JPH0640633B2 - Interference removal antenna device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an antenna device that is effective when applied to a line-of-sight wireless communication system with fading caused by reflected waves from the sea surface or the like.

(Prior art and its problems) Generally, in a line-of-sight wireless communication system in which the propagation path of radio waves includes the sea surface, it is desirable to reduce the influence of reflected waves from the sea surface as much as possible in order to prevent deterioration of communication quality due to fading. . In order to reduce this effect, measures such as a configuration in which the directivity of the antenna is shaped to reduce the gain in the direction of arrival of the reflected wave and a configuration in which space diversity is performed using a plurality of antennas have been conventionally taken.

On the other hand, as one type of line-of-sight wireless communication system in recent years,
The so-called maritime satellite, which is a communication for ships traveling on the sea using communication satellites, has been put to practical use, and the practical application of aeronautical satellite communication for aircrafts is also under consideration. These are collectively referred to as mobile satellite communications, but the antenna mounted on the mobile body must be miniaturized due to the installation space problem. However, the directivity of a small antenna is generally broad and has a low gain. Therefore, if the elevation angle of the communication satellite viewed from the mobile object becomes low, the proportion of the sea surface reflected wave received by the main beam of the antenna increases, and the effect thereof becomes large fading, which deteriorates the communication quality. Actually, the service area of mobile satellite communication is in the range of elevation angle of 5 ° or more, and fading in the vicinity of elevation angle of 5 ° is large.

Therefore, it is conceivable to apply the conventional fading mitigation measures described above to mobile satellite communication.

However, the configuration in which the directivity of the antenna is shaped as described above is not a good idea because it complicates the power feeding system and increases the size of the antenna. Also, in space diversity,
There are drawbacks such as the need for a plurality of antennas and the effect of reducing fading cannot be expected for a transmission signal.

Therefore, in the case of mobile satellite communication,
A method that has a large effect of suppressing the influence of reflected waves and has a small installation space is desirable.

From such a viewpoint, in recent years, attention has been paid to the fact that reflected waves of the sea surface show unique polarization characteristics, and a method of controlling the polarization characteristics of the antenna to reduce fading (hereinafter referred to as “polarization control method”). Was proposed.

The polarization characteristics peculiar to the sea surface reflected wave in this method are as follows. Now, it is assumed that the radio waves emitted from the communication satellite are circularly polarized waves. Considering the reflection coefficient when this radio wave is reflected on the sea surface, the horizontal component of the radio wave is almost 1 regardless of the incident angle to the sea surface, but the vertical component has a smaller reflection coefficient as the incident angle becomes smaller. Become. That is, the horizontal component of the reflected wave does not change, but the vertical component is attenuated by the incident angle, so
The reflected wave on the sea surface arrives at the antenna as an elliptically polarized wave whose major axis is horizontal and whose axial ratio is determined by the angle of incidence on the sea surface. Further, the reflected wave on the sea surface has a characteristic that it is a reverse-polarized polarized wave with respect to the radio wave directly received from the communication satellite.

Therefore, the polarization characteristic of the antenna is equal to the axial ratio of the reflected wave,
If the major axes are orthogonal, the orthogonal conditions for elliptically polarized waves are the same, the axial ratios are equal, the major axes are orthogonal, and there is a reverse rotation relationship, and the reflected wave is received. It will not be done.

The above is the principle of the polarization control method. This method can be easily realized by using a cross-dipole-fed antenna, for example, a parabolic antenna or a short backfire antenna.

