JP2003078327A - Directional antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a compact and thin type directional antenna with a few elements and a simple circuit constitution. SOLUTION: A plurality of vertical polarization antenna elements having the same center frequency are laid closely on the same board surface, and connected to a transmitter-receiver circuit through an antenna switching circuit which selects one of the antenna elements to act it as a radiator, while other antenna elements not connected to the transmitter-receiver circuit act as reflectors. Selecting the antenna element to be active improves the directivity of the antenna. The center-to-center distance of the antenna elements is set to about 0.2-0.4 wavelength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna device for use in a wireless LAN or the like, which has a directivity capable of switching in a plurality of directions and is suitable for mounting on a PC card.

[0002]

2. Description of the Related Art Ideally, an antenna for a wireless LAN should be omnidirectional in the horizontal direction, and when a single antenna is used, a vertically polarized antenna such as a monopole or a capacitance loaded low profile monopole is used. Then omnidirectional surroundings can be obtained. However, in a multipath environment in which reflected waves exist, a null point may occur in a single omnidirectional antenna due to interference between direct waves and reflected waves. Therefore, in order to obtain a stable communication path, a diversity antenna in which two antennas are combined is often used.

There are the following methods for constructing the diversity antenna. Spatial diversity Shift the spatial distance between planar antenna mounting positions by 0.5 wavelength or more,
By receiving radio waves having a large phase difference, the effect of improving the communication path by switching the antennas becomes large, but if the spatial distance is short, the effect of improving diversity is considered to be low. Height diversity Use two antennas that are displaced in the height direction to improve the communication path by switching the antennas. Polarization diversity There are vertical polarization / horizontal polarization, right-handed / left-handed circularly polarized waves, and two orthogonal orthogonal wave combinations, etc., but if these two methods use two omnidirectional antennas, communication is in progress. Also emits radio waves in the direction where there is no communication partner. Further, since it also receives an interference radio wave from an unnecessary direction, it requires an excessive amount of transmission power, resulting in a problem with interference.

Even in the case of a diversity antenna configuration using a plurality of vertically polarized antenna elements of the same frequency, a design method is adopted in which the center distances of the two antenna elements are separated as much as possible. When mounting two vertically polarized metal rod-shaped polarization elements on a PC card, some of them are mounted on both sides of the expanded portion of the PC card (see FIG. 11).

An ideal diversity antenna is one in which two antenna radiators having a semicircular directivity in the horizontal direction are combined and the directivity obtained by switching and combining complements becomes omnidirectional in the surroundings. In the case of a diversity antenna that uses a pair of two semi-circular directional antennas in opposite directions, radio waves are concentrated and radiated or received in the semi-circular target direction that includes the communication partner. However, the transmission power can be reduced, and as a result, the number of multipaths can be reduced, and the advantage is clear.

In order to obtain directivity, as in the well-known Yagi antenna, either a reflector having a resonance frequency lower than that of the feeding element serving as a radiator or a director having a resonance frequency higher than that of the radiator, or A combination of both is known. However, the mounting area becomes large and it is difficult to mount a plurality of PC cards.

The wireless LAN is often used for a PC card for a mobile type notebook personal computer, but the expanded antenna mounting portion on the PC card has a small area of about 50 mm × 40 mm. 50mm is 0.4 at 2.45GHz (wavelength about 122mm)
At a wavelength of 5.2 GHz (about 57 mm wavelength), it is about 0.87 wavelength, and the area occupied by a single vertical polarization directional antenna element is large.
It was difficult to mount two 0.5 wavelength x 0.5 wavelength components.

As a relatively new technology, as shown in FIG. 12, there is one in which four (or six, etc.) plural parasitic elements are arranged around one feeding element having a predetermined center frequency. . Directivity can be switched by selectively switching the resonance frequency of the parasitic element to a frequency that becomes a reflector lower than the center frequency or a frequency that becomes a director higher than the center frequency by switching the reactance element by adding a switch circuit. It is the one.

