An antenna system, used for simultaneous reception and transmission, is coupled by way of a hybrid device to an RF amplifier having less gain than the isolation loss introduced between its output and input by the hybrid. Additional gain, beyond the finite isolation of the hybrid, is provided by an oscillator which is coupled in single-port fashion to the circuit and tends to synchronize with applied signals that are substantially weaker than its output.
In accordance with this invention, a radio repeater of the injection locked scillator type is provided with a feedback circuit for changing the free-running or rest frequency of the locked oscillator so that it follows the frequency deviations of the frequency modulation signal being repeated. This results in a higher gain for the repeater.
A multifunction ultra-high frequency circuit and bidirectional transmission means using such a circuit. The circuit according to the invention comprises a directional coupler, two diodes, a transistor and an access connected to the diodes. The state of the transistor defines several functions of the circuit: modulation, mixing and transmission-reception separation. Application to half-duplex transmission.
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. The radar transponder may thus be used in a high-vibration environment with no substantial introduction of error in velocity measurements caused by using two independent oscillators to formulate the frequency offset.
The invention relates to secondary radar responders which provide a reply in response to a radar signal received from a primary radar transmitter. The frequency of the received radar signal is monitored by the responder and the frequency of the response is brought into agreement therewith so that the response can be received by the primary radar transmitter at its transmission frequency. The invention is particularly applicable to marine radar systems and the responder may form part of a racon or transponder.
A frequency down-converter down converts an input signal having a frequency in a given bandwidth and a frequency up-converter up converts the down converted input signal and imparts a doppler shift to the up converted signal to generate an output signal having a frequency with doppler shift in the given bandwidth.
