JPH11355031A - Antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna wide in band, small in size and capable of being easily arranged in the ridge of a roof. SOLUTION: In this antenna, an antenna element 6 formed into almost a horn shape is arranged so that the center axis is positioned almost vertically to a ground plate 2 and the top part of the horn is positioned on the side of the ground plate 2. Capacitance bodies 8 are installed at prescribed intervals at the peripheral edges of the base part of the antenna element 6. The tips of the capacitance bodies 8 are connected to the ground plate 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an antenna,
In particular, the present invention relates to a grounded antenna having a ground plate.

[0002]

2. Description of the Related Art In recent years, there has been a tendency that it is not preferable to build an antenna for receiving UHF or VHF television broadcasts on a roof due to the beauty of a house. Therefore, installation of an antenna in the ridge of a house is being studied. For example, a monopole antenna in which a ground plate is disposed horizontally in a building, and one radiator is provided perpendicular to the ground plate and at a predetermined interval has been considered.

[0003]

However, this monopole antenna has a relatively narrow band. Therefore, 470M
It is impossible to receive a UHF band having a relatively wide frequency range from Hz to 770 MHz with only one monopole antenna. Therefore, it is necessary to divide the UHF band into a plurality of bands and provide a plurality of monopole antennas for receiving each band. It is difficult to provide multiple antennas for different bands in a narrow space such as a roof ridge.

When a monopole antenna is used, a radiator having a length of about 約 of the center reception wavelength λ is used. For example, if the center reception wavelength is 470 MH
Assuming that z, the length of the radiator is about 160 mm. Since the height of the roof ridge is not too high,
It is also difficult to arrange the radiators in the building.

[0005] It is an object of the present invention to provide an antenna which is broadband and additionally small and which is easy to place in a roof ridge, for example.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is formed on a grounding plate and a horn, and the center axis of the horn is substantially perpendicular to the grounding plate, and An apex of the horn has an antenna element positioned on the ground plate side at a predetermined distance from the ground plate, and power is supplied to the ground plate and the apex of the antenna element.

The horn of the antenna element may be conical or polygonal. Also, the ground plate can be arranged horizontally.

Since power is supplied to the ground plate and the top of the antenna element, this antenna is equivalent to a dipole antenna in which two antenna elements are arranged with the ground plate as a boundary. Since a horn-type antenna element is used, the antenna element functions as a horn-type dipole antenna, which has a wide-band frequency characteristic. Therefore, since it is a single antenna and has a wide band, it is suitable for being placed in a small space, for example, in a roof ridge.

According to the present invention, a capacitor may be provided on the periphery of the bottom surface of the antenna element. This capacitor can also be coupled to a ground plane. As a capacitor,
The conductor may be a straight conductor, and more specifically, a rod. A plurality of such capacitors can be provided at intervals on the periphery of the bottom surface of the horn.

[0010] Many electric charges are present on the bottom surface, which is the outer end of the horn-shaped antenna element of this antenna. If a capacitor for accumulating charges is provided on the bottom surface, the antenna height can be reduced. In this case, the input resistance of the antenna decreases. Therefore, this capacitor is connected to a ground plate to increase the input resistance of the antenna. In order to set the input resistance value of the antenna to a desired value, a plurality of capacitors are provided.

A plurality of antenna elements of the antenna according to the present invention may be provided, and a phase shifter for electrically combining outputs of the antenna elements into the same phase may be provided. In this case, the antenna elements can be arranged at the same distance from each other. As the phase shifter, one constituted by an electric circuit can be used, or the length of a transmission line, such as a coaxial cable, for transmitting from each antenna to a combiner for combining these outputs can be adjusted. By doing so, it can be used as a phase shifter. Note that a plurality of antennas each including a ground plate and an antenna element may be provided.

By making the output of each antenna element in-phase, the overall directivity of each antenna element can be changed to any direction. Therefore, in places where it is difficult to mechanically change the directivity of the antenna, such as in a roof ridge,
Even with this antenna, it is possible to satisfactorily receive radio waves arriving from a desired direction.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An antenna 1 according to one embodiment of the present invention is for receiving a UHF band television broadcast, and has a ground plate 2 arranged horizontally as shown in FIG. doing. The ground plate 2 is made of, for example, metal,
It is formed in a rectangular shape. A plug 4 for connecting a coaxial cable is attached to the ground plate 2. This plug 4
Has an outer contact to which the outer conductor of the coaxial cable is connected, and an inner contact to which the center conductor of the coaxial cable is connected. The outer contact is mechanically and electrically coupled to the ground plate 2. I have.

An antenna element 6 is arranged above one surface of the ground plate 2. The antenna element 6 has a horn shape, for example, a conical shape. The conical antenna element 6 has an open bottom surface and is hollow inside. The antenna element 6 is arranged so that its central axis is located substantially perpendicular to the ground plate 2, and
The apexes are arranged so as to be located on the ground plate 2 side with a small interval. That is, the antenna elements 6 are arranged in an inverted conical shape. The apex of the antenna element 6 is connected to the internal contact of the plug 4.

Therefore, by connecting the coaxial cable to the plug 4, power can be supplied to the ground plate 2 and the antenna element 6, and the antenna 1 composed of the ground plate 2 and the antenna element 6 operates as a ground type antenna. I do. That is, an operation equivalent to a horn-type dipole antenna in which the same antenna element as the antenna element 6 is provided on the side opposite to the side where the antenna element 6 is provided.

