Practical Design Approach to Microstrip Combline-Type Filters

A general circuit model resembling a combline-type structure is developed using the concept of self and mutual node admittances rather than self and mutual capacitances per unit length. The merit of this approach lies in the relative simplicity of design formulas readily applicable to filters utilizing microstrip or stripline construction. It also offers easy adaptability to computer sided design. Equations are derived relating even-odd mode impedances and transmission line lengths to prototype elements and other design parameters.