Simple design technique for TEM-networks having equal-diameter coupled circular cylindrical rods between parallel ground planes

A simple method is presented to realise TEM-networks in coaxial structure form having equal-diameter coupled circular cylindrical rods between parallel ground planes. This method makes use of the available graphs of the normalised self and mutual capacitances of periodical circular cylindrical rods between parallel ground planes and enables the designer of interdigital and combline filters to build these devices with equal-diameter rods fairly easily. A combline filter is given as an example of the design method, and the physical dimensions of the structure have been found starting from the prototype element values.