This horn-type dipole antenna is known to operate as a broadband antenna. Therefore, the antenna 1 including the ground plate 2 and the antenna element 6
Also operate as a broadband antenna, so that it can be used for receiving a relatively wideband UHF band television broadcast.
It is possible to use only groups. In addition, the antenna 1 has a shorter dimension than two antenna elements 6 arranged side by side.

In general, the length from the bottom of the antenna element 6 to the ground plate 2 is set to 1/4 of the center reception wavelength of the UHF band reception frequency. For example, in the case of 470 MHz, the length is about 160 mm. As will be described later, when the ground plate 2 is arranged in the roof ridge so as to be horizontal, this length is still long.

Therefore, in order to reduce the length, a capacitor may be provided at the outer end of the antenna element. This is based on the idea that the antenna height may be low if a capacitor is provided at the outer end because the largest amount of charge is stored at the outer end. This is a so-called top-load type antenna. However, if the height is too low, the input resistance of the antenna will be extremely low. Therefore, it is conceivable to increase the input resistance by grounding the tip of the capacitor.

In the antenna element 1, the antenna element 6
The height from the bottom to the ground plate 2 is set to about １ ／ of the central wavelength of reception (for example, about 105
mm), four capacitors 8 are provided at intervals of 90 degrees from the peripheral edge of the bottom surface, and the tips of these capacitors 8 are coupled to the ground plate 2. As the capacitor 8, a linear metal rod is used. Also, these capacitors 8
The antenna element 6 is mechanically supported on the ground plate 2. Note that the number of capacitors 8 is not limited to four, and may be arbitrarily changed in order to set the input resistance to a desired value.

According to this antenna 1, an antenna suitable for being installed in a roof ridge with the ground plate 2 being horizontal can be received, and the height can be reduced. Becomes

Frequency vs. gain and VSW of the antenna 1
FIG. 2 shows the R characteristics. In this antenna 1, the gain is at least about -1.3 dB and the maximum is 0 dB, and almost constant gain is obtained in a wide band from 470 MHz to 800 MHz. Further, the VSWR is about 3.1 at the maximum and about 1.1 at the minimum, and is a value of VSWR which is sufficiently practical in a wide band of 470 MHz to 800 MHz.

The antenna 1 has directivity in a vertical plane, but has no directivity in a horizontal plane. By arranging a plurality of antennas 1 at predetermined intervals and mixing outputs of the antennas, directivity can be provided. Further, directivity can be varied by feeding a phase difference to the arrayed antennas using a phase shifter.

For example, as shown in FIG. 3 (a), four antenna elements 6 are arranged on a long ground plate 2a at a constant interval d, for example, at a distance of λ / 2 (λ is the central wavelength of reception). Are located. As shown in FIG. 2B, the phase of the output of each antenna element 6 is adjusted by each phase shifter 10 and synthesized by a synthesizer 12. The phase adjustment in the phase shifter 10 is such that the output of each antenna element 6 has a phase difference at which the phase of the radio wave arriving at each antenna element 6 from a predetermined direction matches. That is, phase difference power supply is performed. FIG.
(A), (b), and (c) show a state in which the phase is adjusted by each phase shifter 8 at a frequency of 470 MHz and the directivity is changed in a horizontal plane in the antenna of FIG. Show.

As described above, since the directivity can be changed electrically, the antenna element 6 is disposed on the ridge 16 of the roof 14 having no large space as shown in FIG.
It is suitable when the directivity cannot be changed by changing the position of. In FIG. 5, the illustration of the capacitor is omitted. The entire antenna element 6 is covered by a cover that transmits radio waves.

FIG. 4 uses the phase shifter 10,
The desired directivity can be obtained by adjusting the length of the coaxial cable laid from each antenna element 6 to the synthesizer 12. Further, as shown in FIG. 1, a plurality of antennas 1 each including a ground plate 2 and an antenna element 6 can be provided.

[0026]

As described above, according to the present invention, it is possible to obtain a relatively small-sized broadband antenna while using only one antenna. In addition, one antenna,
A smaller antenna can be obtained while having a wide band. Further, it is possible to obtain an antenna which has a wide band, a small size, and a variable directivity. Therefore, an optimal antenna can be obtained by installing the antenna in a small space such as a roof ridge.

[Brief description of the drawings]

FIG. 1 is a partially broken front view of an antenna according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating gain versus frequency and VSWR characteristics of the antenna of FIG. 1;

FIG. 3 is a front view and a circuit diagram of an antenna according to another embodiment of the present invention.

FIG. 4 is a perspective view showing an installation state of the antenna of FIG. 3;

FIG. 5 is a directional characteristic diagram of the antenna of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna 2 Grounding plate 6 Antenna element 8 Capacitor

Claims (4)

[Claims] A grounding plate formed substantially on a horn, a center axis of the horn being substantially perpendicular to the grounding plate, and a vertex of the horn being spaced apart from the grounding plate by a predetermined distance. And an antenna element which is fed to the ground plate and the apex of the antenna element. 2. The antenna according to claim 1, wherein a capacitor is provided at a peripheral portion of a bottom surface of the antenna element. 3. The antenna according to claim 2, wherein said capacitor is coupled to said ground plate. 4. The antenna according to claim 1, wherein at least a plurality of the antenna elements are provided, and a phase shifter electrically combines outputs of the antenna elements into the same phase.