JPH02883B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a circularly polarized antenna that has a simple and thin structure and emits a conical beam.

(Prior art and problems) Fig. 1 is a diagram showing an example of the application of a conical beam antenna, in which 1 is a ship, 2 is an antenna, and 3 is a line connecting points of equal electric field strength of the conical beam of the antenna. , 4 is a geostationary satellite, 5 is a vertical axis, and 6 is a line indicating the main beam direction.

For example, when communicating between a ship and a satellite,
In order to enable communication without tracking regardless of the movement or direction of the ship, the antenna beam pattern should be such that its main beam faces the satellite from the antenna with respect to the vertical axis 5 as shown in Figure 1. It suffices if it has a shape close to a cone with the direction line as the generating line. This is called a conical beam.

Conventionally, a cross dipole antenna as shown in FIG. 2 has been used as a circularly polarized antenna having a conical beam. In Figure 2, 3 is a line connecting points with equal electric field strength of the conical beam of the antenna, and 5
is a vertical axis, 6 is a line indicating the main beam direction, 7 is a cross dipole, and 8 is a feeder line.

However, this antenna has a three-dimensional structure,
As the antenna height increases and the length of the coaxial line for power feeding differs, the power feeding becomes complicated.

FIG. 3 is a diagram showing another configuration example of a conventional circularly polarized antenna having a conical beam, in which 8 is a feed line, 9 is a radiation conductor plate, 11 is a dielectric, 12 is a conductive substrate, and 16 is a The feed point 17 indicates a microstrip feed line.

This antenna has a planar structure compared to the antenna in Figure 2, but in order to obtain a conical beam, it is necessary to excite opposing elements in opposite phases, and multiple elements and feed distribution lines must be excited. Although the shape is thin, the structure is large in plan.

(Object of the Invention) In order to eliminate these drawbacks, the present invention uses a single-element TMmn ₀ mode excitation microstrip antenna in which m is 2 or more, and
A power supply that excites the radiating conductor plate from 22 points on two straight lines that pass through the center of the radiating conductor plate and are 90/m degrees apart (m is m in TMmn ₀ mode) with a phase relationship such that there is a phase difference of 90 degrees. By arranging the circuit, a conical beam can be obtained with a simple structure consisting of one radiating element and a feeding circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and the like of the present invention will be described in detail below based on drawings of embodiments.

(Embodiment of the Invention) As is well known, the resonant frequency f ₀ of the TMmn ₀ mode excitation microstrip antenna is given by the following equation.

Here, Kmn is the Bessel function of the first kind J′m(X)=0
shows the nth solution of , where C is the speed of light in vacuum,
εr is the dielectric constant of the dielectric of the substrate. Furthermore, ae in equation (1) indicates the effective equivalent radius of the radiation conductor plate, and by considering the fringing effect, it is related to the radiation conductor plate radius a by the following equation.

Here, d is the thickness of the dielectric.

The radiation directivity g (θ, φ) when power is fed to a TMmn ₀ mode excitation microstrip antenna from one feeding point is given by the following equation.

g = (θ, φ) = √ ² + ² where, Eθ = − [Jm _-1 (u) − Jm ₊₁ (u)] cosmφ ... (4) Eθ = [Jm _-1 (u) + Jm _{+ 1} (u)〕cosθsinmφ……(5) Here, J is a Beseel function of the first kind, K ₀ is a propagation constant in free space, and ae is an effective equivalent radius given by equation (2).

In addition, the radiation directivity gc (θ, φ) when exciting circularly polarized waves by two-point feeding is given by g
(θ, φ) is given by the following equation.

gc (θ, φ) = g (θ, φ) + jg (θ, φ - π/2m...(7) Figure 4 is a diagram showing an embodiment of the present invention in the case of m=2 and n=1. The figure shows the case of a one-element microstrip antenna excited in TM ₂₁₀ mode.In Fig. 4, 9 is a radiation conductor plate, and 10 is a radiation conductor plate.
3dB hybrid as a 90 degree phase difference power supply circuit,
11 is a dielectric, 12 is a conductive substrate, 14 is a 1/4 wave line, 15 is a chip resistor, and 16 is a feeding point.

When exciting in TM ₂₁₀ mode, Kmn in equation (1)
is K ₂₁ =3.054.

Figure 5 shows the surface current distribution of the TM ₂₁₀ mode excitation microstrip antenna.
This shows the case where power is supplied from two points on a straight line.

