JP3223742B2 - Microstrip antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microstrip antenna used as a transmission / reception antenna element of a system utilizing microwaves or millimeter waves, such as a wireless LAN, an entry / exit management system, and the like. It relates to something that emits waves.

[0002]

2. Description of the Related Art Generally, a microstrip antenna is provided with a radiation conductor plate having various geometric shapes such as a square, a triangle, and a circle on a dielectric substrate having a ground conductor plate. This is from one or more points of the radiation conductor plate,
By feeding power through a microstrip line or a coaxial cable, the current excited in the radiation conductor plate serves as a radiation source to radiate radio waves into space, and is an open resonance antenna.

Conventionally, in order to generate a circularly polarized wave with a microstrip antenna, a point-symmetrical shape (hereinafter referred to as an orthogonal point symmetry, such as a square or a circle) that completely overlaps the original figure when rotated by 90 degrees around the center. A signal having an equal amplitude and a phase difference of 90 degrees is supplied to two orthogonal points on the radiating conductor plate having the same shape through an external circuit such as a 90-degree hybrid and circularly polarized in a direction perpendicular to the dielectric substrate. There is a two-point feeding system that emits waves. However, this method has a drawback that the axial ratio characteristic of the circularly polarized wave largely depends on the 90-degree hybrid, and the structure of the feed circuit becomes complicated.

In order to compensate for the drawbacks of the two-point feeding method, there is a one-point feeding method using two orthogonal resonance modes of a radiation conductor plate having a symmetrical orthogonal point shape. The principle of operation is that the degeneracy is solved by perturbing the path lengths of the currents of the two resonance modes, and power is supplied from a position at an angle of 45 degrees with the two diagonal lines corresponding to the two resonance modes, so that 90 A quadrature current having a phase difference of degrees and an equal amplitude is generated to excite circularly polarized waves.

FIG. 3 shows a conventional example of a single-point power supply system. The figure shows a microstrip antenna having a square radiating conductor plate fed by a microstrip line. A strip conductor 3 and a radiation conductor plate 4 are formed on a dielectric substrate 2 having a ground conductor plate 1, and the strip conductor 3 is connected to the center of one side of the radiation conductor plate 4. The radiation conductor plate 4 is provided with degenerate separation elements 5a, 5b, 6a, 6b having concave and convex shapes at respective diagonals.

The degenerate separation elements 5a provided on the radiation conductor plate 4
By using 5b, 6a, and 6b, the two resonance modes are degenerated to separate resonance frequencies. By feeding power from the strip conductor 3 at a frequency exactly intermediate between the two resonance frequencies, a quadrature current having a phase difference of 90 degrees from each other in the direction of the degenerate separation elements 5a, 5b and 6a, 6b and having the same amplitude is generated. I do. By combining these, a circularly polarized wave is radiated in a direction perpendicular to the dielectric substrate 2.

[0007]

However, the configuration in which the degenerate separation element having the above-mentioned uneven shape is provided has the following problems. That is, the currents for the two resonance modes flow along two diagonals of the degenerate separation elements 5a, 5b and 6a, 6b. The current distribution at this time is largest at the center of each diagonal, and decreases as approaching the end.

However, the radiation conductor plate 4 occupying most of the radiation
At the end of the diagonal line 5a, 5b, the current flows in two due to the concave shape, and in the diagonal line 6a, 6b, the current flows intensively due to the convex shape. A large difference occurs in the current distribution. This difference degrades the axial ratio characteristics of the circular polarization and the uniformity of the radiation pattern in the two diagonal directions.

The degree of the degenerate separation is related only to the area of the degenerate separation element.
It is necessary to increase the area of the degenerate separation element. However, when the element shape is realized by the above-described uneven portions, the difference between the two diagonal lengths increases, and the uniformity of the radiation patterns in the two diagonal directions further deteriorates.

[0010] In addition, the microstrip antenna is manufactured by using a circuit board manufacturing technique such as pattern printing and etching. However, as the operating frequency of the antenna approaches the millimeter wave region, the size of the radiation conductor plate decreases, and the area of the degenerate separation element also decreases. For this reason, there has been a problem that it is difficult to accurately manufacture an element having a complicated uneven shape.

An object of the present invention is to provide a microstrip antenna which has excellent axial ratio characteristics and a uniform radiation pattern, and can be easily manufactured even in a millimeter wave region. I do.

[0012]

In order to solve the above-mentioned problems, a microstrip antenna according to the present invention is a microstrip antenna having a radiation conductor plate formed opposite a ground conductor plate via a dielectric layer. The radiating conductor plate has a rhombic shape, and circularly polarized waves are radiated by feeding power from a midpoint on one of the four sides.

