JPH1141025A - Helical antenna - Google Patents

Abstract

(57) [Summary] [Problem] To provide an inexpensive helical antenna with a simple structure that can transmit and receive satisfactorily in at least two radio frequency bands with respect to a helical antenna used for a wireless device such as mobile communication. The purpose is to do. SOLUTION: In addition to a helical antenna element 11, a parasitic helical antenna element 14 is arranged concentrically with a winding portion 11A, and is induced by an electromagnetic induction effect generated between two antenna elements when transmitting and receiving radio waves. The impedance characteristic of the helical antenna element 11 is controlled so that each of the helical antenna elements 11 can transmit and receive radio waves in at least two frequency bands satisfactorily using the current flowing through the helical antenna element 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a helical antenna mainly used for radio equipment for mobile communication and the like.

[0002]

2. Description of the Related Art In recent years, there has been a sharp increase in demand for radio equipment for mobile communication such as a cellular phone, and a helical antenna having a low-cost and simple structure using a coil-shaped winding is widely used as the antenna. Have been.

[0003] Such a conventional helical antenna will be described with reference to FIG. FIG. 8 is a cross-sectional view of a conventional helical antenna. In FIG. 8, reference numeral 1 denotes a metal mounting bracket having a mounting portion 1A for a radio device, and 2 denotes a helical antenna element made of copper or a copper alloy. A connecting portion 2A at the end of the helical antenna element 2 is wound around the outer periphery of the cylindrical convex portion 1B of the metal fitting 1, and is electrically connected.

[0004] Above the helical antenna element 2, a uniform coil-shaped winding portion 2 B is formed. A lower end opening 3 A of an insulating case 3 covering the outer periphery of the helical antenna element 2 is bonded by an adhesive 4. The helical antenna 5 is fixed to the mounting bracket 1.

[0005] A mounting portion 1 A of the mounting bracket 1 of the helical antenna 5 is electrically connected to a radio circuit of the radio, and a signal is transmitted between the helical antenna element 2 and the radio circuit via the mounting bracket 1. Is transmitted and received.

In addition, the helical antenna 5 having the above configuration
The characteristic is that when the winding diameter and the winding pitch of the helical antenna element 2 are increased and the number of windings is increased, the frequency is tuned to a low frequency band. And winding part 2
By adjusting the winding diameter, winding pitch, number of turns, etc. of B,
The configuration is such that impedance characteristics of the helical antenna element 2 are set so that radio waves in one frequency band can be transmitted and received satisfactorily.

[0007]

However, in recent years,
In order to diversify the form of mobile communication and to allow more information to be transmitted and received by one radio, 800 MHz used for radios such as mobile phones and PHSs,
An inexpensive wireless device capable of transmitting and receiving a plurality of bands out of frequency bands such as 1.5 GHz and 1.9 GHz is demanded. In the above-mentioned conventional helical antenna, the impedance characteristics of the helical antenna element 2 are set. Radio waves in one frequency band can be transmitted and received satisfactorily, but when transmitting and receiving radio waves in other frequency bands, there is a problem that characteristics such as modulation accuracy and reception sensitivity are deteriorated, making it difficult to transmit and receive radio waves satisfactorily. .

An object of the present invention is to solve such a conventional problem, and an object of the present invention is to provide a helical antenna having a simple structure capable of performing good transmission and reception in at least two radio frequency bands. is there.

[0009]

In order to solve the above-mentioned problems, a helical antenna according to the present invention includes a helical antenna element having a uniform winding diameter and a parasitic helical antenna concentric with a winding portion of the helical antenna element. An element is arranged, and an impedance is used so that radio waves in at least two frequency bands can be transmitted and received satisfactorily by utilizing current induced by electromagnetic induction generated between the two antenna elements when transmitting and receiving radio waves. The characteristic is controlled.

According to the present invention, it is possible to obtain an inexpensive helical antenna having a simple structure and capable of performing good transmission and reception in at least two radio frequency bands.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is a helical antenna element having a connection portion with an antenna matching circuit at one end and a winding portion formed in a coil shape having a uniform winding diameter. And a helical antenna composed of a coilless parasitic helical antenna element having a uniform winding diameter and arranged concentrically with the winding portion of the helical antenna element. A helical antenna capable of controlling the impedance characteristics of a helical antenna element using current induced by electromagnetic induction generated between the helical antenna element and a parasitic helical antenna element to transmit and receive radio waves in at least two frequency bands. Is obtained.

