JPH02189035A - Antenna system - Google Patents

Abstract

PURPOSE:To prevent an interference wave and to improve the reliability by a stationary and simple circuit by applying phase shift processing to two outputs of an orthogonally polarized branching filter including a wave reflected in a sea surface and synthesizing the result of the processing. CONSTITUTION:A 90 deg. polarizer 2, an orthogonally polarized branching filter (OMT) 3 and a phase shifter 51 feeding a phase lead of 45 deg. or no phase shift to an output of the polarizer, a phase shifter 52 feeding a phase lag of 45 deg. or a phase shift of + or -90 deg. and a combiner(COMB) 6 combining outputs of both the phase shifters 51, 52 are provided to the system. Thus, it is notified that a 45 deg. component appears in combined X, Y component of a direct wave and an interference wave, and the two outputs of the polarizer are combined by feeding phase shifts of +45 deg., -45 deg. to the outputs respectively. Since fading due to the reflection in the sear surface is eliminated, fading is eliminated inexpensively with high reliability and a small and stationary circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an antenna device, and particularly to an antenna device that prevents interference waves due to fading due to sea surface reflection in the field of wireless communication such as satellite communication.

[Conventional technology]

Figure 5 shows, for example, "Radio Research Quarterly Report: Vol. 34.Special 6.
It is a block diagram showing a conventional interference wave removal device using fading shown in March 1988 J. In the figure, 1 is an antenna, 2 is a circularly polarized wave generator (pola
90@-POL from riserH onwards), 3 is an ortho-sode transduce
r; hereinafter referred to as OMT), 4 is an attenuator 41 and a phase shifter 42
This is an interference wave removal circuit consisting of. In addition, in the above document, 2 and 3 are combined into 90"-3dB hybrid 3
It is called 1.

Next, the operation will be explained.

Inmarsat Maritime Satellite Communication's communication service area is the sea area where the satellite elevation angle is 5 degrees or more. By the way, when a left-handed circularly polarized wave (normal rotation component) is incident on the sea surface, the reflected wave is separated into left-handed (normal rotation) and right-handed (anti-rotation) components, and the angle of elevation is 5.
It is known that the anti-rotational component becomes larger than the normal-rotating component if the rotational angle is greater than 1°.

On the other hand, at the terminal T3 of the circularly polarized antenna, the sum of the normal rotation component, which is a direct wave, and the normal rotation component E, which is a direct wave, is transmitted to the terminal T3.
The anti-rotation component EL due to sea surface reflection is output as follows.

T 3: Eo + Et e j (φ and 900
> T4: E, Ie' C In a normal circularly polarized antenna, the anti-rotating component generated by reflection output to the terminal T4 is consumed as wasted power by the terminating resistor. However, as understood from the above formula, 73
．． When both outputs of T4 are added so that El and EL have equal amplitudes and opposite phases, EII8Jφ blade and EL8Jfφ
It can be seen that both components of L-11g+') cancel each other out, and only the direct wave component E0 is extracted. Figure 5 shows a fading removal function configured based on this principle.The actual configuration is based on the principle described here, with a low Two noise amplifiers (LNA) are used, each inserted immediately after the two outputs of the OMT.

If this method is adopted, it is also possible to control only the phase shift of the anti-rotational component without controlling the amplitude so that the amplitude is always maximized.

[Problem to be solved by the invention]

Conventional interference wave removal devices are configured as described above, so when performing interference wave removal with a small antenna, especially an antenna with an aperture diameter of 10λ (λ: wavelength) or less, and a wideband high frequency circuit. Since it is necessary to install an interference wave removal circuit on the back side of the antenna, it has been difficult to realize an antenna device with an interference wave removal circuit. Furthermore, an attenuator (ATT) that provides variable attenuation is required depending on the amount of interference of interference waves, and an LNA (low noise amplifier) is required from the perspective of G/T performance of the earth station. Furthermore, it was necessary to control the phase shifter and attenuator according to the amount of interference.

This invention was made to solve the above-mentioned problems of the conventional circuit, and it is possible to miniaturize the circuit, make it simple, and provide a certain amount of coupling to prevent interference waves (low?: Ii). The purpose of this invention is to obtain an antenna device that can realize the following.

[Means to solve the problem]

The antenna device according to the present invention has a 90@phase cover plate (90
"-Polarizer) and a polarization splitter (OMT), a phase shifter that gives a 45# phase (45" lead) or a 00 phase to one output of the polarization splitter, and a -Polarizer to the other output of the polarization splitter.
A phase shifter that provides 5@phase (45° delay) or ±90° phase, and a synthesizer (COM) that combines the outputs of both phase shifters.
B).

[Effect]

In the present invention, with the above-described configuration, two orthogonal polarized components of the OMT output are phase-shifted and synthesized, so that fading can be removed using a small, simple, and fixed circuit.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows an antenna device according to an embodiment of the present invention. In the figure, the same reference numerals as in FIG. In the case of the figure, the synthesizer 6 is provided in the X-POL component direction (horizontal direction) of the OMT 3. Also, 12 is a switch that turns the fading prevention circuit ON to 10FF in accordance with the antenna elevation angle corresponding to the angle where fading occurs noticeably, generally in the ground angle of 10'' to 20''. This circuit is a fading prevention circuit when the satellite uses right-handed circular polarization, and when the satellite uses left-handed circular polarization, 6 and 12 in Figure 1 are in the Y-POL component direction (vertical direction). The same circuit is sufficient except that it is replaced with .

