JPH0361363B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a circularly polarized wave generating loop antenna.

[Prior Art and Its Disadvantages] Circularly polarized antennas have been used in radars for a long time, and have recently been rapidly used for communications with moving objects such as satellite communications.

Conventionally, helical antennas, cross dipole antennas, loaded loop antennas, patch antennas, and the like have been used as circularly polarized antennas.

By the way, among the antennas mentioned above, in the case of a cross dipole antenna, it is necessary to feed power to the dipole antennas of equal length with different phases from each other. I needed a vessel.

[Object of the Invention] The present invention has been made in view of the above-mentioned circumstances, and its purpose is to generate circularly polarized waves that can obtain stable characteristics with a simple structure without using a power divider or a phase shifter. The purpose is to provide a loop antenna.

[Summary of the Invention] The circularly polarized wave generating loop antenna according to the present invention has a structure in which a branch conductor with a length of about a quarter wavelength is installed in parallel to a loop conductor, and feeding terminals are provided at both ends of the loop conductor. By supplying power from this power supply terminal, circularly polarized waves are generated at the tip of the branch conductor.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a circularly polarized wave generating loop antenna 1 according to the present invention, in which a branch conductor 12 is electrically coupled to the inside of a rectangular loop conductor 11, and a feed line is connected between each conductor. They share elements that serve as antennas and elements that serve as antennas. loop conductor 1
1 is provided with power supply terminals 13a and 13b at both ends, and when excited with these power supply terminals 13a and 13b,
A balanced mode current and an unbalanced mode current flow through the loop conductor 11 and the branch conductor 12, and it is possible to excite the voltage necessary to generate circularly polarized waves at the tip of the branch conductor 12. If this were to be achieved using a conventional power supply method, a power divider and a phase shifter would be required, but in the present invention, these devices can be used because the branch conductors 12 are connected. It is possible to realize a circularly polarized wave generating loop antenna without the need for a circularly polarized wave generating loop antenna.

Antenna 1 with the above structure was designed and prototyped as shown in Figure 2, and as a result of experiments with a center frequency of 2 GHz, the axial ratio (ratio between the maximum and minimum electric field values) indicates how much circularly polarized the wave is. ) has become as shown in Figure 3. The solid lines are calculated values, and the circles are measured values. In the experiment, antenna 1 was replaced with reflector 1.
4 via a semi-rigid cable 15, and the distance between the reflector 14 and the antenna 1 is 40 mm.
It is said that As is clear from this, it can be seen that the polarization is good near 2 GHz. Regarding the gain of this antenna 1, the theoretical and experimental results are as shown in Fig. 4, and the gain is about 8 dB. Furthermore, the directivity characteristics of this antenna viewed in a plane including the axis of the radiation direction are as shown in FIGS. 5a and 5b. Figure a shows the directivity in the xz plane, and figure b
indicates the directivity in the yz plane.

6a and 6b show the rotation direction of circularly polarized waves generated by the antenna 1 in the positive direction of the z-axis. Figure a shows left-handed circularly polarized waves, and Figure b shows right-handed circularly polarized waves.

Next, the basic principle of the antenna of the present invention will be explained. Now, if we decompose the antenna 1 shown in Fig. 7 into a balanced system and an unbalanced system, each of the balanced system A in Fig. 8a
is expressed as an unbalanced system B shown in Figure b. however,
The characteristic impedance Z ₀ of the line in the balanced system A is expressed by the following equation.

Z ₀ = 120ln d/a (Ω) ...(1) (a: radius of branch conductor, d: distance between branch conductor and loop conductor) Also, the coefficient k applied to the voltage of unbalanced system B is the voltage distribution ratio It is.

In order to generate left-handed circularly polarized waves, the voltages shown in FIG. 8b should have the same amplitude and a phase difference of 90 degrees. That is, V ₁ /V ₀ =−j (2). To realize this through the transmission line shown in Figure 8a, sλ/4 ...(3) (λ: wavelength) Z ₀ R/k ² ...(4) (R: input resistance of a single loop conductor) ). Therefore, the total circumference of the loop is 1~
This can be achieved with 2λ.

