JPH03208402A - Frequency adjustment method for microwave antenna - Google Patents

Abstract

PURPOSE:To adjust the frequency characteristic with a simple method by measuring the frequency characteristic of a microwave antenna and revising at least one of the thickness of a radome and the specific dielectric constant of the material when the measured frequency characteristic is deviated from the desired frequency characteristic so as to correct the deviation. CONSTITUTION:A radome 13a has a thickness dr being 1/4 of a wavelength lambdaof a microwave signal sent/received by the antenna or below and a cylinder inner face 13ai is fixed while being bonded to a side face of a disk circumference of a dielectric board 10. As the specific dielectric constant of the radome 13a increases, the resonance frequency of the said microstrip antenna is lowered. As the thickness of the radome 13a is made thicker, the resonance frequency of the said microstrip antenna is lowered. When the measured resonance frequency is deviated from the desired resonance frequency, at least one of the thickness of the radome 13a and the specific dielectric constant of the material is revised to select the radome 13a whose deviation is corrected among the plural radomes 13a and the selected radome is mounted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a frequency adjustment method for microwave antennas such as microstrip antennas and slot antennas.

[Prior Art 1] Figures 3(A) and 3(B) show a conventional linearly polarized microstrip antenna with a radome.

In Figure 3 (A) and (B), the ground conductor 1 is placed on the bottom surface.
A circular radiation conductor 12 having a diameter shorter than the diameter of the dielectric substrate 10 is formed at the center of the upper surface of the disk-shaped dielectric substrate IO on which the dielectric substrate 1 is formed. Further, in order to protect the antenna, the dielectric substrate 10 and the radiation conductor 12 are covered with a cylindrical radome 13 having a cylindrical bottom surface 13s on the radiation surface of the microstrip antenna. Here, the radome 13 is made of a dielectric material having a relative permittivity εr of about 1 and a thickness sufficiently shorter than the wavelength λ of the microwave signal transmitted and received by the microstrip antenna, and is connected to the radiation conductor 12. The distance g from the radome 13 is set to be sufficiently larger than the wavelength λ of the microwave signal so that the radome 13 does not affect the radiation characteristics of the microstrip antenna. Further, power is supplied to a position P radially displaced from the center O of the radiation conductor 12 via a coaxial cable 20 consisting of a center conductor 2I and a ground conductor 22, for example.

Generally, the resonant frequency of this linearly polarized microstrip antenna is uniquely determined by the dielectric constant and thickness of the dielectric substrate 10 and the diameter of the radiation conductor 12.

Furthermore, in addition to the configuration of the linearly polarized microstrip antenna, a conventional circularly polarized microstrip antenna is configured by, for example, forming two rectangular notches at the outer peripheral edge of a radiation conductor.

These two notches operate as a mode degeneracy separation element for emitting circularly polarized radio waves.

In order to radiate circularly polarized radio waves from this microstrip antenna, it is desirable to have the axial ratio, which is the ratio of the short axis of the circularly polarized wave, close to 1, and the size of the notch that makes this axial ratio the best. is uniquely determined by the dielectric constant and thickness of the dielectric substrate, and the diameter of the radiation conductor, and the frequency at which the axial ratio is the best is also determined by these three parameters.

[Problems to be Solved by the Invention] In the conventional linearly polarized microstrip antenna described above, the three parameters of the dielectric constant and thickness of the dielectric substrate IO and the diameter of the radiation conductor 12 change due to manufacturing variations. In this case, there is a problem that the resonant frequency of the microstrip antenna changes.

Further, in the above-described conventional circularly polarized microstrip antenna, there is a problem that, as in the case of linearly polarized waves, when the above three parameters change, the frequency at which the axial ratio is the best changes.

An object of the present invention is to provide a microwave antenna in which a radiation conductor and a ground conductor are formed via a dielectric substrate, and at least the radiation conductor is covered with a radome. When the frequency characteristics of the microwave antenna, such as the resonant frequency and the frequency at which the axial ratio is the best, deviate from the desired frequency characteristics, it is possible to adjust the frequency characteristics of the microwave antenna to the desired frequency characteristics. An object of the present invention is to provide a method for adjusting the frequency of a microwave antenna.

