TW405279B - Antenna for communicating with low earth orbit satellite - Google Patents

Abstract

To provide an antenna for communicating with a low earth orbit (LEO) satellite which is small-sized and light and can track a LEO satellite at high speed at a small-sized earth station using a LEO satellite, the above antenna uses an offset parabolic antenna-type reflector and a primary feed is installed in the focal position of the parabolic of revolution forming the reflector. The quantity of an offset of an offset parabolic antenna is selected so that antenna gain is maximum at the minimum operational elevation. The primary feed is mechanically independent of the mobile reflector, is attached and fixed to a radiator supporting part. In the meantime, the reflector is turned based upon an azimuth axis and an elevation axis according to AZ-EL mount.

Description

V. Description of the invention (1) [Background of the invention] Field of the invention The present invention relates to an antenna for communication with low earth orbit satellites, and more particularly to a low earth orbit (LE 0) satellite used to rotate around the earth. The ground station of a satellite communication system is used to communicate with low earth orbit satellites and automatically track the antenna of each satellite. Description of Conventional Technology Recently, a high-frequency signal using a Ka band (20 to 30 G Η z) via a plurality of LEO satellites has been proposed to provide users around the world with high speeds ranging from several Mbps to several tens of Mbps. Data plan. In such a satellite communication system using a plurality of LEO satellites, since each satellite will be out of sight in a relatively short time when viewed from a small ground station, it needs to be tracked over a wide range. To date, most of the techniques for an antenna used to track satellites, such as ground station antennas for stationary and mobile satellites, are well known. As for the tracking method, for example, there are three conventional methods: (a) single-pulse tracking method, which is used to continuously detect whether the antenna is tracking the satellite at the center of the beam, and to control the direction of the radiation pattern of the antenna always equal to Satellite direction; (2) Step-by-step tracking method, which is used to shift the antenna at a fixed time interval and adjust its azimuth, and its receiving level is the maximum; and (C) program tracking method, based on satellite orbit estimation information To change the orientation of the antenna. For a method that supports mobile antennas, there are two practices

405279 5. Description of the invention (2) Known methods: (1) AZ-EL bracket to transfer the azimuth and elevation angle of the mobile antenna; and (2) XY bracket to transfer the mobile antenna to a satellite orbit perpendicular to the satellite orbit direction. The AZ-EL bracket is the most commonly used method. One axis (azimuth axis) is placed perpendicular to the ground, and the other axis (elevation axis) is placed horizontally. In the XY bracket, the X-axis system horizontal to the ground is perpendicular to the y-axis, and the y-axis system rotates together with the X-axis. The XY bracket is suitable for tracking the LE0 satellite moving near the zenith at high speeds. However, because the two axes are located at a high position from the ground, the X Y bracket has mechanical defects. Next, a satellite tracking technique of an antenna of a conventional actual ground station for tracking satellites will be described in detail with reference to the drawings. Figure 11 shows the construction of a conventional antenna for a ground station for tracking satellites. Figure 11 shows an example of a large antenna for a ground station for tracking satellites. The main reflector is a Cassegrain antenna with a diameter of 13 meters. This antenna uses a driving mechanism based on the AZ-EL bracket to track the satellite, and both its azimuth axis and elevation axis are driven by a spiral crane driving mechanism. In order to simplify the structure, the driving mechanism may be allowed to continuously drive in the range of the azimuth axis direction only within 10 degrees of soil, and a limited driving method is adopted. When the antenna needs to be pointed at a larger angle in the other direction, that is, Loosen a set screw to turn the antenna slowly. For the elevation axis, continuous drive is possible from 0 to 90 degrees. The primary transmitter is mounted to the main mirror and is driven together with the main mirror. Figure 12 shows another conventional ground station antenna for tracking satellites, and a small ground station antenna for tracking satellites is also known to me.

