JPH0467363B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a circularly polarized antenna, and particularly to a circularly polarized loop antenna.

Background Art This type of circularly polarized wave antenna is used in various communication systems that require circularly polarized waves, and is particularly used in mobile objects such as automobiles and airplanes that must not have external protrusions. As a circularly polarized antenna suitable for the
A circularly polarized loop antenna having a configuration as schematically shown in FIG. 9 and FIG. 9 has been proposed. This kind of circularly polarized loop antenna can be used not only on moving objects such as cars and airplanes, but also in cases where there is not much space for installing the antenna, or when it is necessary to embed the antenna in a card-like object. It is suitable for

In the circularly polarized loop antenna shown in FIG. 8, a grounding plate 31 is provided on the back surface of a dielectric substrate 30, and a loop-shaped conductor 32 is provided on the surface of the dielectric substrate 30. The loop conductor 32 has a wavelength of λ/4 (λ: wavelength).
A pair of power feeding terminals 32A, 32B and 32C, 32D are provided at two shifted positions, respectively. Two power supply terminals 32A, 32B on one side
, two parallel wires 43A extend from a coaxial line 41A connected to a signal source 40A via a balun circuit 42A.
The two parallel wires 43B extending from the coaxial line 41B connected to the signal source 40B via the balun circuit 42B are connected to the other two power supply terminals 32C and 32D. The conventional circularly polarized loop antenna shown in FIG. 8 radiates circularly polarized waves by feeding with a phase difference of 90° between terminals 32A, 32B and terminals 32C, 32D.

The loop antenna for circularly polarized waves shown in FIG. 9 has a grounding plate 51 on the back surface of a dielectric substrate 50, and perturbation elements 53 and 54 to radiate circularly polarized waves on the surface of the dielectric substrate 50. A loop-shaped conductor 52 is provided. The loop-shaped conductor 52 is provided with a pair of power feeding terminals 52A and 52B at predetermined positions. Two parallel wires 63 extending from a coaxial line 61 connected to a signal source 60 via a balun circuit 62 are connected to these two power supply terminals 52A, 52B, respectively. The conventional circularly polarized loop antenna shown in FIG. 9 radiates circularly polarized waves by feeding power from the two power feeding terminals 52A and 52B.

Problems to be Solved by the Invention Among the conventional circularly polarized loop antennas mentioned above, the eighth one requires feeding from two locations with equal amplitude and a phase difference of 90°, and each feeding line has , a balun circuit is required to convert from a coaxial line (unbalanced circuit) to two parallel lines (balanced circuit). Therefore, not only the structure of the antenna itself becomes complicated, but also the connection for feeding the antenna becomes complicated, resulting in an overall high price. Moreover, a space is required near each power feeding terminal to arrange a balun circuit and two parallel wires for power feeding, and the space for arranging the antenna also becomes large. Furthermore, it has been difficult to obtain ideal radiation characteristics of circularly polarized waves.

Among the conventional circularly polarized loop antennas described above, the one shown in FIG. 9 is simpler than the one shown in FIG. 8 in that it only needs to be fed from one location. However, it is necessary to provide two power feeding terminals in the loop for feeding power, and the feeding line still requires a balun circuit, which not only complicates the structure of the antenna but also increases the The connections for this were also complicated and required space. Also, 2 in the loop
Since the terminal is provided, a gap is created in that part, making it difficult to obtain ideal radiation characteristics.

An object of the present invention is to provide a loop antenna for circularly polarized waves that can solve the problems of the prior art as described above.

Means for Solving the Problems According to the present invention, in a circularly polarized loop antenna in which a ground plate and a loop conductor having a perturbation element so as to radiate circularly polarized waves are opposed to each other with a dielectric interposed therebetween, an L-shaped element extending from a predetermined position of the loop conductor into the loop for a predetermined distance, a center conductor of a power feeding coaxial line being connected to the L-shaped element, and an outer conductor being connected to the grounding plate. It is characterized by what it did.

Embodiments Next, the present invention will be described in more detail with respect to embodiments of the present invention based on FIGS. 1 to 7 of the accompanying drawings.

FIG. 1 is a perspective view schematically showing the structure of a circularly polarized loop antenna as an embodiment of the present invention.
As shown in FIG. 1, the circularly polarized loop antenna of this embodiment has a grounding plate 11 on the back surface of a dielectric substrate 10, and a circular loop conductor 12 on the surface of the dielectric substrate 10. It is said to have a microstrip shape. The loop conductor 12 is provided with perturbation elements 13 and 14 so as to radiate circularly polarized waves at radially opposite positions indicated by reference symbols a and b. Furthermore, the loop conductor 12 is provided with the reference symbol c according to the invention.
An L-shaped element 15 is provided extending radially inwardly from the position indicated by d to the position indicated by reference d. In FIG. 1, reference symbol h indicates the thickness of the dielectric substrate 10, and reference symbol _Lf indicates the length of the L-shaped element 15.

In the circularly polarized loop antenna of this embodiment, the center conductor 21 of the coaxial line 20 for feeding is directly connected to the tip d of the L-shaped element 15 through the through hole provided in the ground plate 11 and the dielectric substrate 10. The outer conductor 22 of the coaxial line 20 is directly connected to the ground plane 11 .