Means for Solving Problem E] The method for adjusting the frequency m of a microwave antenna of the present invention includes forming a radiating conductor and a grounding conductor via a dielectric substrate, and covering at least the radiating conductor with a radome. A method for adjusting the frequency of a microwave antenna, wherein the radome is positioned within a range where the frequency characteristics of the microwave antenna change when at least one of the thickness of the radome and the dielectric constant of the material is changed. The microwave antenna is placed close to the radiation conductor, and the frequency characteristics of the microwave antenna are measured. If the measured frequency characteristics deviate from the desired frequency characteristics, the thickness of the radome and the dielectric constant of the material are determined. The above-mentioned deviation is corrected by changing at least one of the following.

[Operation J According to the present invention, the radome is located at a position within a range where the frequency characteristics of the microwave antenna change when at least one of the thickness of the radome and the dielectric constant of the material is changed. The microwave antenna is installed close to the radiation conductor, and the frequency characteristics of the microwave antenna are measured. If the measured frequency characteristics deviate from the desired frequency characteristics, the thickness of the radome and the dielectric constant of the material are determined. The frequency characteristics of the microwave antenna can be adjusted by correcting the deviation by changing one of the two.

Therefore, even if the thickness of the dielectric substrate, its dielectric constant, or the diameter of the radiation conductor changes due to manufacturing variations, for example, the dielectric substrate or the radiation conductor can be changed without processing the dielectric substrate or the radiation conductor. The frequency characteristics of the microwave antenna can be adjusted, and a microwave antenna having a desired resonant frequency can be obtained.

[Example] Hereinafter, an example according to the present invention will be described with reference to the drawings.

First Embodiment FIG. 1(A) is a partially cutaway view of a linearly polarized microstrip antenna with a radome, which is the first embodiment of the present invention, and FIG. It is a longitudinal cross-sectional view about the AA' line of (A).

In Fig. 1 (A) and (B), Fig. 3 (A) and (
Components that are the same as those in B) are given the same reference numerals.

In Figure 1 (A) and (B), the ground conductor 1 is placed on the bottom surface.
A diameter DC shorter than the diameter Dd of the dielectric substrate 10 is placed at the center of the upper surface of the disk-shaped dielectric substrate lO on which the dielectric substrate 10 is formed.
A circular radiation conductor 12 is formed. In addition, in order to protect the antenna, the upper surface of the dielectric substrate IO on which the radiation conductor I2 and the radiation conductor 12 are formed is a cylindrical bottom surface parallel to the surface of the radiation conductor 12 on the radiation surface of the microstrip antenna. It is covered with a cylindrical radome 13a having 13as. Here, the radome 13a has a thickness dr equal to or less than 1/4 of the wavelength λ of the microwave signal transmitted and received by this antenna, and its cylindrical inner surface 13ai is bonded to the circumferential side surface of the disc of the dielectric substrate IO. It is fixed and mounted close to the radiation conductor 12 such that the distance g between the cylindrical bottom surface 13as and the radiation conductor 12 is 1/2 or less of the wavelength λ of the microwave signal.

Furthermore, a position 1 deviated in the radial direction from the center O of the radiation conductor 12
Coaxial cable 20 for feeding power to the radiation conductor 12 in the tPj
The center conductor 21 of the coaxial cable 20 is connected to the ground conductor 11 directly below the position P.
is connected.

When a microwave signal is input to the linearly polarized microstrip antenna configured as described above via the coaxial cable 20, a linearly polarized electromagnetic wave corresponding to the microwave signal is generated perpendicular to the surface of the radiation conductor 12. is radiated through the surface 13as of the radome 13a in the direction.

The inventor has determined that the dielectric constant εr is 2.6 and the thickness dr is 1.
．． omm glass-filled Teflon resin substrate, relative dielectric constant (r
is 4.5 and the thickness dr is 1.0 mm and 1.6 mm, and Alron Co., Ltd. (A
Each radome 13a is formed using an Ibushiramucin (trade name) substrate made by LRON), and each radome 13a is used to form a linearly polarized microstrip with each radome having the configuration shown in FIGS. 1(A) and (B). An antenna and a linearly polarized microstrip antenna without a radome were formed, and the input end reflection coefficient S11 and absolute gain Ga of each microstrip antenna were measured. Here, the dielectric substrate 10 is an alumina substrate having a relative dielectric constant tr of 9.6, a diameter Dd of 98 mm, and a thickness of 7.0 mm, and the radiation conductor 12 is made of silver palladium. has a diameter DC of 32 mm and is further provided with a ground conductor
is made of silver palladium similar to the radiation conductor 12.

Further, the distance g between the bottom surface 13as of the radome 13a and the radiation conductor 12 was set to 1 mm.

