JPS6157725B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to microstrip antennas, and more particularly to a new type of gain-enhancing microstrip line antenna with a dielectric radome.

Conventional microstripline antennas (hereinafter referred to as MSL antennas) are shown in Figures 1 to 4.
There are various types as shown in each figure. In Figure 1, a ground conductor 2 is uniformly formed on the back surface of a dielectric substrate 1, and a meandering strip conductor 3 is formed on the front surface, consisting of alternating portions parallel to the Z-axis and portions parallel to the Y-axis. It forms a traveling wave antenna, and by appropriately combining the lengths of the part parallel to the Z axis and the part parallel to the Y axis, linearly polarized waves parallel to the Z axis and linearly polarized waves parallel to the Y axis are generated. A traveling wave antenna can be formed that radiates linearly polarized waves or circularly polarized waves. Figure 2 shows a traveling wave antenna that radiates linearly polarized waves parallel to the Y-axis, which consists of a ground conductor 2 uniformly formed on the back surface of a dielectric substrate 1 and a strip conductor 4 bent in a zigzag pattern on the front surface. was formed. Figure 3 shows a ground conductor 2 on the back side of a dielectric substrate 1.
This is a traveling wave antenna that radiates linearly polarized waves parallel to the Z axis, which is formed by uniformly forming a strip conductor 5 on its surface and bent into the shape of a Franklin antenna, which is a type of folded antenna. In FIG. 4, a ground conductor 2 is uniformly formed on the back surface of a dielectric substrate 1, and a straight line, a square loop, a straight line,
It forms a traveling wave antenna that radiates circularly polarized waves, consisting of a strip conductor 6 that is periodically bent as a square loop.

Generally, the operating gain of this type of MSL antenna is
Although the width of the strip conductor, its geometrical shape such as its bent shape, and its radiated polarization type may vary, it is determined by the number of radiating elements, that is, approximately the length in the longitudinal direction of the substrate. However, since there is a limit to its length, the operating gain is uniquely determined when the total length of the antenna is given.

On the other hand, one method of increasing the gain of an antenna is a short backfire antenna (hereinafter referred to as
(abbreviated as SBF antenna). Now, if λ _p is the wavelength corresponding to the frequency used, this SBF antenna has a large circular reflector 8 at a position of λo/4 behind the dipole antenna 7, and a small circular reflector 9 at a position of λo/4 in front of the dipole antenna 7. The electromagnetic waves radiated from the dipole antenna 7 are reflected by both reflectors 8 and 9.
This method sharpens the radiation beam and increases the gain by causing multiple reflections between the two. In this case, the electromagnetic wave is diffracted from the end of the small reflector 9 and radiated in a direction perpendicular to the small reflector 9. Therefore, if the diameter of the small reflector 9 is increased, the reflection coefficient of this portion increases, but the blocking effect also increases, so there is a limit to its size.

Generally, when an antenna is installed outdoors,
A dielectric radome is a device that blocks rain, snow, wind, etc., but allows electromagnetic waves to pass through. In this case, various methods have been used to reduce the reflection of electromagnetic waves from the radome as much as possible and to prevent the directivity characteristics of the antenna from being impaired. For example, as shown in FIG. 6a, the thickness t of the dielectric flat plate 10 is reduced to reduce reflection, or the thickness of the dielectric flat plate 10 shown in FIG. 6c is increased by an integral multiple of λ/2 (for example, is 1x)
The influence of the dielectric flat plate is minimized by selecting the However, λ〓 is the wavelength of the plane wave in the dielectric medium, and λ〓
=λo/√ _r , where ε _r is the relative dielectric constant. On the other hand, when the thickness t of the dielectric flat plate 10 shown in FIG. 6b is an odd multiple of λ/4 (in the example, 1 times), the influence is strongest, and the incident electromagnetic wave is reflected at its maximum, making it difficult to use it in a radome. is nonconforming.
Note that the arrows in FIG. 6 indicate the incident wave p, the transmitted wave q, and the reflected wave r, and the magnitude of the reflection and transmission is illustrated by the length of the arrow.

