Suspended substrate strip line filters with flat delay

A procedure has been developed for designing narrowband suspended substrate stripline (SSS) microwave filters in the comb form. The design is based on an even-degree lowpass lumped prototype network of a ladder nature. An auxiliary coupling has been introduced to flatten the delay characteristics. A frequency transformation has been worked out to transform the characteristics of the lumped filter to the microwave region. Explicit formulas have been derived for physical dimensions of the SSS lines from the relationships between the characteristic admittance and the static capacitances of the lines and the element values of the prototype network.<>