Development of design Approaches for passive RF and microwave circuits using periodical structures.

Abstract

This thesis deals with several design and analysis techniques for RF/microwave passive circuits such as interconnects, filters, and antennas that offer circuir size reduction and lower fabrication cost associated with future integrated communication systems. Presented are new design approaches to enhance performance of passive circuits and offer the ability to reduce size, minimize mismatch, reduce group delay variation, and alleviate unwanted odd-mode excitation. This work is developed by exporing and using periodic structure behavior in coplanar waveguide (CPW) designs. Periodic structures are known to have bandgaps such as those seen in electromagnetic bandgap (EBG) designs. Circuit based models were developed to predict the stop-band frequency range and to reduce computational time associated with full wave models. To reduce circuit size slow-wave designs can be employed. Thus, periodic structures in the form of interdigitated designs can be used to achieve this function when operating well below the bandgap frequency range. Herein, interdigitated coplanar waveguide designs are developed by increasing both inductance and capacitance per unit length to reduce circuit size, control signal phase, and match signal velocity. Geometrical characteristics of the proposed structures are analyzed with the S-paramters, effective dielectric constant, and attenuation constant. Design guidelines, which relate the effective dielectric constant to geometrical parameters, are also developed. To suppress slot-line mode excitation in circuits with structures, namely right-angle bends, slow wave structures can be used. In this work, novel designs for wire-bond free circular interdigitated bends are presented and compared to circuits with right-angle bends. Also shown is a novel alternative approach which presents a fast-wave design method and exploits it for suppression of slot-line mode excitation. In filter design, the interdigitatated approach is used to (1) reduce the size of a standard EBG based stopband filter by approximately 45% and (2) reduce the size of an ultra-wide band (UWB) bandpass filter by 40% when combined coupled line with meandered slot. Lately, annular ring slot antennas are miniaturized by leveraging the periodic nature of meander geometry to reduce the surface area of single- and dual-band annular ring slot antennas by 40% and 35%, respectively. The performance of all structures is evaluated by comparing modeled designs to the measured one in this thesis.