FIG. 4 is a graph showing the frequency characteristics of the input end reflection coefficient Sll [dB] at the feed point P when the relative dielectric constant εr of the radome 13a of this linearly polarized microstrip antenna is changed, and FIG. , is a graph showing the frequency characteristics of the input end reflection coefficient Sll [dB] at the feeding point P when the thickness dr of the radome 13a is changed.

As shown in FIG. 4, it can be seen that as the dielectric constant εr of the radome 13a increases, the resonant frequency of the microstrip antenna decreases. This is considered to be because by increasing the dielectric constant εr of the radome 13a, the dielectric constant of the dielectric substrate 10 when viewed from the entire microstrip antenna is equivalently increased.

As shown in FIG. 5, it can be seen that as the thickness dr of the radome 13a increases, the resonant frequency of the microstrip antenna becomes lower.

This is considered to be because by increasing the thickness dr of the radome 13a, the relative dielectric constant of the dielectric substrate 10 when viewed from the entire microstrip antenna is increased isometrically.

FIG. 6 is a graph showing the characteristics of the absolute gain Ga [dBil] of the linearly polarized microstrip antenna when the thickness dr of the radome 13a of the linearly polarized microstrip antenna is changed. It is a graph showing the characteristic of the absolute gain Ga [dBil of the strip antenna when the dielectric constant εr of the radome 13a of the strip antenna is changed.

As shown in FIGS. 6 and 7, it can be seen that even when the thickness dr and relative dielectric constant εr of the radome 13a are changed, the absolute gain of the microstrip antenna hardly changes.

As explained above, the radome 13a is placed close to the radiation conductor 12 at a position within a range where the resonant frequency of the microstrip antenna changes when the thickness of the radome 13a and the dielectric constant of the material are changed. By changing the material constituting the radome 13a and changing the relative dielectric constant εr, or by changing the thickness dr of the radome 13a, the microstrip can be improved without substantially changing the absolute gain Ga. The resonant frequency of the antenna can be changed.

Therefore, a plurality of various radomes 13a having different thicknesses dr and dielectric constants εr are manufactured in advance, and after manufacturing a microstrip antenna consisting of a radiation conductor 12, a dielectric substrate IO, and a ground conductor 11, the microstrip One of the plurality of radomes 13a is attached to the antenna, and the resonant frequency of the microstrip antenna is measured. Here, when the measured resonance frequency deviates from the desired resonance frequency, at least one of the thickness of the radome 13a and the dielectric constant of the material of the plurality of radomes 13a is changed to correct the deviation. A radome 13a capable of correcting this is selected and installed. Thereby, a microstrip antenna having a desired resonant frequency can be obtained. That is, as stated in the section on the problem to be solved by the invention, the three parameters of the dielectric constant and thickness of the dielectric substrate 10 and the diameter of the radiation conductor 12 change due to manufacturing variations, and the Even if the resonant frequency of the microstrip antenna changes, by selecting the radome 13a, it can be done without processing the radiation conductor 12 or the dielectric substrate lO.
An advantage is that a linearly polarized microstrip antenna with a desired resonant frequency can be obtained.

In the above first embodiment, a case has been described in which the radiation conductor 13 has a circular shape, but the radiation conductor 13 is not limited to this, and may have any other shape such as a rectangle.

Second Embodiment FIG. 2(A) is a partially cutaway view of a circularly polarized microstriped knob antenna with a radome, which is a second embodiment of the present invention, and FIG. FIG. 2 is a longitudinal cross-sectional view taken along line BB' in FIG. 2(A). In FIGS. 2(A) and (B), the same parts as in FIGS. 1(A) and (B) are given the same reference numerals.

This circularly polarized microstrip antenna is shown in Figure 1 (A
The difference from the linearly polarized microstrip antenna of the first embodiment shown in ) and (B) is that notches 14a and 14b are formed in the radiation conductor 12a, and the other configuration is the same as that of the first embodiment. This is similar to the linearly polarized microstrip antenna of the first embodiment.

As shown in FIGS. 2(A) and (B), the radiation conductor 1
2a at an angle of 45° in a clockwise direction from the feeding point P, and 135° in a counterclockwise direction, with the center O of 2a as the center.
Notches 14a and 14b having a radius W perpendicular to the radial direction of the radiating conductor 12a and a length Q parallel to the radial direction are formed at each outer peripheral edge end of the radiating conductor 12H at an angle of .degree.

In the circularly polarized microstrip antenna configured as described above, the notch 14a of the radiation conductor 12a,
14b operates as a mode degeneracy separation element, and when a microwave signal is input via the coaxial cable 20, a circularly polarized electromagnetic wave corresponding to the microwave signal is transmitted to the radiation conductor 1.
The surface 13as of the radome 13a in the direction perpendicular to the surface of the radome 2a
radiated through.

