Abstract: A system for indicating the direction of a source of radio waves received by a circular antenna array (12) includes a Butler matrix (18) that receives the array outputs and feeds the resultant matrix outputs to correction circuits (22) whose transfer functions are the inverses of the direction-independent factors of antenna patterns generated by antenna elements driven at relative phases that advance around the array at rates that complete an integral number of cycles in one circuit of the array. The resultant corrected signals are fed to a compressive receiver (26), which accordingly generates an output on an output port whose position indicates the direction of the source of the signal.

Abstract: A spread spectrum detector utilizes compressive receiver techniques and squaring of the incoming signal to detect the presence of a spread spectrum signal and to obtain its center frequency, with the squaring cancelling the pseudo-random code. Once having determined the center frequency, the gated output of the compressive receiver's dispersive delay line may be directly demodulated without resort to code correlation, by applying the output of the dispersive delay line to a narrowband filter set to the detected center frequency. Narrowband interfering signals are rejected by a continuous comb filter, hard limiters for the filter outputs and a summing device. The same narrowband signal rejection can be accomplished by hard limiting the output of the compressive receiver delay line and then returning to the time domain with an additional dispersive delay line having a dispersive characteristic inverse to that of the compressive receiver delay line.

Abstract: A method and apparatus are provided for sorting signals from compressive receivers in accordance with the type of modulation on the signal, so as to be able to establish the identity of the signal short of fully demodulating it. It has been found that signals from a compressive receiver which are insufficiently sampled for complete demodulation can be identified by "histograms" in which each designated condition, such as the number of consecutive 1's or 0's is graphed against the number of occurrences of this designated condition over a period of time, designated a "data collection interval." The result is a pattern or diagram which is characteristic of the modulation type, such that FSK, DFSK, PSK, hand morse, machine morse, anomolous morse, AM, SSB, and multitones can be distinguished one from another. Moreover, it is possible to recognize two-way voice communication.