Here, a conventional example of an antenna system that realizes the polarization control method is shown in FIG. 1 and will be described. In Fig. 1 (a), 1
Is a crossed dipole antenna element in which the dipole element # 1 and the dipole element # 2 are arranged so as to be orthogonal to each other, 2 is a 90 ° phase shifter for forming a circular polarization antenna, and 3 is the polarization characteristic of the antenna. The variable phase shifter 4 for controlling the control circuit 4 is a synthesizing circuit. Among the radio waves sent from the satellite, the radio wave received by one of the dipole antenna elements # 1 is sent to the synthesis circuit 4. The radio wave received by the other dipole antenna element # 2 passes through the 90 ° phase shifter 2 and is then input to the variable phase shifter 3. Here, by changing the phase shift amount of the variable phase shifter 3, that is, the additional phase shift amount in the range of 0 to 90 °, the polarization characteristic of the antenna is circularly polarized as shown in FIG. 1 (b). It can be arbitrarily set from a wave to a linearly polarized wave that coincides with the axis 30 '. Where axis 30 'is the first
Virtual line 3 connecting the tips of dipole elements # 1 and # 2 in Figure (a)
It is orthogonal to 0.

Therefore, the virtual line 30 is set parallel to the horizontal line, and the phase shift amount of the variable phase shifter 3 is controlled according to the incident angle of the reflected wave on the sea surface (equal to the elevation angle at which the radio wave arrives from the satellite to the antenna). For example, it is possible to satisfy the orthogonal condition of the polarization characteristic of the antenna and the polarization characteristic of the reflected wave described above, and suppress the sea surface emission fading.

The above is an example of the configuration of the antenna feeding circuit that faithfully executes the fading reduction by the polarization control method based on the principle. However, since the polarization characteristics of the sea surface reflected wave largely change with changes in the satellite elevation angle, the additional phase shift required to make the antenna polarization characteristics orthogonal to that of the sea surface reflected wave is Therefore, the variable phase shifter 3 and a circuit for controlling the variable phase shifter 3 are required, which has a drawback that the insertion loss increases and the system becomes complicated.

(Objects and Features of the Invention) The present invention provides an interfering wave elimination antenna device that has less loss in the antenna feeding system as compared with the above configuration example and can be realized with a small size and a simple configuration.

The present invention relates to two linear polarization antenna elements, a phase shifter connected to one of the two linear polarization antenna elements, an output of the phase shifter, and the two linear polarization antenna elements. In the antenna device having a synthesizer for synthesizing the other output of the antenna device and configured to direct the communication satellite, when the elevation angle with respect to the communication satellite is less than a predetermined angle near 10 °, the phase shifter The phase shift amount is fixed to a fixed value within the range of 130 to 140 degrees, and is characterized in that it has a function of fixing the elevation angle of the antenna device to a predetermined value in the vicinity of 10 °.

(Structure and Operation of the Invention) Hereinafter, the principle of the present invention will be described with reference to the drawings.

First, Fig. 2 shows an example of maritime satellite communication. Focusing on satellite elevation angles of 5 ° and 10 ° (minimum operating elevation angle is 5 °) and antenna gain of 18 dBi, where fading is a particular problem, the additional phase shift amount is The fading amount when changed is shown. In the figure, the offset angle is the angle obtained by offsetting the main beam of the antenna from the arrival direction of the direct wave to the high elevation angle direction. From the figure (b), there is no big difference in the fading amount between the offset angle of 0 ° and 5 ° at the elevation angle of 10 °.
When the offset angle is 5 ° at the elevation angle of 5 ° in (a), the fading reduction effect is exhibited in the range where the additional phase shift amount is small. In addition, at the elevation angle of 5 ° in the figure (a), the additional phase shift amount that minimizes the fading amount when the offset angle is 5 ° is 40 ° to 50 °, which is the elevation angle in the conventional polarization control method. At 10 ° (corresponding to an offset angle of 0 ° in FIG. 3B), this optimum addition phase shift amount is almost the same. This is shown in Figure 2.
In the example shown in (a) and (b), the additional phase shift amount is fixed at 40 ° to 50 °, and the offset angle is set to 5 at the elevation angle of 5 ° shown in Fig. 2 (a).
No offset at 0 ° of elevation shown in Fig. 2 (b) (0
)), The fading amount is almost the minimum at both elevation angles, suggesting that a considerable fading reduction effect can be expected.

