JP2507935Y2 - Circularly polarized loop antenna - Google Patents

Description

TECHNICAL FIELD The present invention relates to a circularly polarized wave antenna, and more particularly to a circularly polarized wave loop antenna.

2. Description of the Related Art Circularly polarized antennas of this type are used in various communication systems that require circularly polarized waves. In particular, it is necessary to prevent external projections from being provided on moving bodies such as automobiles and airplanes. As a circularly polarized wave antenna suitable for such a case, the present inventors have previously proposed a circularly polarized wave loop antenna having a structure as schematically shown in FIGS. 6 and 7 of the accompanying drawings. Such a circularly polarized loop antenna is also used for applications other than moving objects such as automobiles and airplanes, where there is not much space to install the antenna or when it is necessary to embed the antenna in a card. It is suitable for

In the circularly polarized loop antenna shown in FIG. 6, a ground plate 31 is provided on the back surface of the dielectric substrate 30, and a loop conductor 32 is provided on the front surface of the dielectric substrate 30. The loop conductor 32 includes
A pair of power supply terminals 32A, 32B and 32C, 32D are provided at two positions shifted by λ / 4 (λ: wavelength).
One of the two power supply terminals 32A and 32B has two parallel terminals extending from a coaxial line 41A connected to the signal source 40A via a balun circuit 42A.
Each line of the line 43A is connected, and each of the other two power supply terminals 32C and 32D is connected to each of two parallel lines 43B extending from the coaxial line 41B connected to the signal source 40B through the balun circuit 42B. . The conventional circular polarization loop antenna shown in FIG. 6 has a phase difference of 90 degrees between terminals 32A and 32B and terminals 32C and 32D.
Circularly polarized wave is radiated by the power supply set at °.

The circularly polarized loop antenna shown in FIG. 7 is provided with a ground plate 51 on the back surface of a dielectric substrate 50 and has perturbation elements 53 and 54 on the surface of the dielectric substrate 50 so as to radiate circularly polarized waves. A loop-shaped conductor 52 is provided. The loop conductor 52 is provided with a pair of power supply terminals 52A and 52B at predetermined positions. Parallel two lines 63 extending from the coaxial line 61 connected to the signal source 60 through the balun circuit 62 to the two power supply terminals 52A and 52B.
Are connected to each other. The conventional circular polarization loop antenna of FIG. 7 radiates circular polarization by feeding power from the two feeding terminals 52A and 52B in this manner.

Problems to be Solved by the Invention Of the above-mentioned conventional circular polarization loop antennas, the sixth
In the case of the one shown in the figure, it is necessary to feed power from two locations with equal amplitude and a phase difference of 90 °. Moreover, for each feed line, a coaxial line (unbalanced circuit) is converted into two parallel lines (balanced circuit). Balun circuit is required. Therefore, not only the structure of the antenna itself becomes complicated, but also the connection for feeding the electric power becomes complicated, resulting in a high price as a whole. In addition, a space for arranging the balun circuit and the parallel two wires for the power supply is required near each power supply terminal, and the space for arranging the antenna also becomes large. Moreover, it was difficult to obtain an ideal circularly polarized radiation characteristic.

Of the above-mentioned conventional loop antennas for circular polarization,
Compared to the one shown in Fig. 6, the one shown in the figure is simplified in that power supply from only one place is required. However, the loop needs to be provided with two power supply terminals for power supply, and the power supply line still requires a balun circuit, which not only complicates the structure of the antenna but also increases the power supply of the antenna. The connection for this was complicated, and space was needed for that. Further, since the loop is provided with two terminals, a gap is created at that portion, so that it is difficult to obtain an ideal radiation characteristic.

Therefore, as a solution to such a conventional problem, the present inventor has developed a circularly polarized loop antenna having a configuration as disclosed in Japanese Patent Laid-Open No. 214304/1990.
In this circularly polarized loop antenna, a ground plate 11A is provided on the back surface of the dielectric substrate 10A and a circular loop conductor 12A is provided on the front surface of the dielectric substrate 10A, as schematically shown in the perspective view of FIG. It has a microstrip shape. And
The loop conductor 12A is provided with perturbation elements 13A and 14A so as to radiate circularly polarized waves at positions facing each other in the radial direction indicated by reference characters a and b. Further, the loop conductor 12A is provided with an L-shaped element 15A extending radially inward from the position indicated by the reference sign c to the position indicated by the reference sign e through the reference sign d. However, the portion from the reference symbol c to the reference symbol d is also regarded as a part of the L-shaped element and will be referred to as an L-shaped element. In FIG. 8, reference numeral h indicates the thickness of the dielectric substrate 10A, and reference numeral L _f indicates the length of the L-shaped element 15A. In this circularly polarized loop antenna, the coaxial cable 20A for feeding
The center conductor 21A is directly connected to the tip d of the L-shaped element 15A through a through hole provided in the ground plate 11A and the dielectric substrate 10A, and the outer conductor 22A of the coaxial wire 20A is directly connected to the ground plate 11A. Connected.

