Abstract: A secondary radar uses monopulse reception techniques to improve the estimate of the aircraft position and to improve the reliability of the reply decoding process. Digital signal processing techniques are utilized to replace the analog circuit used in the prior implementations. The secondary radar implements monopulse processing using a half angle phase method wherein the sum and difference signals are encoded in a complete phasor. The detection of the signal and extraction of the azimuth angle data is implemented using a digital receiver concept. The complex phasor is sampled at an intermediate frequency, down converted to baseband and detected. The azimuth angle is computed using arithmetic methods implemented by digital signal processing circuitry.

Abstract: A single-scan editor of bird echoes uses range rate to aid in identifying bird echoes. The range rate is preferably calculated from change in phase between one interpulse period to the next interpulse period and both unfiltered and MTI filtered signals are used for the calculation of change in phase. The unfiltered phase difference is used if the logarithm of the total power of the phase difference exceeds a predetermined threshold during at least one of the interpulse periods and if not, the MTI filtered phase difference is used if the total power of the MTI filtered signal exceeds a corresponding predetermined threshold. If neither threshold exceeds the corresponding threshold, no calculation is made. Due to the relationship between phase difference and range rate, several possible range rates correspond to most phase differences. Therefore, an occurrence of each of the possible range rates is counted over the course of a cycle.