Tracking system with beam switching antenna

• US 4,881,078 A
• Filed: 05/31/1988
• Issued: 11/14/1989
• Est. Priority Date: 05/29/1987
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Kuramoto, Akio, Nakayama, Makoto, Shimizu, Ryuji, Yamane, Toshinobu
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Issing, Gregory C.
• Application Number:
  US07/200,215
• Time in Patent Office: 532 Days
• Field of Search: 342/359, 342/368, 342/371, 342/372, 342/374, 342/439, 342/422, 342/425, 342/426, 342/427, 342/420, 342/74, 342/75, 342/77, 342/79, 342/81, 342/155, 342/157, 343/754, 343/757
• US Class Current: 342/155
• CPC Class Codes: G01S 3/20 derived by sampling signal received by an antenna system having periodically-varied orientation of directivity characteristic
• CPC Class Codes: G01S 3/42 the desired condition being maintained automatically
• CPC Class Codes: H01Q 3/08 for varying two co-ordinates of the orientation
• CPC Class Codes: H01Q 3/24 varying the orientation by switching energy from one active radiating element to another, e.g. for beam switching

Abstract

In a tracking system for a stationary satellite, a phased array is used for an antenna mounted on an automobile. The phased array antenna has a sharp beam which is switched between two different directions in azimuth. The antenna beam is switched between the two directions periodically by control of phase constants in a feeding circuit of the antenna and comparison is made in strength between signals received before and after the beam switching to obtain an error signal as an azimuth error signal. Then, the antenna is mechanically moved in azimuth according to the azimuth error signal until the azimuth error signal becomes zero. In a case the antenna beam is also switched between two directions in elevation, the antenna beam is switched in elevation during an interval between successive two times of the beam switching operation in azimuth and detects a difference in strength of signals received before and after the switching in elevation to thereby produce the difference as an elevation error signal. The antenna is mechanically moved in elevation according to the elevation error signal until the elevation error signal becomes zero.

Claims

1. In a tracking system for tracking an electromagnetic energy source which comprises an antenna for receiving the electromagnetic energy, receiver means coupled with the antenna through feeding means for producing a signal of the electromagnetic energy received by the antenna as a receive signal, and moving means for mechanically and angularly moving the antenna so as to point the antenna to the electromagnetic energy source to thereby maximize the receive signal strength, the improvement which comprises:

said antenna being a radiator having an antenna beam which is changeable in direction in response to variation of an electric characteristic in said feeding means;

selection signal generating means for producing a first and a second selection signal alternately;

said feeding means comprising electric variable means which is variable in impedance as the electric characteristic from one to another of a first and a second value, said antenna beam being directed in a first direction when said electric variable means has said first value, said antenna beam being directed in a second direction when said electric variable means has said second value, said first and said second directions having a predetermined small angular difference, said electric variable means having said first and said second values alternately in response to said first and said second selection signals alternately produced to thereby switch said antenna beam from one to the other of said first and said second directions;

detection means coupled with said receiver means for detecting said received signal to produce a detected signal;

processing means coupled with said detection means for deciding the detected signal strength before and after switching of said antenna beam to produce an error signal; and

said moving means coupled with said processing means and responsive to said error signal for mechanically and angularly moving said antenna to thereby reduce said error signal.

2. A tracking system as claimed in claim 1, wherein said antenna beam has a pattern which is sharp in azimuth and broad in elevation, said first and said second directions being different from one another in azimuth, said moving means moving said antenna in azimuth.

3. A tracking system as claimed in claim 1, which further comprises decision means coupled with said receiver means for deciding a level of said receive signal to produce a control signal when said receive signal level is lower than a predetermined reference level, means responsive to said control signal for generating a constant driving signal, said moving means angularly moving said antenna in a predetermined rotating direction at a constant speed in response to said constant driving signal.

4. A tracking system as claimed in claim 1, which further comprises oscillating means for oscillating a reference signal having a predetermined frequency, said detection means being coupled with said oscillating means and carrying out a coherent detection of said receive signal by said reference signal to produce said detected signal.

5. A tracking system as claimed in claim 4, which further comprises switching signal generating means coupled with said oscillating means for generating a switching signal synchronous with said reference signal, said selection signal generating means being coupled with said switching signal generating means and generating said first and said second selection signals alternatingly in synchronism with said switching signal, and wherein said processing means comprises:

delivering means coupled with said detection means and said switching signal generating means for delivering said detected signal to a first output as a first detected signal and a second output as a second detected signal alternatingly in synchronism with said switching signal;

first sample and hold means coupled with said first output for sampling said first detected signal and holding a level of said first detected signal as a first level;

second sample and hold means coupled with said output for sampling said second detected signal and holding a level of said second detected signal as a second level; and

comparing means coupled with said first and said second sample and hold means for comparing said first and said second levels to produce a difference of said first and said second levels as said error signal.

6. A tracking system as claimed in claim 5, wherein said antenna comprises a dielectric plate and two antenna elements arranged on said dielectric plate to form a phased array each of the antenna elements being formed in a spiral form as a microstrip line on the dielectric plate.