V. Description of the invention (3) ^ In it, although an open-ended antenna is used as the above-mentioned large antenna, miniaturization and weight reduction can still be achieved. Figure 12 shows a parabolic antenna used in a ship's ground station in accordance with INMARSAT Standard A, and a cross-pole and bipolar (cr 〇ssdi ρ ο 1 e) and a reflecting plate are set on the rotating parabolic reflection The focal point of the mirror is used as a primary transmitter. In this antenna, the reflector and the transmitter are integrated. In order to track satellites, the parabolic antenna is driven using a 4-axis bracket (obtained by combining the AZ-EL bracket and the XY bracket). The above technology is described in "Introduction to Maritime Satellite Communications", by Toshio Sato, published on July 25, 2011, by the Japan Institute of Communications. As mentioned above, the use of traditional antennas as satellite communication technology for tracking satellites can be effectively applied to the case of extremely small tracking ranges (compared to geostationary satellites). However, the above-mentioned conventional antennas are not suitable for the above-mentioned applications. The reason for tracking and communicating with LEO satellites is as follows: In other words, in the traditional antennas for satellite communications, because the transmitter and the mirror system are combined together, and an antenna is rotated when tracking the satellite, the The antenna to be rotated is heavy and the driving system is large, so it is difficult to track at high speed, and the area of the radome covering the antenna is increased. In a satellite communication system using LEO satellites, considering that many small ground stations are installed in each home, the size of the entire antenna required is as small and light as possible. However, miniaturization and light weight are a major problem. . In addition, since the primary transmitter is combined with the mirror system and an antenna is rotated, in order to be able to feed the primary transmitter also during the rotation,

5. Description of the invention (4) The condition is stable, and the radio frequency (RF) transmitting / receiving unit with a feeding system such as a low noise amplifier and a high frequency power amplifier also needs to be installed close to the primary transmitter. However, in this case, the weight of the antenna also increases the weight of the RF transmitting / receiving section. Under this condition, it can also be understood that the RF transmitting / receiving part is separated from the mirror and fixed. However, in order to maintain a stable connection independent of the displacement caused by rotating the power feeding part, the power feeding line must be flexible and must be flexible. A rotary joint and other rotary joints are used. Therefore, the problem is that the antenna used for satellite communication is complicated and expensive. As mentioned above, the object of the present invention is to provide an antenna for communication with low earth orbit satellites, which is used in a small ground station to communicate with a plurality of LEO satellites. Such an antenna system can achieve miniaturization and weight reduction. , And can track a LEO satellite at high speed. [Comprehensive description of the invention] In order to achieve the above object, an antenna for communicating with a low earth orbit satellite according to the present invention is based on an antenna for communicating with a low earth orbit satellite. The antenna is a low earth orbit satellite. In the satellite communication system, it is used on the ground side and uses an offset aperture antenna to mechanically track the above-mentioned low earth orbit satellite. Here, the above-mentioned antenna is mechanically tracked by the following method: the primary transmitter of the fixed-open antenna is directed toward a low earth conducting satellite, and only the reflector of the antenna is wound around an azimuth axis and an elevation axis. Spin. Specifically, the present invention provides: a mirror with a predetermined rotation parabolic offset, and an AZ-EL bracket connected to the reflection