This invention skillfully combines the properties of the three methods mentioned above, namely, the MSL antenna, the SBF antenna, and the dielectric radome, and in particular applies the properties of the dielectric radome in reverse, resulting in a completely new increase in gain.
The purpose is to provide MSL antennas.

That is, the present invention radiates linearly polarized waves or circularly polarized waves, which are formed by having one or more periodically bent strip conductors on the surface of a dielectric material provided with a flat ground conductor on at least the back surface. In a microstripline antenna formed to absorb energy, a dielectric plate is provided on the surface side of the dielectric in parallel with the planar ground conductor with a certain space between the dielectric and the dielectric. The thickness of the plate is selected to be approximately an odd number multiple (odd numbers include 1) of 1/4 of the wavelength λ in the dielectric plate, and the distance between the back surface of the dielectric plate and the above-mentioned planar ground conductor is approximately selected. This is a microstripline antenna whose essential feature is that it is set to one half of the free space wavelength λo.

Preferably, the thickness of the dielectric plate is approximately 4 of λ
It will be reduced to 1/1.

More preferably, the material of the dielectric plate has a large dielectric constant.

More preferably, the dielectric is a dielectric of a printed circuit board that overlaps the planar ground conductor in approximately the same area.

Hereinafter, the present invention will be explained in detail with reference to embodiments of the drawings.

FIG. 7 is an external perspective view of a microstripline antenna as an embodiment of the present invention, and FIG. 8 is a plan view a, a front view b, and a side view c.
are shown respectively.

In FIGS. 7 and 8, reference numeral 11 denotes a substrate made of a flat dielectric material of an appropriate thickness, and a flat ground conductor 12 (thin film with a thickness of approximately 35 μm) is provided over the entire back surface of the substrate.
m) is provided. A reinforcing metal plate 13 is made of a material such as iron, aluminum, or brass, and is bonded to the ground conductor 12. 14 is the substrate 11
A strip conductor made of copper, for example, is formed on the surface of the printed circuit board by selective etching _.
It consists of A ₁₃ and Y-direction sides B ₁ to _{B 12} , and is formed by sequentially and alternately combining the Z-direction sides and the Y-direction sides and bending them into a crank shape or meandering shape, and the length of each side is approximately λ. _g /2. However, λ _g is the line wavelength corresponding to the frequency used. A dielectric flat plate 1 with a thickness T at a height H above the planar ground conductor 12 and parallel to the surface of the planar ground conductor 12.
5 is covered with metal side plates 16, 16.
It is designed to be supported from both sides.

In the MSL antenna according to this embodiment, a traveling wave or the like propagates through the strip conductor 14, and when this wave travels, the strip conductor 14
17 in Figure 9 to prevent reflected waves from occurring at the bending part.
As clearly shown in , the corner ends have been removed in the form of a right isosceles triangle.

An example of the dimensions of each part of the antenna shown in FIGS. 7 and 8 will be shown below with reference to the reference numerals specified in FIG. 9. However, the length of each direction side is the length along the center line.

(a) Substrate material: Rexolite 1422 (product name: Oak Inc., USA) Relative dielectric constant: εr=2.53 (b) Substrate thickness: 0.79mm (c) Substrate width: 90mm (d) Substrate length: 160mm (e) Width of strip conductor 12 W ₁ : 2 mm (F) Length of side A in Z direction L ₁ : 11.8 mm (G) Length of side B in Y direction L ₂ : 11.8 mm (H) Angle α of each corner: 90゜Here, we will briefly touch on how to make the board part of such a prototype MSL antenna. The meandering strip conductor 14 is formed by appropriately selectively etching one side of a thin plate-shaped conductive material, for example, a copper plate, which is stretched on both sides of the dielectric plate 11 with low dielectric loss. This can be obtained by leaving only the part of . The metal conductor plate with a wide and uniform back surface that has not been etched can be used as it is as the ground conductor 12 of the antenna. Therefore, the main polarized wave component of the MSL antenna manufactured by the above manufacturing method shows an almost circular single-sided radiation pattern toward the front surface of the substrate 11 where the strip conductor 14 is stretched, and almost no radiation pattern toward the back surface where the ground conductor 12 is stretched. No radiation of electromagnetic waves takes place, and conditions are favorable for the formation of a radiation beam.

