Short-range homodyne radar system

A homodyne radar system comprising:

• an oscillator configured to generate a transmit signal;
• an antenna configured to transmit the transmit signal and to receive a receive signal;
• a low noise amplifier configured to amplify the received signal to provide an amplified signal;
• a mixing subsystem configured to receive and mix the transmit signal and the amplified signal to produce an output signal;
• and
• a velocity-compensated directional coupler coupled to the antenna, the oscillator, the low noise amplifier and the mixing subsystem, the velocity-compensated directional coupler being connected and configured to provide a low-loss transmission path from the antenna to the low noise amplifier and a high-loss transmission path from the oscillator to the antenna;
• wherein the velocity-compensated directional coupler includes a second transmission path, and wherein the low-loss transmission path and the second transmission path each includes a plurality of notches.

A method of isolating a received signal from a transmitted signal in a homodyne radar system, comprising:

• generating a transmitted signal at an oscillator;
• sending the transmitted signal through a high loss path of a directional coupler to an antenna for transmission, the directional coupler including a first transmission line, an input port at a first end of the first transmission line, a through port at a second end of the first transmission line, a second transmission line, a coupled port at a first end of the second transmission line, and an isolated port at a second end of the second transmission line, the first end of the first transmission line being proximate the first end of the second transmission line, and the second end of the first transmission line being proximate the second end of the second transmission line, the oscillator being coupled to the coupled port and the antenna being coupled to the input port;
• receiving a received signal at the antenna;
• sending the received signal through a low loss path of the directional coupler to an amplifier, the amplifier being coupled to the through port of the directional coupler, and the low loss path being provided by the first transmission line;
• amplifying the received signal to provide an amplified signal;
• and
• mixing the transmitted signal and the amplified signal using a mixing system coupled to the isolated port of the directional coupler.