Next, the operation and characteristics of the circularly polarized loop antenna having such a configuration will be explained with particular reference to FIGS. 2 to 7.

2 is a plan view schematically showing the antenna shown in FIG. 1, and FIG. 3 is a cross-sectional view schematically showing the antenna shown in FIG. 1. In these FIGS. 2 and 3, the length of the horizontal portion of the L-shaped element 15 is L _f , and the length of the horizontal portion of the L-shaped element 15 is
2 and the ground plate 11 is h. Here, in order to consider various operating characteristics of this antenna, the target wavelength λ is set to 0.1 m, h is fixed to 0.05λ, and the strip width W of the L-shaped element 15 and the loop conductor 12 is fixed to approximately 0.02λ. Length of glyph element 15
First, I measured the change in input impedance by changing L _f . The measurement results are shown in FIG. As you can see from the graph in Figure 4,
As L _f becomes longer, the reactance changes from capacitive to inductive. When L _f =0.24λ, the input impedance is a pure resistance of 46Ω.

Next, by varying L _f , the circular polarization factor, i.e.
We measured changes in the axial ratio, which is the long-axis electric field/short-axis electric field. The measurement results are shown in FIG. As can be seen from the graph in FIG. 5, when L _f =0.24λ, it becomes a circularly polarized wave with a frontal axis ratio of 1.0 dB. The result of measuring the current distribution on the loop 12 at this time is
Shown in the figure. The current distribution on the loop shown in FIG. 6 is a traveling waveform current distribution.

Next, FIG. 7 shows actual measured values of the radiation pattern due to such current distribution. As is clear from the radiation pattern in FIG. 7, the electric field has a maximum value at θ=0° in FIG. 3, that is, in the front direction of the antenna.

As can be seen from the above, according to the configuration of the antenna shown in FIG. It is distributed over 12. At this time, perturbation element 1 at point a and point b
3 and 14, the current has a traveling waveform with substantially uniform amplitude as shown in FIG. 6, so that rotating radio waves are emitted. Since the circumference of the loop 12 is selected to be approximately equal to the target wavelength λ, that is, the wavelength used, the electric field pattern becomes stronger in front of the antenna. Note that the radiation from the transmission line caused by the L-shaped element 15 can be ignored because the thickness h is extremely small relative to the target wavelength λ.
Further, by adjusting the length L _f of the L-shaped element 15, the impedance looking toward the antenna from the point e can be made into a pure resistance. That is, from the above measurement results, if the thickness h of the dielectric substrate is set to 1/20 of the target wavelength λ, then the length L _f of the L-shaped element 15 is set to approximately 1/4 of the target wavelength λ. Bye. Furthermore, the above measurement results are based on the assumption that the dielectric constant of the dielectric substrate 10 is 1, that is, the dielectric is air, but if a dielectric substrate with a dielectric constant higher than 1 is used, the wavelength Therefore, the antenna can be made smaller.

Furthermore, although the loop conductor is circular in the above-described embodiment, the present invention is not limited to this, and the loop conductor may be square.

Effects of the Invention The circularly polarized loop antenna of the present invention can feed power by simply connecting the center conductor of the power feeding coaxial line to the L-shaped element and directly connecting the outer conductor to the ground plate. Therefore, power can be fed from one terminal to one location, making it extremely simple and inexpensive. Moreover, since a complete loop can be formed without creating any gaps in the loop conductor, ideal circularly polarized radiation characteristics can be easily obtained. Further, since a balun circuit or the like is not required for power supply connection, space is not taken up for power supply connection, and the overall size can be made smaller.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing the structure of a circularly polarized loop antenna as an embodiment of the present invention, FIG. 2 is a plan view schematically showing the antenna of FIG. 1, 3 is a cross-sectional and schematic diagram of the antenna of FIG. 1, FIG. 4 is a diagram showing the relationship between the length of the L-shaped element and the input impedance in the antenna of FIG. 1, and FIG. The figure shows the relationship between the length of the L-shaped element and the axial ratio in the antenna of Fig. 1. Fig. 6 shows the current distribution on the loop in the antenna of Fig. 1. Figure 6 is a diagram showing actual measured values of radiation patterns based on current distribution, Figure 8 is a schematic diagram showing an example of a conventional circularly polarized loop antenna, and Figure 9 is a diagram showing a conventional circularly polarized loop antenna. FIG. 3 is a schematic diagram showing another example of a loop antenna. 10... Dielectric substrate, 11... Ground plate, 12...
...Loop conductor, 13, 14...Perturbation element, 15...
... L-shaped element, 20 ... coaxial line, 21 ... center conductor, 22 ... outer conductor.

Claims (1)

[Claims] 1. In a circularly polarized loop antenna in which a ground plate and a loop conductor having a perturbation element so as to radiate circularly polarized waves face each other with a dielectric interposed therebetween, a predetermined distance from a predetermined position of the loop conductor within the loop is provided. A loop antenna for circularly polarized waves, comprising an L-shaped element extending over the area, a center conductor of a power feeding coaxial line being connected to the L-shaped element, and an outer conductor being connected to the ground plate. .