JP2817250B2 - Diversity antenna - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a diversity antenna used for a diversity receiver in wireless reception, and more particularly to a small diversity antenna suitable for a mobile phone.

(Prior Art) In an indoor wireless communication device using an electric current, a wall, a floor, a ceiling, various fixtures, or a structure such as a building exists between a transmission antenna and a reception antenna.

Therefore, the radio wave that reaches the receiving antenna is a composite of reflected waves, transmitted waves, diffracted waves, etc., in addition to the direct waves.
Because of the interference of radio waves, the received electric field strength fluctuates with time, that is, fading occurs.

When fading occurs, the received electric field strength is reduced at the position of the node of the standing wave, so that the quality of the received signal is reduced and the S / N of the speech signal synthesis is deteriorated. In addition, in the case of digital data transmission, a problem such as deterioration of a bit error rate occurs, and reception sometimes becomes impossible.

In order to reduce the reception failure due to the fading, various types of diversity reception have been adopted in mobile communication and the like.

As these diversity reception systems, a space diversity system, a frequency diversity system, a time diversity system, a polarization diversity system and the like are known.

Of these, spatial diversity is the most common, and is a method in which two antennas are usually arranged at intervals on the order of wavelength and the outputs of these antennas are combined.

Frequency diversity uses a plurality of carriers separated so that each fading characteristic has a sufficiently independent relationship.

The time diversity is to transmit the same information at a time interval and select the information with the higher reception level on the receiving side.

Polarization diversity uses two orthogonal polarization planes (normally vertical polarization and horizontal polarization) as polarization planes of radio waves, and generally the fading of these two polarization planes is independent. In polarization diversity, a transmitted radio wave has orthogonal polarization components as it is repeatedly reflected, transmitted, diffracted, etc., and is received in combination with a horizontally polarized antenna and a vertically polarized antenna. .

For this purpose, use a cross dipole antenna,
A diversity antenna combining a microstrip antenna and a slot antenna disclosed in -290147 is used.

The diversity antenna disclosed in JP-A-63-290147 has a configuration as shown in FIG. That is, a microstrip antenna for receiving an electric field component is formed on the front surface, and a slot antenna for receiving a magnetic field component orthogonal to the electric field component is formed on the back surface. In addition, a property is used in which the phases of the electric field fading and the magnetic field fading are shifted theoretically by λ / 4.

(Problems to be Solved by the Invention) As described above, there are various methods for diversity reception. When space diversity is used, for example, when the frequency of a radio wave is 380 MHz, one wavelength is about 79 cm, and two antennas are used. The distance between the two needs to be 20 to 30 cm, and there is a disadvantage that the size cannot be reduced.

Regarding the space diversity effect, it has been reported that the diversity effect was confirmed even when the 1/2 wavelength dipole was separated by about 0.1 wavelength (IEICE Technical Report Vol.89, No.135).
"Space Diversity Effect of Vertical Antenna Arrangement in Land Mobile Communication"), also in this case, the dipole length is about 39cm,
An antenna spacing of about 5 cm was required.

Next, in the case of frequency diversity, it is difficult to apply frequency diversity because the use efficiency of radio waves is low and the frequency of mobile communication is strongly restricted.

In time diversity, when the fading frequency is slow, the diversity effect is reduced, and the information transmission efficiency is further reduced.

In the case of polarization diversity, the use of a cross dipole has the disadvantage that the antenna configuration becomes three-dimensional and does not become compact. Further, the antenna having the configuration shown in FIG. 12 has a disadvantage that the copper foil on the back surface must be sufficiently larger than the slot, and the microstrip antenna and the slot antenna must be arranged at a certain distance.

In addition, in the case of a frequency of 380 MHz, when a glass epoxy substrate having a dielectric constant of ε _r = 4 is used, both the microstrip antenna and the slot antenna have a size of about 20 to 30 cm, and there is a disadvantage that the size cannot be reduced. As described above, a small and portable wireless device cannot be realized by the above-mentioned diversity receiving method.

An object of the present invention is to solve the above-mentioned disadvantages and to provide a diversity antenna suitable for a small and portable diversity receiver.

