CONDUCTOR-BACKED ASYMMETRICAL COPLANAR WAVEGUIDE AND MULTILAYER FILTERS

Abstract

The conductor-backed asymmetrical coplanar waveguide, also known as the micro coplanar strip (MCS) line, offers several advantages compared to the commonly used micro strip line and coplanar waveguide. However, the MCS line and its discontinuities are not well characterized and there are no closed form design equations for the MCS line. In this Accelerated Master Program's (AMP) thesis, new closed form equations for the characteristic impedance and effective permittivity of the MCS line is derived. Procedures for the design of MCS end-coupled half wavelength long resonator filters are proposed. A 2-section MCS end-coupled half wavelength long resonator filter with a specified centre frequency of 10 GHz and bandwidth of 4% is designed using the outlined procedures. The measured response of the designed filter is in good agreement with the specifications. The MCS line with finite planar ground width is also studied. The finite ground MCS line results in greater circuit miniaturization and higher impedance line can be design. 2-section finite ground MCS end-coupled half wavelength long resonator filters with varying ground width are designed and fabricated. The measured responses are in good agreement with the design specifications. However, it was observed that if the ground width is too narrow, undesirable propagation modes set in and the filter response becomes very lossy. The high impedance property of finite ground MCS line was exploited in designing a stepped impedance lowpass filter and its measured response compares well with the specifications given. The measured cutoff frequency is 1.75 GHz with 18.8 dB attenuation at 3.75 GHz. Next, multi-layer micro strip filters are investigated. Multi-layer filters allow greater flexibility in circuit design, as well as greater bandwidth and compactness. A 10 GHz narrowband 2-dielectric-layer 5-section overlap-gap-coupled micro strip resonator filter is designed. The study of multilayer filters is extended to parallel-coupled micro strip filters. New broadband 2-dielectric-layer 5-section parallel-coupled micro strip filter is designed. The designed filter has a measured bandwidth of 53 % about a centre frequency of 8.36 GHz. The achieved bandwidth is significantly higher than the 20 % limit of conventional single-dielectric-layer parallel-coupled microstrip filter.