Combined ECCM/diversity tropospheric transmission system

Claim 1

A signal communications system of the type utilizing the troposphere as the communication medium, and provided with receiver and transmitter apparatus in which said transmitter apparatus comprises: means for generating a pair of coded message information signals; means for generating a timing reference signal; and means for multiplexing said message information signals with said timing reference signal for communication of said message information at selected time intervals within a predetermined transmission period; said coded signal generating means generating a pair of coded signals which upon receipt and detection by a receiver apparatus in communication with said transmitter apparatus produces an output signal having an impulse autocorrelation function during its selected time interval in said predetermined transmisson period; and said receiver apparatus comprises: a receiver coupled to said transmitter, a demultiplexer coupled to said receiver, and a matched filter autocorrelation detector coupled to said demultiplexer to provide said output signal, said matched filter autocorrelation detector including a pair of adder circuits, a plurality of time delay circuits for successively delaying the application of received coded pulses to input terminals of said adders by one interval of time each, a plurality of phase control circuits for reversing the polarities of selected code pulses applied at said input terminals in accordance with the predetermined code patterns of said coded pulses, a common adder circuit connected to said pair of adder circuits to provide an output signal, and a diversity receiver maximal ratio combiner coupled to said output signal of said matched filter autocorrelation detector for extracting signal returns from the tropospheric medium at increased signal-to-noise power ratio, said diversity receiver including a narrowband pulse repetition frequency lock loop for synchronizing to the transmitted information bit, a gate generator connected to said lock loop for providing a gating signal of pulse width equal to the width of the individual noise code bits, delay means for progressively delaying said gating signal by increments of bit width and extracting uncorrelated multipath returns, a plurality of normally closed gates receiving said matched filter output signal and said gating signal, a plurality of voltage comparators and adjustable amplitude control circuits connected with the output of respective noramlly closed gates, the output of said voltage comparators being connected as a further input to said amplitude control circuits, a source of reference voltage connected to said voltage comparators, and a linear adder circuits coupled to the outputs of said amplitude control circuits to provide a combined output proportional to the strength of the individually adjusted signals from said amplitude control circuits.