(Means for Solving the Problems) In order to achieve this object, in a diversity antenna according to the present invention, in a diversity antenna having a plurality of antennas, each of the plurality of antennas has a sufficient number of wavelengths of a received wave. A loop antenna having a small electrical length of one size, and being arranged so that the feeding points are opposite to each other on the same plane so as to be close to each other by several tenths of the wavelength. .

(Operation) In a small antenna sufficiently smaller than the wavelength, its directivity and polarization characteristics tend to be non-directional and non-polarization characteristics. When such small antennas are arranged very close to each other on the order of several tenths of the wavelength, even in the case of the same type of small antenna, the directivity and the polarization characteristics change due to the interaction between the antennas.

The same phenomenon occurs in the case of different types of small antennas.

As a result, the antenna operates so as to produce a diversity effect at an antenna interval much smaller than that required for a conventional spatial diversity receiver.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

One embodiment of the diversity antenna according to the present invention and its operation will be described with reference to FIGS.

FIG. 1 is a diagram showing a state in which a diversity antenna of the present invention is mounted on a wireless device. In FIG. 1, 1 and 2 are loop antennas, 3 is a dielectric substrate, 4 is a ground wire, 5
Denotes a power supply line, and 6 denotes a wireless device housing. In an actual configuration, a matching circuit for impedance matching is added to the loop antennas 1 and 2, but is omitted in the present invention. The antennas 1 and 2 are connected to a diversity switching circuit as shown in FIG. 2 or FIG. In FIG. 2, 7 is a high-frequency switch, 8 is a receiving circuit, 9 is an AF signal output, 10 is a received field strength signal, 11 is an antenna switching circuit,
12 is an antenna switching signal. In FIG. 2, when the reception electric field strength signal 10 becomes lower than a predetermined level at the time of reception with one antenna, the switch 7 is switched and the other antenna is received.

Also, in FIG. 3, 8, 8 'are receivers, 9, 9' and
16 is an AF signal output, 10 and 10 'are reception field strength signals, 13 is a comparison circuit, 14 is an AF signal switching circuit, and 15 is an AF signal switching signal.

In the above configuration, the comparison circuit 13 operates so that the receiver on the antenna side having the higher reception level is always selected to perform diversity reception.

Next, a diversity effect unique to the present invention will be described with reference to FIGS.

FIG. 5 shows a directivity pattern measured by disposing only the loop antenna 1 alone and arranging it as shown in FIG. In FIG. 4, reference numeral 17 denotes a ground plane. The loop antenna 1 is arranged in parallel with the ground plane 17, and transmission is performed with horizontal polarization and vertical polarization. At this time, the loop antenna is a rectangular loop antenna having a size of 50 mm × 10 mm and made of copper foil on a glass epoxy substrate. In FIG. 5, the solid line is the electric field strength for horizontal polarization reception, and the broken line is the electric field strength for vertical polarization reception. The directivity pattern is not symmetrical with respect to the 0 ° axis because of the impedance matching circuit formed on the loop antenna 1.

Next, as shown in FIG.
FIG. 7 and FIG. 8 show the directivity patterns when the and the loop antenna 2 are arranged with the feeding point reversed.

FIG. 7 shows the directivity pattern of the loop antenna 1, and FIG. 8 shows the directivity pattern of the loop antenna 2. The solid line indicates the electric field intensity for horizontal polarization reception, and the broken line indicates the electric field intensity for vertical polarization reception.

Comparing FIG. 5 with FIGS. 7 and 8, it is understood that the interaction between the loop antenna 1 and the loop antenna 2 causes a change in the directivity pattern.

The fact that diversity reception is performed will be described below with reference to FIGS. 7 and 8.

7 and 8, the solid line is used as a horizontally polarized wave receiving antenna with respect to radio waves from an angle direction outside the broken line, and the angle direction where the broken line is outside the solid line. Acts as a vertically polarized wave receiving antenna with respect to the radio wave from.

FIG. 9 shows the difference between the horizontal polarization reception level and the vertical polarization reception level. The solid line indicates the case of the loop antenna 1 and the broken line indicates the case of the loop antenna 2. The radio wave from the angle direction where the level difference is a negative value acts as a vertically polarized receiving antenna (hatched area), and the radio wave from the angle direction where the level difference is a positive value It acts as a horizontally polarized receiving antenna for radio waves.