V. Description of the invention (5) 405279 mirror, which is used to track the above-mentioned low earth orbit satellite by rotating the above-mentioned mirror based on an azimuth axis and an elevation axis; a primary transmitter for emitting on the above-mentioned mirror A predetermined beam; a feeding unit to feed the primary transmitter; and a transmitter support unit to support the primary transmitter, so that the primary transmitter can be independent of the reflection Mirror and subject to fixation. The above-mentioned offset value is set on the condition that a maximum antenna gain is obtained at a predetermined minimum operating elevation angle. [Brief description of the diagram] FIG. 1 is a block diagram showing the composition of an offset parabolic antenna for communication with low earth orbit satellites, which is equivalent to the first embodiment of the present invention; FIGS. 2A and 2B illustrate the offset of FIG. 1 Fig. 3 A and 3 B illustrate the definition of the elevation axis of Fig. 2 A and 2 B; Fig. 4 shows an imaginary diagram of a LE 0 satellite; Fig. 5 shows a satellite communication system using an LE 0 satellite; Fig. 6 shows the tracking range according to the present invention; Fig. 7 shows the relationship between the propagation loss, antenna gain and total propagation loss at an elevation angle; Fig. 8 shows an offset Cassegrain for communication with low earth orbit satellites Antenna composition block diagram, equivalent to the second embodiment of the present invention; FIG. 9 is a composition block diagram showing an offset Cassegrain antenna for communication with a low-earth satellite, corresponding to the third embodiment of the present invention Figure 10 is a block diagram showing the composition of an offset Gregorian antenna for communication with low earth orbit satellites, which is equivalent to the first embodiment of the present invention.

405279_ V. Description of the invention (6) Three embodiments; Figure 1 1 shows the external appearance of a traditional large-scale ground station antenna tracking technology; and Figure 12 shows a conceptual view of a traditional small-scale ground station antenna tracking technology . [Description of symbols] 1 ~ 1 time transmitter 2 ~ offset mirror 3 ~ AZ-EL bracket 4 ~ feeding unit 5 ~ transmitter supporting unit 6 ~ RF transmitting / receiving unit 7 ~ antenna supporting unit 8 ~ rotation Parabolic axis 9 ~ Azimuth axis [Fig. 2A, 2B] 9 ~ Parabolic surface [Fig. 3A, 3B] 1 0 ~ Elevation axis 1 1 ~ Orbital surface 1 2 ~ Satellite tracking range [Fig. 6] 12 ~ Primary mirror [Fig. 8 , 9] 1 3 to small ground station [Figure 6] 1 3 to sub-reflector [Figure 8] 1 4 to circular hole

Page 10-465279- V. Description of the invention (7) 1 5 ~ Main mirror 16 ~ Sub mirror 1 0 0 ~ Antenna for communication with low earth orbit satellite [Description of preferred embodiment] 1. First Embodiment Next, a first embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a block diagram showing the composition of an antenna for communication with a low earth orbit satellite, which corresponds to a preferred embodiment of the present invention. As shown in FIG. 1, the antenna 100 for communicating with a low earth orbit satellite according to the present invention includes: a primary transmitter (horn) 1 for transmitting or receiving a signal in the Ka band; an offset mirror 2. A predetermined paraboloid of rotation is provided; an AZ-EL bracket 3 is connected to the mirror 2 to rotate an azimuth axis and an elevation axis and track the satellite; a power supply unit 4 is used to feed power to 1 A secondary transmitter 1; a transmitter support section 5 for fixing a primary transmitter 1; an RF transmitting / receiving section 6 composed of a low noise amplifier and a high frequency power amplifier; and an antenna support section 7, used to fix the entire antenna. This antenna uses an offset parabolic antenna type reflector antenna, and the primary transmitter 1 is installed at the focal position of the rotating paraboloid forming the reflector 2. I choose the offset of the offset parabolic antenna, so that the antenna gain can be maximized at the minimum operating elevation angle (described later). The primary transmitter 1 including a movable structure has a structure that is mechanically independent of the mirror 2 and is fixed to the transmitter support 5. At the same time, we formed the reflector 2 so that it could be rotated by the AZ-EL bracket 3 based on the azimuth axis and the elevation axis. From 1 launcher 1