Fig. 3 shows the antennas at an elevation angle of 5 °, without fading reduction, with an optimum additional phase shift amount at an elevation angle of 10 °, when mechanically offset by 5 °, and for each of the conventional polarization control methods. The amount of fading with respect to the gain is shown. From the figure, the antenna gain is 10 to 20 dBi.
It is understood that, within the range, the method of the present invention can be expected to have a fading reduction effect that is almost the same as that of the conventional polarization control method.

As described above, according to the present invention, in the above example, the additional phase shift amount is fixed to a value that minimizes the fading value when the elevation angle is 10 °, and the antenna beam is mechanically offset by 5 °. Has created the following advantages.

(1) In the conventional system, the antenna was mechanically moved up to a minimum operation elevation angle of 5 °. Therefore, it was necessary to always move the antenna beam up to a satellite elevation angle of 5 ° in consideration of the rolling motion of the ship. However, even if the satellite elevation angle is 5 °, the antenna does not move below 10 ° even if the satellite elevation angle is 5 °. The movable range can be made smaller than in the past, and as a result, miniaturization (especially height) of the antenna system can be expected.

(2) According to the polarization control method, since the offset angle is 0 °, the optimum additional phase shift amount when the satellite elevation angle is 5 ° is shown in Fig. 2 (a).
Although it is about 70 °, it is less than this when the elevation angle is 10 °, and the optimum additional phase shift amount is 40 ° to 50 °. When this additional phase shift amount is given, the antenna polarization becomes an elliptical polarization with an axial ratio corresponding to the additional phase shift amount, and loss (polarization) due to polarization mismatch with the circularly polarized wave from the satellite. Wave loss) occurs. Conventional polarization control method (additional phase shift amount = 70
In the present invention, this polarization loss is 1.7 dB, but in the present invention, it is 0.7 when a fixed phase shift of 40 ° to 50 ° is applied.
It results in a polarization loss of dB. This has the advantage that the present invention can reduce the polarization loss with respect to direct waves, and the fading mitigation efficiency is correspondingly good.

(3) For example, as in the case of this example, when the satellite elevation angle where fading is a problem is 10 ° or less, a fixed additional phase shift amount of 40 ° to 50 ° is given, and for example, fading is almost a problem. If an elevation angle of 15 ° or more is not achieved and a switch mechanism is added that makes the additional phase shift amount 0 ° (normal antenna), the variable phase shifter as shown in Fig. 1 is not required, and the weight of the antenna is reduced and the power feeding system loss is lost. Can be expected to have the effect of reducing

For example, in terms of the power feeding system loss, when the variable phase shifter is used in the conventional polarization control method, the loss is about 1.5 to 2 dB, and when the fixed phase shifter according to the present invention is used. The loss is about 1 dB. Furthermore, if a feeder of a length that gives a predetermined phase difference is used instead of the fixed phase shifter,
The loss is about 0.3 dB, and the reduction effect is clear.

(Example) The fourth cormorant shows an example of the present invention excluding the driving part of the antenna device. In the figure, 1, 2 and 4 are the same as those in FIG. 1, and 5 is a fixed phase shifter capable of switching between 0 ° and 40 ° to 50 ° as the phase shift amount. The operation of the above embodiment will be described. 1, 2 and 4 are the same as in FIG. The fixed phase shifter 5 sets the phase shift amount to 0 ° or a constant value in the range of 40 ° to 50 ° depending on whether the satellite elevation angle is larger or smaller than a preset elevation angle (for example, 15 °). The signal input to the fixed phase shifter 5 receives the change in the phase shift amount and is input to the combining circuit 4. In this embodiment, it is necessary to control the line connecting the tips A and B of the cross dipole to be parallel to the horizontal line (for example, control by a mechanism that mechanically rotates the antenna 1). ) In 90
° Instead of the phase shifter 2 and the combining circuit 4, the outputs of the antenna elements # 1 and # 2 are combined by using the variable power distributor 6 as shown in FIG. If the polarization characteristics of are made orthogonal to that of the reflected wave from the sea surface,
The above control becomes unnecessary.