7. A tracking system as claimed in claim 6, wherein said electric variable means comprises phase shift circuit means comprising impedance elements and diode means, said phase shift circuit means having a first phase constant as said first value when said diode means is not conductive, said phase shift circuit means having a second phase constant as said second value when said diode means is conductive, said selection signal generating means comprising;

biasing means for producing a bias voltage for making said diode means conductive; and

switching means coupled with said biasing means and said switching signal generating means for switching off and on said biasing means alternately in response to and in synchronism with said switching signal to deliver no bias voltage as said first selection signal and said bias voltage as said second selection signal to said diode means.

8. In a tracking system for tracking an electromagnetic energy source which comprises an antenna for receiving the electromagnetic energy, receiver means coupled with the antenna through feeding means for producing a signal of the electromagnetic energy received by the antenna as a receive signal, and first and second moving means for mechanically and angularly moving the antenna in azimuth and elevation, respectively, so as to point the antenna to the electromagnetic energy source to thereby maximize the receive signal strength, the improvement which comprises:

said antenna being a radiator having an antenna beam which is changeable in direction in response to variation of an electric characteristic in said feeding means;

selection signal generating means for producing a first, a second, a third, and a fourth selection signal alternately;

said feeding means comprising electric variable means which is variable in impedance as the electric characteristic from one to another of a first, a second, a third, and a fourth value, said antenna beam being directed in a first direction when said electric variable means has said first value, said antenna beam being directed in a second direction when said electric variable means has said second value, said first and said second directions having a predetermined small angular difference in azimuth, said antenna beam being directed in a third direction when said electric variable means has said third value, said antenna beam being directed in a fourth direction when said electric variable means has said fourth value, said third and said fourth directions having a predetermined small angular difference in elevation, said electric variable means having said first, said second, said third, and said fourth values alternatingly in response to said first, said second, said third, and said fourth selection signals alternatingly produced to thereby switch said antenna beam from one to another of said first, said second, said third, and said fourth directions;

detection means coupled with said receiver means for detecting said receive signal to produce a detected signal;

processing means coupled with said detection means for deciding the detected signal strength before and after switching of said antenna beam to produce an azimuth error signal and an elevation error signal;

said first moving means coupled with said processing means and responsive to said azimuth error signal for mechanically and angularly moving said antenna is azimuth to thereby reduce said azimuth error signal; and

said second moving means coupled with said processing means and responsive to said elevation error signal for mechanically and angularly moving said antenna in elevation to thereby reduce said elevation error signal.

9. A tracking system as claimed in claim 8, which further comprises oscillating means for oscillating a reference signal having a predetermined frequency, said detection means being coupled with said oscillating means and carrying out a coherent detection of said receive signal by said reference signal to produce said detected signal.

10. A tracking system as claimed in claim 9, which further comprises switching signal generating means coupled with said oscillating means for generating a first and a second switching signal synchronous with said reference signal, said first and said second switching signals having said predetermined frequency and a half of said predetermined frequency, respectively, said selection signal generating means being coupled with said switching signal generating means and generating said first, said second, said third, and said fourth selection signals alternatingly in synchronism with said first switching signal, and wherein said processing means comprises:

first delivering means coupled with said detection means and said switching signal generating means for delivering said detected signal to a first output as a first detected signal and to a second output as a second detected signal alternatingly in synchronism with said first switching signal;

first sample and hold means coupled with said first output for sampling said first detected signal and holding a level of said first detected signal as a first level;

second sample and hold means coupled with said second output for sampling said second detected signal and holding a level of said second detected signal as a second level;

comparing means coupled with said first and said second sample and hold means for comparing said first and said second levels to produce a difference of said first and said second levels as an error signal;

second delivering means coupled with said comparing means for delivering said error signal to a third output as said azimuth error signal and to a fourth output as said elevation error signal.

11. A tracking system as claimed in claim 10, wherein said antenna comprises a dielectric plate and four antenna elements arranged in a matrix form on said dielectric plate to form a phase array, each of the antenna elements being formed in a spiral form as a microstrip line on the dielectric plate.

12. A tracking system as claimed in claim 11, wherein said first value and said third value are a common value, said first direction and said third direction being a common direction, said electric variable means comprising phase shift circuit means comprising impedance elements and first and second diode means, said phase shift circuit means having said common value when both of said first and second diode means are not conductive, said phase shift circuit means having said second value when said first diode means is conductive with said second diode means being not conductive, said phase shift circuit means having said fourth value when said second diode means being conductive with said first diode means being not conductive, said selection signal generating means comprising:

biasing means for producing a bias voltage for making said first and second diode means conductive;

first switching means coupled with said biasing means and said switching signal generating means for switching off and on alternately in response to and in synchronism with said first switching signal to deliver no bias voltage as said first selection signal and said bias voltage as said second selection signal to said first diode means in response to said second switching signal; and

second switching means coupled with said biasing means and said switching signal generating means for switching off and on biasing means alternately in response to and in synchronism with said first switching signal to deliver no bias voltage as said third seletion signal and said bias voltage as said fourth selection signal to said second diode means in response to said second switching signal.