The circularly polarized loop antenna of FIG. 8 can be fed by simply connecting the center conductor of the feeding coaxial wire to the L-shaped element and the outer conductor to the ground plate. Power can be supplied from one terminal at one location, which can be very simple and inexpensive. Moreover, since a perfect loop can be formed without forming a gap in the loop conductor, an ideal circularly polarized radiation characteristic can be easily obtained. In addition, since a balun circuit or the like is not required for power supply connection, space is not required for connection for power supply, so that the size can be reduced as a whole. However, in a circularly polarized loop antenna having such a configuration that the strip width of the L-shaped element 15A is the same as the strip width of the loop conductor 12A, for example, the relative permittivity of the dielectric substrate is 1, the target free space wavelength λ Is 0.1m, and the coaxial cable to connect
When the characteristic impedance of 20A is 50Ω, the front axis ratio
To obtain a circularly polarized wave of 1.0 dB, the strip width W of the L-shaped element 15A and the loop conductor 12A is 0.02λ, and the L-shaped element 15A
It is necessary to set the length L _f of the dielectric substrate 10A to 0.24λ, and in such a dimensional relationship, in order to achieve impedance matching with the coaxial line 20A, the thickness h of the dielectric substrate 10A is set to 0.05λ.
And must be.

However, as a recent application field of this type of antenna, for example, there is a case where it is used by being embedded in a card-shaped one, and in such an application field, there is a limit to the thickness of the card, and therefore, It has been desired to reduce the thickness of the entire antenna as much as possible. As described above, in the circularly polarized loop antenna configured as shown in FIG.
When the target free space wavelength λ is determined, the thickness h of the dielectric substrate 10A must be set to 0.05λ, and the thickness h of the dielectric substrate 10A is set to 0.05% in order to reduce the thickness of the antenna.
If it is thinner than λ, the input impedance of the antenna is 50
It will deviate from Ω and impedance matching with the coaxial line 20A will not be possible. Coaxial wire 20A
It may be possible to connect an impedance converter between the coaxial wire 20A and the antenna in order to achieve impedance matching between the antenna and the antenna, but this requires a separate space for the impedance converter, This will hinder miniaturization and thinning.

SUMMARY OF THE INVENTION An object of the present invention is to provide a circularly polarized loop antenna capable of achieving further miniaturization and thickness reduction in view of the above-mentioned problems of the prior art.

Means for Solving the Problems According to the present invention, a ground plate and a loop conductor having a perturbation element so as to radiate a circularly polarized wave are opposed to each other with a dielectric material sandwiched therebetween. An L-shaped element having a strip portion extending into the loop substantially parallel to the dielectric surface is provided, a center conductor of a feeding coaxial line is connected to the L-shaped element, and an outer conductor is connected to the ground plate. In the circularly polarized loop antenna configured as described above, the strip portion of the L-shaped element has a first strip portion having the same width as the width of the loop conductor extending from the loop conductor, and the first strip. A second strip portion following the portion, and the length of the first strip portion is such that when the loop conductor is viewed from a boundary point between the first strip portion and the second strip portion. Impedance is a pure resistance, and the length of the second strip portion is equal to a quarter of the propagation wavelength on the feeding coaxial line. When the impedance of the feeding point is Z ₀ and the impedance of the loop conductor viewed from the boundary point between the first strip portion and the second strip portion is Z ₁ , the width of the second strip portion is Is characterized in that the impedance of the feed line by this second strip portion is equal to the square root of the product Z ₀ Z ₁ .

Embodiments Next, the present invention will be described in more detail with reference to FIGS. 1 to 5 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, in the circularly polarized loop antenna of this embodiment, a ground plate 11 is provided on the back surface of a dielectric substrate 10,
It has a microstrip shape in which a circular loop conductor 12 is applied to the surface of 10. The loop conductor 12 is provided with perturbation elements 13 and 14 so that circularly polarized waves can be radiated to positions facing each other in the radial direction indicated by reference signs a and b.
Is provided. Further, according to the present invention, the loop conductor 12 is radially inward from a position indicated by reference numeral c,
L that extends through the reference symbol d to the position indicated by the reference symbol e
A V-shaped element 15 is provided. However, the portion from the reference symbol c to the reference symbol d is regarded as a part of the L-shaped element, and L
We will call it a V-shaped element. In FIG. 1, reference numeral h indicates the thickness of the dielectric substrate 10, and reference numeral L
_f indicates the length of the L-shaped element 15.

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

Next, the operation and characteristics of the circularly polarized loop antenna having such a configuration will be described with reference to FIGS. 2 to 5.