The structure capable of generating circularly polarized waves based on the above principle is a combination of FIGS. 8a and 8b, and can generally be expressed as shown in FIG. 9. If power is supplied to one of the terminals 20 ₁ to 20 ₆ of this structure and the other terminals are opened or shorted, antennas with various structures as shown in Fig. 10 a to d can be obtained, and circularly polarized waves can be generated in the same way. be able to. Figure a shows a loop antenna constructed by cutting the loop at a point about a quarter of a wavelength and connecting it with a coupling line of the same length. Figure b shows a loop antenna with a branch conductor installed outside the loop antenna. Figure c shows a branch conductor with both ends open inside the loop antenna, and Figure d shows a branch conductor that is open near the feeder and the other end connected to the loop antenna.

The axial ratio is set to 0 dB when the total loop length is between 1 and 2λ.
(complete circular polarization). In this range,
The gain change is in the range of ±1dB. In addition, by changing the loop length etc., the input conductance can be reduced by 1.
~15ms, the input susceptance can be changed by -6 to 2ms. The best structure among these is
This is the structure shown in FIG. This has a total loop length of 1.2λ and the widest axial band. The input admittance in this case is as shown in FIG. When focusing on gain and input admittance, desired characteristics can be obtained by making slight changes from this optimal structure.

In the above embodiment, a rectangular loop antenna has been described, but the present invention may also be applied to a circular loop antenna 2 as shown in FIG. In the figure, 31 is a loop conductor, 32 is a branch conductor,
33a and 33b indicate power supply terminals. In this case, the antenna operates in the same way as the antenna shown in FIG. 10d.

FIGS. 13 and 14 respectively show applied antennas using the above basic antenna.
FIG. 13 shows an example in which this antenna is applied to a Yagi antenna, where 34 corresponds to a reflector, 35 corresponds to a radiator, and 36 corresponds to a waveguide. Therefore, this antenna is a circularly polarized antenna that is highly sensitive to radio waves arriving from the right direction.

In FIG. 14, for example, a large number of antennas 1 are printed on a printed board 37 to form a planar antenna that feeds power from below.

[Effects of the Invention] As described above, the circularly polarized wave generating loop antenna according to the present invention has the following advantages: (1) The structure can be as simple as attaching a branch conductor to an ordinary loop antenna, and no power divider or phase shifter is required. Therefore, it is possible to realize a circularly polarized wave generating loop antenna with an extremely simple structure.

(2) Approximately 20% of the bandwidth can be obtained with an axial ratio of 1.5 dB or less, and it has the widest band characteristics among conventional small circularly polarized antennas of about one wavelength.

(3) In the case of an antenna placed on a reflector, the gain is approximately 8 dB, and since the gain of the antenna itself is high, it is suitable for array formation.

[Brief explanation of drawings]

Fig. 1 is a plan view showing a circularly polarized wave generating loop antenna according to an embodiment of the present invention, Fig. 2 is a perspective view showing a prototype example of the antenna, and Fig. 3 is an axial ratio characteristic of the antenna shown in Fig. 2. FIG. 4 is a characteristic diagram showing the gain of the same antenna, FIG. 5 is a characteristic diagram showing the directivity, FIG. 6 is a diagram showing the generation state of circularly polarized waves, and FIGS. 7 to 10. The figures are diagrams for explaining the basic principle of the present invention, Figure 11 is a characteristic diagram of the input admittance of the antenna in Figure 2, and Figure 12 is a circularly polarized wave generating loop antenna according to another embodiment of the present invention. FIG. 13 is a diagram showing an example in which the present invention is applied to a Yagi antenna, and FIG. 14 is a diagram showing an example in which the present invention is applied to a planar antenna. 1, 2...Circularly polarized wave generating loop antenna, 11...
...Loop conductor, 12...Branch conductor, 13a, 13
b...Power supply terminal.

Claims (1)

[Scope of Claims] 1. A circularly polarized wave generating loop antenna comprising a loop conductor and a branch conductor of about a quarter wavelength installed in parallel to the loop conductor. 2. The circularly polarized wave generating loop antenna according to claim 1, wherein the loop conductor is square. 3. The circularly polarized wave generating loop antenna according to claim 1, wherein the loop conductor is circular. 4. The circularly polarized wave generating loop antenna according to any one of claims 1 to 3, wherein the branch conductor is installed inside the loop conductor. 5. The circularly polarized wave generating loop antenna according to any one of claims 1 to 3, wherein the branch conductor is installed outside the loop conductor. 6. The circularly polarized wave generating loop antenna according to any one of claims 1 to 5, wherein the branch conductor has one end connected to the loop conductor and the other end open. 7. The circularly polarized wave generating loop antenna according to any one of claims 1 to 5, wherein the branch conductor is open at both ends.