JPH03113901A - Two-wire loop antenna - Google Patents

Abstract

PURPOSE:To match the antenna with a feeder without use of a special matching circuit by forming a two-wire loop antenna comprising two antenna conductors on an insulation base and selecting the interval between the inner and the outer antenna conductors to be 1/100 of the operating wavelength or below. CONSTITUTION:A 1st antenna element conductor 20 arranged in a loop is formed on an insulation base 1 and a 2nd antenna element conductor 20a arranged in a loop is formed along the element conductor 20. The interval between the 1st and 2nd antenna element conductors is selected to be 1/100 of the operating wavelength or below and the two conductors 20, 20a form one loop antenna. Moreover, the interval S of the loops is made narrow as above, then the resonance frequency of each loop is made close to each other and the antenna acts like one loop antenna taking the distance between the conductors as the wire width. Thus, it is possible to match the input impedance with the characteristic impedance of the feeder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a two-wire loop antenna, and is particularly suitable for use as a window glass antenna for automobiles.

[Summary of the invention]

A two-wire loop antenna consisting of two antenna conductors arranged in a loop with a narrow interval is constructed on an insulating surface, and the interval between the inner antenna conductor and the outer antenna conductor is set to 1/100 of the wavelength used. This is a two-wire loop antenna that can be matched with a feeder line without using a special matching circuit by doing the following.

[Conventional technology]

In-vehicle AM by attaching an antenna conductor to the car window glass
Glass antennas for automobiles are known which supply received signals to radio receivers, FM radio receivers, television receivers, etc. (for example, Japanese Utility Model Publication No. 50-33951, Japanese Patent Application Laid-Open No. 52-44541, etc.). Such an antenna conductor is often provided on a rear window glass that has a large area. However, since the central portion of the rear window glass is used by the driver to visually check the rear of the vehicle, it is not desirable to attach an antenna conductor there. Additionally, in general, a heating conductor is often provided in the central part of the window to remove fogging that occurs on the window glass surface (an antenna conductor cannot be attached to the rear window glass). When installing an antenna conductor in a antenna, it was installed in a narrow position at the top or bottom of the antenna.However, if the installation area was small, the antenna conductor had to be routed in a complicated manner to widen the band, or a parasitic element array was installed as in the Yagi-Uda antenna. Therefore, conventional glass antennas have been unable to obtain good frequency characteristics over the entire FM broadcast band, for example.

Incidentally, a loop antenna is known as an antenna that has a relatively wide band despite its simple configuration.

Since the loop antenna can be installed along the edge of the glass surface, it is convenient to install it on a window glass that has a heating conductor in the center.

[Problem to be solved by the invention]

Generally, a loop antenna has a high input impedance; for example, when a horizontally long rectangular loop antenna formed for FM broadcast reception is fed on its long side, the impedance is as high as about 300 [Ω]. Therefore, for example, 50 [Ω
] When the coaxial feeder cable is connected directly to the power supply terminal, sensitivity decreases due to impedance mismatch. For this reason, in the past, it was necessary to provide a special matching circuit to match the loop antenna and the feed line.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to enable matching with a power supply line without using a special matching circuit.

[Means to solve the problem]

The two-wire loop antenna of the present invention includes a first antenna element conductor 20 arranged in a loop shape on an insulating surface 1, and a first antenna element conductor 20 arranged in a loop shape on the insulating surface along the first antenna element conductor 2o. a second antenna element conductor 20a, the distance between the first antenna element conductor 20 and the second antenna element conductor 20a is narrower than one-hundredth of the wavelength of the frequency band used; The two conductors 2o and 2°a constitute one loop antenna.

[Effect]

The distance S between each loop formed by two conductors is equal to the wavelength 100 of the frequency band in which the loop antenna is used.
When the antenna is narrowed to about one-fold, the resonant frequencies of each loop become close to each other, and the loop antenna operates as one loop antenna whose line width is the distance from each conductor to the other. The conductor width of an antenna element affects the input resistance value during resonance, and generally, the thicker the conductor width, the lower the input impedance. Furthermore, the loop antenna can be considered to have half-wavelength dipole antennas formed on each of its opposing sides, and the presence of the inner loop conductor reduces the mutual coupling of these dipole antennas and lowers the mutual impedance. By selecting the spacing S between the inner and outer antenna conductors 20.20a, it is possible to match the input impedance to the characteristic impedance of the feed line.

