JP3483096B2 - Monopole antenna - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monopole antenna that is smaller than the wavelength used, and relates to a technique for correcting deterioration of a radiation pattern due to miniaturization of a plane conductor ground plane.

[0002]

2. Description of the Related Art FIG. 14 shows an example of a conventional monopole antenna. The monopole antenna 10 is a dipole antenna having a symmetrical structure, and the antenna height is suppressed to half by using a plane conductor ground plate according to the principle of a mirror image. The conductor ground plane 2 used for operating the monopole antenna 10 equivalently to a dipole antenna requires an infinite size, but in reality, a finite plane circular or rectangular conductor plate is used. When the size of the plane conductor ground plane 1 becomes the same as or smaller than the wavelength at the used frequency, the edge effect of the ground plane appears and the peak of the radiation pattern tilts upward from the ground plane. The inclination becomes larger as the size of the ground plane becomes smaller (Reference: Ohmsha, Institute of Electronics, Information and Communication Engineers, “Antenna Engineering Handbook, Chapter 3, Basic Antenna, Section 2 Monopole (Unipole) Antenna, Binomial on the finite ground plane) Therefore, the gain on the same plane (horizontal plane) as the plane conductor plate is reduced, and the radiation pattern of the original dipole antenna is largely changed.

Such a problem becomes a problem, for example, when a monoplane antenna having a common plane ground plane is used and a monopole antenna is added to the antenna to make it have multiple resonances. If the resonance frequency of the added monopole antenna is sufficiently lower than the resonance frequency of the original monopole antenna, the ground plane is smaller than that of the newly added monopole antenna, causing the aforementioned radiation pattern change. ,
As a result, variations in the radiation pattern due to changes in frequency become a problem.

As described above, in a monopole antenna having a small ground plane with respect to the wavelength, it is difficult to direct the peak direction of the radiation pattern in the same direction as that of the plane conductor plate so as not to reduce the gain in the horizontal plane.

[0005]

As described above, in the conventional monopole antenna 10, it is difficult to reduce the size of the plane conductor ground plate 2 without changing the radiation pattern. It is an object of the present invention to solve such a problem and to provide a method of suppressing a change in radiation pattern while using a plane conductor ground plane smaller than conventional ones.

[0006]

(1) The invention of claim 1 is a flat conductor ground plate, and the flat conductor ground plate is provided on the flat conductor ground plate.
The present invention relates to a monopole antenna having a pair of linear radiating elements having a monopole structure and a feeding portion provided between the pair of linear radiating elements and a plane conductor ground plane. According to claim 1, in particular, the pair of linear radiating elements have substantially equal resonance frequencies and are fed with the same phase and the same amplitude, and the size of the plane conductor ground plate is set sufficiently smaller than the resonant wavelength of the linear radiating element. To be done . Then, the pair of linear radiating elements are flat conductors.
They are installed near the opposite edges of the main plate.

(2) In the invention of claim 2, in the above (1), when the plane conductor ground plate is rectangular, its short side is short, when it is elliptical, its short diameter is short, and when it is circular, its diameter is: Approximately 1/3 to 1 of the resonance wavelength of the linear radiating element
It is set to about / 4 or less. (3) In the invention of claim 3, in the above (1), the pair of linear radiating elements are configured to have the same structure and dimensions.

( 4 ) In the invention of claim 4 , in the above item (4), the size is smaller than the resonance wavelength of the pair of linear radiating elements and the dimension (short side, minor axis or diameter) of the flat conductor ground plate is 1.
A single or a plurality of linear radiating elements having a monopole structure having a resonance wavelength of about 0 to 1.2 times or less are provided on the planar conductor ground plate.

[0009]

DETAILED DESCRIPTION OF THE INVENTION

(Embodiment 1) FIG. 1 is a view showing a first embodiment of the present invention and shows a structure of an antenna device in a perspective view. This antenna device includes two linear radiating elements 1a and 1b, a rectangular flat conductor ground plate 2, and power feeding portions 3a and 3b for feeding power to the radiating elements 1a and 1b, respectively.

Although the radiating element used is a normal monopole element in FIG. 1, it is not limited to this as long as it is a linear antenna having a monopole structure. For example, in order to suppress the height of the antenna, a resistance loaded monopole antenna or an inverted F antenna as shown in FIGS. 2 and 3 may be used. The distance between the two linear radiating elements 1a and 1b arranged on the plane conductor plate should be separated to some extent, but the linear radiating elements 1a and 1b should be arranged close to each other up to about 0.1 times the wavelength λ at the resonance frequency of the linear element. You may. Further, the positions of the two linear radiating elements 1a and 1b arranged on the flat conductor plate 2 may be arbitrary positions as long as a certain distance is provided as described above, but in the sense that the characteristics of the two radiating elements are made uniform, It is desirable to dispose symmetrically or point symmetrically with respect to the conductor ground plane 2. However, two linear antennas 1
If the resonance frequencies and radiation patterns of a and 1b are substantially the same, for example, if they have the same structure and size, this does not apply.