The present embodiment will be described below using mathematical formulas.

Generally, when a satellite uses elliptically polarized waves, dividing the arriving wave into X and Y components gives the following equation.

Here, E, EL are the dextrorotatory component and the levorotary component, respectively,
T is the angle (referred to as tilt angle) that the long axis of the ellipse makes with the X axis.

Figure 2 shows how an antenna mounted on a marine vessel receives direct waves from a satellite and reflected waves from the sea surface. In Figure 2, 7 is the reception pattern of the antenna 11 mounted on a vessel 20, and 8 is the state of the satellite radio wave, 9 is the reflected wave from the sea surface, and g is the relative electric field strength in the direction of the reflected wave of the reception pattern. Figure 3 also shows the reflection coefficient at the sea surface. Also 1
0 indicates the grounding angle θ (=90″−incident angle) of the incident wave on the sea surface.

The fourth part depicts the relationship between Ex, Ey (incident electric field) and reflected waves E', E' from the sea surface 30 when θ is 10@ or more. In other words, when the direct wave in equation (1) and the reflected wave in equation (3) are input to the antenna, they pass through 90"POL, and the X, Y of OMT
The output of each direction component is as follows. In other words, there are two direct wave OMT outputs. +Evo becomes. Further, the OMT outputs Er8° and E'7° of the reflected waves are here, r is the reflection coefficient (amplitude) of the sea surface, and δ is the reflection coefficient (phase) of the sea surface.

Therefore, Note that when the frequency is 10 GHz or more, δ=.

Here, B corresponds to a phase delay due to the optical path difference between the direct wave and the reflected wave.

Therefore, the combined output of the direct wave and reflected wave is E″8°.

E”V. are each becomes.

Therefore, if the satellite is right-handed circularly polarized, it becomes EL-0, where, The second term is the interference wave caused by the reflected wave. Among these, gr is smaller than g,
Equation (7) is approximated as follows.

Same as above < If gr is ignored, the α [phase] formula approximately follows: "8°e J 40I!" If 1°e-J7 is created, the electric field E of the composite wave is B = f ELej tJ'...
- Indicated by (2).

In this way, according to this embodiment, focusing on the fact that a 45° component appears in the combined X and Y components of the direct wave and interference wave, the two outputs of the polarization demultiplexer have a phase of +45° - 45°. Since fading due to sea surface reflection is removed by giving and combining the signals, fading can be removed with high reliability and at low cost using a small and fixed circuit.

In addition, in the above example, +4! y@phase shifter and -45″
Although the phase shifter is shown here, it is sufficient to give a relative phase, so if the +45° phase shifter is set to 06, the 145" phase shifter becomes the 190@ phase shifter (right rotation). For polarized waves), +
It may also be a 90° phase shifter (in the case of left-handed polarization).

In addition, in the above embodiment, interference waves (fading waves) are prevented by performing phase processing and combining two orthogonal polarization components of the OMT output, but the above-mentioned equation (8) and aυ
As shown in the formula, the same effect can be obtained by simply reducing g.

A so-called low side lobe antenna may be used as a method of reducing this g, but a mere low side lobe antenna will reduce the aperture efficiency.

Therefore, by using an antenna having asymmetric side ropes in the elevation plane as shown in FIG. 6, the same effects as in the above embodiment can be expected.

Note that in order to create such an asymmetrical side rope within a specific plane (in this case, in the elevation angle direction), it is sufficient to give a third-order and 15th-order coma aberration to the phase distribution of the aperture distribution of the antenna.

〔Effect of the invention〕

As described above, according to the antenna device according to the present invention,
Since the two outputs of the orthogonal polarization splitter, including the waves reflected from the sea surface, are phase-shifted and synthesized, interference waves can be prevented using a fixed and simple circuit, and the device can be made small and inexpensive, while also being highly reliable. It has the effect of obtaining something with high sexiness.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is an interference conceptual diagram showing the path of interference waves due to fading due to sea surface reflection, Fig. 3 is a diagram showing seawater reflection characteristics (theoretical values), 4
This figure is a schematic diagram of reflection on the sea surface, FIG. 5 is a diagram showing a conventional embodiment, and FIG. 6 is a diagram showing an asymmetric side rope shape that aims to reduce side lobes in the direction of the sea surface. In the figure, 1 is an antenna, 2 is a circularly polarized wave generator, 3 is an orthogonal polarization splitter, 51 and 52 are phase shifters, 6 is a combiner, 12 is a switch, and 13 is a dummy load.

Claims (1)

[Claims] (1) In the antenna device, a 90° phase cover plate that generates a circularly polarized wave based on a received signal, a polarization splitter that separates the output of the 90° phase cover plate into two mutually orthogonal polarized waves, and the polarization splitter A phase shifter that gives a 45° or 0° advance phase to one port of the wave shifter, and 45° to the other port.
Alternatively, an antenna device comprising a fading prevention circuit comprising a phase shifter that provides a delayed phase of ±90°, and a combiner that combines the outputs of both phase shifters.