In this dissertation we first present the analysis and design of a hybrid lumped-element coupler in which the loss of components is considered. Analyses show that the return loss or isolation can be significantly improved by an optimum selection of the components quality factors. The feasibility of the given idea is proved by fabricating a prototype coupler which was tested on a Rogers 4003 PCB. The measurement results show that by using optimum quality factor, the return loss reaches -56dB. A low power tunable active capacitor (TAC) is also proposed to generate a tunable capacitor with negative resistance. Using the proposed TAC, we provide a low power tunable inductor with independently tunable inductance and equivalent series resistance. The proposed active inductor is employed in a coupler at 4 GHz. The coupler simulation results show the coupling coefficient ranges from -7dB to +1.3dB with S 11 and S 41 better than -12.1dB and -34.5dB, respectively, with power consumption of less than 6.71mW. The designed coupler has the frequency tuning range of 2.4 GHz – 4.2 GHz with both return loss and isolation better than -25dB. Finally, the noise analysis shows that the coupler output referred noise voltage is less than in all states. Key Words lumped-element coupler, tunable coupler, limited quality factor, active capacitor, tunable inductor