In the antenna constructed as described above, a coaxial connector is attached to the left end S of the strip conductor 14 to serve as a feeding point. On the other hand, the right end Q of the strip conductor 14 is an open end so that waves traveling from the feed point S are totally reflected, thereby operating as a standing wave antenna. At this time, the length of each side A and B is approximately λ
Since _g /2 is selected, the side A in the Z direction operates as a radiator, and the side B in the Y direction operates as a transmission line. Therefore, FIG. 8 shows a case where the number of radiators is 13.

Next, the antenna described above has increased gain.
The operating principle of the MSL antenna will be explained using FIG. The antenna in Figure 8 is now on side A in the Z direction.
Since this is an array antenna with 13 radiators, a case will be described below in which a dielectric flat plate 15 is disposed above the radiators on one Z-direction side A at an arbitrary position.

A part of the plane wave vertically incident on the dielectric flat plate 15 having a thickness of T=λ/4 is transmitted as shown in FIG. 6b, and the rest is reflected. At this time, dielectric flat plate 1
The reflection coefficient ρ of 5 is given by ρ=1−εr/1+εr (1), regardless of the polarization plane of the plane wave. The above formula (1) is a dielectric flat plate 15 with thickness T.
10a, the dielectric flat plate 15 in FIG. 10a is equivalently shown in FIG. 10b with an infinitesimal thickness and a reflection coefficient of ρ.
The reflective film 18 is virtually replaced with the reflective film 18 . On the other hand, since the strip conductor 14 has the ground conductor 12, an image conductor 19 is formed corresponding to the strip conductor as shown in FIG. 10a. Therefore, the composite radiation conductor A0 of the strip conductor 14 and the image conductor ₁₉ is equivalently placed at the origin O in FIG. 10b. This equivalent radiating conductor
Although A ₀ is a directional wave source (direction X), it will be handled below assuming that it is an omnidirectional wave source (emitting in all directions X, Y, and Z). Now, assuming that the ground conductor 12 and the equivalent reflective film 18 are infinitely large, part of the electromagnetic waves radiated from the equivalent radiation conductor A ₀ will pass through the equivalent reflective film 18, and the rest will be reflected and further transmitted to the ground conductor. 1
2, part of the light passes through the equivalent reflection film 18, and the remaining part is reflected. By repeating this process, the electromagnetic waves pass through the equivalent reflective film 18 one after another.
The electromagnetic waves that are multiply reflected between the ground conductor 12 and the equivalent reflective film 18 are gradually attenuated. At this time, the closer the value of the reflection coefficient ρ of the equivalent reflective film 18 is to 1| (where 1 means opposite phase), the greater the number of multiple reflections. This multiple reflection looks like the equivalent radiation conductor A ₀ and the image conductor A ₁ , A ₂ , A ₃ , ......An...
... and A' ₁ , A' ₂ , A' ₃ , . . . A'n . . . as an infinite sequence in FIG. Now, since the radiation is performed only on the upper half of the ground conductor 12, the image conductor arrays A' ₁ , A' ₂ , A' _{3 .} . . A'n, . . . are ignored in the following explanation. Good fit. Therefore,
Equivalent radiation conductor A ₀ and its image conductor array A ₁ , A ₂ ,
It is a good idea to consider A ₃ , ……An, ……. This is regarded as a one-dimensional radiating element array having a tapered amplitude distribution determined by the reflection coefficient ρ of the equivalent reflective film 18 at equal intervals of 2H and sequentially attenuating. Now, if the amplitude of the equivalent radiation conductor A ₀ is I ₀ , then the amplitude In of each image conductor An is ρ ⁿ Io. Earth conductor 12
If the distance H between the equivalent reflective films 18 is chosen to be λ ₀ /2, then
The distance between each element is 2H=λ ₀ , and therefore the directivity D of this one-dimensional radiating element array is simply expressed by the following equation.