Further, in this embodiment, the shape of the plane conductor ground plane 2 is rectangular, but the shape is not limited to this, and may be, for example, a circular shape or a shape similar thereto, and the size is the short side of the rectangle. , The ellipse minor diameter or the diameter of the circular conductor plate is sufficiently smaller than the operating wavelength λ, and 1/3 to 1 / of λ
It may be about 4 or slightly smaller. Feeding power to the two linear antennas 1a and 1b should be in phase and have the same amplitude, and if the power feeding method therefor can realize in-phase and same amplitude excitation, it does not depend on the form of coaxial line, microstrip line, etc. Such a method is also acceptable.

When such a monopole two-element array is excited with the individual elements having the same phase and the same amplitude, the combined radiation pattern of the two-element array antenna can form a null point in the zenith direction of the ground plane. As a result, the peak direction of the radiation pattern directed upward from the plane conductor plate is oriented in the horizontal plane direction, and the same characteristic as the radiation pattern of the dipole antenna alone which is the source of this antenna is obtained.

Since this characteristic does not depend on the size of the plane conductor ground plane, it has a feature that the ground plane can be made smaller than the wavelength used. Therefore, if this method is adopted, the size can be made smaller than the conventional monopole antenna without degrading the radiation characteristic. We conducted experiments to see if these things could be realized. FIG. 4 shows the dimensions of the antenna used for the experiment. The design frequency of this antenna is 280 MH
z, and the size of the ground plane is about 1 of the wavelength at 280 MHz.
It uses a small size of about / 3. Further, the two radiating elements are respectively installed near the opposite edges of the ground plane, and the area where a single radiating element can be effectively used is further smaller, resulting in a monopole antenna array using a very small plane ground plane.

The monopole element used uses an inverted F type antenna in order to suppress the height, and further has a tip end wound in a coil shape for the purpose of shortening the antenna length. In the inverted-F antenna, the current concentrates on the portion that rises vertically from the ground plane, and almost no current flows at the tip of the antenna that is parallel to the ground plane. Therefore, even if the tip of the antenna is wound into a coil, it does not affect the operation of the antenna.

First, the radiation patterns of the horizontal plane (xy plane in FIG. 4) and the vertical plane (zx plane) of the inverted F antenna alone are shown in FIGS. As can be seen from the vertical plane radiation pattern of FIG. 6, when the plane ground plane smaller than the wavelength is used, the peak direction of the radiation pattern shifts to the upper direction of the ground plane and completely shifts to the zenith direction. As a result, the gain in the horizontal plane is reduced, and the null point in the zenith direction formed when a sufficiently large ground plane is used is completely eliminated.

Next, FIGS. 7 and 8 show the array-synthesized horizontal plane and vertical plane pattern when two inverted F antennas are fed with the same phase and the same amplitude. As you can see from the radiation pattern on the vertical plane, the maximum peak direction is parallel to the ground plane,
Moreover, the null point is formed properly in the direction of the zenith of the ground plane. In this way, even a monopole antenna that uses a plane conductor plate that is smaller than the wavelength has a two-element array structure.
If the two antennas are excited in phase and with the same amplitude, the change in the radiation pattern can be suppressed, and the antennas can be downsized. (Embodiment 2) FIG. 9 is a view showing a second embodiment of the present invention, and its structure is shown in a perspective view. This antenna device comprises a combination of the monopole array antenna described in the first embodiment and the second monopole antenna. That is, the two linear radiating elements 1a and 1b which are excited with the same phase and the same amplitude, and the linear monopole radiating element 6 which operates by resonating at frequencies different from those of the radiating elements 1a and 1b, the rectangular flat conductor ground plate 2, Power supply units 3a, 3b and 3c for supplying power to the radiating elements 1a, 1b and 6 are provided.

If the resonant frequency of the radiating element 6 is different from the resonant frequency f1 of the linear radiating elements 1a and 1b, the linear radiating element having a different shape such as an inverted F antenna, or the slot antenna will have a particular shape and type. It doesn't matter. Further, in this example, the number of the radiating elements 6 is one, but this number is not limited and a plurality may be provided. The resonance frequency of the radiating elements 1a and 1b excited with the same phase and the same amplitude is f1, and the resonance frequency of the linear radiating element 6 is f2. The resonance frequencies f1 and f2 are designed to be, for example, f2 = 2 × f1, and the size of the ground plane is such that the length of the short side of the rectangle is the linear radiating element 6.
The resonance frequency f2 is about the wavelength. When such a construction, regarded as the plane conductor ground plate practically sufficiently large relative to the linear radiating element 6, the radiation pattern of the linear monopole radiating element 6 is relatively close characteristics as the dipole antenna. On the other hand, as described in the first embodiment, the radiation patterns of the radiating elements 1a and 1b are excited with the same phase and the same amplitude, so that a radiation pattern equivalent to that of a dipole can be obtained even if a ground plane having a small size with respect to the wavelength of the resonance frequency is used. can get.

In this way, the plurality of resonance frequencies f1 and f2 are
When the antennas with are arranged on the same plane conductor ground plane, even if the size of the plane conductor ground plane is adapted to the antenna having a high resonance frequency, the first plane having the pair of elements 1a and 1b is formed.
The antenna and the second antenna having the radiating element 6 have substantially the same radiation pattern as the dipole antenna at the frequencies f1 and f2, respectively.