The inventor has determined that the dielectric constant εr is 2.6 and the thickness dr is 1.
．． Omm glass-filled Teflon resin substrate, relative dielectric constant tr
is 4.5 and the thickness dr is 1.0 mm and 1.6 mm, and Alron Co., Ltd. (A
Each radome 13a is formed using an Ibushiramucin (trade name) substrate made by LRON), and each radome 13a is used to
A circularly polarized microstrip antenna with a radome and a circularly polarized microstrip antenna without a radome having the configurations shown in FIGS. 2(A) and (B) were formed, and the axial ratio of each microstrip antenna was measured. Ta. In addition, each material, diameter, and thickness of the dielectric substrate lO1 radiation conductor 12a and the ground conductor 11, as well as the radome 1
The distance g between the radiation conductor 3a and the radiation conductor 12a is the same as in the first embodiment.

FIG. 8 is a graph showing the frequency characteristics of the axial ratio [d, B] of this microstrip antenna when the dielectric constant εr of the radome 13a of the circularly polarized microstrip antenna is changed, and FIG. , is a graph showing the frequency characteristics of the axial ratio [dB] of the microstrip antenna when the thickness dr of the radome 13a is changed.

As shown in FIG. 8, in the case where there is no radome 13a, the frequency at which the axial ratio [dB] is closest to O and the axial ratio is the best is approximately 1562 MHz. It can be seen that as the relative dielectric constant εr of the radome 13a increases, the frequency at which the axial ratio becomes the best becomes lower. Also, as shown in Figure 9, the radome! It can be seen that as the thickness dr of 38 increases, the frequency at which the axial ratio of the microstrip antenna becomes optimal becomes lower.

As is well known, the resonant frequency of the circularly polarized microstrip antenna can be adjusted by connecting an impedance matching circuit to the feeding point of this antenna after the frequency adjustment of the above-mentioned axial ratio.

As explained above, the radome i3a is radiated to a position within a range where the frequency at which the axial ratio of the microstrip antenna is the best changes when the thickness of the radome 13a and the dielectric constant of the material are changed. Conductor 12a
The material constituting the radome 13a may be changed to change the relative dielectric constant εr, or the radome 13a may be provided close to the radome 13a.
By changing the thickness dr, it is possible to change the frequency at which the axial ratio of the microstrip antenna is the best without substantially changing the absolute gain Ga.

Therefore, a plurality of various radomes 13a having different thicknesses dr and dielectric constants εr are manufactured in advance, and after manufacturing a microstrip antenna consisting of a radiation conductor 12a, a dielectric substrate lO, and a ground conductor 11, the microstrip One of the plurality of radomes 13H is attached to the antenna, and the frequency at which the axial ratio of the microstrip antenna is the best is measured. Here, when the measured frequency deviates from the desired transmission/reception frequency, at least one of the thickness of the radome 13a and the dielectric constant of the material of the plurality of radomes 13a is changed to correct the deviation. A radome 13a that can be corrected is selected and installed. This makes it possible to obtain a circularly polarized microstrip antenna having a desired frequency with the best axial ratio.

That is, as described in the section on problems to be solved by the invention, the three parameters of the dielectric constant and thickness of the dielectric substrate 1O and the diameter of the radiation conductor 12a change due to manufacturing variations, and the Even if the frequency at which the axial ratio of the microstrip antenna is the best changes, by selecting the radome 13a, it is possible to achieve this without processing the radiation conductor 12a or the dielectric substrate IO.
There is an advantage that a circularly polarized micro-stripe antenna having a desired frequency with the best axial ratio can be obtained.

In the above second embodiment, the case where the electromagnetic field between the radiation conductor 12a and the ground conductor 11 is in the fundamental mode has been described, but the axial ratio is not limited to this, and the microstrip antenna in the higher mode also has an axial ratio. Adjustment of the optimum frequency can be made in a similar manner. Note that the radiation conductor 12
When the electromagnetic field between a and the ground conductor 11 is generally in the TMmn mode (m and n are natural numbers as is known).
, the notch is formed at the outer peripheral edge end of the radiation conductor 12a at an angle σ expressed by the following equation (1) in a clockwise direction from the feeding point P with the center O of the radiation conductor 12a as the center. be done.

σ-±45/m+ 90 N/m ['] = (
1) Here, N is an integer, one or more cutouts are formed at the above positions where N is an even number, and one or more cutouts are formed at the above positions where N is an even number, so that the total Two or more cutouts are formed.

