Abstract: A radar reply transponder for use with existing radar tracking systems wherein a reply pulse is generated and trasmitted in response to an associated interrogation pulse. The reply pulse is delayed in time and offset in frequency by a precise amount with respect to the interrogation pulse, but it is nevertheless phase coherent therewith so as to preserve the required Doppler frequency information and thereby permit accurate velocity measurements. Phase coherence is effectively maintained by utilizing a single continuously operating local oscillator for down-converting the received interrogation pulse to an intermediate frequency as well as up-converting the signal information to provide the delayed and frequency offset reply pulse. The precision frequency offset is obtained by switching in an additional reactance element in the oscillator-determining circuitry during the time up-converting is being effected.

Abstract: An antenna system is disclosed that is suitable for use in the transmission of communication signals from expendable marker buoys. The antenna system is designed such that the antenna is interiorly disposed within the buoy, which eliminates the need for antenna seals and antenna automatic extension mechanisms.The antenna is top loaded to permit the use of a relatively short vertical section. The antenna is attached to a ground plane skirt which is capacitively coupled through a dielectric form for establishing good radio frequency (RF) connection to the water surface within which the antenna system operates. The dielectric medium is provided by the outer housing of the buoy and hence the water surface becomes the effective ground plane for the antenna. In this manner, therefore, the antenna system does not require components to be extended beyond the interior of the buoy housing.