In this thesis, an efficient optimization method is described for synthesizing lens antennas fabricated in low permittivity plastic materials to achieve wide scanning performances. The method is based on an antenna in reception representation. The optimized parameters are the location and orientation of the antenna feeder, lens angular region and its shape by adding Zernike polynomials to standard ellipsoidal shape. The synthesized lens antennas achieve scan losses lower than 3dB while scanning up to 60°. The presented theoretical results are validated using full wave simulations. Furthermore, an efficient analysis method based on Geometrical Optics and ray tracing is developed. This method is applied to the study of multi lens Quasi-Optical structures. The presented theoretical results are validated by multi surface Physical-Optics approach.

This thesis report focuses on possible methods of digital implementation of motional feedback in a bass loudspeaker. In this thesis, the control system will be created for a monopole and a dipole speaker specifically. It does so by sketching the outlines of such a system and examining possible designs for the components required to suppress distortion which is mainly created by the speaker. This thesis shows that the digital implementation indeed allows filtering with very little latency but there are limitations in accuracy due to the conversion from the analogue to the digital domain. It is shown in this thesis that a partly analogue and partly digital system is desired for better error correction. A desired input-output gain of 30=29.54dB is achieved. The controller that is suggested is a controller based on the transfer function of the speaker. By transforming the input signal with the inverse of this open-loop transfer, the closed-loop transfer will be flattened. The instrumentation amplifier used to subtract the feedback signal from the input signal is designed such that the influence of the quantization noise is minimized. Loop-gain is added by the instrumentation amplifier, the controller and voltage-to-current amplifier. By creating loop-gain as much as possible using the digital implementation, noise is suppressed from 30dB up to 90dB within the range of frequencies of interest. The designed components in the motional feedback system allow a loop-gain up to 70dB and an input to output voltage gain of 30dB before instability occurs.