A compact combline filter design and optimization using the Cauchy method

A 10th-order direct-coupled combline filter is designed and optimized using the Cauchy method in this paper. The fabricated filter's tuning procedure is via a real-time Cauchy extracting system. The filter is synthesized based on Chebyshev low-pass prototype with a fractional bandwidth up to 15.2% centred at 889.4MHz. The average insertion loss of the fabricated filter is lower than 0.72dB. The measured results are obtained in good agreement with the predicted ones.