According to a second aspect of the present invention, in the first aspect, the winding diameter and the winding pitch of the parasitic helical antenna element are the same as those of the helical antenna element. Since the winding diameter and the winding pitch of the antenna element and the parasitic helical antenna element are the same, a parasitic helical antenna element is arranged between each winding of the helical antenna element, and the two antenna elements are wound on the same cylindrical surface. And has a simple structure, and has an effect that the antenna can be easily assembled.

According to a third aspect of the present invention, in the first aspect, the winding diameter of the parasitic helical antenna element is different from the winding diameter of the helical antenna element. By making the winding diameter of the parasitic helical antenna element larger or smaller than the winding diameter of the helical antenna element,
Since the winding pitch and arrangement interval of each antenna element can be set freely, impedance characteristics are controlled by changing the phase and magnitude of the induced current, and stable transmission and reception characteristics of radio waves in a predetermined frequency band Is obtained.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIGS. 1 to 7,
The helical antenna element, which is a main component of the helical antenna, is described with a winding diameter, a winding pitch, a wire diameter, and the like larger than actual dimensions so as to be easily understood.

(Embodiment 1) FIG. 1 is a sectional view of a helical antenna according to a first embodiment of the present invention, and FIG. 2 is a circuit diagram showing a state where the antenna is mounted on a radio.
In FIG. 1, the helical antenna 10 is conceptually described with its configuration omitted.

In FIG. 1, reference numeral 11 denotes a helical antenna element made of copper or a copper alloy; 12, a metal mounting bracket having a mounting portion for a radio device; 13, a core rod made of insulating resin; The upper coil-shaped winding portion 11A is wound around a core rod 13 having a lower end fixed to a cylindrical concave portion 12A of the mounting bracket 12, and a connecting portion 11B at a lower end of the helical antenna element 11 is connected to a concave portion 12A of the mounting bracket 12. And is electrically connected to the mounting bracket 12.

A parasitic helical antenna element 14 having the same winding diameter and winding pitch as the helical antenna element 11 is provided between the windings of the winding portion 11A of the helical antenna element 11.
The helical antenna 10 is formed by being wound insulated from the mounting bracket 12 and covered with an insulating resin 15 formed by insert molding on the outer periphery.

Reference numeral 16 denotes a wireless device. The helical antenna 10 is mounted and fixed on a housing 17 made of an insulating resin of the wireless device 16, and the mounting bracket 12 is connected to a feeding line 18 by an antenna matching circuit inside the wireless device 16. 19, and the antenna matching circuit 19 is connected to the frequency band A via the switch 20.
And a wireless circuit 22 operating in the frequency band B.

The antenna matching circuit 19 usually has 50
It has a function of matching the impedance of the helical antenna 10 set to Ω and the radio circuits 21 and 22, and is connected to the radio circuit 21 when transmitting and receiving radio waves using the frequency band A by switching the switch 20. When a radio wave is transmitted / received using the frequency band B, it is configured to be connected to the wireless circuit 22.

The characteristics of the helical antenna 10 having the above configuration will be described with reference to FIGS.

The characteristics of the antenna are evaluated by directional characteristics for evaluating whether or not radio waves are transmitted and received uniformly around the antenna, and a high-frequency band of 150 MHz or more used for a mobile communication radio such as a mobile phone. In the above, it is common to perform evaluation using impedance characteristics which are usually set to 50Ω, so both characteristics will be described.

FIGS. 3A and 3B are plan views schematically showing a model used for evaluating the characteristics of the helical antenna 10. In FIG. 129 mm, 32 mm wide metal plate, this metal plate 2
3 is a connection portion 11 at the lower end of the helical antenna element 11
B, and a parasitic helical antenna element 14 is arranged between each turn of the helical antenna element 11.

The helical antenna element 11
The helical antenna element 14 and the parasitic helical antenna element 14 each use a copper alloy wire having a wire diameter of 0.5 mm, a winding diameter of 7 mm, a winding pitch of 3 mm, and a winding height of the helical antenna element 1.
1 is 11.3 mm, and the parasitic helical antenna element 14 is 8.1 mm.

The above model has a center frequency of 850 MHz.
When the high-frequency power in the frequency band A is supplied, the substantial equivalent electrical length of the helical antenna element 11 becomes about ４ wavelength of the supplied high-frequency power, and a current distribution corresponding thereto is generated in the helical antenna element 11. The current is also induced in the parasitic helical antenna element 14 by the electromagnetic induction.