In the embodiment shown in Fig. 4, power is supplied from two points on two straight lines passing through the center and forming an angle of 45 degrees, so the surface current distribution is as shown in Fig. 5b, and the internal The electromagnetic fields are orthogonal to each other. That is, the radiated electromagnetic fields of the TM ₂₁₀ mode excitation microstrip antenna are also orthogonal, and the circular deviation is radiated by feeding the two feeding points so that the feeding phase difference is 90 degrees. At this time, since it is excited in the TM ₂₁₀ mode, the radiation electromagnetic field in the vertical axis direction is 0, and it remains a radiation-directed conical beam. Therefore, as in this example,
In the case of the TM ₂₁₀ mode excitation microstrip antenna, a circularly polarized conical beam can be obtained with one element by feeding power with a phase difference of 9 degrees from two points on two straight lines forming a 45 degree angle.

An example of radiation directivity calculated using (7) is shown in the sixth section.
As shown in the figure. The parameter in the figure is the specific dielectric constant of the dielectric of the substrate.

Note that FIG. 4 shows a case where a 3 dB hybrid is used as a circuit for generating a 90 degree phase difference. In this way, by providing the power supply circuit on the same surface as the radiating element, power can be supplied from the back of the board using one connector. In this case, a simpler antenna configuration can be achieved by terminating the hybrid dummy end using a 1/4 wavelength line and a chip resistor.

Although the TM ₂₁₀ mode has been described above, the same applies to other modes, for example,
For TM ₃₁₀ mode with m=3 and n=1,
Kmn=4.201, from a point on a straight line making 30 degrees
Similar results can be obtained by feeding with a 90 degree phase difference.

FIG. 7 is a diagram showing another embodiment of the present invention, in which reference numeral 13 indicates a parasitic conductive plate. As in this example, by loading the parasitic conductor plate in parallel above the radiating conductor plate, the resonant frequency characteristic of the microstrip antenna when the parasitic conductor plate is not loaded is changed to the resonant frequency due to the loading of the parasitic conductor plate. The characteristics are superimposed and the resonant frequency characteristics change. Therefore, a wide area can be achieved by appropriately selecting the interval and size ratio of the two conductor plates.

Figure 8 shows when the parasitic conductor plate is loaded and when it is not loaded.
An example of VSWR characteristics is shown. It can be seen that the area is expanded by loading the parasitic conductor plate.

Furthermore, if a parasitic conductor plate as shown in Fig. 7 is constructed by printing it on a printed circuit board, and a dielectric material such as foamed plastic stick is sandwiched and bonded between the parasitic conductor plate and the radiation conductor plate, the radiation Since the conductor plate and the feeder circuit are hidden and weather resistance is increased, it is possible to obtain a stable antenna that is less affected by aging.

(Effects of the Invention) As explained above, the circularly polarized conical beam antenna of the present invention uses a single-element high-order mode excitation microstrip antenna and a 90-degree phase difference circuit arranged on the same plane as the antenna. By feeding power from two suitable points, there is an advantage that a conical beam can be obtained with a simple configuration, and it can be applied, for example, as an antenna mounted on a mobile body in communication using a satellite.

[Brief explanation of drawings]

Fig. 1 shows an example of the use of a conical beam antenna, Fig. 2 shows a conventional cross dipole array antenna, and Fig. 3 shows another configuration example of a conventional circularly polarized antenna with a conical beam. Fig. 4 shows an embodiment of the present invention, Fig. 5 shows a surface current distribution of a TM ₂₁₀ mode excitation microstrip antenna, and Fig. 6 shows an example of calculation of radiation directivity. FIG. 7 is a diagram showing another embodiment of the present invention,
FIG. 8 is a diagram showing an example of actually measured VSWR characteristics. 1...Ship, 2...Antenna, 3...Line connecting points of equal electric field strength of the antenna's conical beam,
4...Geostationary satellite, 5...Vertical axis, 6...Line indicating the main beam direction, 7...Cross dipole, 8...
Feeding line, 9... Radiation conductor plate, 10... 90 degree phase difference feeding circuit, 11... Dielectric, 12... Conductor substrate,
13... Parasitic conductor plate, 14... 1/4 wavelength line,
15... Chip resistor, 16... Power supply point, 17...
Microstrip feed line.

Claims (1)

[Claims] 1 It has a structure in which a conductor substrate is spread on one side of a dielectric plate, and a radiating conductor plate and a parasitic conductor plate are arranged on the other side of the dielectric plate, and a vertical line passing through the center of the radiating conductor plate In a TMm ₁₀ -mode excited microstrip antenna with m of 2 or more, which minimizes the radiated electromagnetic field on the axis, the antennas pass through the center of the radiating conductor plate to each other with a phase relationship such that there is a 90 degree phase difference in the radiating direction. A circularly polarized conical beam antenna characterized by having a feeding circuit that excites a radiation conductor plate from two points on two straight lines forming an angle of 90/m degrees (m is m in TMm ₁₀ mode).