Waveguide and Coaxial Lowpass Filters

This chapter explores the methods for synthesizing the transfer and reflection polynomials, suitable for two important classes of lowpass filter (LPF): the distributed stepped impedance (SI) filter and the mixed lumped/distributed filter. For the synthesis of SI and lumped/distributed LPFs, the microwave structures support only certain types of filter function. Since the main function of an LPF is to reject noise and interfering signals up to frequencies that can be several times the cutoff frequency, preservation of the integrity of the reject bands is critical. A microwave LPF can be realized in rectangular waveguide, coaxial transmission‐line, or planar technology. The synthesis of the prototype network for a lumped/ distributed or SI LPF is a progressive process: extracting the electrical components one by one in sequence from the defining polynomials, building up the ladder network, and finishing when the final component has been extracted and the polynomials are of zero degree.