However, |ρ|<1. Now, since ρ ^N →0 for a large value of N, equation (2) becomes D=1+|ρ|/1−|ρ| (3). This means that the larger the reflection coefficient ρ, the more directivity D
shows that it is large. For now, the above formula is
By substituting the relationship in (1), we finally derive the formula (4), D=εr...(4), and we can read a new meaning into this formula. In other words, what the result of equation (4) means is that electromagnetic waves are multiple reflected between the ground conductor 12 and the dielectric flat plate 15, but in this case, the antenna directionality increases as a dielectric material with a larger relative permittivity εr is used. This shows that the property D increases, that is, the gain increases. The above calculation results were obtained by treating the equivalent radiation conductor A ₀ as an omnidirectional wave source, but in reality A ₀ is a directional wave source in the X direction, so the gain is even higher only in the X direction. The relationship proportional to the dielectric constant εr is exactly the same.

Next, we will discuss how to increase the gain of the embodiment shown in Fig. 8, which was prototyped based on the above-mentioned theoretical background.
The experimental results of the MSL antenna are shown below. This is the case when the Z direction side A, that is, the number of radiators is 13. Two types of dielectric flat plates 15 were used: a commercially available acrylic plate (εr=2.64) and a glass plate (εr=4.30). 11 shows the relationship between the height H and the operating gain G, with the thickness T of the dielectric flat plate 15 being constant. FIG. 12 shows the relationship between the thickness T and the operating gain G, with the height H being constant. In FIGS. 11 and 12, curves U1 and U2 are acrylic plates, curve V1,
V2 indicates the actual value of the glass plate, and the height H is approximately λ
0/2, and the thickness T is about λ/4, the operating gain G shows its maximum value. Next, the XY plane electric field directivity characteristic curve near the maximum value of the operating gain G is
Shown in the figure. FIG. 13a shows the dielectric flat plate 15
In this case, the gain G = 14.5 dBi (i indicates the ratio with the omnidirectional antenna) and the beam width Δθ = 65.5° are observed. (εr=2.64), when the thickness T=5 mm and the height H=16 mm, a gain G=17.4 dBi and a beam width Δθ=32.4° are observed. When a glass plate (εr=4.3) is used, and the thickness T=4 mm and the height H=16 mm, the gain G=
19.4dBi and beam width Δθ=26.3° were observed.
Note that all experimental results were conducted at a frequency f = 9.3 GHz.

From the above experimental results, to qualitatively describe the advantages of this embodiment, the beam width Δθ is narrower by simply providing the dielectric flat plate 15 above the substrate 11 compared to the case where the dielectric flat plate 15 is not covered. Therefore, the operating gain G increases. Furthermore, the larger the value of the relative permittivity εr, the higher the operating gain G. That is, the separation distance H between the planar ground conductor 12 and the back surface of the dielectric flat plate 15 is 0.4 to 0.4 with respect to the free space wavelength λ _p .
0.6λ _p or approximately λ _p /2 and dielectric flat plate 1
The optimum value is achieved when the thickness T of the dielectric plate 15 is 0.15 to 0.3λε, that is, approximately λε/4, with respect to the wavelength λε in the medium of the dielectric flat plate 15. This shows a maximum reflection coefficient when the thickness T of the dielectric flat plate 15 is λε/4, and when the separation distance H is λ _p /2, a kind of translucent aperture resonance occurs between the flat ground conductor 12 and the dielectric flat plate 15. It can be considered that the oscillator is configured to be in a resonant state, resulting in an increase in gain. Therefore, if the material of the dielectric flat plate 15 that functions as a radome has a high relative permittivity, the reflection coefficient will increase accordingly, and a higher gain can be expected. Also,
It has been stated that the optimum thickness T of the dielectric flat plate 15 is approximately 1/4 of the wavelength λε in this dielectric medium, but as is clear from FIG. 12, generally an odd number of λε/4 is used. You may choose to double (including 1x).

