance excluding the ratio band.
Although it was almost suitable as an antenna for portable radio devices, there was no freedom in the element length, and higher frequencies,
In the quasi-microwave frequency band such as 1.5 [GHz] band and 2 [GHz] band, l <H, and the elevation angle performance cannot be maintained. On the other hand, in the antenna of the present invention, the element length can be freely set. Since it has a certain degree, it is sufficiently applicable to a portable radio for a quasi-microwave frequency band wireless communication system in the future.

Since the matching circuit section 7 constitutes a transformer circuit using the inductance L ₃ , the center conductor and the outer conductor are in a DC short-circuited state when viewed from the antenna feeding point side. Therefore, a surge current due to a surge voltage such as static electricity applied to the antenna element or the like due to force majeure can be avoided to the ground, and the internal circuit of the wireless device can be protected. Further, the similar operation also has an effect of suppressing external noise and internal noise.

The antenna of the present invention, for example, when mounting and operating a vehicle or the like, has an earth effect of a sufficiently large area for a free space wavelength with respect to a used frequency of 900 [MHz] band or quasi-microwave frequency band or more. Since it is installed on the mobile object that has it, the element image effect due to the wide area ground can be expected, and the desired elevation angle performance can be obtained under conditions relaxed from the mobile wireless device installation conditions. Bandwidth performance can be obtained.

At high frequencies above 900 [MHz],
The inductance transformation circuit L ₃ can be formed as a microstrip line on the copper clad laminated printed board, and the antenna structure can be made compact and the performance can be stabilized in mass production. If these effects are neglected, it is of course possible to form a three-dimensional coil.

FIG. 3 shows another embodiment of the present invention, in which the same symbols as in FIG. 1 are the same or similar members, 9 is an insulator, and 10 is a power feeding connector. Figure 4 shows a conventional whip antenna 5 /
The frequency vs. VSWR characteristic (ratio band characteristic) of the 8λ type, the 3 / 8λ type and the whip antenna of the present invention are shown.

FIG. 10 shows a shape of a holder portion of an antenna element as still another embodiment of the present invention which is improved to be suitable as a whip antenna for a mobile phone such as a cellular antenna. FIG. 11 shows an equivalent circuit of the above embodiment.

[0026] For the antenna element length l of the cellular antenna about 3 [lambda] / 8, the reactance component jX _L of the antenna element portion 8 are distributed 50～500Omu.
Since it is desirable to minimize the jX _L to improve the antenna characteristics, in the embodiment of FIG. 10 in order to cancel the reactance component proposes holder portion shape that can be added to compensate for the reactance component of -jX _L . Figure 10
In FIG. 11, 11 is a resin holder, 12 is a lock nut, 13 is a ring spring, 14 is a transceiver housing wall, and the antenna element 1 is pierced through the holder 11 and is held so as to be movable up and down. The band can be adjusted by finely adjusting the antenna element length 1 depending on the installation position. The ring spring 13 is pressure-bonded to the lower part of the holder 11 and is connected to the matching circuit section 7.

In FIG. 11, the capacitance C ₂ is the ring spring 1
3 and the lower part of the holder 11, which is connected in series to the matching circuit 7,
It has the effect of canceling the reactance component jX _L of the antenna element 1 so that the capacitive reactance is added to the antenna element portion 8. Further, the capacitance C ₁ is obtained from the structure portion of the lock nut 12 and the upper portion of the holder 11. Since this is added in parallel to the anthena element element 8, the antenna impedances Zr and C ₂
It has an auxiliary function of measuring the matching with. The capacitance values of C ₁ and ₂ can be calculated by the following formula.

[0028]

[Equation 1]

Where ε _s is the relative dielectric constant of the holder 11,
D ₁ / D ₂ is the dimensional ratio of the upper and lower parts of the holder 11, the lock nut 12, and the ring spring 13, and D ₁ = 2d ₁ ,
D ₂ = 2d ₂ . Therefore, the above capacitance values are ε _s , D ₁ ,
It can be adjusted with D ₂ , l ₁ and l ₂ .

[0030]

As described above, according to the present invention, it is possible to obtain a whip antenna having a comparatively simple structure and having a significantly improved bandwidth performance as compared with the conventional one. In particular, if the present invention is applied to a whip antenna for a mobile phone such as a cellular antenna and the holder portion is configured,
The impedance matching can be further optimized by adding a reactance component for compensation. Also, in the holder part, not only can the band be adjusted according to the installation position of the lock nut, but if the holder is made of resin, it can be integrally molded, and since there is less friction, the length of the antenna element can be adjusted. Can be done smoothly.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention.

FIG. 2 is an equivalent configuration diagram and an equivalent circuit diagram of the above embodiment.

FIG. 3 is a schematic view showing another embodiment of the present invention.

FIG. 4 is a diagram showing frequency-VSWR characteristics of various conventional whip antennas and the whip antenna of the present invention.

FIG. 5 is an ideal directional characteristic diagram of a whip antenna system in land mobile communication.

FIG. 6 is a schematic configuration diagram and an equivalent circuit diagram of various conventional whip antennas.

FIG. 7 is a characteristic diagram of impedance change according to element length and thickness of a whip antenna.

FIG. 8 is a diagram showing an example of vertical in-plane directional elevation angle characteristics when the length of the whip antenna element and the pseudo housing radio made of metal are changed.

FIG. 9 is a characteristic diagram of balance dipole antenna length and gain change.

FIG. 10 is a schematic view showing a main part of another embodiment of the present invention.

11 is an equivalent circuit diagram of the embodiment of FIG.

[Explanation of symbols]

 1 Antenna Element 2 Antenna Feeding Terminal 3 Insulator 4 Matching Box 5 Matching Board 6 Feeding Cable 7 Matching Circuit Section 8 Antenna Element Section 9 Insulator 10 Feeding Connector T Transceiver C Insertion Capacitor

Front page continuation (72) Inventor, Suika Shinagawa, 4-7 Kitamachi, Warabi-shi, Saitama Prefecture, Japan Atena Co., Ltd. Warabi factory (72) Inventor, Katsuji Muroi, 4-7 Kitamachi, Warabi-shi, Saitama Japan Antena Co., Ltd. Warabi factory

Claims (3)

[Claims] 1. An antenna element having a fixed dimension within a range of approximately ¼ wavelength to ½ wavelength and a matching circuit are connected to a matching circuit by a DC coupling non-coupling means, and the matching is performed. Wideband characteristic whip antenna for wireless communication, characterized in that the circuit is configured to be in a DC short circuit state when viewed from the end of the wireless device connection direction. 2. A holder part for holding the antenna element so as to be vertically movable, the holder part being connected to the matching circuit and having a compensating reactance component for canceling the reactance component of the antenna element. The broadband characteristic whip antenna for wireless communication according to claim 1. 3. The holder part includes a resin holder for holding the antenna element, a lock nut screwed onto an upper part of the holder, and a link spring pressed onto the lower part of the holder. The wideband characteristic whip antenna for wireless communication according to claim 2.