As can be seen from FIG. 9, the loop antenna 1 and the loop antenna 2 are equally low in the location ratio of acting as a horizontally polarized wave receiving antenna or a vertically polarized wave receiving antenna.

Therefore, the loop antenna 1 and the loop antenna 2
By arranging as shown in the figure, diversity reception based on changes in directivity patterns and polarization patterns is performed.
In actual radio wave propagation, radio waves arrive from various directions due to reflection, diffraction, and the like. In such a case, diversity reception is performed.

Next, the actually manufactured diversity antenna will be described. The loop antenna 1 and the loop antenna 2 are mounted on the upper surface of the wireless device casing 6 as shown in FIG. The frequency is 380 MHz (λ （79 cm). The loop antenna 1 and the loop antenna 2 are made of a copper foil on a glass epoxy substrate having a thickness of 0.8 mm.
66λ. Each antenna is impedance-matched by LC and has an impedance of 50Ω.

A diversity receiving apparatus having the above-mentioned diversity antenna was arranged as shown in FIG. 10, and a correlation coefficient between outputs of each antenna was measured. Note that the transmission antenna 18 is a horizontal polarization standard dipole antenna, and the correlation coefficient was measured while the diversity receiver 19 was kept at a height of 1.5 m and moved in the horizontal direction. FIG. 11 shows an example of the result of the correlation coefficient measurement. In this measurement, the correlation coefficient was 0.2.

As described above, according to the present invention, a diversity antenna having a sufficiently low correlation coefficient between the antennas can be constituted by an antenna having a size of several tenths of the wavelength.

(Effect of the Invention) As described above, the diversity antenna according to the present invention is characterized in that it is very small.

Therefore, according to the present invention, it is possible to provide a small size and excellent portability diversity receiving apparatus.

Moreover, since each antenna is a small antenna, it does not only have sensitivity in a specific direction like a standard dipole antenna, but also has diversity close to non-directional characteristics due to changes in the polarization and directional patterns. This has the advantage of having sensitivity in almost all directions.

Furthermore, since the correlation coefficient between the diversity branches is sufficiently low, a large drop in the received electric field due to fading is eliminated, and good diversity reception is possible.

As described above, the diversity antenna according to the present invention is suitable for a wireless device such as a mobile phone which is small and requires sensitivity in all directions.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a case where the diversity antenna of the present invention is mounted on a radio, FIG. 2 and FIG. 3 are block diagrams showing a configuration example of a diversity switching circuit, and FIG. , FIG. 5 is a characteristic diagram of the directivity of the loop antenna 1, FIG. 6 is a schematic diagram for explaining the directivity measurement of the diversity antenna of the present invention, FIG. 7, FIG.
The figure is a characteristic diagram of the directivity of the diversity antenna of the present invention,
FIG. 9 is a characteristic diagram showing the polarization characteristics of the diversity antenna of the present invention, FIG. 10 is a schematic diagram illustrating the measurement of the correlation coefficient of the diversity antenna of the present invention, and FIG. 11 is a diagram of the reception wave of the diversity antenna of the present invention. Example of fading waveform,
FIG. 12 is a schematic diagram for explaining a conventional diversity antenna. 1 ... loop antenna, 2 ... loop antenna, 3 ...
Dielectric substrate, 4 ground wire, 5 power supply line, 6 radio housing, 7 high frequency switch, 8, 8 'reception circuit,
9, 9 ', 16: AF signal output, 10: Received field strength signal, 11
…… Antenna switching circuit, 12 …… Antenna switching signal, 13…
... Comparator circuit, 14 ... AF signal switching circuit, 15 ... AF signal switching signal, 17 ... Ground, 18 ... Standard dipole antenna,
19 ... Diversity receiver.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 7/08 H01Q 19/00 H01Q 3/24

Claims (1)

(57) [Claims] In a diversity antenna having a plurality of antennas, each of the plurality of antennas is a loop antenna having a minute electrical length of a size of several tenths of the wavelength of a received wave, and each of the plurality of antennas has the same wavelength. A diversity antenna, wherein each feeding point is arranged on a same plane so as to be close to a tenth of a distance so that the feeding points are opposite to each other.