Two-axis antenna direction control system

• US 4,418,350 A
• Filed: 03/23/1981
• Issued: 11/29/1983
• Est. Priority Date: 03/23/1981
• Status: Expired due to Fees

• Current Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Rosen, Harold A.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US06/246,793
• Time in Patent Office: 981 Days
• Field of Search: 343/100 ST, 343/100 AD, 343/119, 343/16 M, 343/117 R
• US Class Current: 342/359
• CPC Class Codes: H01Q 1/1257 using the received signal strength
• CPC Class Codes: H01Q 3/005 using remotely controlled antenna positioning or scanning

Abstract

An antenna pointing control system primarily useful for aiming and controlling a communications satellite directional antenna. The invention makes use of a ground based pilot station which transmits an up-link signal to the satellite, including frequency differentiated communication signals and command and control signals. The command and control signals are referred to as the beacon or pilot signal. The pilot signal is a triangular frequency modulation waveform. The communications signals and the pilot signal are received by a common directional antenna on the satellite. A microwave network coupled to a multiple feed horn assembly of the antenna and responsive to the pilot signal produces pilot signal components including a sum signal and east-west and north-south error signals indicative of the corresponding angular errors between the desired antenna pointing direction and the direction from the satellite to the pilot station. Subsequent processing of the pilot signal components in a command and control receiver yields both command information and steering signals, the latter for controlling the antenna pointing direction with respect to the pilot station.

Claims

1. In a communication system, an arrangement for producing an antenna pointing error signal, comprising:

a two-dimensional antenna assembly having feed horns and a reflector for receiving a radiated frequency modulated signal from a remote signal source;

means connected to said antenna feed horns for producing a sum signal and two orthogonally related difference signals;

means for combining said difference signals in phase quadrature relationship; and

circuit means including a directional filter having a flat amplitude response and linear phase shift over the frequency range of frequency modulation for combining said sum signal with said combined difference signals thereby to produce an antenna pointing error signal.

2. In a communication system, an arrangement for producing an antenna pointing error signal, comprising:

an antenna assembly including a reflector for receiving a beacon signal which periodically deviates in frequency from the low end to the high end of its frequency band and back;

a plurality of antenna feed horns disposed at the focal plane of said reflector;

a biconjugate hybrid junction network coupled to said antenna feed horns to provide a sum signal, a N-S pointing error signal and an E-W pointing error signal;

a phase quadrature hybrid junction network coupled to said biconjugate hybrid junction network for combining said pointing error signals in phase quadrature relationship; and

circuit means coupled to said biconjugate hybrid junction network and to said phase quadrature hybrid junction network and including a directional tracking filter for combining said sum signal with said combined pointing error signals, said directional tracking filter being tuned to the frequency band of said beacon signal and having a flat amplitude response and a linear phase response over the frequency band of said beacon signal with a phase difference of 360°

between the low and high frequency extremes of said beacon signal to thereby produce an amplitude modulated antenna pointing error signal containing the combined N-S and E-W antenna pointing error information.

5. Apparatus as set forth in claim 2 in which said circuit means further includes a phase quadrature hybrid junction network having individual input arms coupled to said first named phase quadrature hybrid junction network and to said directional tracking filter, respectively, for producing said amplitude modulated antenna pointing error signal containing the combined N-S and E-W antenna pointing error information.

3. In a communication system, an arrangement for producing an antenna pointing error signal, comprising:

a directional antenna having a reflector and four antenna horns disposed in a rectangular group in the focal plane of said reflector for receiving a radiated frequency modulated signal from a remote signal source;

means supporting said antenna to move angularly in first and second orthogonally related planes;

means connecting all of said feed horns to produce a sum signal, to produce a difference signal when said antenna is pointed away from said signal source in said first plane and to produce a further difference signal when said antenna is pointed away from said signal source in said second plane;

means receiving said difference signals for combining said difference signals in phase quadrature relationship; and

circuit means including a directional filter having a flat amplitude response and a linear 360°

phase shift over the frequency range of said frequency modulation for combining said sum signal with said combined difference signals to thereby produce an antenna pointing error signal.

4. A two-axis antenna direction control system comprising:

an antenna reflector for receiving a beacon signal which periodically deviates in frequency from the low end to the high end of its frequency band and back;

a plurality of antenna feed horns disposed at the focal plane of said antenna reflector;

a biconjugate hybrid junction network coupled to said antenna feed horns to provide a sum signal, a N-S error signal, and an E-W error signal;

a phase quadrature hybrid junction network coupled to said biconjugate hybrid junction network for combining said N-S error signal and said E-W error signal in phase quadrature to produce a combined error signal;

circuit means coupled to said biconjugate hybrid junction network and to said phase quadrature hybrid junction network and including a directional tracking filter, for coupling said sum signal over to and combining it with said combined error signal, said directional tracking filter being tuned to the frequency band of said beacon signal, said directional tracking filter having a flat amplitude response and a linear phase response over the frequency band between the low and high frequency extremes of said beacon signal, said directional tracking filter having a relative phase difference of 360°

between the low and high frequency extremes of said beacon signal, as the frequency of said beacon signal is deviated from the low end to the high end of its band and back, the phase of said sum signal is shifted through 360° and

back, causing said combined error signal to become amplitude modulated with the modulation envelope of the emplitude modulation containing the combined N-S and E-W error information, said combined error signal thereby containing amplitude and frequency modulation signal components;

an AM detector coupled to said circuit means for recovering the modulation signal component of said combined error signal to produce a demodulated AM signal;

an FM discriminator coupled to said circuit means for recovering the frequency modulated signal component from said combined error signal;

a time gate generator circuit coupled to said discriminator for developing two gating signals, one at the rate of the frequency modulated signal, and the other at twice the rate of the frequency modulated signal;

a pair of phase detectors each coupled to said AM detector and to said time gate generator circuit, one of said phase detectors detecting the demodulated AM signal with the gating signal having the rate of the frequency modulated signal to provide a DC N-S error signal, the other of said phase detectors detecting the demodulated AM signal with the gating signal having the rate of twice the frequency modulated signal to provide a DC E-W error signal; and

individual means, one responsive to said DC N-S error signal and one responsive to said DC E-W error signal for controlling angular movements of said antenna assembly about said two axes.

6. Apparatus as set forth in claim 4 in which said circuit means further includes a phase quadrature hybrid junction network having individual input arms coupled to said directional tracking filter and to said first named phase quadrature hybrid junction network, respectively, for producing said combined error signal having amplitude and frequency modulated signal components.