JPS5810004B2 - disc antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circular plate antenna in which a conductive circular plate and a conductive ground plate are arranged substantially parallel to each other and omnidirectional radio waves are radiated from the gap therebetween.

Recently, the development of underground shopping malls has been remarkable, but the wireless communication systems necessary for firefighting and police activities in such limited areas are two methods: laying leaky cables inside the underground shopping malls, and installing cables at regular intervals inside the underground shopping malls. One method is to install an antenna in the basement and connect the antenna to an underground terminal using a cable.

The following conditions are usually required for antennas used in underground malls or similar locations that fall under the latter category.

Firstly, the frequency of communication radio equipment currently in use is 15.
Although it is concentrated in the 0MHz band, there is a possibility of shifting to the 400MHz band in the future, so the 150MHz band and 400M
A dual frequency band antenna in the Hz band is required.

Second, the ceilings of underground shopping malls are often slightly higher than a person's height, and when installing an antenna on the ceiling, it is necessary to minimize the height of the antenna as much as possible. For example, it is desirable to use a disc-shaped antenna with a thickness as thin as possible and non-directionality in the horizontal plane.

The present invention meets the above-mentioned requirements, and its purpose is to provide a circular plate antenna that has a pattern suitable for installation in underground malls and the like and that can effectively switch between two frequency bands.

In order to achieve the above object, the disc antenna of the present invention has a pair of conductor discs and a conductor ground plane arranged approximately parallel to each other at appropriate intervals, and a point on the circumference of the conductor disc and the opposite point on the conductor ground plane. A signal of a predetermined frequency is supplied between the points, and a point on the conductor disc different from the power supply point and the opposite point on the conductor ground plate are short-circuited and grounded to connect the conductor disc and the conductor ground plate. It is characterized by radiating non-directional radio waves from a gap sandwiched between the two and separated by the ground plate, and further includes a second frequency radio wave on the conductor disc with the conductor disc serving as a conductor ground plate. Conductor disks corresponding to the first and second frequencies are arranged approximately parallel to each other at appropriate intervals, and a ground plate and a feeding point are placed between the conductor disks corresponding to the first and second frequencies. A coaxial feed line that is provided in the same manner as the ground plate and feed point and that feeds the conductor disk corresponding to the second frequency is aligned with the ground plate of the conductor disk that corresponds to the first frequency to correspond to the first frequency. It is characterized by being led onto a conductive ground plane.

The present invention will be described in detail below with reference to examples.

FIG. 1 and FIG. 2 are diagrams explaining the principle of the present invention.

As shown in FIG. 1, consider an antenna in which a conductor disk 1 is arranged substantially parallel to a conductor ground plane having an infinite width.

A signal supplied by the signal source 4 between the conductor disk and the grounded conductor ground plane at a point 2 on the circumference of the conductor disk 1 propagates through the space between the conductor disk and the conductor ground plane, and A constant standing wave electric field distribution is generated around the .

Now, if we ground a point 3 on a suitable conductor disk, which is different from the feeding point 2 on the conductor disk 1, with a grounding plate 5, the electric field distribution around the conductor disk 1 and in the gap between the conductor ground plate will be as shown in Figure 2. As shown by the dotted line, there is an almost sinusoidal settlement distribution with zero at the grounding point.

In this case, if the circumference length is chosen to be one wavelength or less, no electric field reversal will occur in the distribution of this settled wave type field, so the phase will be the same at any position on the circumference, and the radiation directivity due to these electric field distributions will be similar to that of the conductor ground. There is no null point where the radiated electric field becomes zero in a plane parallel to .

In particular, if the circumferential length of the circular antenna 1 is selected to be about 1/2 wavelength, not only will the radiation directivity become almost non-directional, but the antenna will resonate and the radiation efficiency will improve.

FIG. 3 shows an embodiment of the disc antenna of the present invention.

The figure shows a center frequency of 150 MHz and a disk diameter of 32 MHz.
0mm, main plate diameter 500mm, distance between disk and main plate 1
50 mm, and the feeding point A is provided at a position facing the grounding plate B.

Further, FIG. 4 shows an example of actually measured frequency characteristics of impedance at the feeding point of the antenna shown in FIG.

When the distance between the disk and the ground plate is increased or decreased from 100 mm, the impedance changes accordingly, as shown by the dotted line and the dashed-dotted line in the figure.

For example, if the characteristic impedance of the feed line is 50Ω, impedance matching can be achieved at 150 MHz by setting the interval to 150 mm.

FIG. 5 shows an example of actually measured radiation directivity in the horizontal plane of a circular plate antenna with a 1/2 wavelength circumference at 150 MHz, and a radiation electric field distribution without a null point 1 was obtained.

