Wataru Chujo

Techniques for antenna sidelobe suppression and laser power reduction in optically controlled array antenna

The required output power of a laser source and suppression of antenna sidelobe level are discussed for an optically controlled array antenna in which microwave amplitude and phase distributions are generated and controlled using optical Fourier transform and heterodyne/homodyne detection. A heterodyne detection model using two laser diodes, the frequency difference of which is set to desired microwave frequency, is compared with an original homodyne detection model, using an external frequency modulator. The heterodyne detection model may be favorable from the viewpoint of available laser diode output power. For example, the required laser output power in the heterodyne detection model can be about 10-15 dB less than that in the homodyne detection model in order to obtain the same C/N0 value of microwave signal. It is also shown that the antenna sidelobe level can be suppressed by about 20 dB without changing beamwidth by using a reference beam with a tapered distribution.