Then, due to the influence of the high-frequency current induced in the parasitic helical antenna element 14, the current distribution state such as the amplitude and phase of the high-frequency current flowing through the helical antenna element 11 is changed, and as a result, the impedance of the helical antenna element 11 is changed. Is changed within a predetermined range, and the current distribution of the helical antenna element 11 becomes maximum at the connection portion 11B as shown by the hatched portion in FIG.

Also, the center frequency is set to 2150 in this model.
When high-frequency power in the frequency band B of MHz is supplied,
Since the effective equivalent electrical length of the helical antenna element 11 is about 波長 wavelength of the supplied high frequency power, the current distribution is as shown by the hatched portion in FIG. Is the minimum.

The directional characteristics of the model having such current distribution characteristics are calculated using the position of the antenna as the origin of the coordinates, XY,
A description will be given with reference to a radiation pattern diagram that indicates in which direction and how much energy the antenna emits in each plane of YZ and XZ.

FIG. 4A is a radiation pattern diagram in the frequency band A of the above model, and FIG. 4B is a radiation pattern diagram in the same frequency band B. In FIG. In, the radiation characteristics of the XY plane indicate the omnidirectionality desired for a radio antenna, and as is generally well known in the example of Yagi-Uda antenna,
The result is the opposite of the method of adding directivity to the antenna by adding a rod-shaped parasitic antenna element to the rod-shaped antenna element.

In FIG. 4B of the frequency band B, the radiation pattern has a null pattern indicating directivity in the X-axis direction on the XZ plane or the YZ plane. In this case, since the wireless device is used in an inclined state, it can be regarded as horizontal directivity in this inclined state, and shows the desired omnidirectionality of the antenna for the wireless device as in the case of the frequency band A. Was verified.

Next, the impedance characteristics of the helical antenna 10 at this time will be described with reference to FIG.

FIG. 5A is called a Smith chart, and when impedance Z = R + jX, R = 0 to + ∞, X
= −∞ to + ∞ is mapped in a unit circle, and the closer the locus of the impedance is to the vicinity of the center of the circle, the closer to the desired impedance.

In the figure, the measurement results when high frequency power in the vicinity of the frequency bands A and B are supplied to the helical antenna element 11 of the above model are indicated by *, and the value of the supplied frequency (unit: MHz) is indicated by *. Although described next to,
The results show that the vicinity of 800 MHz to 900 MHz and the vicinity of 2100 MHz to 2200 MHz are near the center of the circle, and are close to the desired impedance of 50Ω in the bands with center frequencies of 850 MHz and 2150 MHz.

FIG. 5B shows a VSWR in which the horizontal axis indicates the transmission / reception frequency and the vertical axis indicates the VSWR (voltage standing wave ratio).
The characteristic diagram shows that the closer the VSWR value is to 1.0, the closer the impedance characteristic of the antenna is to the desired impedance value. The result obtained by the numerical analysis simulation is shown by a solid line, Are shown by dotted lines.

Comparing the two trajectories, the solid line and the dotted line show almost the same frequency characteristics although there is a slight deviation. Here, as in the case of FIG.
around z ~ 900MHz and 2100MHz ~ 2200
In the vicinity of MHz, the value of VSWR approaches 1.0,
It can be seen that the desired impedance is approached in the bands centered at 50 MHz and 2150 MHz.

As described above, according to the present embodiment, in addition to the helical antenna element 11, the parasitic helical antenna element 14 is arranged concentrically with the helical antenna element 11 so that the two antenna elements are located between the two antenna elements when transmitting and receiving radio waves. Since the impedance characteristics of the helical antenna element 11 are controlled by using the current induced by the electromagnetic dielectric action generated in the helical antenna, a simple structure and an inexpensive helical antenna capable of good transmission and reception in at least two radio frequency bands. A type antenna can be obtained.

In the above description, the center frequency of the frequency band A is 850 MHz, and the center frequency of the frequency band B is 2
Although the case where the frequency is set to 150 MHz has been described, it is needless to say that the frequency band of radio waves that can be transmitted and received can be freely set by changing the winding diameter, the winding pitch, the number of turns, and the like of the helical antenna element 11 and the parasitic helical antenna element 14. It is.

Further, the closer the helical antenna element 11 and the parasitic helical antenna element 14 are arranged, the greater the electromagnetic induction between them and the greater the induced current. By appropriately setting the arrangement distance in consideration of the above, it is possible to transmit and receive a better radio wave.