By the way, it is not necessarily appropriate for an antenna to be installed on the ceiling in an underground installation, for example, for the distance between the circular plate and the ground plate, that is, the thickness of the antenna to be as much as 150 mm.

Therefore, if the distance between the disk and the ground plate is selected to be, for example, about 70 mm, as is clear from the measurement example in Figure 4, at frequencies where the circumferential length of the conductor disk is approximately 1/2 wavelength, the It can be seen that this is the feed point impedance.

In order to efficiently operate an antenna with such thickness by connecting a commonly used coaxial feed line with a characteristic impedance of 50Ω, it is necessary to connect a transmission line with an appropriate characteristic impedance and electrical phase angle to the antenna. It is necessary to insert it between the cable and the coaxial feeder line to match the impedance of both.

Figure 6a. b is an explanatory diagram showing the configuration of a specific embodiment of the present invention to which this method is applied.

In FIG.
A grounding plate 15 is provided between the two pairs of points, and a power feeding plate 14 is provided at a different point on the circumference of the conductor disk 11 or at a point opposite thereto on the conductor ground plate 11.

The outer conductor of the coaxial feed line 16 is connected to the ground plate 15, and the inner conductor 13 is connected to the above-mentioned feed plate 14 through a hole 17 provided in the ground plate 15.

In the figure, the power supply plate 14 is attached to the conductor base plate 12, but it may be attached to the conductor disc 11.

In this case, impedance matching between the coaxial feed line 16 and the antenna is achieved by appropriately selecting the width a of the extended portion of the inner conductor 13 and the height h from the conductor ground plane, as shown in the A-A' cross section of the figure. It is done.

The principle of impedance matching in the above embodiment will be explained below.

FIGS. 7 and 8 show the structure of the antenna shown in FIG. 6 by dividing it into parts that perform the main electrical operations and showing them by equivalent circuits.

7 shows a case where the power supply plate 14 is attached to the conductor base plate 12, and FIG. 8 shows a case where the power supply plate 14 is attached to the conductor disc 11.

To explain the case of FIG. 7, there is a characteristic impedance between the coaxial feeder line 16 having a characteristic impedance Zo and a disc antenna having an impedance ZA, which is made up of the disc 11 and the inner conductor 13 with equal constraints. Z.

', a strip line with a length of 1 is connected in series, and the ground plane 12 and the inner conductor 13 are connected in parallel to the connection end of the coaxial feeder 16.
The characteristic impedance Z is composed of

', it can be considered that a stripline stub whose tip is short-circuited with a feeder line 14 having a length of 1 is connected.

Therefore, by selecting the width a and height h of the extension of the inner conductor 13, the impedance Z of each stripline can be determined.

', Zo'' is determined, and the strip line connected between the coaxial feed line and the antenna roughly matches the real part of the impedance, and the stub of the strip line connected in parallel to the coaxial line roughly matches the imaginary part of the impedance. It is now possible to align parts.

In the case of FIG. 8, the power supply plate 14 is attached to the disc 11, but it is composed of a strip line composed of the disc 11 and the inner conductor 13, and a main plate 12 and the inner conductor 13. It is clear from both figures that the equal constraints are the same as in the case of FIG. 7, only that the roles of the strip line and the strip line are interchanged.

Figures 9a and 9b show the construction of a concrete embodiment of the pond of the present invention.

Figure a shows the attachment portion of the coaxial feeder line 16 to the ground plate 15.

That is, a vertical elongated hole 17 is provided in the ground plate 15, and the outer conductor of the coaxial feeder line 16 is connected to the mounting base 18, and the inner conductor 13 is extended through the elongated hole 17 to connect the feeder plate 14 or 14.
’, and the mounting position of the mounting base 18 and the inner conductor 1
By adjusting the mounting position on the power supply plate 14 or 14' of No. 3, the height h shown in FIG. 6 can be varied and impedance matching can be performed.

As shown in the examples in Figures 6 and 9 above, this can be achieved by appropriately selecting the size and position of the inner conductor extension provided between the feed point of the conductor disc or conductor ground plate and the ground plate. The characteristic impedance can be arbitrarily selected, and the above-mentioned transmission line type impedance matching transformer can be constructed.

Figures 10a and 10 are 150MHz.

This figure shows the impedance measurement value of a circular antenna having a circumference of 1/2 wavelength of 400 MHz, and impedance matching can be performed using the above-mentioned inner conductor extension section in accordance with the required frequency.

In addition, according to this power feeding method, the extended portion of the inner conductor between the power feeding plate and the ground plate of the conductor disc or conductor ground plate is sufficiently shielded by the conductor disc, so it has little effect on the electromagnetic field distribution around the circumference. First, the influence on the radiation characteristics, that is, the shape change to the radiation pattern can be ignored.

In an actual circular antenna, as shown in the supplementary explanatory diagram outside the main part of FIG.
It is sufficient to use a slightly larger disk.