2 is a plan view schematically showing the antenna of FIG. 1, and FIG. 3 is a cross sectional view schematically showing the antenna of FIG. 2 and 3, the length of the horizontal portion of the L-shaped element 15 is L _f , and the distance between the loop conductor 12 and the ground plate 11 is h. L _f is composed of lengths L _f ′ and L _f ″, L _f ′ is the length from point d to point c ′, and L _f ″ is the length from point c ′ to point c. Here, c'is a point at which the impedance of the loop conductor 12 viewed from c'is a pure resistance, and the length dc 'is set to be a quarter of the propagation wavelength λg on the feed line. Further, if the impedance of the feeding coaxial line at the point e is Z ₀ (for example, 50Ω) and the impedance considering the loop conductor 12 from the point c ′ is Z ₁ , the impedance of the feeding line dc ′ can be obtained by multiplying the product Z ₀ Z ₁ by Take the square root. However, the strip width of the feed line c'c is set to be the same as the strip width W of the loop conductor 12. Also, the power supply line
The impedance of dc ′ is determined by the strip width W ′, the thickness h of the dielectric substrate and the relative permittivity ε _r . At this time, the input impedance considering the L-shaped element from the point e becomes a pure resistance (for example, 50Ω), and when L _f ′ = 0.25λg, it becomes a circular polarization in the front direction, and the current distribution on the loop is the fourth. The traveling waveform current distribution is as shown in the figure.

Next, the measured values of the radiation pattern based on such current distribution are shown in FIG. As is clear from the radiation pattern in FIG. 5, the electric field has the maximum value in 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. 1, for example, the current from the feeding coaxial line 20 having an impedance of 50Ω is an L-shaped element 15 having an impedance of 109Ω operating as an impedance converter. And the impedance remains matched.
It reaches the point c of 237Ω and is distributed on the loop 12. At this time, the perturbation elements 13 and 14 at the points a and b cause the current to have a traveling waveform with substantially uniform amplitude as shown in FIG. 4, so that rotating radio waves are radiated. Since the circumference of the loop 12 is selected to have a length substantially equal to the target propagation wavelength λg, that is, the used propagation wavelength, the electric field pattern becomes stronger in front of the antenna. The radiation from the transmission line by the L-shaped element 15 can be ignored because the thickness h is extremely small with respect to the target free space wavelength λ. For example, from the measurement result, the thickness h of the dielectric substrate can be set to 1/100 of the target free space wavelength λ.

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 rectangular.

Effect of the Invention The circularly polarized loop antenna of the present invention can be fed by simply connecting the center conductor of the feeding coaxial wire to the L-shaped element and the outer conductor to the ground plate. Therefore, the power can be supplied from one terminal at one place, which is very simple and inexpensive. Moreover, since it is possible to make a perfect loop without making a gap in the loop conductor,
An ideal circularly polarized radiation characteristic can be easily obtained. Further, since a balun circuit or the like is not required for power supply connection, a space is not required for connection for power supply, so that the size can be reduced as a whole. Furthermore, even if the thickness of the dielectric substrate is made very thin, impedance matching at the time of power feeding can be achieved without the need for a separate impedance converter,
The thickness of the entire antenna can be made thinner, which is suitable for embedding in a card or the like.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing the structure of a circularly polarized loop antenna as an embodiment of the present invention, and FIG. 2 is a plan view schematically showing the antenna of FIG. FIG. 3 is a schematic cross-sectional view of the antenna of FIG. 1, and FIG.
FIG. 5 is a diagram showing a current distribution on a loop in the antenna of FIG. 1, FIG. 5 is a diagram showing measured values of a radiation pattern due to the current distribution as shown in FIG. 4, and FIG. FIG. 7 is a schematic diagram showing an example of a circularly polarized loop antenna,
Schematic showing another example of a conventional loop antenna for circular polarization,
FIG. 8 is a schematic diagram showing still another example of the circularly polarized loop antenna. 10 …… Dielectric substrate, 11 …… Ground plate, 12 …… Loop conductor,
13, 14 ... Perturbation element, 15 ... L-shaped element, 20 ... Coaxial wire, 21 ... Central conductor, 22 ... Outer conductor.

Claims (1)

(57) [Scope of utility model registration request] 1. A ground plate and a loop conductor having a perturbation element so as to radiate a circularly polarized wave are opposed to each other with a dielectric interposed therebetween, and the dielectric surface extends from a predetermined position of the loop conductor into the loop. A circularly polarized wave having an L-shaped element having a strip portion extending substantially in parallel with the central conductor of the feeding coaxial line is connected to the L-shaped element, and an outer conductor is connected to the ground plate. In the loop antenna, the strip portion of the L-shaped element has a first strip portion having the same width as a width of the loop conductor extending from the loop conductor, and a second strip portion continuing from the first strip portion. The length of the first strip portion is such that the impedance of the loop conductor seen from the boundary point between the first strip portion and the second strip portion is a pure resistance. Are as such, the length of the second strip portion, said being equal to one quarter of the propagation wavelength on the feeding coaxial line, the impedance of the feeding point of the feeding coaxial line Z ₀ and the impedance of the loop conductor viewed from the boundary point between the first strip portion and the second strip portion is Z ₁ ,
A circularly polarized loop antenna, wherein the width of the second strip portion is such that the impedance of the feed line by the second strip portion is equal to the square root of the product Z ₀ Z _1. .