[0013]

According to the above construction, the degenerate separation required for generating circularly polarized waves is performed by making the lengths of two diagonal lines on the radiation conductor plate different. Therefore, the shapes of the current distributions in the two diagonal directions are similar, and the element area required for degenerate separation is uniformly allocated to the periphery of the conductor plate, so that the shape change of the conductor plate is small. As a result, the shape change of the current distribution in the two diagonal directions is further reduced, and an excellent circular polarization axis ratio and a uniform radiation pattern can be obtained.

Further, according to the above configuration, since the shape of the radiation conductor plate is a simple quadrilateral, it is possible to manufacture the radiation conductor plate with high accuracy even in a millimeter wave region where the antenna frequency is small.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the microstrip antenna of the present invention will be specifically described with reference to the drawings. FIG. 1 is a plan view showing one embodiment of the microstrip antenna of the present invention. The difference from the conventional microstrip antenna is that the shape of the radiating conductor plate 4 formed on the dielectric substrate 2 is not a square with right angles but a diamond shape. Is characterized by having different lengths.

FIGS. 2A and 2B are diagrams for explaining the operation of the embodiment. Arrows 7a and 7b in FIG. 2 indicate currents of two resonance modes flowing through the square and rhombic radiating conductor plates 4, respectively. .

In the square radiation conductor plate 4 shown in FIG. 2A, since the lengths of the diagonal lines are equal, the two resonance modes degenerate and have the same resonance frequency. Here, when power is supplied from the strip conductor 3 to the center of one side of the radiation conductor plate 4 at a resonance frequency, the resonance currents 7 having the same amplitude and the same phase corresponding to the two resonance modes degenerate in the diagonal direction of the radiation conductor plate 4.
a and 7b flow, and a linearly polarized wave is radiated into space from the combination thereof.

As shown in FIG. 2 (b), while maintaining the power supply position, a slight perturbation is given to the length of the diagonal line of the radiation conductor plate 4 to change the path length of the flowing current. Are degenerate and have different resonance frequencies.

In FIG. 2B, since the current path flowing in one diagonal is shorter than the current path flowing in the other diagonal, the resonance frequency of the resonance mode in the 7a direction is higher than the resonance frequency of the resonance mode in the 7b direction. Become.

Therefore, by appropriately setting the lengths of the two diagonal lines and supplying power at an appropriate frequency between the two resonance frequencies, a phase difference of 90 degrees is obtained in the directions of 7a and 7b, and the amplitude is equal. Can generate a large orthogonal current,
It becomes possible to radiate circularly polarized waves into space from the combination of these.

As described above, if the degenerate separation is performed by changing the lengths of the two diagonal lines on the radiation conductor plate, the current distribution shapes in the two diagonal directions become similar, and the element area required for the degenerate separation is obtained. Are uniformly allocated to the periphery of the conductive plate, and the shape change of the conductive plate is small. For this reason, the shape change of the current distribution in the two diagonal directions is reduced, and an excellent circular polarization axis ratio and a uniform radiation pattern can be obtained.

Further, since the shape of the radiation conductor plate is a simple quadrilateral only by the difference between the lengths of the two diagonal lines,
High-precision fabrication is possible even in the millimeter-wave region where the antenna frequency is small when the frequency used is small.

[0023]

As described above, according to the present invention, in which the shape of the radiation conductor plate is rhombic and power is supplied from the middle point on one of the four sides, the radiation conductor plate has an excellent circular polarization axis ratio and a uniform radiation pattern. Also, it is possible to realize a microstrip antenna that can be manufactured with high accuracy even in a millimeter-wave region where the antenna size is minute when the operating frequency is minute.

[Brief description of the drawings]

FIG. 1 is a plan view showing one embodiment of a microstrip antenna of the present invention.

FIG. 2 is a diagram illustrating the operation of the antenna.

FIG. 3 is a plan view and a sectional view showing a conventional microstrip antenna.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ground conductor plate 2 Dielectric layer 3 Strip conductor 4 Radiation conductor plate 5a, 5b, 6a, 6b Degenerate separation element 7a, 7b Current in both resonance modes

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-276904 (JP, A) JP-A-5-29825 (JP, A) JP-A-4-316202 (JP, A) JP-A-3-316 49404 (JP, A) JP-A-4-122105 (JP, A) JP-A-6-232627 (JP, A) JP-A-59-161102 (JP, A) JP-A-60-197002 (JP, A) JP-A-4-199903 (JP, A) JP-A-6-326508 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01Q 13/08 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A microstrip antenna in which a radiation conductor plate is formed facing a ground conductor plate via a dielectric layer, wherein the radiation conductor plate has a rhombic shape, and power is supplied from a midpoint on one of four sides. A microstrip antenna that emits circularly polarized waves.