Further, as shown in FIG. 13, by connecting a variable reactance element to the parasitic element, the resonance frequency of the parasitic element is controlled by the control voltage from the frequency of the reflector lower than the center frequency to the frequency higher than the center frequency. An adaptive antenna that continuously changes up to the frequency of the wave filter has also been proposed.

In order to switch the directivity of four (or more), all of them are provided with four switch circuits, additional reactance elements, or four variable elements in addition to the common feed element and the four parasitic elements. Requires a reactance element. Therefore, not only the number of parts increases and the cost increases, but also the mounting area increases, and the control algorithm becomes complicated, and it takes a long time for the control to converge.

[0011]

DISCLOSURE OF THE INVENTION The present invention provides a directional antenna device in which a plurality of antenna elements can be mounted on a small area such as a PC card to realize cost reduction and switching control is easy. is there. Since the directional antenna concentrates and radiates radio waves within the radiation angle, it does not radiate radio waves except at the radiation angle and does not receive interfering radio waves from that direction. Further, therefore, the antenna gain is high, and the transmission power required for communication can be set lower than that of the omnidirectional antenna.

It is an object of the present invention to provide a directional antenna device which does not require complicated control because the directional switching circuit does not need to perform frequency switching and can be configured with only a simple antenna switch. The switching is performed by simply selecting the switch position that maximizes the reception output, and minimizes the control convergence time.

[0013]

According to the present invention, a plurality of low-height antenna elements are arranged close to each other, and one of the antenna elements is used as a radiation or reception element, and the other elements are operated as reflectors. By doing so, the above problems are solved.

That is, in an antenna device in which directivity can be switched using a plurality of antenna elements, vertically polarized antenna elements having the same center frequency are arranged close to each other on the same substrate, and feeding points of the respective antenna elements are arranged. And a transmission / reception circuit are connected via an antenna switch circuit, and any one antenna switch circuit is operated so that power can be supplied only to that antenna element.

One of the antenna elements is made to operate as a radiation or reception element, and the other antenna element is made to float and operated as a reflector. The number of antenna elements is two or more, and up to about four elements can be similarly configured and can be put to practical use.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A pair of vertically omnidirectional vertically polarized antennas having the same frequency is used as a feeding antenna connected to a transmitting / receiving circuit by an antenna changeover switch, and the other is a parasitic antenna separated by a switch. . When these antenna elements are moved closer than 0.5 wavelength, 0.1
At ~ 0.4 wavelength, the parasitic antenna element operates as a reflector, and the gain directivity of the feeding antenna becomes weaker on the parasitic antenna element side and stronger in the opposite direction.

In the two-direction switching diversity antenna, two antenna elements having the same center frequency are used, and the central axis in the antenna radiation direction is switched by 180 ° so that the same element can be used as both a radiator and a reflector. (Fig. 4). It is possible to switch the center axes of directivity every 120 ° and 90 ° by arranging the same center frequency for three elements and four elements and arranging them at equal intervals on the same circumference (FIGS. 5 and 6).

As a result, the maximum antenna gain of the radiator having directivity is increased by about 2 to 3 dB as compared with the case where the single element is used as the surrounding omnidirectional antenna, and the insertion loss due to the antenna changeover switch is supplemented. be able to.

[0019]

EXAMPLES Examples of the present invention will be described below. Figure
7 (A) is a plan view and FIG. 7 (B) is a front sectional view showing a dielectric planar antenna which is an omnidirectional antenna suitable for the directional antenna device according to the present invention. In the case of the 5.2 GHz band, a dielectric ceramic plate 71 having a relative permittivity of 8 and a diameter of 10 mm and a thickness of 3.5 mm is used to form a capacitance loading electrode 73 on the front surface and a ground electrode 75 on the back surface. And ground electrode 75 bridge electrode
It was connected at 77.

