ADAPTIVE SWEPT-FREQUENCY ACTIVE RADAR SEEKER

• US 3,728,724 A
• Filed: 02/12/1971
• Issued: 04/17/1973
• Est. Priority Date: 02/12/1971
• Status: Expired due to Term

• Current Assignee: Frederick C. Alpers
• Original Assignee: Frederick C. Alpers
• Inventors: Alpers, Frederick C.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US05/115,117
• Time in Patent Office: 795 Days
• Field of Search: 343/7.5
• US Class Current: 342/83
• CPC Class Codes: G01S 13/343 using sawtooth modulation
• CPC Class Codes: G01S 13/4445 amplitude comparisons monopulse, i.e. comparing the echo signals received by an antenna arrangement with overlapping squinted beams
• CPC Class Codes: G01S 13/685 using simultaneous lobing techniques

Abstract

An adaptive swept frequency active radar seeker comprising an antenna, microwave components, and signal processing circuits arranged to provide guidance of a missile against a ship or prominant land target under all weather conditions. Microwave CW transmitter signals of moderate power are generated by one microwave tube. The frequency of the signals is controlled by a swept generator. The microwave signal is passed through a sidewall coupler, where a small portion is bled off for use in synthesizing a local oscillator signal for heterdyne reception. Means are provided to control the swept generator by controlling the sweep rate and by controlling the sweep amplitude.

Claims

1. In an active radar seeker, the combination comprising:

a. a microwave energy generating means for generating continuour wave microwave energy, b. transmitting circuit means and receiving circuit means coupled to said microwave energy generating means for transmitting microwave energy in the direction of a target to be detected and for receiving microwave energy reflected from the target to be detected, c. an offset frequency oscillator for generating a desired offset frequency signal, d. two frequency tripler circuits connected in series and to said offset oscillator for providing an output signal nine times the offset frequency signal, e. a first mixer circuit coupled to the output of said frequency triplers and to said microwave energy generating means for generating a first intermediate frequency, f. three frequency doubler circuits connected in series and to said offset oscillator for providing an output signal eight times the offset frequency signal, g. a second mixer circuit coupled to the output of said frequency doubler circuits and to the output of said first mixer circuit for providing the heterodyning signal at the desired offset frequency to said transmitting and receiving circuit means, h. a sweep generator coupled to said microwave energy generating means for controlling the output frequency of said microwave energy, i. circuit control means coupled to said sweep generator and to said transmitting and receiving circuit means and being responsive to a measure of the distance to the target reflecting the transmitted energy for controlling the amplitude and frequency of the sweep generator output voltage.

2. The active radar of claim 1 wherein said transmitting and receiving circuit means include;

a. a dual feed antenna, b. a sum channel and a difference channel, said sum and difference channels being coupled to said dual feed antennas by means of a hybrid junction whereby the sum of the signals received by the dual feed will be fed to said sum channel and difference in the signals received by the channel feed will be fed to said difference channel, c. a filter bank being coupled to the output of said sum channel for providing a plurality of output signals whose amplitudes vary over a range dependent on the frequencies of the signal fed through said sum channel, d. a filter bank being coupled to the output of said difference channel for providing a plurality of output signals whose amplitudes vary over a range dependent on the frequencies of the signals fed through said difference channel.

3. The active radar of claim 2 wherein a logic circuit means is coupled to the outputs of the filter banks of said sum and difference channels and being responsive to the strongest signal from said sum channel for selecting the strongest output signal from each of said channels.

4. The system of claim 3 wherein said circuit control means includes, control switch means coupled to said logic circuit and to said sweep generator for coupling a corrective signal being responsive to the selected signal from said sum channel for adding a corrective sweep rate control voltage to said sweep generator when the target is at ranges longer than a predetermined range and coupling corrective sweep amplitude control voltages to said sweep generator when the target is at ranges shorter than said predetermined range.

5. The system of claim 3 wherein a phase sensitive detectioN means is coupled to the outputs of said sum and difference channels and being responsive to the amplitude of the selected difference signal and the relative phase of the selected sum and difference signals for providing an output voltage representing directional information of the target with respect to the transmitting and receiving antenna.

6. In an active radar seeker, the combination comprising:

a. a microwave energy generating means for generating continuous wave microwave energy, b. transmitting circuit means and receiving circuit means coupled to said microwave energy generating means for transmitting microwave energy in the direction of a target to be detected and for receiving microwave energy reflected from the target to be detected, c. a mixer having a first input coupled directly to the output of said microwave energy generating means and a second input coupled through a short delay line to the output of said microwave energy generating means for generating an intermediate frequency signal whose instantaneous frequency is proportional to the change in frequency of the microwave energy generating means during the preceding interval of the duration of the delay introduced by the delay line, d. pulse generating means coupled to the output of said mixer for generating one pulse for each cycle of the intermediate frequency signal, e. integrator circuit means for converting the pulse to a direct current voltage whose amplitude is directly proportional to the number of pulses per unit of time, f. a source of sweep rate control voltage, g. a source of sweep amplitude control voltage coupled to said integrator circuit means, h. differential amplifier means having a first input coupled to said integrator circuit means, a second input coupled to said source of sweep rate control voltage and having an output coupled to said microwave energy generating means for adjusting the sweep rate in accordance with the direct current voltage output of said differential amplifier means.