A.Hakhoumian, H.Hayrapetyan, T.Zakaryan, R.Martirosyan, S.Martirosyan, A.Muzhikyan, V.Nikoghosyan, N.Poghosyan, T.Poghosyan, K.Rustamyan
CW short range radar system is presented, which is a transceiver with a 2-stage frequency conversion. Such a design is estimated on the basis of several considerations. First, the radar designed for measuring low-frequency Doppler should have as little phase noise of the transmitter as possible. Secondly, such design allows to distribute the total gain between the amplifiers at different frequencies, and makes it possible the simultaneous achievement of both high linearity over a wide dynamic range and necessary pass-through amplification. In single-antenna systems, due to the limited level of isolation of a circulator and non-ideal antenna matching, is the parasitic leakage of the signal at the receiver input. To increase the isolation between the transmitter and receiver, the compensation network of leakage signal is used, which adjusts the compensating signal in order to achieve the minimum DC output video signal. Application of the compensator allows to achieve suppression of the leakage power to -38 dB in the operating band. Achieved level of suppression in single-antenna system limits the transmitter power to 20 dBm and target range to 1 km. Further development of the system consists in the use of two separate transmitting and receiving antennas, which significantly reduces the level of leakage power at the receiver input. Such a gain in noise may increase the range of the radar more than 3 times. Increased distance to the target leads to an increase in phase noise of the system relative to the level of the received signal to the quadratic law and, thus, limits the range of the radar, which can not be increased by increasing the transmitter power, as in the case of recording only its own thermal noise receiver. For the values of phase noise of applied generators and transmitter power of 30 dBm, the values of SNR for phase and thermal noises will become comparable at distance of 10 km. Application of other generators, e.g. based on Gunn diodes, would reduce the range of up to 3 km due to the increase of phase noise.