An experiment was conducted to confirm whether this can be realized. FIG. 10 shows a perspective view and dimensions of the antenna used for the experiment. The first antenna, that is, the monopole two-element array antennas 1a and 1b, is the same as the one in the embodiment of FIG.
The same thing as a and 5b is used. The second antenna 6 is a wideband monopole antenna 7a, 7b (Japanese Patent Application No. 7-32).
1906) and its design band is 800 MHz or more. In this example, two wideband antennas are used for transmission and reception. The radiation pattern of this wideband antenna is almost the same as that of a monopole antenna from 800 MHz to about twice the frequency band.
The size of the plane conductor ground plane is 300 x 300 mm, 800
The wavelength is approximately 0.8 of the wavelength in MHz, which is sufficiently large for a wideband monopole antenna.

28 of this antenna is shown in FIGS.
Figure 3 shows the horizontal and vertical plane radiation patterns at 0 MHz, 900 MHz and 1500 HMz. In this way, the same radiation pattern as the dipole antenna is obtained for all frequencies, and multiple monopole antennas are configured on the same ground plane, and the size of the plane conductor ground plane is adjusted to the antenna with high resonance frequency. It is possible to design the antenna effectively.

[0021]

As described above, according to the present invention, a monopole antenna is radiated even if the plane conductor ground plane is made smaller than the used wavelength by feeding an array of 2 elements with the same phase and the same amplitude. A change in pattern can be suppressed, and as a result, an antenna with high space efficiency can be obtained as compared with the conventional monopole antenna.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the invention of claim 1.

FIG. 2 is a perspective view showing another embodiment of the invention of claim 1;

FIG. 3 is a perspective view showing still another embodiment of the invention of claim 1;

FIG. 4 is a perspective view of an antenna used in an experiment, which is an embodiment of the invention of claim 1;

5 is a diagram showing a horizontal plane (xy plane in FIG. 4) radiation pattern of the inverted F antenna element 5a or 5b alone in FIG. 4;

6 is a diagram showing a radiation pattern of a vertical plane (zx plane in FIG. 4) of the inverted F antenna element 5a or 5b alone in FIG.

7 is a diagram showing a horizontal plane (xy plane in FIG. 4) radiation pattern of the monopole antenna of FIG. 4;

8 is a diagram showing a radiation pattern of a vertical plane (zx plane in FIG. 5) of the monopole antenna of FIG.

FIG. 9 is a perspective view showing an embodiment of the invention of claim 4 ;

FIG. 10 is a perspective view of the monopole antenna used in the experiment according to the fourth embodiment.

11 is a diagram showing a radiation pattern on a horizontal plane and a vertical plane of the first monopole antenna having the inverted F elements 5a and 5b of FIG.

12 is a diagram showing a radiation pattern on a horizontal plane and a vertical plane of the broadband antenna 7a or 7b of FIG. 10 (measurement frequency 9
00 MHz).

13 is a diagram showing a radiation pattern on a horizontal plane and a vertical plane of the broadband antenna 7a or 7b of FIG. 11 (measurement frequency 1
500 MHz).

FIG. 14 is a perspective view showing the structure of a conventional monopole antenna.

─────────────────────────────────────────────────── --Continued from the front page (56) Reference JP-A-7-79189 (JP, A) JP-A-8-186420 (JP, A) JP-A-8-250925 (JP, A) JP-A-8- 288895 (JP, A) JP 60-100841 (JP, A) Actual flat 7-42213 (JP, U) Actual flat 8-1427 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01Q 1/24 H01Q 9/30 H01Q 21/00 H01Q 21/06

Claims (4)

(57) [Claims] 1. A rectangular, circular or elliptical flat conductor ground plate, a pair of linear radiating elements having a monopole structure provided on the flat conductor ground plate, the pair of linear radiating elements and the flat conductor ground plate. In a monopole antenna having a feeding section respectively provided between the pair of linear radiating elements, the pair of linear radiating elements have substantially the same resonance frequency and are fed with the same phase and the same amplitude. short side if, in the case of circular diameter, the length of the minor axis in the case of oval, rather sufficiently smaller than the resonance wavelength of each of the linear radiating element, the pair of linear radiating elements, the planar conductor Opposite the main plate
The monopole antenna is characterized in that it is installed near each edge . 2. The resonance of the linear radiating element according to claim 1, wherein the planar conductor ground plate has a short side when it is rectangular, a short diameter when it is elliptical, and a diameter when it is circular. A monopole antenna having a wavelength of about 1/3 to 1/4 or less. 3. The monopole antenna according to claim 1, wherein the pair of linear radiating elements have the same structure and dimensions. 4. The unit according to claim 1 , which is smaller than the resonance wavelength of the pair of linear radiating elements and about 1.0 to 1.2 times the dimension (short side, minor axis or diameter) of the flat conductor ground plane. A monopole antenna in which a single or a plurality of linear radiating elements having a monopole structure having a resonance wavelength equal to or smaller than that are provided on the plane conductor ground plane.