The above configuration and operation will be described in more detail with reference to FIGS. 5 (a) (b) (c).

FIG. 5 (a) is a specific example of the drive control system of the antenna device. The figure shows the azimuth angle (AZ) called AZ-EL manout.
Is an example of a system in which the antenna 1 is directed in the satellite direction by controlling the angle of elevation and the angle of elevation (EL). Where 1
Is an antenna, 7 is an elevation (EL) axis, 8 is a motor M ₁ for driving the elevation axis, 9 is an angle detector D ₁ for detecting an elevation, 10 is an azimuth (AZ) axis, and 11 is an azimuth. Motors M ₂ and 12 for driving the angular axis 10 are angle detectors D ₂ and 13 for detecting an azimuth angle, drive motors M ₃ and 14 for controlling the rotation angle of the antenna 1 are rotations of the antenna 1. The angle detectors D ₃ and 15 for detecting the angle control the primary radiator of the antenna or the antenna body from the radiator to the main reflector so that the virtual line of the antenna shown in FIG. 1 is parallel to the horizontal line. The antenna control unit 16 controls the antenna pointing direction in the horizontal plane based on the azimuth information obtained from the angle detector 12 (D ₂ ), and 17 the elevation angle obtained from the angle detector 9 (D ₁ ). EL control to control antenna pointing direction in vertical plane based on information The control part, 20 is a signal indicating that the satellite elevation angle is 10 ° or less.

The antenna 1 is controlled as follows.

For example, a moving body such as a ship has a geographical position as navigation information, and the position of a satellite is known in advance. Therefore, the azimuth (AZ) information and the elevation angle (EL) information for pointing the satellite from the ship can be obtained from them. Further, when the antenna system has a so-called self-tracking function of detecting the arrival method of the beacon radio wave from the satellite, the AZ information and the EL information can be obtained therefrom. AZ control unit 16 and EL control unit
17 inputs AZ information or EL information,
This is compared with the azimuth angle and the elevation angle of the antenna 1 detected by the angle detector 12 and the angle detector 9, respectively, and the motors 11 and 8 are driven by the difference signals, and the AZ
The control is performed so that the information and the azimuth angle of the antenna 1 match and the EL information and the elevation angle of the antenna 1 match.

Here, in the case of a ship, shaking is involved. This upset information is
Detected using a gyro attached to the hull, A
The Z control unit 16 and the EL control unit 17 use this as shaking information to perform shaking compensation control. Furthermore, as mentioned above, the imaginary line 30 of the antenna 1 shown in FIG. 1 must always be kept parallel to the horizontal line. For this reason, the motion information is also supplied to the antenna controller 15 and compared with the rotation angle information of the antenna 1 detected by the angle detector 14 (information indicating the amount of deviation between the virtual line 30 and the horizontal line). The motor 13 controls the virtual line 30 to a desired angle so that it becomes parallel to the horizontal line. Also, in FIGS. 5 (b) and 5 (c), 18 and 19 are switches,
Upon receiving the signal 20 from the control unit, when the elevation angle is 10 ° or less, the mode is switched to the fixed phase shifter.

Here, in order to carry out the present invention, if the EL control unit 17 is collapsed, the following or function is added.

When the elevation angle becomes 10 ° or less, a signal 20 to that effect is generated and an offset angle is given.
The EL axis 7 is controlled so that the sum of the information and the offset angle is always 10 °. That is, when the satellite elevation angle is α (≦ 10 °), the offset angle is (10−α) °. Signal 20 is
The switches 18 and 19 shown in FIG. 5 (b) are operated to switch to the fixed phase shifter 5 side. The additional phase shift amount at this time is shown in FIG.
From the characteristic of the offset angle of 0 ° in (b), a phase shift amount of about 40 ° to 50 ° that gives the maximum effect is given.

