On energy potential of millimeter-wave radar

One of the most serious problems of a short-pulse millimeter (MM) wave radar is deficit of its energy potential. The radar range upper limit of about a few kilometers is caused mostly by two factors: (1) low energy of transmitting signal pulses restricted by generator overheating or breakdown of waveguiding structures; and (2) decreasing of signal energy received because of small aperture of antenna necessary to keep a high survey rate. It is possible to keep a high survey rate and energy potential of the radar when decreasing wavelength if both the transmitting antenna gain and the receiving antenna area are fixed. This may be done if a multi-beam receiving antenna fills the transmitting antenna beam so that the radar angular resolution is determined by received beamwidths. The idea may be realized in different ways. The direct one is using a matrix receiver placed at the focal plane of a mirror or lens receiving antenna. State of art of MMIC technology allows one to build compact multi-element matrix receivers for frequencies up to 100 GHz. The other way is using phase-array antennas where the multi-beam operation mode may be created by a beam-forming circuit. Splitting the transmitter energy to a set of beams can also be performed by frequency-switching antennas.