Note that the metal plates 16, 16 supporting the dielectric flat plate 15 shown in FIG. 8 may be made of a dielectric (insulator) other than metal, although they have a slight influence on the directivity characteristics, and may be made of a dielectric (insulator) instead of metal. This metal plate 16,1 provided
6 (same as the width of the substrate 11) is preferably selected to be 1.5λ _p or more. This is because the rate of gain increase is low below 1.5λo. In general, it may be infinitely wide, but since the rate of increase in gain slows down (saturates) at about 4λo (according to experiments), it is practically preferable to select it within the range of 1.5λo to 4λo. Thereby, an appropriate size of the dielectric flat plate 15 can be defined. Furthermore, in the above embodiment, the radiator of the MSL antenna was formed using a selective etching technique of the printed circuit board, but this was done for the reason that the manufacturing technique was simple, and the lower part of the strip conductor 14 was The dielectric substrate 11 does not have to be uniformly flat, and even more extreme, even if it does not exist, it will not affect the operating characteristics and the strip conductor 14 may simply be floating in the air. This has also been confirmed through experiments. In other words, the dielectric substrate 11 functions as a support for the strip conductor 14 and is not a main component of the present invention. However, it can be said to be more preferable because it can be easily manufactured by selectively etching the printed circuit board and the back surface can be used as the planar ground conductor 12. In addition, in the above-mentioned example, the thickness of the dielectric substrate 11 was set to 0.1λo or less.

The MSL antenna according to the present invention provides an increase in gain regardless of the polarization direction when the main beam direction is directly in front (X-axis direction). Therefore, in addition to the embodiment of linearly polarized waves parallel to the Z axis shown in FIG. 7, the present invention can also be applied to linearly polarized MSL antennas and circularly polarized MSL antennas parallel to the Y axis.

By the way, the strip conductor 4 in Fig. 2 has a zigzag shape and is oriented parallel to the Y axis for a linearly polarized MSL antenna, and the strip conductor 6 in Fig. 4 has a straight line, a square loop, a straight line, a square loop, etc. Observation results obtained by conducting experiments with the circularly polarized MSL antennas in which the height of the dielectric plate 15 was selected to be H=λo/2 confirmed that the gain G increased in all cases. That is, according to the present invention
MSL antennas operate regardless of polarization.

Furthermore, the MSL antenna bodies 20 formed as shown in FIG. 7 may be arranged symmetrically as shown in FIG. 14, and used as a pair to feed power from the center. In addition, it is possible to increase the gain by disposing a dielectric flat plate 15 on the top of a planar array antenna provided with a plurality of arbitrary antenna rows, and this is shown in FIG. 15.

Next, since there has recently been a particular demand for higher gain in circularly polarized MSL antennas, we will further demonstrate how useful the present invention is by presenting other embodiments to which the present invention is applied and examining experimental data. make an argument.

In FIG. 16, a dielectric flat plate 15 is provided above an MSL antenna 30 in which the U-shaped portion of a single strip conductor 30' operates as a circularly polarized wave radiator. The dimensions (mm) are as shown in Figure 16, and U
The parallel arm sides of the U-shaped part are 7 mm, the base is 12 mm, and the straight piece connecting the U-shaped part is 20 mm,
The number of radiators is 6, and the frequency used is f=9.3GHz. The conditions are H for acrylic board (εr=2.64)
= 16, T = 5 (mm), and for a glass plate (εr = 4.3), H = 16, T = 4 (mm). As a result, excellent characteristics as shown in FIG. 17 were obtained. That is, FIG. 17a shows the case where there is no dielectric flat plate 15.
b is the XY plane electric field directivity characteristics (θ=
90°) curve. The gain G is for a
8.0dBi, 11.6dBi for b, 14.7dBi for c
It was hot. Furthermore, the axial ratio AR is 1.14 for a and b for
1.22, c is also 1.22, and there is almost no deterioration in the axial ratio. From this experimental result, the XY plane electric field directivity characteristics show that the higher the dielectric constant, the sharper the beam width, and at the same time, the gain is 3.6 dB for b, and 3.6 dB for c.
This shows an increase of 6.7dB.