The bridging electrode 77 is composed of a conductor film formed on the wall surface of the through hole formed in the central portion of the dielectric substrate 77,
A conductor pin 79 is inserted into this through hole. Conductor pin 79
Has a thickness that changes inside the through hole, and is thin so that it contacts the bridge electrode 77 on the front surface side and does not contact the back surface side from the impedance matching point. The metal pin 79 is connected to the transmission / reception circuit via the antenna switch circuit.

Although the antenna elements as shown in FIG. 7 are arranged close to each other on the substrate, in the case of the above elements, the antenna elements of two elements are separated from each other by a distance between the centers of 11 mm (about 0.2 mm).
Wavelength) to 20 mm (about 0.35 wavelength). As shown in FIG. 8, each antenna element is connected to the transmission / reception circuit via the antenna switch circuit.

The distance between antenna elements is the element diameter.
If they are brought close to 10 mm, they will come into contact with each other. The directivity was stronger when the mutual center distance was 11 mm than when it was 20 mm. In order to further reduce the distance, it is necessary to reduce the diameter of the antenna element.

The above dielectric planar antenna itself has a 50Ω matching structure inside and has a 50Ω matching terminal. Even if this terminal is opened or the 50Ω matching connection is made, the change in the resonance frequency is small, so that it is suitable for the application of the present invention because it has a low profile structure. A 5.2 GHz capacitively loaded dielectric monopole antenna can also be designed with a diameter of 6 mm and a thickness of 5 mm. As shown in Fig. 1, a printed wiring board can be used.
Antenna elements 11a, 11b on the surface of 10 on the circumference with a radius of 7.5 mm
Can also be placed close together.

A vertically polarized monopole antenna composed of two conductor rods and having the same center frequency is used.
Equivalent characteristics can be obtained by arranging mm (0.2 wavelength) to 20 mm (0.35 wavelength) or less. However, the feeding of the conductor rod monopole antenna requires a complicated external matching circuit, which raises the problem that the antenna height becomes as high as 13 mm.

FIG. 2 shows another embodiment of the present invention, which uses three antenna elements. If three dielectric monopole antennas with a diameter of 10 mm and a thickness of 3.5 mm are placed at a 3-minute point for each 120 ° on a circle with a radius of 6.5 mm in the 5.2 GHz band, the center distance between the antenna elements will be about 11 mm. The directivity shown in FIG. 5 is obtained by connecting only the shaded antenna elements to the transceiver circuit.

FIG. 3 shows another embodiment of the present invention, which uses four antenna elements. Dielectric monopole antenna 4 with a diameter of 10 mm and a thickness of 3.5 mm in the 5.2 GHz band
If the individual elements are placed at quadrants at 90 ° intervals on a circle with a radius of 7.5 mm, the center spacing between antenna elements will be approximately 10.6 mm. If only the antenna elements with hatching are connected to the transmitting / receiving circuit, the directivity shown in FIG. 6 can be obtained.

In the above description, only one of the plurality of antenna elements is connected to the transmission / reception circuit, but it is also possible to feed power to two of three or four elements. By this, it becomes possible to set the switching to the directivity more finely.

The directional antenna device according to the present invention, as shown in FIG. 9, has a plurality of dielectric planar antennas mounted on the surface of the expanded portion of the PC card, so that the wireless L
It can be used as an antenna for AN. This expanded part has an area of about 40 mm x 30 mm, and there is no problem in mounting a dielectric antenna element with a diameter of about 10 mm.

In FIG. 10, four dielectric antenna elements are formed in one dielectric substrate, and mounting on the substrate becomes easy.

[0030]

According to the present invention, the antenna device capable of switching the directivity can be formed on a substrate having a small area. Therefore, it is possible to realize a thin directional antenna device that can be mounted on an expanded portion of a PC card in a wireless LAN or the like.