When the elevation angle becomes 10 ° or less, a signal 20 to that effect is issued, and the control of the EL axis 7 is stopped except for motion compensation. The function of the signal 20 controlling the switches 18, 19 is similar to.

In this function, since the elevation angle of the antenna 1 is fixed at 10 °, an offset angle of 5 ° is given when the arrival angle of the radio wave is 5 °, and 0 ° when it is 10 °. The offset angle. Therefore, the fixed phase shifter is
Assuming that there is an arbitrary phase shift amount of 5 °, the minimum fading value in the characteristic (dotted line) of the offset angle 5 ° of Fig. 2 (a) at an elevation angle of 5 °, and Fig. 2 (b) at an elevation angle of 10 °. A fading mitigation effect is obtained, which is the minimum value of the characteristic (solid line) of the offset angle of 0 °.

In the above explanation, it is assumed that the phase shifter can be switched to the fixed phase shifter at an elevation angle of 10 ° or less. The value of the elevation angle at which the switching is performed is as shown in FIGS. 2 (a) and 2 (b). And the amount of phase shift to be given. Further, in the above example, the fixed phase shifter 5 is used to give the amount of phase shift, but a feeder having a length giving a desired amount of phase shift may be replaced with this. As another specific example, if the variable power distributor 6 is used instead of the combination circuit 4 and the 90 ° phase shifter 2 in FIG. As described above, the antenna control unit 15 shown in FIG.

(Effects of the Invention) As described above, the present invention has advantages that it is simple and has a good fading reduction effect as compared with the conventional method, and that the antenna system is reduced in size and weight.

In the above explanation, the case where the antenna is fixed in the direction in which the satellite elevation angle is 10 ° has been described, but it is also possible to fix it at another elevation angle depending on the target case.
Further, it is of course possible to finely set the additional phase shift amount and the offset angle in several steps.

[Brief description of drawings]

1 (a) and 1 (b) are block diagrams and polarization characteristic diagrams for explaining the conventional polarization control method, and FIGS. 2 (a) and 2 (b) are characteristic diagrams of fading amount with respect to additional phase shift amount. FIG. 3 is a characteristic diagram of the fading amount with respect to the antenna gain comparing the fading reduction effect of the present invention with a conventional polarization control method, and FIGS. 4 (a) and (b) are block diagrams of an embodiment of the present invention. 5 (a) (b) (c) are block diagrams for explaining the detailed configuration and operation of the method of the present invention. 1 ... Cross dipole feeding antenna element, 2 ... 90 ° phase shifter, 3 ... variable phase shifter, 4 ... combining circuit, 5 ... fixed phase shifter, 6 ... variable power distributor, 7 ... ... elevation shaft, 8 ...... motor (M _1), 9 ...... angle detector (D _1), 10 ...... azimuth axis, 11 ...... motor (M _2), 12 ...... angle detector (D ₂₎ , 13 ...... Motor (M ₃ ), 14 ...... Angle detector (D ₃ ), 15 ...... Antenna control section, 16 ...... AZ control section, 17 ...... EL control section. 18, 19 …… Switch, 30 …… Virtual line, 30 ′ …… Axis.

Front Page Continuation (72) Inventor Takayasu Shiokawa 2-23, Nakameguro, Meguro-ku, Tokyo International Telegraph and Telephone Corporation Laboratories (56) Reference JP-A-57-159138 (JP, A)

Claims (1)

[Claims] 1. Two linear polarization antenna elements, a phase shifter connected to one of the two linear polarization antenna elements, an output of the phase shifter, and the two linear polarization antennas. An antenna device comprising a synthesizer for synthesizing the other output of the element and configured to direct to a communication satellite, wherein the phase shifter is used when the elevation angle with respect to the communication satellite is equal to or less than a predetermined angle near 10 °. The amount of phase shift of is fixed to a constant value within the range of 130 to 140 degrees, and the function of fixing the elevation angle of the antenna device to a predetermined value in the vicinity of the above 10 degrees is provided. Antenna device.