Abstract: In accordance with the teachings of the present invention, a passive tracking system (30) and method of passively determining a range (R) to a remote signal emitter (10) elevated a distance above ground level (14) is provided. The method includes aligning an antenna (32) also elevated above ground level (14) substantially in the direction of the remote signal emitter (10). The antenna (32) receives combined radiated energy along a direct path (16) from the remote signal emitter (10) as well as radiated energy that has bounced off the ground level (14) and has been received along a bounce path (18) from the remote signal emitter (10). The range (R) to the remote signal emitter (10) is calculated based upon the combined direct and bounce path signals. Correlation processing and geometric triangulation is employed to calculate the range (R) to the remote signal emitter (10).

Abstract: In accordance with the teachings of the present invention, a radar system (20) and method of determining the range (R) to a remote target (14) is provided. The method includes computing a plurality of simulated M-dimensional points (x.sub.o (t)) as a function of return pulse arrival times over a range of expected return pulse arrival times (t.sub.1 through t.sub.2). The computed simulated points (x.sub.o (t)) are stored as function of return pulse arrival times in a memory (42) of the system (20). An antenna (10) is aligned in the direction of the remote target (14) and transmits at least one electromagnetic pulse (12) in the direction of the remote target (14) such that the pulse (12) reflects off the remote target (14) as a return pulse (16). The return pulse (16) is sampled at M different times representing a M-dimensional measured point (x). The measured point (x) is compared with each of the simulated points (x.sub.o (t)) stored in the memory (42) for determining which of the simulated points (x.sub.

Abstract: All modules of an active antenna array with the exception of a module under test are disabled. Samples representative of the output of the transmit and receive phase shifter outputs of the module under test are taken for successive pairs of transmit/receive modes of operation at the N successive phase increments of the module under test. Fast Fourier transforms (FFTs) are performed over the samples separately for transmit and receive states, and the power in each FFT filter for each state is detected. Power comparison between the power in filter 1 (numbered from 0) and the power in the sum of filters 2 through (N-1) is then used to determine whether the module under test is defective.

Abstract: Compensation for a failed element of an active antenna array is acheived by turning the failed element off and selecting a plurality of adjacent, properly working elements as local compensators. A selected voltage and phase increment is then added to the complex output voltage which each local compensator would normally produce. The magnitude of the voltage increment is selected by dividing the magnitude of the failed element's voltage, were it not failed, by the number of compensators. The phase increment is selected to scan the associated voltage increment at a depression angle of about 30 degrees below the horizon.

Abstract: A guard for an active antenna array is formed from first and second subarrays of the elements of the antenna, the first and second subarrays each being quadrant symmetric and having respective center phases which are 90 degrees apart. This arrangement greatly reduces nulls in the resultant guard pattern.