Accurate Cascade Synthesis of High-Order Stopband Filters

Stopband filters are often implemented by a constant-impedance line tapped by blocks which create transmission zeros. The design of such filters today suffers from poor numerical accuracy of the available synthesis techniques and is thus analytically limited to low order or otherwise to very time-consuming symbolic computations, and only extensive circuit or electromagnetic optimizations can overcome such limitations. Traditional cascade synthesis methods can however be substantially revisited to allow for orders beyond 30 and hence find an ideal application in stopband filters with extreme selectivity requirements, as described in this work.