This thesis focuses on planar filters operating at the circuit board level. Planar filters have gained increasing attention due to their low losses, wide bandwidths, and compact size, which are essential for modern communication systems. The introduction provides background information on the motivation for the study, along with its goals and research questions. Theoretical discussions cover fundamental aspects of filters, including an exploration of substrate properties such as FR-4, various transmission line types like microstrip, Stripline, and Suspended stripline, and the mathematics behind lumped element and distributed element filters. Different filter characteristics are considered, and a literature review examines previous methods, techniques, and software tools used for filter design to inform the methodology of this work. 

Based on the literature review, CST (Computer Simulation Technology) and AWR (Applied Wave Research) are selected as software tools for simulation and design facilitation. An interdigital and a combline bandpass filter are used as references for a broadband filter. The study demonstrates that broader bandwidth filters can be achieved using high-pass and low-pass filters. Results present S-parameter data for simulated filters compared with fabricated and measured filters.

Simulation results indicate that Suspended stripline exhibits a wider bandwidth characteristic compared to microstrip. The fabricated and measured filters generally exhibit good agreement with simulation results, except for one case discussed in detail in section 6.2.1. The literature review and discussion also address the limitations of the FR-4 substrate for high-frequency applications and suggest alternative substrate types for this study.