In Figure 18, the circularly polarized MSL antenna in Figure 17 is coupled in two parallel lines as shown, and the radiator is 3λ _g /4 (details on how to choose dimensions are shown in Figure 19). The figure shows the shape shifted in the longitudinal direction. Note that λ _g is the line wavelength of the traveling wave, and the reason why it is shifted by 3λ _g /4 is to cancel out the grating globe that would occur in the longitudinal direction of the antenna in the case of a single strip conductor. Furthermore, in order to operate such a circularly polarized MSL antenna body, it is common to connect a matching load R as shown in FIG. 20 to realize circularly polarized radiation based on a traveling wave. The antenna in FIG. 20 emits right-handed circularly polarized waves, and the antenna in FIG. 21 emits left-handed circularly polarized waves. Figures 22 to 24 are respectively
Various configuration patterns of the MSL antenna body are shown, with FIG. 22 showing an example of a linear array antenna, FIG. 23 showing an example of a planar array antenna, and FIG. 24 showing an example of a planar multiple array antenna.

In the above description, all antennas have been described as transmitting antennas, but it is obvious that they can also be configured as receiving antennas.

As described in detail above, according to the present invention, the structure is as simple as adding a dielectric flat plate of an appropriate thickness above the main body of the MSL antenna, which can be constructed in a planar shape.
Moreover, the dielectric flat plate functions as both a gain increaser and a radome, and operates independently of the plane of polarization.Furthermore, the overall thickness is just under one wavelength, making it possible to create a small, lightweight, and high-gain planar antenna. It has many advantages such as being configurable.

[Brief explanation of the drawing]

1 to 4 are diagrams each showing an example of the configuration of a conventional microstripline antenna, FIG. 5 is an explanatory diagram showing an example of the configuration of a short backfire antenna, and FIG. It is an explanatory view of a body radome. FIG. 7 is a perspective view of a microstripline antenna with increased gain according to an embodiment of the present invention, and FIG. 8 is a projection view thereof, in which a is a plan view, b is a front view, and c is a side view. FIG. 9 is a plan view for explaining the detailed dimensions of the strip conductor in the embodiment shown in FIGS. 7 and 8, and FIG. 10 shows the operating principle of gain increase in the embodiment shown in FIGS. Figures 11 and 12 are diagrams for explanation, respectively, showing gain characteristic curves actually measured using the antenna of the example, and Figure 13 is a diagram showing the electric field directionality in the XY plane actually measured using the antenna of the example. It is a characteristic curve, and a is when the dielectric flat plate 15 is not covered.
b is the case where the acrylic plate is covered, and c is the case where the glass plate is covered. 14 and 15 are projection views of MSL antennas having various configurations of strip conductors, respectively, as other embodiments of the present invention.
FIG. 16 shows still another embodiment of this invention,
This is a schematic perspective view of a crank-shaped MSL antenna in which the U-shaped part of the strip conductor operates as a circularly polarized wave radiator, and FIG. When the body plate is not covered, b is the case when the acrylic plate is used, and c is the case when the glass plate is used. Figure 18 shows an example of the configuration of an MSL antenna that exhibits even better characteristics than the circularly polarized MSL antenna shown in Figure 17. Figure 19 is an explanatory diagram showing how to select the dimensions of the strip conductor, and Figure 20 is a practical example. It is a schematic plan view in the case of operating. 21st
24 through 24 are diagrams showing patterns of strip conductors when a planar array antenna is constructed by combining a plurality of antennas shown in FIG. 18, respectively. 11... Dielectric substrate, 12... Planar ground conductor,
14... Strip conductor, 15... Dielectric flat plate.

Claims (1)

[Scope of Claims] 1. A dielectric material having a flat ground conductor on its back surface and periodically bent strip conductors formed to radiate linearly polarized waves or circularly polarized waves. In the microstrip line antenna, a dielectric plate is provided on the surface side of the dielectric body in parallel with the planar ground conductor with a certain space between the dielectric body and the thickness of the dielectric plate is approximately λ. 〓/4 (However,
λε is an odd multiple (1, 3,
5...... times), and the separation distance between the back surface of the dielectric plate and the above ground conductor to be approximately λo/2 (however, λo
is a free space wavelength). 2. The microstripline antenna according to claim 1, wherein the dielectric plate has a thickness of approximately λ/4. 3. The microstripline antenna according to claim 1 or 2, wherein the relative permittivity of the dielectric plate is selected to be large. 4. The microstripline antenna according to any one of claims 1 to 3, wherein the dielectric is a dielectric of a printed circuit board that overlaps the planar ground conductor in approximately the same area.