JPH0414304A - Stacked loop antenna - Google Patents

Abstract

PURPOSE:To improve the directivity and the gain of an antenna pattern even comparatively simple and has a small occupied area by adding a reactance element conductor to each loop conductor to bring the antenna impedance close to a pure resistance. CONSTITUTION:Reactance element conductors 13a, 13b are formed to points parted by 180 deg.C respectively with respect to terminal parts 12a, 12b of loop conductors 10a, 10b. The conductors 13a, 13b are swollen in U-shape from part of the conductors 10a, 10b in the centrifugal direction and the U-shaped parts cancel reactive component of the antenna impedance when viewing from the terminals 12a, 12b to bring the antenna impedance close to a pure resistance. That is, the antenna impedance when viewing from a feeding point is brought into a pure resistance by the addition of the conductors 13a, 13b. Thus, the matching loss between the antenna and the transmission cable is reduced to improve the gain, the phase shift of the received waves between the loops is decreased, the dip in the directivity in the loop connection direction is compensated to make the directivity close to omnidirectivity, and an excellent gain and the omnidirectivity are obtained even from the antenna with comparatively simple pattern and less occupied area.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a twin-loop antenna, and is particularly suitable for use in an antenna printed on an insulator such as a window glass as a telephone antenna for automobiles. It is.

[Conventional technology]

As a UHF band antenna attached to a car window, etc., a pair of half-wavelength half-loop-shaped conductor elements are branched from the feed point in both left and right directions along a ground conductor, the terminal end of each conductor element is grounded, and the antenna is connected to the feed point. A twin-loop antenna configured to perform unbalanced power feeding is known (Japanese Patent Laid-Open No. 62-69704, US Pat. No. 4,721.964).

FIG. 11 shows a conventional example in which the above-mentioned twin loop antenna is printed on the rear window glass of an automobile.

In FIG. 11, reference numeral 1 denotes a transmitting/receiving antenna for, for example, a car-mounted telephone, which is printed on a rear window glass 2 together with an anti-fog heater wire 3 and a radio (FM/AM) antenna conductor 4. The transmitting/receiving antenna 1 is mounted on the body 5 of the automobile.
A pair of half-loop elements 1a and 1b are provided along the feed point 6 and branched left and right from the feed point 6. The terminal ICs 11d of the elements 1a and 1b are grounded, and unbalanced power is fed to the feed point 6 from the core wire of the coaxial feed cable 7.

This transmitting/receiving antenna 1 has a UHF frequency of 850 to 950 MHz.
It shows good gain in the band and almost omnidirectional directional characteristics.

[Problem to be solved by the invention]

The transmitting/receiving antenna 1 shown in FIG. 11 has disadvantages in that it has a slight drop in directivity with respect to radio waves arriving from the side of a car, and its gain is somewhat smaller than that of a pole antenna or the like.

The present invention aims to solve this problem and improve directivity and gain.

[Means for Solving the Problems] The twin-loop antenna of the present invention includes two connected loop-shaped conductors, a feeding point formed at the connecting portion of each loop, and a reactance element loaded on each of the loop-shaped conductors. It consists of a conductor.

(Effect) The impedance of the antenna seen from the feed point approaches pure resistance by adding the reactance element conductor.Therefore, matching loss between the antenna and transmission cable is reduced and gain is improved, and the phase of the received wave between the loops is reduced. The deviation becomes smaller, the drop in directivity in the direction of loop connection is compensated for, and the directionality approaches omnidirectionality.

〔Example〕

FIG. 1 shows the conductor pattern of the twin loop antenna of the present invention. This conductor pattern can be formed by printing a conductive material on an insulating surface or by embedding conductive wires in an insulator. This twin-loop antenna includes two joined circular loop conductors 10a and 10b, and a pair of power feeding terminal portions 12a and 12b are formed across a gap 11 having a length of about 2 mm formed at the joined portion. One of these power supply terminal portions 12a and 12b (for example, 12a) is used for a signal, and the other is used for grounding.

A reactance element conductor 1 is placed at a portion 180' apart from the terminal portions 12a and 12b of each loop conductor 10a and 10b.
3a and 13b are formed.

Each reactance element conductor 13a, 13b is formed by bulging a part of the loop conductor 10a, 10b in a U-shape in the centrifugal direction, and the terminal 12a, 12b of the loop conductor 10a, 10b
It has the effect of canceling out the reactance component of the antenna impedance seen from the surface, making it close to pure resistance.

The antenna in Figure 1 has a frequency of 1
The radius of the loop conductors 10a, 10b is determined to operate as a wavelength twin loop antenna. If the design frequency is 900MHz, one wavelength is 333.3 mm
This is the relative dielectric constant ε of the insulating material to which the antenna conductor is attached.
1 causes the wavelength to be shortened.

Using glass (ε, = 3.0) as the insulating material, the shortening factor is 0.58 7-h, and the shortened wavelength is λ' = 333.3 Xo, 58 = 192.5 ( am)
It is. Therefore, the radius of the loop conductors 10a and 10b is set to R=192.5/2π=30.6 (mm). Note that the conductor width in this example is 4. It is Otrm.

The dimensions of the reactance element conductors 13a and 13b are determined such that the width of the U-shaped channel is 9.6 mm and the depth L is such that the reactance seen from the terminals 12a and 12b is minimized. The Smith chart and standing wave ratio SWR graph in FIG. 2 show impedance characteristics when L=25.

Also, as a reference in FIG. 3, the reactance element conductor 12a,
12b shows a Smith chart and an SWR graph of a conventional antenna pattern without 12b.