In the above second embodiment, a case has been described in which the radiation conductor 12a has a circular shape, but the radiation conductor 12a is not limited to this, and may have any other shape such as a rectangle.

In the above second embodiment, a circularly polarized microstrip antenna having a notch in the radiation conductor has been described, but the present invention is not limited to this. It can be applied to various circularly polarized microstrip antennas such as a type circularly polarized microstrip antenna.

Other Embodiments In the first and second embodiments described above, linearly polarized wave and circularly polarized microstrip antennas are respectively described, but the invention is not limited to this. It can be widely applied to microwave antennas formed through a substrate.

In the first and second embodiments described above, if the measured frequency characteristics of the microstrip antenna deviate from the desired frequency characteristics, at least one of the thickness of the radome 13a and the dielectric constant of the material Although the above-mentioned deviation is corrected by attaching another modified radome 13a, the present invention is not limited to this, and a separate dielectric substrate may be attached to the upper surface 13as of the radome 13a by a method such as bonding. The above deviation may be corrected.

[Effects of the Invention] As detailed above, according to the present invention, in a microwave antenna in which a radiation conductor and a ground conductor are formed via a dielectric substrate, and at least the radiation conductor is covered with a radome, the above-mentioned a radome is provided close to the radiation conductor at a position within a range where the frequency characteristics of the microwave antenna change when at least one of the thickness of the radome and the dielectric constant of the material is changed; Measure the frequency characteristics of the microwave antenna, and if the measured frequency characteristics deviate from the desired frequency characteristics, correct the deviation by changing at least one of the thickness of the radome and the dielectric constant of the material. By doing so, the frequency characteristics of the microwave antenna can be adjusted.

Therefore, even if the thickness of the dielectric substrate, its dielectric constant, or the diameter of the radiation conductor changes due to manufacturing variations, for example, the dielectric substrate or the radiation conductor can be changed without processing the dielectric substrate or the radiation conductor. There is an advantage that the frequency characteristics of the microwave antenna can be adjusted and a microwave antenna having a desired resonant frequency can be obtained.

[Brief explanation of drawings]

FIG. 1(A) is a partially cutaway plan view of a linearly polarized microstrip antenna with a radome, which is the first embodiment of the present invention, and FIG. 1(B) is a line AA' in FIG. 1(A). 2(A) is a partially cutaway plan view of a circularly polarized microstrip antenna with a radome, which is a second embodiment of the present invention, and FIG. 2(B) is a longitudinal sectional view along the line. 3(A) is a partially cutaway plan view of a conventional linearly polarized microstrip antenna with a radome, and FIG. 3(B) is a longitudinal sectional view taken along line BB' of ) is a vertical cross-sectional view taken along the c-c' line of the linearly polarized microstrip antenna of the first embodiment, and FIG. A graph showing the frequency characteristics of the reflection coefficient Sll, FIG. 5 shows the input end reflection coefficient S at the feed point of the linearly polarized microstrip antenna of the first embodiment when the thickness of the radome is changed.
FIG. 6 is a graph showing the characteristics of the absolute gain Ga of the linearly polarized microstrip antenna of the first embodiment when the radome thickness of the microstrip antenna is changed; The figure is a graph showing the characteristics of the absolute gain Ga of the linearly polarized microstrip antenna of the first embodiment when the dielectric constant of the radome is changed. A graph showing the frequency characteristics of the axial ratio of a polarized microstrip antenna when the dielectric constant of the radome of the polarized microstrip antenna is changed. Figure 9 shows the thickness of the radome of the circularly polarized microstrip antenna of the second embodiment. 3 is a graph showing the frequency characteristics of the axial ratio of the microstrip antenna when the height is changed. 1O...Dielectric substrate, 11...Grounding conductor, 12.128...Radiation conductor, J3a...Radome, dr...Thickness of radome.

Claims (1)

[Claims] (1) A frequency adjustment method for a microwave antenna in which a radiation conductor and a ground conductor are formed via a dielectric substrate, and at least the radiation conductor is covered with a radome, the radome being and the dielectric constant of the material, and the frequency characteristics of the microwave antenna are measured at a position close to the radiation conductor within a range where the frequency characteristics of the microwave antenna change when at least one of the dielectric constant of the material is changed. If the measured frequency characteristics deviate from the desired frequency characteristics, at least one of the thickness of the radome and the dielectric constant of the material is changed to correct the deviation. How to adjust the frequency of a microwave antenna.