The antenna element is used by switching between the radiator and the reflector, and the switching can be performed only by the operation of the antenna switch circuit. Therefore, directivity in a predetermined direction can be realized with a limited number of elements, the circuit configuration can be simplified, and the switching control logic circuit can be simplified.

Further, as compared with the case of using a single element, the gain can be improved by about 2 to 3 dB, the insertion loss of 1 dB due to antenna switch switching can be sufficiently covered, and a practical directional antenna device can be obtained. can get.

[Brief description of drawings]

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

FIG. 2 is a plan view showing another embodiment of the present invention.

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

FIG. 4 is an explanatory diagram of directivity of the directional antenna device according to the present invention.

FIG. 5 is an explanatory diagram of directivity of the directional antenna device according to the present invention.

FIG. 6 is an explanatory diagram of directivity of the directional antenna device according to the present invention.

FIG. 7 is a plan view (A) and a front sectional view (B) of a dielectric antenna used for the directional antenna according to the present invention.

FIG. 8 is a block diagram of a circuit using the directional antenna device according to the present invention.

FIG. 9 is a plan view showing another embodiment of the directional antenna device according to the present invention.

10 (A) is a plan view and FIG. 10 (B) is a front view showing another embodiment of the directional antenna device according to the present invention.

FIG. 11 is a perspective view showing a conventional antenna device.

FIG. 12 is a perspective view showing a conventional antenna device.

FIG. 13 is a perspective view showing a conventional antenna device.

[Explanation of symbols]

10: Wiring board 11: Dielectric antenna element

Claims (7)

[Claims] 1. In an antenna device comprising a plurality of antenna elements and capable of switching directivity, vertically polarized antenna elements having the same center frequency are arranged closely on the same substrate, and feeding points of the respective antenna elements are provided. A directional antenna device, characterized in that a transmitter and a transmitter / receiver circuit are connected via an antenna switch circuit, and any one antenna switch circuit is operated so that power can be supplied only to that antenna element. 2. An antenna device comprising a plurality of antenna elements and capable of switching directivity, in which vertically polarized antenna elements having the same center frequency are arranged at equal intervals on the same circumference on the same substrate, A directional antenna device characterized in that a feeding point of an antenna element and a transmission / reception circuit are connected via an antenna switch circuit, and any one antenna switch circuit is operated so that power can be fed only to that antenna element. 3. In an antenna device comprising two antenna elements and capable of switching directivity, vertically polarized antenna elements having the same center frequency are arranged closely on the same substrate, and feeding points of the respective antenna elements are provided. A directional antenna device, characterized in that a transmitting and receiving circuit is connected via an antenna switch circuit, and one antenna switch circuit is operated so that power can be supplied only to that antenna element. 4. An antenna device comprising three antenna elements and capable of switching directivity, vertically polarized antenna elements having the same center frequency are arranged on the same circumference of the same substrate at approximately 120 ° intervals, A directional antenna device characterized in that a feeding point of each antenna element and a transmission / reception circuit are connected via an antenna switch circuit, and any one antenna switch circuit is operated so that power can be fed only to that antenna element. . 5. In an antenna device comprising four antenna elements and capable of switching directivity, vertically polarized antenna elements having the same center frequency are arranged on the same circle on the same substrate at substantially 90 ° intervals, A directional antenna device characterized in that a feeding point of each antenna element and a transmission / reception circuit are connected via an antenna switch circuit, and any one antenna switch circuit is operated so that power can be fed only to that antenna element. . 6. The directional antenna device according to claim 1, wherein the center spacing of the antenna elements is 0.1 to 0.4 wavelengths of their center frequencies. 7. The antenna element comprises a capacitance loading electrode on the front surface of a dielectric substrate and a ground electrode on the back surface, and a bridge electrode connecting the electrodes to a through hole formed in the center of the dielectric substrate. The directional antenna device according to any one of claims 1 to 5, which is an antenna element that is fed to an impedance matching point of the bridge electrode.