Further, when the helical antenna 10 of the present embodiment is mounted on a wireless device equipped with a wireless circuit operating only in one frequency band, radio waves can be transmitted and received in a wider frequency band than in the conventional system. This also has the advantageous effect that it can be performed.

(Embodiment 2) FIG. 6 is a sectional view of a helical antenna according to a second embodiment of the present invention. In FIG. 6, the coil-shaped winding portion 11A of the helical antenna element 11 is located at the center. It is wound around the core rod 13 and the lower end is electrically connected to the mounting bracket 12 as in the first embodiment, but the winding diameter of the parasitic helical antenna element 25 is the same as that of the helical antenna element 11. The winding diameter D2 is larger than the winding diameter D1 of the antenna 11A. The parasitic helical antenna element 25 is fixed to the outer periphery of the helical antenna element 11 by insert molding with an insulating resin 26, and the outer periphery of the case 27 is made of an insulating resin. A helical antenna 24 is configured to cover.

In FIG. 7, the winding diameter of the parasitic helical antenna element 29 is smaller than the winding diameter D1 of the winding portion 28A of the helical antenna element 28.
2 and the parasitic helical antenna element 2
9 is wound around a central core rod 13, a helical antenna element 28 is fixed to an outer periphery thereof by insert molding with an insulating resin 26, and the outer periphery is formed of an insulating resin case 2.
7 covers the helical antenna 30.

As described above, according to the present embodiment, since the winding diameter D2 of the parasitic helical antenna elements 25 and 29 is different from the winding diameter D1 of the helical antenna elements 11 and 28, the winding pitch of each antenna element Can be easily changed to finely control the phase of the current induced in the parasitic helical antenna elements 25 and 29, and the winding distances D1 and D2 are changed to reduce the arrangement interval of each antenna element. Since the magnitude of the current induced by various settings can be easily controlled, the impedance characteristics can be controlled accurately and precisely, so that stable transmission and reception characteristics can be obtained in each of two different frequency bands. Is what you can do.

In addition, the winding pitch and winding height of the helical antenna elements 11 and 28 need not be reduced between the windings of the helical antenna elements 11 and 28 because the windings of the parasitic helical antenna elements 25 and 29 need not be arranged between the windings of the helical antenna elements 11 and 28. Accordingly, the height of the helical antennas 24 and 30 can be reduced.

The helical antennas 24 and 3
Since the method of mounting the wireless device 0 on the wireless device and the main characteristics are the same as those in the first embodiment, the description is omitted.

[0044]

As described above, according to the present invention, there is obtained an advantageous effect that it is possible to realize an inexpensive helical antenna with a simple structure capable of performing good transmission and reception in at least two frequency bands of radio waves. Can be

[Brief description of the drawings]

FIG. 1 is a sectional view of a helical antenna according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a state where the antenna is mounted on a wireless device.

FIG. 3 (a) is a plan view of the same characteristic evaluation model and shows a current distribution in a frequency band A. FIG. 3 (b) is a plan view and shows a current distribution in a frequency band B.

FIG. 4 (a) Frequency band A based on the same characteristic evaluation model
(B) Radiation pattern diagram for the same frequency band B

5A is a Smith chart, and FIG. 5B is a VSWR (voltage standing wave ratio) characteristic diagram.

FIG. 6 is a sectional view of a helical antenna according to a second embodiment of the present invention.

FIG. 7 is a sectional view of the same.

FIG. 8 is a sectional view of a conventional helical antenna.

[Explanation of symbols]

 10, 24, 30 Helical antenna 11, 28 Helical antenna element 11A, 28A Winding part 11B Connection part 12 Mounting bracket 12A Depression 13 Core rod 14, 25, 29 Parasitic helical antenna element 15, 26 Insulating resin 16 Radio 17 Case 18 Feeding line 19 Antenna matching circuit 20 Switch 21, 22 Wireless circuit 23 Metal plate 27 Case

Claims (3)

[Claims] A helical antenna element having a connection portion with an antenna matching circuit at one end, and a winding portion formed in a coil shape having a uniform winding diameter, and a coil portion concentric with the winding portion of the helical antenna element. A helical antenna composed of coiled parasitic helical antenna elements with a uniform winding diameter arranged. 2. The helical antenna according to claim 1, wherein the winding diameter and the winding pitch of the parasitic helical antenna element are the same as those of the helical antenna element. 3. The helical antenna according to claim 1, wherein the winding diameter of the parasitic helical antenna element is different from the winding diameter of the helical antenna element.