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This paper summarizes the results of investigations, conducted by authors on the so called “active microwave antennas” – the structures, in which microstrip antenna is connected with active semiconductor element without intermediate feeder. The most attention is focused to the processes of microwave generation, particularly in the active antenna array. Active antenna, in this case antenna-oscillator (AO), looks as a planar log-periodic antenna, integrated with field-effect transistor at the dielectric substrate with metalized back side. Output microwave power of single AO was 5-7 mW at the frequency near 20 GHz with efficiency up to 20%. The opportunity of spatial power combining was studied for the linear and two-dimension arrays. It was shown, that during the operation of two AOs with frequency difference less than 50 MHz mutual synchronization takes place, mostly due to the surface wave excitation in the dielectric substrate. Meanwhile for the effective power combining in two-dimensional array of 4 or more elements external signal source is necessary or special reflector can be used. Computer modeling and experimental study have shown that depending on the dielectric substrate thickness generation of monochromatic, multifrequency or chaotic signals is possible with output both to the free space and to the waveguide structures.

ACTIVE MICROSTRIP ANTENNAS AND ANTENNA ARRAYS WITH FIELD-EFFECT TRANSISTORS