Page 11 _405279_ V. Description of the invention (8) One or the other signals are fed to the RF transmitting / receiving section 6 through the feeding section 4. The AZ-EL bracket 3, the transmitter support section 5, and the RF transmitting / receiving section 6 are mounted on the antenna support section 7. Next, the operation of the antenna 100 for low earth orbit satellite communication of FIG. 1 will be explained. Figures 2A and 2B illustrate the tracking mechanism of such an antenna, and particularly show the mirror 2 and the primary transmitter 1 for tracking, respectively. FIG. 2A shows the front view of the reflector 2 and the primary transmitter 1. The solid line shows the position of the mirror 2 at the minimum operating elevation angle 0 M1N, and the dotted line shows the reflector 2 assuming that the elevation angle approaches 90 degrees. s position. Figure 2B shows the mirror 2 and the primary emitter 1 viewed from the side, respectively. It can also be clearly understood from these illustrations that an azimuth axis 9 is rotated around a straight line (connecting the center of the mirror 2 and the center of the primary transmitter 1), and the mirror 2 is centered on the azimuth axis 9 And rotate 360 degrees. Reference numeral 8 indicates an axis of the rotating object plane. Meanwhile, FIGS. 3A and 3B illustrate an elevation angle axis, and the elevation angle axis in these two figures refers to the inside of the rotating paraboloid passing through the offset mirror 2 from the intersection (center) of a rotating parabolic axis 8 and a parabolic surface 9. For a line in which a radial straight line touches an orthogonal axis in a paraboloid of rotation. An angle is centered on the axis of the elevation angle and changes between the minimum operating elevation angle and 90 degrees. The AZ-EL bracket 3 drives the mirror 2 so that the mirror can be rotated around the azimuth axis 9 and the elevation axis 10 to track the satellite. Even when the mirror 2 is rotated, the primary transmitter 1 is always fixed at the focal position of the parabola, because the primary transmitter 1 is fixed by the transmitter support 5.

Page 12 — 405279 5. Description of the invention (9) As mentioned above, according to the satellite communication antenna of the present invention, the reflector 2 can be rotated around the azimuth axis and can be tracked in all directions. The elevation angle showing the directivity can be changed by rotating the mirror 2 about the elevation axis, and the directivity in the zenith direction of the elevation angle of 90 degrees can be obtained. Then, the required tracking angle range of an antenna for communication with a low earth orbit satellite as described above will be explained. Fig. 4 is an imaginary view showing that most LE0 satellites are arranged on a plurality of orbital planes across the earth to cover the whole world. As shown in Fig. 4, a satellite communication system covering the whole world is provided by arranging a plurality of LE0 satellites throughout the earth, so that any satellite can be seen anywhere on the earth. LE0 satellite means a satellite located in an elliptical orbit (including circular orbit) at an altitude of nearly 1500 km on the ground, and it is assumed that at an altitude of 1,000 km, the orbital period of each satellite is approximately 1 hour 4 5 Minute. Assuming the height of a satellite is 765 km and its minimum operating elevation is 30 degrees, the number of satellites to be deployed on the same orbital plane is 20, and 10 beacon planes are required to cover the world. That is, the total number of satellites required is 200. The number of satellites required is based on the satellite's altitude and minimum operating elevation. Even if the satellites are at the same altitude, assuming an operating elevation of 20 degrees, the number of satellites required is 9 8; assuming an operating elevation of 10 degrees, the number of satellites required is 45. Fig. 5 is a conceptual diagram showing a wide-band satellite communication system using LE0 satellites. As shown in Figure 5, in this system, one of the low-speed channels of nearly 64 kbps using L-band (1.5 to 1.6 GHz) multi-beams is provided for small users (such as portable terminals). 'And use K a belt at small ground stations

