1.11. This instrument has two independent antennas (that cover the same geometric area) and RF circuits. The result is that, when a signal is present, the signal components from each leg into the multiplier are highly correlated (essentially identical in amplitude and phase) while the noise terms are uncorrelated. Thus, only the cross-correlated signals produce a direct volt- age to the integrator. The theoretical advantage of the correlation radiome- ter over the square-law radiometer is that it requires 3 dB less SIN for the 10 Large Doppler may modify this strategy somewhat. Low Probability of Intercept Communications same PD and PFA performance. If two antennas are to be used, however, it is also possible to have each antenna cover one-half of the specified geo- metric area (3 dB gain increase), which then produces the same SIN per- formance with two wideband radiometers (operating independently) as that for the correlation radiometer. An advantage of the half-coverage dual- antenna system is that it gives some directional information (say, left versus right) which the correlation radiometer is incapable of since its antennas cover the same overlapping area. the threshold maintenance problem for the correlation receiver is essentially the same as that for the square-law receiver except that the former does not produce a direct voltage which is a function of the noise levels. this slightly simplifies the calculation of the threshold value from the statistical measurements made toward its determination. Overall, the tradeoffs between a correlation receiver and two independent square-law receivers are slight, and system performance and complexity are virtually the same. One disadvantage of every wideband square-law or correlation type of detector is that it is sensitive to any form of signal, i.e., it will respond equally as well to the communicator's FH signal or to any other extraneous signal irrespective of modulation form and bandwidth (provided that its fre- quencies fall within (fo, Wss)) as long as it has