Further, the conductor disk 11 is supported by an insulating support rod 19 provided between it and the conductor base plate 12.

Next, a configuration in which the circular plate antenna is used for two waves will be described.

According to Figure 2, if the circumference of the disk is approximately 1/2 wavelength long, an almost sinusoidal standing wave distribution will occur, and almost omnidirectional radiation directivity will be obtained as shown in Figure 5. , and the antenna becomes resonant.

If such an antenna is used for two waves, for example, 15
When sharing between 0MHz and 400MHz, if the antenna perimeter is set to about 1/2 wavelength for 400MHz, the antenna will resonate at 400MHz, but at 150MHz.
In this case, the resonance point is significantly shifted, and the radiation efficiency decreases.

In addition, the antenna circumference is approximately 1/2 for 150MHz.
In terms of wavelength, at 150 MHz, as shown in Figure 2, there is a standing wave distribution that is almost sinusoidal and almost non-directional.
At 00MHz, the perimeter is 1 as shown in Figure 12.
It becomes a little less than 1/2 wavelength, and a standing wave distribution of 10 and - is generated on the circumference, and a null point is generated in the radiation directivity, so that no directivity is achieved.

For the above reasons, it is extremely difficult to use a circular plate antenna consisting of a pair of circular plates and a ground plate in both a negative frequency and a frequency twice or more higher than the negative frequency.

Therefore, in such a case, it is appropriate to operate each disc antenna having a circumference of about 1/2 wavelength independently at each frequency, and to combine these signals using a demultiplexer.

By the way, in order to arrange two disc antennas of different sizes so that the space factor is small, a method can be considered in which a smaller antenna is stacked on top of a larger antenna.

In this case, the coaxial feeder line of the antenna mounted on the top must be led to the ground plane of the lower antenna, where a plug for the feeder line is normally provided.

Unlike conventional type antennas, a disc antenna always has a shorting plate that shorts the disc and the ground plane at one point on the circumference, so the coaxial feed line of the upper antenna should be connected along the shorting plate of the lower antenna. By leading the power to the ground plane of the lower antenna, power can be fed to the upper antenna without affecting the performance of the lower antenna.

Therefore, by stacking disk antennas that resonate at each frequency, guiding the coaxial feed line of the upper antenna to the lower part along the shorting plate, and combining the signals of the upper and lower antennas via a splitter, It is possible to realize a dual-wave antenna that is omnidirectional at each frequency and resonates at each frequency.

FIGS. 13a and 13d are explanatory diagrams showing the configuration of a shared antenna for two frequencies of 150 MHz and 400 MHz, which is a practical example of the present invention.

As shown in the plan view of FIG. A circular antenna consisting of 251 and a conductor disk 211 arranged parallel to the circular antenna as a conductor base plate.
A grounding plate 2 that connects a conductor disk 212 having a 1/2 wavelength circumference of 0 MHz and a conductor disk 211 by short-circuiting it.
This is a stack of 52 circular antennas.

6 or 9 shows coaxial feed lines 261, 262 which are connected to the ground plates 251, 252 of these two circular antennas by entering them into a branching filter 27 via a plug 28 from the coaxial feed line and branching into two. The outer conductors are attached to the grounding plate as shown in FIG. .

Figure C shows the power supply plate attached to the conductor base plate, and Figure d shows the power supply plate attached to the conductor disc.

In addition, the feed line 262 of the 400 MHz disc antenna is 15
15 along the ground plate 251 of the 0MHz circular antenna.
By guiding the 400MHz disc antenna to a branching filter installed on the conductor ground plane of the 0MHz disc antenna and preventing the feed line 262 of the 400MHz disc antenna from affecting the characteristics of the 150MHz disc antenna, the 400MHz disc antenna 1 antenna
This makes it possible to stack and feed power on top of a 50MHz circular antenna.

The ground plates of both circular antennas are placed close to each other on the same side, and the feeder lines are installed at the shortest possible distance.

With this configuration, the radiation electric field is not affected as described above.

As explained above, one 400MHz circular antenna
Placed on top of 50MH2 disc antenna and 400MH
By using the conductive ground plate of the 150 MHz circular plate antenna in common with the conductive plate of the 150 MHz circular plate antenna, a configuration of a dual-wave antenna with a good space factor can be obtained.

Furthermore, by aligning the grounding points of the 400 MHz disc antenna and the 150 MHz disc antenna in the same direction, the coaxial feed line leading to the duplexer can be connected over the shortest distance without affecting the radiated electric field.

With this structure, there is no mutual interference between the 150 MHz signal and the 400 MHz signal, and the 150 MHz.

It has been found that directivity in the horizontal plane in which no null point occurs in all directions in the horizontal plane at 400 MHz can be obtained.

