JPH03114303A - Broad band loop antenna - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the impedance due to high order harmonic resonance of a parasitic closed loop in the operating band by short- circuiting conductors of a multiplex loop antenna provided on an insulation base. CONSTITUTION:Plural loop antennas 2, 3 whose resonance frequency differs are provided in parallel on a glass face to make the frequency characteristic broad. Moreover, the adjacent loop antennas 2, 3 are short-circuited by short- circuit wires 10, 11 to interrupt a closed loop 7 formed between the adjacent loop antennas 2, 3 thereby moving the high order resonance point at the outside of the operating band. Thus, the production in the operating band of the resonance current deteriorating the impedance characteristic is blocked.

Description

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

[Summary of the invention]

This is a wideband loop antenna in which conductors of a multiple loop antenna provided on an insulating surface are short-circuited to prevent impedance deterioration due to high-order resonance of a parasitic closed loop from occurring within the operating band.

[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. Further, generally, a heating conductor is often provided in the central portion to remove fogging that occurs on the window glass surface, and an antenna conductor cannot be attached thereto. For this reason, when an antenna conductor is provided on the rear window glass, it is provided in a narrow position above or below the antenna conductor.

[Problems to be Solved by the Invention] Therefore, it is difficult to widen the band by wiring the antenna conductor in a complicated manner, or to widen the band by providing a parasitic element array as in the Yagi-Uda antenna. For this reason, conventional glass antennas have not been able 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. but,
In the case of a loop antenna, there is also one resonant frequency, so a single loop cannot satisfy the required band characteristics.

Therefore, it is conceivable to connect a plurality of loop antennas having different resonant frequencies within the required band in parallel to widen the band.

However, in reality, when multiple loop antennas were connected in parallel, a point of impedance deterioration occurred within the required band, and the wideband performance as predicted theoretically could not be obtained.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to compensate for the impedance deterioration of a multiple loop antenna so as to obtain wideband frequency characteristics.

[Failure to solve the problem]

The broadband loop antenna of the present invention has an insulating surface (window glass 1
) are provided to form multiple loops on the
A plurality of loop-shaped antenna conductors 2.3 connected in parallel to the common feeding point 4, and a short-circuit line 10.1 that short-circuits and connects each loop-shaped antenna conductor 2.3 at a position other than the above-mentioned parallel connection.
1.

[Effect]

A plurality of loop antennas 2.3 having different resonance frequencies are provided in parallel on a glass surface to widen the frequency characteristic. In addition, the adjacent loop antennas 2.3 and 10.1 are short-circuited.
1, the closed loop 7 formed between the adjacent loop antennas 2 and 3 is separated, and its high-order resonance point is moved outside the band of use. This prevents resonance current from occurring within the operating band, which would degrade the impedance characteristics.

〔Example〕

FIG. 1 is a front view of a rear window glass of an automobile showing an embodiment of the present invention. An antenna conductor is provided on the inner surface of the rear window glass 1, and is used as a glass antenna for receiving FM broadcasts. In the embodiment, printed wiring is carried out almost along the edge of the rear window glass 1, and a double loop antenna 2.3 having a similar shape to the rear window glass 1 is attached. That is, the rear window glass 1 of the embodiment has a shape close to a horizontally long rectangle, and both the outer loop antenna 2 and the inner loop antenna 3 are rectangular loops similar to this.

A feeding point 4 for extracting the received power induced by the outer loop antenna 2 and the inner loop antenna 3 to the outside is provided on one surface of the rear window glass. Incidentally, since FM broadcast waves in Japan are horizontally polarized waves, the feeding point 4 is provided at the center of the long side to increase the efficiency of extracting received power.

Note that when a glass antenna is constructed by printing wiring on a glass surface in this manner, the propagation speed of high-frequency current flowing through the antenna conductor decreases due to the dielectric constant of the glass. Therefore, the outer loop antenna 2 and the inner loop antenna 3
The wavelength of the high-frequency current flowing through a conductor placed in a vacuum is shorter than the wavelength of a high-frequency current of the same frequency flowing through a conductor placed in a vacuum.

Therefore, when designing a glass antenna, it is necessary to take the shortening rate into consideration, but for ease of explanation, the examples will be described using numerical values converted to the length of a conductor in vacuum.

In FIG. 1, the length of each part of the outer loop antenna 2 is such that the long side a=1,250 mm and the short side b=62511 mm. Further, the length of each part of the inner loop antenna 3 is formed such that the long side C=1+130 m and the short side d=505*x. Each antenna 2.3 is short-circuited on both sides of the feed point 40, that is, at both ends of each loop antenna 2.3, and is connected to a common feed line 8 at the feed point 4.

When the outer loop antenna 2 and the inner loop antenna 3 are short-circuited in this way, as shown in the closed loop explanatory diagram of FIG. , it has been found that a third closed loop 7 is parasitically generated between these two loop antennas 2.3. The loop length of this third closed loop 7 is approximately equal to the sum of the main loop 5 and the sub-loop 6, which is approximately 7140+*m. Therefore, this third
When the loop 7 operates as a second harmonic antenna, the calculated resonant frequency is 34MIIz, and due to this high-order resonance, there is a point where the impedance characteristics deteriorate between the resonant frequency of the main loop 5 and the resonant frequency of the sub-loop 6. arise.

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

As a result of the experiment, the distance e from the feed point 4 to the short circuit point was 312
．． By setting the frequency to 5 tm, a good wide band was realized. FIG. 3 shows the results of measuring the frequency change of input reflection by connecting the short-circuited double rectangular loop antenna constructed in this manner to the feeder line 8 having a characteristic impedance of 200 (Ω). In Fig. 3, the characteristic curve A shown by the solid line is the first
The characteristics of the glass antenna of the example shown in the figure are shown, and a characteristic curve B shown by a broken line shows the characteristics of the glass antenna configured with the antenna pattern of FIG. 2.

The valleys f5 and f6 in the song vAB in FIG. 3 are the resonance points of the main loop 5 and the sub-loop 6 in FIG. This is the deteriorated part. At this peak "7", the reflection is abnormally large and the voltage standing wave ratio VSWR is 2 or more, making it impossible to use it as an antenna.

The trough (, r (, r is the resonance point of the main loop 5 and the sub loop 6 corresponding to f5 and f6 of the curve B. As a result of the second harmonic resonance point of the loop 7 moving out of the band, the VSWR between the valleys f and l f6 r is 2 or less.

Therefore, according to the short-circuit double loop antenna having the configuration shown in FIG. 1, wideband characteristics with a VSWR of 2 or less were obtained in a band of 73 to 100 MHz or more. The measured value of the fractional bandwidth is 30%, which is about six times the fractional bandwidth of the single loop antenna, which is 5.3%. Therefore, the shorted double loop antenna of the embodiment has F
It has sufficient performance as a receiving antenna for the M broadcast band.

Next, an example in which the present invention is applied to a UHF band TV broadcast receiving antenna is shown in the antenna pattern diagram of FIG. Since the wavelength in the UHF band is short, the antenna can be configured in a small size, and the area required for installation is small. The example shown in FIG. 4 shows an example in which the antenna is installed on a side window glass, and is configured as a short-circuited double triangular loop antenna. In this case, the outer loop antenna 15 is an equilateral triangle with a side length L+=250 mm, and the inner loop antenna 16 is an equilateral triangle with a side length Lz=166 m. In isolation, the outer loop antenna 15 resonates with 400 MHz radio waves, and the inner loop antenna 16 resonates with 600 MHz radio waves.

A common feeding point 4 for each loop antenna 15.16 is connected to the fourth
It is provided at the vertex located on the lower side in the figure. In addition, the outer loop antenna 15 and the inner loop antenna 16 are short-circuited by shorting wires 17 to 20 at four locations in total, including both ends of the side facing the feeding point 4 and the center portions of both sides of the feeding point 4. .

The input incidence of the short-circuited double triangular loop antenna constructed in this way is as shown in Fig. 5, and is 470 MHz.
Good performance was obtained over substantially the entire television broadcast band of the TJHF band from 0.98 to 770 MHz.

Although rectangular and equilateral triangular loop antennas have been described in the above embodiments, other loop shapes, such as circular, may also be used.

In addition, as shown in the antenna pattern diagram of FIG. 6, the outer loop antenna 22 and the inner loop antenna 23 are
It may also consist of two lines with a constant spacing narrower than /100 wavelengths. In this case, each inner conductor of each of the outer and inner loop antennas 22 , 23 is made into a parasitic closed loop, and the end of each outer conductor is connected in parallel to the feeder line 8 . Shorting wire 10.1
1 couples the outer conductors of each antenna 22, 23 together.

In this way, by selecting the spacing between the two wires, an input impedance value different from that obtained by configuring a loop with a single wire can be obtained, and good band characteristics can be obtained even if a 50Ω feeder line 8 is used, for example. It will be done.

Note that various feeding points may be selected depending on the state in which the antenna is used. For example, in the case of a rectangular loop antenna, the feeding position is as shown in the feeding point explanatory diagrams of the rectangular loop antenna in Fig. 7(a) to (C).
), short side feeding in Figure 7(b), vertex feeding in Figure 7(c)
Since there are three types of long-side power feeding, it is only necessary to select the optimal power feeding position from these. Note that even in the case of loop antennas of other shapes, the position of the feeding point can be determined so that the frequency characteristics of the input impedance are optimized.

〔Effect of the invention〕

As described above, the present invention provides a shorting line that divides the parasitic loops formed in the multi-loop antenna, so that the high-order resonance point of the parasitic loops can be moved outside the band of use. Therefore, a wideband multiple loop antenna can be obtained by reducing the deterioration of the antenna impedance within the operating band due to the above-mentioned high-order resonance.

[Brief explanation of drawings]

FIG. 1 is a front view of an automobile window glass showing one embodiment of the present invention, FIG. 2 is an antenna pattern diagram for explaining various closed loops formed by two adjacent loop antennas, and FIG. Figure 1 is a reflection characteristic diagram of the glass antenna in the FM broadcast band, Figure 4 is an antenna pattern diagram showing a different embodiment from Figure 1, and Figure 5 is the UHF band of the glass antenna formed in the antenna pattern of Figure 4. FIG. 6 is an antenna pattern diagram showing an example in which one loop antenna is constructed using two lines at regular intervals, and FIG. 7 is an explanatory diagram of a feeding point. In addition, in the symbols used in the drawings, 1-- Antenna 3 - - - - - - - Inner loop antenna 4 - - - - - - - Feeding point 5
−−111・・・〜・・−−−−−−−1 main loop 6
・・−・−・−・−・−・Sub loop 7・−−−
−−・−1−−−−−−−−Third loop 8−・・
・−・−・−・−・・−Feeder line 10・〜−−−−−・
−−−−1−−−−−Short wire 11・−・−・−−−～−
---...This is a short circuit wire. Agent Katsu Tsuchiya Glass Antenna 3rd Loop Figure 2 2 Lala! , Tsuyoshi ζ)゛Special life Figure 3

Claims (1)

[Claims] A plurality of loop-shaped antenna conductors are provided so as to form multiple loops on an insulating surface and are connected in parallel to a common feeding point, and each loop-shaped antenna conductor is connected in a manner other than the above parallel connection. A broadband loop antenna comprising: a short-circuit wire that short-circuits at a position;