Page 13-405279- V. Description of the invention (ίο) (commonly referred to as the quasi-millimeter wave band of 20 to 30 GHz) Most high-speed data of spot beams are provided for large-scale users (such as ships, aircraft and small-scale office). The present invention relates to an antenna for communication with a low earth orbit satellite, and this antenna is mainly the latter (used for a small ground station). FIG. 6 shows the tracking range of an LE0 satellite provided with a runway 1 1 viewed from a small ground station 13. As shown in Figure 6, the minimum operating elevation angle 0MIN is determined based on the relationship between the number of LE0 satellites and the above-mentioned altitude, and the satellite tracking range 12 is equivalent to the area represented by the oblique line, that is, from the minimum operating elevation angle θ MIN to The overall area of the omnidirectional angle in the zenith direction. Next, Fig. 7 shows the relationship between the propagation loss (A) and the offset parabolic antenna gain (B). The propagation loss (A) includes free space loss based on an elevation angle and loss due to rain attenuation. Figure 7 also shows the sum of the propagation loss (A) and the antenna gain (B), that is, the total propagation loss including the antenna gain (C = A + B). In FIG. 7, the minimum operating elevation angle 0 MIN is set to 40 degrees. We can adjust an offset to maximize the antenna gain at this elevation angle, and use the transmission frequency of 30 GHz in the Ka band to calculate the propagation loss. Therefore, Fig. 7 shows that the total propagation loss is maximum at a minimum operating elevation of 40 degrees, and that the total propagation loss is smaller when the elevation angle approaches the zenith. The reason is that due to the deviation from the ideal state of the parabolic mirror, the directivity gain in the zenith direction is low. However, in satellite communications in the microwave, millimeter-wave, and other bands, the antenna gain is required. This is because when the elevation angle is the smallest, the distance of the satellite is the longest and free

Page 14 4Θ5-27 »5. Description of the invention (π) The largest space loss, the longest distance through the rainfall area, and the largest amount of rainfall attenuation, and when in the zenith direction, the above attenuation is the smallest. Therefore, even if the elevation angle is set to the zenith direction, the problem can be really reduced by setting an appropriate value as the minimum operating elevation angle. 2. Second Embodiment The first embodiment of the present invention using an offset parabolic antenna is as described above, however, the present invention is not limited to such an antenna provided with a single mirror. That is, for the second embodiment of the present invention, one of the offset Cassegrain antennas provided with a plurality of mirrors can also be used. As shown in FIG. 8, reference numeral 12 denotes a main mirror with a rotating paraboloid. As described above, a predetermined offset is applied to the main mirror, and the maximum antenna gain can be obtained at the minimum operating elevation angle. Reference numeral 1 3 denotes a pair of mirrors, which are formed by a rotating hyperboloid, and the rotating hyperboloid uses a focal point of a rotating paraboloid as a focal point. Since the other focal point of the rotating hyperboloid is located in the area of the main mirror 12, a circular hole 14 for radiating a beam from the primary transmitter 1 is provided to the main mirror 12. Since the remaining reference numerals are similar to those in FIG. 1, their descriptions are omitted. In this embodiment, the antenna structure is complicated because an antenna provided with a plurality of mirrors is used. However, since the primary transmitter 1 feeds power from the back of the main mirror 12, the following effects can be produced: Reduce feed loss, make it easier to connect to send / receive department, and avoid interruption of tracking range. 3. Third Embodiment Furthermore, for the third embodiment of the present invention, one of FIG. 9 is used.

Page 15 _405279_ V. Description of the invention (12) An offset Cassegrain antenna with a plurality of reflectors. In this embodiment, the offset Cassegrain antenna provided with a plurality of mirrors in FIG. 8 is also used. However, this embodiment is different from the second embodiment in that the position of the primary transmitter 1 is located at the main Outside the mirror 12 area. 4. Fourth Embodiment Furthermore, for the fourth embodiment of the present invention, an offset Gregory antenna provided with a plurality of mirrors can also be used. In this embodiment, a predetermined offset is applied to the main mirror 15 having a rotating paraboloid, so that the maximum antenna gain can be obtained at the minimum operating elevation angle. The sub-mirror 16 with a rotating elliptical surface shares the focal point of the rotating paraboloid. The phase center of the primary transmitter 1 is located at the other focal point of the rotating ellipse. According to the structures of the second to fourth embodiments using the antenna provided with a plurality of mirrors, compared with the antenna of the first embodiment, the feeding loss is further reduced, the primary transmitter is fixed, and the overall antenna is The height is further reduced. As described above, the antenna for communication with low earth orbit satellites according to the present invention can produce the following effects: First, by isolating the sidelobe characteristics of the antenna from the electromagnetic radiation of cross polarization, it can be optimized. The minimum elevation angle in the satellite channel obtains the best characteristics of maximum propagation loss and rainfall attenuation. This is because of the use of offset parabolic antennas, offset Cassegrain antennas and other antennas, and these antennas are at the minimum The maximum elevation is obtained by operating the elevation angle. In particular, since the LE0 satellite system uses a millimeter wave band and has a large rainfall attenuation, the above-mentioned effect is significant.

