Georgia Journal of Science

Article Title

Implementation of a Low Cost Low Pass Filter Using Microstrip Structure**


My goal was to design and implement a RF/Microwave low pass filter using microstrip structure. Microstrip structure is an ideal choice for designing RF/Microwave filters due to their compactness, planar structure and easier implementation on a planar circuit board. Such microstrip based filters also offer high accuracy at a low cost for implementation. A low-pass filter is a filter that allows low frequencies to pass through and impedes high frequencies; which is the opposite of a high-pass filter. For filter design and Electro-Magnetic (EM) simulation I have used a free EM simulator Sonnet Lite, which solves Maxwell’s equations and generates scattering matrix elements such as S11 and S21. The low pass filter of order n=3 was implemented using FR4 substrate material commonly available in Printed Circuit Boards (PCB) with a dielectric constant of 4.4. The transmission line of the microstrip is constructed with conducting copper tape on the FR4 dielectric substrate of thickness 1.5mm. The frequency response of the filter is tested using a Vector Network Analyzer (VNA) and compared with the simulated S11 and S21. Ideally creating a microstrip structure involves photo-lithography process for fabrication, which requires a clean-room facility with additional expensive equipment. Here I have demonstrated low pass filters with similar accuracy can also be constructed at a much lower cost using commercially available materials.

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