In the disc antenna of the present invention, a pair of conductor discs and a conductor ground plane are arranged approximately parallel to each other at appropriate intervals, but when implemented, a null point is created in the radiated electric field in a plane parallel to the conductor ground plane. The relationship between the two does not necessarily have to be parallel, but may be inclined.

The conductor disk can also be realized by a polygon that approximates a given disk.The mutual positional relationship between the feeding point and the grounding point of a single disk antenna must overlap, making it physically impossible. It can be realized in any state.

FIG. 13a shows the grounding plates 251, 252 and the power feeding plate 141.
142 is arranged at a symmetrical position with respect to the center of the conductor disks 211, 212.

The grounding plates 251, 252 and the feeding plates 141, 142 are arranged at asymmetrical positions with respect to the centers of the conductor disks 211, 212, as shown in FIG. Even if the transmission lines 231' and 232' are connected to each other, a null point will not occur in the radiation directivity in a plane parallel to the conductive ground plane of the circular antenna according to the present invention.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams explaining the principle of the present invention, Figure 3 is a diagram showing the configuration of an embodiment of the disc antenna of the present invention, and Figure 4 is the feeding point of the antenna shown in Figure 3. Figure 5 is a diagram showing an example of actually measured frequency characteristics of impedance in the horizontal plane, Figure 5 is a diagram showing an example of actually measured radiation directivity in the horizontal plane of a circular plate antenna with a 1/2 wavelength circumference, and Figures 6a and b include the feeding method. Figures 7 and 8 are diagrams showing the configuration of a specific embodiment of the present invention.
Figure 9 showing an electrical equivalent circuit of the antenna shown in Figure 9.
Figures a and b are diagrams showing the configuration of a specific embodiment of the pond including the power supply method, and Figures 10a and 10 are each 150M
Figure 11 is a supplementary explanatory diagram of an embodiment of the present invention. Figure 12 is a circle with an antenna perimeter of approximately 1/2 wavelength of 150 MHz. A diagram showing the standing wave distribution at 400 MHz of a plate antenna, Figure 13 a = d is a diagram showing the configuration of a dual frequency antenna of 150 MHz and 400 MHz of the pond embodiment of the present invention, and Figure 14 shows the grounding plate and power supply. It is an explanatory view showing a case where the plates are arranged asymmetrically with respect to the center of the conductor disk, and in the figure, 11, 211, 212 are the conductor disks, 12
．． 22 is the conductor ground plate, 13.231゜232 is the inner conductor, 1
4 is a power supply plate, 15, 251, 252 is a ground plate, 16, 2
61 and 262 are coaxial feeder lines, 17 is a hole, 18 is a mounting base,
19 is a support rod, 231 and 232 are transmission lines, 27 is a duplexer, and 28 is a plug.

Claims (1)

[Claims] A pair of conductor disks and a conductor base plate are arranged approximately parallel to each other at an appropriate interval, and a predetermined frequency is set between the conductor disk and the opposing point on the conductor base plate at one point on the circumference. A point on the conductor disc that is different from the power supply point on the conductor disc and its opposite point on the conductor ground plate are short-circuited and grounded using a ground plate. A circular antenna characterized by radiating omnidirectional radio waves from a gap separated by a ground plane. 2 A pair of conductor disks corresponding to the first frequency and a conductor ground plate are arranged approximately parallel to each other at an appropriate interval, and a second A signal having a frequency of 1 is supplied, a point on the conductor disc different from the power supply point and the opposite point on the conductor ground plate are short-circuited and grounded using a ground plate, and the conductor disc is placed on the conductor disc. The second conductor base plate
Conductor disks corresponding to the frequency are arranged approximately parallel to each other at appropriate intervals, and a ground plate and a feeding point are placed between the conductor disks corresponding to the first and second frequencies. A coaxial feed line that is provided in the same manner as the ground plate and the feed point of the plate and that feeds power to the conductor disk corresponding to the second frequency is connected to the first
A circular plate antenna, characterized in that it is guided onto a conductive ground plate corresponding to a first frequency along a ground plane of a conductive circular plate corresponding to a first frequency. 3. Arranging a pair of conductor disks and a conductor base plate approximately parallel to each other at an appropriate interval, and feeding a signal of a predetermined frequency between one point on the circumference of the conductor disk and the opposite point on the conductor base plate, A point of the pond different from the power feeding point of the conductor disk and its opposite point on the conductor ground plate are short-circuited and grounded with a ground plate, and a hole is further provided in the ground plate to connect the outer conductor of the coaxial power feed line to the ground plate. The inner conductor is passed through the hole in the ground plate and extended to the feed point, and connected to the conductor disk or the conductor ground plate, and the dimensions of the extended portion are selected to perform impedance matching with the coaxial feed line. A disc antenna featuring: