Beam-shaping reflectors for gyrotrons-a technique based on measured amplitude distributions with reconstructed phase distributions

Techniques for reflector designs which precisely shape microwave beams are presented. The design procedures presented here use an iterative, diffraction-based process to produce beam-shaping mirrors. The design algorithm uses the phase distributions of computer-simulated beams to determine perturbations to reflector surfaces. The target output beam often must satisfy very demanding specifications and the input beam is usually obtained from measurements. An iterative, diffraction-based phase reconstruction algorithm has been developed which recovers the phase distribution from intensity distribution measurements over several beam cross sections. Several mirrors have been designed, fabricated, and tested for a Gaussian output beam distributions with good results. A technique for redesigning only the last of the pair of shaping mirrors is also presented. This technique allows the phase distribution of the target beam to change with each iteration.