A Tunable Rejection Filter

The theory and design of a tunable bridge-type narrow-band rejection filter are given for the general case, considering elements with dissipation. Range of adjustment and effect of manufacturing variations are discussed with the help of impedance circle diagrams. Approximate attenuation formulas for various levels of attenuation are derived, and a convenient graphical method of studying performance is suggested. A formula for the effective width of a special arrangement of two filters in tandem is derived.