JPH08181526A - Diversity antenna circuit - Google Patents

Abstract

PURPOSE: To realize a sufficient diversity effect through optimizing adjustment with a simple structure of the antenna circuit of a antenna changeover diversity configuration. CONSTITUTION: A reception level of an envelope detector 7 is compared with a reference level at an input terminal by an envelope comparator 8 and a changeover switch 11 is used to connect an antenna 1 or 2 to a receiver 6. Feeding points 3, 4 of the antennas 1, 2 and a switching point of the changeover switch 11 are connected by a transmission line 10, the impedance of the transmission line 10 matches the impedance of the receiver 6 and the electric length is adjusted to be an integer multiple of λ/2. Even when the distance between the antennas 1, 2 is at least about 0.5λ, the similar radiation pattern to that of a single unit of each antenna is realized and the diversity effect expected by the single unit characteristic is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna circuit having an antenna switching diversity structure.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional example in which a space diversity antenna is composed of two antennas.

In the figure, 1 and 2 represent antenna elements # 1 and # 2, respectively, and 3 and 4 are feeding points of each antenna, and 5
Is a changeover switch, 6 is a receiver, 7 is an envelope detector, 8 is an envelope comparator, and 9 is a reference antenna switching level input terminal. The antenna is switched by comparing the reference level of the input terminal 9 with the envelope of the antenna reception signal detected by the envelope detector 7 by the envelope comparator 8, and when the detected signal is below the reference level, the antenna is changed by the changeover switch 5. Switching from # 1 to antenna # 2 or vice versa, an antenna with good reception conditions is selected.

[0004]

The radiation characteristic of a single dipole antenna is almost a perfect circle. However, when the distance between the two antennas # 1 and # 2 is narrowed as described above,
One antenna affects the radiation directivity of the other antenna, causing a deformation in the radiation pattern. For this reason, there is a drawback that the radiation pattern of each antenna of the diversity antenna circuit cannot be reproduced.

An object of the present invention is to provide an antenna circuit having an antenna switching diversity structure, and even when the antenna interval is at least about 0.5λ, where λ is the wavelength.
It is to reproduce the radiation pattern equivalent to the case of a single antenna for each antenna by a simple structure and optimization adjustment so that the diversity effect expected from the characteristics of the single antenna can be sufficiently obtained.

[0006]

The above-mentioned object is to connect each antenna and a switching section of a changeover switch circuit by a transmission line, and set the electrical length of the transmission line to an integral multiple of λ / 2 where λ is the wavelength. It is achieved by adjusting the length.

[0007]

When the above means is used, the transmission line between each antenna and the switching portion of the changeover switch circuit has an electrical length of λ / 2.
The input reactance of the antenna is X = ∞ by adjusting the length to be an integral multiple of. At this time, even if the distance between the antennas is about 0.5λ, the radiation patterns of substantially perfect circles are present in the individual antennas without affecting each other, and as a result, a sufficient diversity effect is obtained.

[0008]

EXAMPLES The present invention will be described in detail below with reference to examples. FIG. 1 shows an embodiment of the present invention, and the same reference numerals as those in FIG. 6 indicate the same or corresponding portions. A simple change-over switch 11 is used as a change-over switch circuit that changes over according to the output of the envelope comparator 8, and the antennas 1 and 2 are switched over. The feeding points 3 and 4 of the antennas 1 and 2 and the switching portion of the changeover switch 13 are connected by a transmission line 10, and the transmission line 10
When is not selected, its electrical length is adjusted so that the impedance becomes close to open when viewed from the antenna. As the cable forming the transmission line 10, a semi-rigid cable, a coaxial cable, a microstrip line, or the like is used.

FIG. 2 shows an electrical length and an input reactance characteristic (a) when an open stub is constructed with a cable having a characteristic impedance Zo. As shown in (b), when the electrical length l of the cable is 1 = λ / 4 or less where λ is the wavelength, the reactance (capacitive) is Xc = Zo,
When l = λ / 4, the reactance is X = 0, l = λ / 4
Reactance (inductive) at λ / 2 is X
The reactance when _L = Zo and l = λ / 2 is X = ∞. Since the actual resistance of the conductor forming the transmission line 10 is quite low, the resistance of the open stub due to the transmission line 10 can be almost ignored, and therefore it can be regarded as only the reactance component.

FIG. 3 is a layout diagram showing two dipole antennas # 1 and # 2 arranged at intervals of 0.5λ, with antenna # 1 being a fed dipole antenna and # 2 being a dipole antenna loaded with reactance X. Indicates.

FIGS. 4 and 5 show radiation patterns when the antenna # 2 of the two dipole antennas # 1 and # 2 arranged as shown in FIG. 3 is terminated with various reactances X.

The characteristic of a single dipole antenna is almost a perfect circle, and as is clear from the figure, the reactance X = ∞Ω.
When, it can be said that the characteristics are almost reproduced. X = ∞
Since Ω becomes when the electric length of the transmission line is an integral multiple of λ / 2, by setting the electric length of the cable to λ / 2, the distance between the antennas # 1 and # 2 is about 0.5λ. However, each antenna exhibits radiation characteristics almost equal to the characteristics of a single antenna, and as a result, the sufficient diversity effect expected from the characteristics of a single antenna can be obtained.

As described above, a diversity antenna circuit having a high diversity effect can be realized by optimizing the adjustment so that the electric length of the transmission line is an integral multiple of λ / 2, and the antennas # 1 and # 2 each have a radiation characteristic. Therefore, it is possible to develop each antenna separately, and it is possible to increase the certainty of the diversity effect.

The transmission line 10 of this embodiment may be any transmission line matched with the receiver or the transmitter, and various lines other than the above embodiments can be used. Further, the antenna is not limited to the dipole antenna and can be implemented, and can be similarly realized even when the number of diversity branches is three or more.

[0015]

As described above, according to the present invention, the radiation characteristic equivalent to that of the antenna alone can be reproduced for each antenna constituting the diversity by a simple structure and optimization adjustment. In addition, by doing so, the diversity effect expected from the characteristics of the antenna alone can be sufficiently obtained.

Further, the wireless device adopting the present invention can also be made small in size, low in price and high in performance.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the electrical length of an open stub and the input reactance.

FIG. 3 is an explanatory diagram of the arrangement of antennas.

FIG. 4 is a radiation pattern diagram under various reactance loads.

FIG. 5 is a radiation pattern diagram when various reactance loads are applied.

FIG. 6 is a conventional configuration diagram.

[Explanation of symbols]

1 ... Antenna # 1, 2 ... Antenna # 2, 3, 4 ... Antenna feeding point, 6 ... Receiver, 7 ... Envelope detector, 8 ... Envelope comparator, 9 ... Standard switching level input terminal, 12 ... Transmission Line, 13 ... Changeover switch.

Claims (1)

[Claims] 1. In a diversity antenna circuit which is used by connecting to a receiver or a transmitter by selecting an antenna having the best condition among a plurality of antennas, a transmission line is connected between each antenna and a switching unit of a changeover switch circuit. Then, the diversity antenna circuit is characterized in that the electrical length of the transmission line is adjusted to a length of an integral multiple of λ / 2 with the wavelength as an input.