As can be seen from the comparison between FIG. 2 and FIG. 3, when the reactance element conductors 13a and 13b are added, the characteristic impedance Z, = 50Ω (normalized impedance Z/Z, =
Antenna impedance close to 1.0) is 820-94
Obtained in the 0MHz band.

In addition, in the receiving frequency band of 850 to 940 MHz and the transmitting frequency band of 910 to 940 MHz of the car phone, SWR
is 1.5 or less, and it can be seen that the consistency with the feeder cable is improved compared to the conventional method (FIG. 3).

FIG. 4 shows the directional characteristics of the antenna conductor shown in FIG. 1, and FIG. 5 shows the directional characteristics of a conventional antenna conductor without reactance element conductors 13a and 13b. As can be seen from the comparison between FIG. 4 and FIG. 5, the antenna conductor of the example is
In particular, the gain on the sides in the direction of travel has been improved, and the beam has a directional characteristic that is almost omnidirectional. Note that in FIGS. 4 and 5, the reference gain OdB is a dipole antenna, and measurements were made for vertical polarization.

Moreover, FIG. 6 shows the horizontal plane (0 to 3
60°) (dotted line) and the frequency characteristic of a conventional antenna pattern without reactance element conductors 13a and 13b (-dotted chain line). As can be seen from the figure, the antenna pattern of the example is 800 to 960 MHz.
The average gain in this band is about 2 dB, which is an improvement over the conventional example. Note that the standard (OdB) for the graph in FIG. 6 is a dipole antenna, and measurements were made using vertically polarized waves.

As shown in Figures 2, 4, and 6, the gain and directivity of the twin loop antenna of the example are improved because the matching with the feeding cable is improved and matching loss is reduced. This is because the phase shift between the received waves of the left and right loops has become smaller.

Since the twin loop antenna shown in FIG. 1 has a symmetrical top and bottom half, it can be operated as a mirror antenna using only one half. In this case, as shown in FIG. 7, the half-loop conductors 10a, 10b and the L-shaped reactance in the upper half of FIG. Element conductors 13a and 13b are arranged, and reactance element conductor 13a
, 13b are provided and grounded, and the core wire of the coaxial power supply cable 7 is connected to the power supply terminal portion 12a at the junction of the half-loop conductors 10a, 10b. In the example shown in FIG. 7 as well, the heater wire 3 and the radio antenna conductor 3 may be formed on the surface of the glass 2 as in the conventional case shown in FIG.

Furthermore, as shown in FIG. 8, half-loop conductors 10a, 10b
A ground line 15 is formed by printing on the glass surface together with the L-shaped reactance element conductors 13a and 13b, and the L-shaped reactance element conductor 13a,
It is also possible to arrange the conductors such that each terminal end of the power supply cable 13b is coupled together with the outer conductor (ground) of the power supply cable 7.

Further, as shown in FIG. 9, a plurality of half-loop conductors 10a,
10b may be connected and L-shaped reactance element conductors 13a and 13b may be added to the ends thereof. Alternatively, as shown in FIG. 10, a straight conductor 16 may be inserted between the half-loop conductors 10a and 10b, and the half-loop conductors 10a and 10b may be separated to the left and right. The length of the straight conductor 16 is 1/2 of the wavelength
An integer multiple of is good.

Note that on each side described above, the loop conductors 10a, 10b are circular or semicircular, but may be polygonal.

〔Effect of the invention〕

As described above, the present invention adds a reactance element conductor to each loop conductor of the twin-loop antenna to make the antenna impedance close to pure resistance, so even a relatively simple antenna pattern occupying a small area can achieve good gain and Provides omnidirectional performance.

[Brief explanation of drawings]

Figure 1 is a conductor pattern diagram showing an embodiment of the twin loop antenna of the present invention, Figure 2 is a Smith chart and SWR graph showing the impedance characteristics of the antenna in Figure 1, and Figure 3 corresponds to Figure 2. Figure 4 is the directional characteristic diagram of the antenna of Figure 1, Figure 5 is the directional characteristic diagram of the conventional twin loop antenna,
Figure 6 shows the gain of the antenna in Figure 1 and the conventional antenna.
Graphs of frequency characteristics, Figures 7 to 10 are diagrams showing conductors on the window glass surface of a car showing an example of a mirror image antenna, Figure 11
The figure shows the conductor arrangement of a conventional automobile window glass antenna. In addition, in the symbols used in the drawings, 2.---------------------Rear window glass 3-------------------------Heater Line 4-
・－－－－－－－－－・－１－－－Radio antenna 5
−−−−−1・−・−・−・−Body 7−−−−−−−
-1・---1---・Power supply cable 10a, 10
b ----------Lou 7" 4 bodies 132.12b -
----Feeding points 13a, 13b--Reactance element conductor 15-----------
It is a grounding conductor.

Claims (1)

[Claims] 1. A twin-loop antenna comprising two connected loop-shaped conductors, a feeding point formed at the connecting portion of each loop, and a reactance element conductor added to each of the loop-shaped conductors. 2. The twin loop antenna according to claim 1, wherein the reactance element conductor is made of a U-shaped folded conductor, and the antenna impedance seen from the feeding point is close to pure resistance. 3. The loop-shaped conductor is composed of two connected half-loop conductors and a grounding conductor arranged to close the recess, and the reactance element conductor is connected to the end of the half-loop-shaped conductor and the grounding conductor. 2. The twin-loop antenna according to claim 1, comprising an L-shaped conductor that couples the antenna.