Page 16-V. Description of the invention (13) Second, because the primary transmitter is fixed, there is no need to provide an elastic part for the feeder and the waveguide, which can simplify its structure and increase its reliability. Third, because the part driven to track the satellite is only a mirror, it can reduce the driving weight, can perform high-speed tracking, and make the driving mechanism small and lightweight.

Page 17

Claims (1)

6. Application patent scope 405279 1. An antenna for communication with low earth orbit satellites. In a satellite communication system using low earth orbit satellites, it is used in a ground station. An offset open antenna Earth orbiting satellites are used for mechanical tracking. 2. For example, the antenna for communication with low earth orbit satellites in the scope of patent application, wherein the mechanical tracking is by fixing a primary transmitter of the open antenna, and in the direction of the low earth orbit satellite, based on An azimuth axis and an elevation axis are achieved by rotating only a mirror of the open antenna. 3. An antenna for communication with a low earth orbiting satellite, which is used in a ground station in a satellite communication system using a low earth orbit satellite, and includes: a reflector with a predetermined parabolic offset of rotation; An AZ-EL bracket is connected to the mirror, and is used to track the low-Earth orbit satellite by rotating the mirror based on an azimuth axis and an elevation axis; A predetermined beam is radiated on the mirror; a power feeding section for feeding the primary transmitter; and a transmitter support section for supporting the primary transmitter, so that the primary transmitter can be independent It is fixed to the mirror. 4. For the antenna for communication with low earth orbit satellites in item 3 of the scope of patent application, the value of the offset is set such that the antenna gain is maximized at a predetermined minimum operating elevation angle. P.18 _ ^ 05279_ VI. Patent application scope 5. For the antenna for communication with low earth orbit satellites in item 4 of the patent application scope, where: the predetermined minimum operating elevation angle is at the low earth orbit satellite The tracking limit in the elevation direction; and the predetermined minimum operating elevation angle is determined based on the number of satellites placed on the same orbital plane as the low-Earth orbiting satellite. 6. For the antenna for communication with low earth orbit satellites in the scope of patent application No. 3, wherein the antenna is an offset parabolic antenna. 7. The antenna for communication with low earth orbit satellites, such as in claim 3, wherein the antenna is an offset Cassegrain antenna. 8. The antenna for communication with low earth orbit satellites according to item 3 of the patent application, wherein the antenna is an offset Gregorian antenna. 9. For the antenna for communication with low earth orbit satellites in the scope of patent application No. 3, wherein:-the azimuth axis is rotated about a straight line connecting the center of the mirror and the center of the primary transmitter; and ' The elevation axis is in contact with a line orthogonal to the rotating parabola from a point of intersection (center) of the rotating paraboloid axis and a paraboloid through a radial straight line in the rotating paraboloid of the offset mirror. 10. For the antenna for communication with low earth orbit satellites in the scope of patent application item 3, wherein a range tracking the low earth orbit satellite is in the elevation direction from the minimum operating elevation to the zenith, and in the azimuth direction The range is from 0 degrees to 360 degrees. Page 19 6. Application for special application in 11. If the antenna used for communication with low earth orbit satellites in item 3 of the patent application scope, wherein the antenna for communication with low earth orbit satellites is in a microwave band or a millimeter A band transmits / receives a high-frequency signal. Page 20