〔Example〕

FIG. 1 shows an antenna pattern diagram for explaining the basic structure of the glass antenna of the present invention. ta+~(C1 in Figure 1 has a different power supply system, but the conductor patterns are all the same, and the ratio of the long side to the short side is 2 = 1.
The outer loop antenna 2 is formed into a horizontally long rectangle.
A parasitic loop 20a is loaded inside the 0.

The outer loop antenna 20 has a total length of 3.40 m and is used as an FM broadcast receiving antenna. Furthermore, the parasitic loop 20a is formed in a rectangular shape similar to the outer loop antenna 20.
The distance S between the parasitic loop 20a and the parasitic loop 20a is the same over the entire circumference.

By changing this interval S, the characteristics of the outer loop antenna 20 change. FIG. 2 shows the relationship between the interval S and the input impedance at resonance, and FIG. 3 shows the relationship between the interval S and the resonant frequency. In Figures 2 and 3,
The X mark is the characteristic of the short side feeding shown in Figure 1 (al), the Δ mark is the characteristic of the vertex feeding shown in Figure 1 (bl), and the mouth mark is the characteristic of the short side feeding shown in Figure 1 (C
) is the characteristic of long-side power feeding. Note that the spacing S in each figure is expressed based on the wavelength of the used frequency band.

As is clear from Figure 2, the input impedance at resonance differs depending on the power supply method, but in any case,
When the interval S is made small, that is, the parasitic loop 20a
When the antenna is brought closer to the outer loop antenna 20, the input impedance at resonance is lowered. In this case, the change in the input impedance of the long side feed is remarkable, and the input impedance, which was close to 300 CΩ when the parasitic loop 20a is not loaded, decreases to less than 50 CΩ when the interval S is reduced to about 1/200 wavelength. descend.

In the case of long-side feeding, it can be approximated that a λ/2 dipole antenna is formed on each of the upper and lower sides. A parasitic loop 20a is connected between these two dipole antennas.
When loaded, the mutual coupling between the antennas on the top side and the bottom side becomes considerably small, and the conductor width of the antenna element changes and the self-impedance also decreases, so it is thought that the input impedance decreases.

Furthermore, by changing the interval S, the resonant frequency changes as shown in FIG. In other words, as the input impedance changes, the resonant frequency also changes.

In addition, in the case of long side feeding, the interval S is 3/100 wavelength (λ)
In this case, the effect of the parasitic loop 20a becomes only on the input impedance, and the resonant frequency converges to the same value as that of the single loop.

By changing the interval S in this way, the input impedance of the antenna can be changed, so matching with the feed line can be achieved without providing a special matching circuit.

In the example shown in Fig. 1, the parasitic loop 20a is provided inside the outer loop 20, but the loop provided on the inner side and the outer loop are connected by a conductor at the feeding point, so that power is also fed to the inner loop. You can.

FIG. 4 is a front view of a rear window glass of an automobile showing an embodiment in which a glass antenna is constructed using such a two-wire loop antenna. The rear window glass 1 is formed into a shape close to a horizontally long rectangle, and an outer loop antenna 2 is provided approximately along the edge of the rear window glass 1. Therefore, the shape of the outer loop antenna 2 is a horizontally long rectangular loop similar in shape to the rear window glass 1. The outer loop antenna 2 is arranged at a predetermined interval 1. Two conductors spaced apart,
12a and 2b, with an interval (.

is set to 1/100 or less of the wavelength of the used frequency band. The conducting wire 2b is in a parasitic closed loop.

Similar to the outer loop antenna 2, a loop antenna 3 consisting of two conductive wires 3a and 3b arranged at a predetermined interval t2 is disposed inside the outer loop antenna 2. The conducting wire 3b is a parasitic closed loop. Each end of these loop antennas 2 and 3 and the antennas 2a and 3a are connected to the same feed line 8 at a feed point 4 provided at the center of the lower part of the rear window glass 1.

