A compact, high power notch filter with adjustable F0 and bandwidth

The network described is a notch filter, synthesized as a capacitively-coupled short circuited shunt stub design. A well-known equivalence between open circuited, quarter wavelength high-impedance stubs, and capacitively coupled short-circuited stubs of lower impedance, is used iteratively to achieve a design with some innovative features: The shunt stubs are all the same impedance; typically; 50 Ω. The series 90 degree coupling lines are also the same impedance (again typically 50 Ω). Dimensions and components may thus be easily selected for high-power and low-loss operation. The coupling capacitors (which are in series with the stubs) are adjustable without compromising Q. Re-entrant stubs are used which allow a mixed lumped-distributed stub response and easy adjustment of stub lengths. A rugged coaxial construction is adopted with nothing cantilevered or unsupported. These features result in a design which is quite compact, tunable over a wide range of center frequencies, allows for adjustable bandwidth and thus selectivity, while intrinsically exhibiting high-power capability, low passband loss, and suitability for operation in demanding environments