The conductor spacing of each part of the double loop antenna of the embodiment shown in FIG.
The input reflection coefficient when connected to the feed point 4 was as shown in FIG. That is, in the 70-90MHz FM broadcast band,
Good consistency with a VSWR of 2 or less was obtained.

In addition, as in the embodiment shown in Fig. 4, two loop antennas are connected to one
When connected in parallel to two feeding vA8s, as shown in the closed loop explanatory diagram of FIG. Parasitically formed during 2.3. The length of this third closed loop 7 is approximately equal to the sum of the lengths of the main loop 5 and the sub loop 6.

That is, for example, the length of each part indicated by the symbol a w d in FIG. 4 is a = 1,250 ss, b = 62
5 m, c = L130 x*, d = 505 +u
When the glass antenna is configured for FM broadcast reception, the length of the third closed loop 7 is approximately 7.140 m.

Therefore, when this third loop 7 operates as a second harmonic antenna, the resonant frequency is 84Mtlz,
A point of impedance deterioration occurs between the resonant frequency of the main loop 5 and the resonant frequency of the sub-loop 6.

In order to prevent such inconvenience, in the embodiment, as shown in FIG.
The third loop 7 is cut off by short-circuiting the third loop 7. This increases the resonant frequency of the third loop 7 and moves its second harmonic out of the reception band. Therefore, there is no deterioration of impedance characteristics due to the second harmonic within the reception band, and the frequency characteristics of the glass antenna can be favorably widened.

The shorting wire 10.11 can be a solid or stranded conductor or a printed conductor. In the latter case, an insulating film is formed on the conductive wire 2b by printing or the like, and a printed conductor is formed thereon.

As a result of the experiment, the distance e from the feed point 4 to the short circuit point was 312
．． By setting the width to 5 mm, a good wide band was realized. The short-circuit double rectangular loop antenna configured in this way has a voltage standing wave ratio VSWR of 2 or less over the entire FM broadcast band of 70 to 90 MH2, which almost satisfies the performance required for an FM broadcast receiving antenna. did.

In addition, when configuring a multiple loop antenna in this way,
It may be triple or more.

〔Effect of the invention〕

As described above, in the present invention, two loop-shaped antenna conductors with a narrow interval are arranged on an insulating surface, and the input impedance is arbitrarily set according to the interval between the two antenna conductors, so that a special matching circuit is provided. It is now possible to match the power supply line without using a

[Brief explanation of drawings]

Figure 1 is a conductor pattern diagram for explaining the operating characteristics of the two-wire loop antenna of the present invention, and Figures 2 and 3 are diagrams of the conductor pattern.
Figure 2 shows an impedance characteristic diagram, Figure 3 shows a frequency characteristic diagram, and Figure 4 shows an example of a glass antenna configured using the two-wire loop antenna of the present invention. FIG. 5 is a front view of the window glass, FIG. 5 is an impedance characteristic diagram of the antenna in FIG. 4, and FIG. 6 is an explanatory diagram of a closed loop formed by two loop antennas. In addition, in the codes used in the drawings, 1.・Outer loop antenna 3・−・・・・・−・・−・−Inner loop antenna 4−・・−・−・・−・−・−−−Feeding point 5−・−・−・−・・・・−Main loop 6−−−−−
−・−１１１−−−・−Subloop 7−・・−・・・−・
--・・Third loop 8−・−・−−−−−1−−−−・
-Feed lines io, tt---- short circuit wires.

Claims (1)

[Claims] 1. A first antenna element conductor arranged in a loop shape on an insulating surface, and a second antenna element conductor arranged in a loop shape on the insulating surface along the first antenna element conductor. an antenna element conductor, the interval between the first antenna element conductor and the second antenna element conductor is narrower than 1/100 of the wavelength of the frequency band used, and the two conductors form one loop. A two-wire loop antenna characterized by configuring an antenna. 2. A large number of the above two-wire loop antennas are provided so as to form multiple loops on an insulating surface, and each two-wire loop antenna is connected in parallel to a common feeding point, and each of the two-wire loop antennas is connected in a manner other than the above parallel connection. 2. The two-wire loop antenna according to claim 1, wherein the two-wire loop antenna is short-circuited at one position.