Band-pass filters with linear phase

A set of techniques has been developed which permits the simultaneous realization of flat pass band transmission (±0.15 db experimental) linear phase (to within ±5° experimental) over most (1 - 1/N) of the nominal pass band, where N is the number of "in-band" poles. Outside the pass band, the attenuation skirts are steep; experimentally, 40 db has been obtained within 1/N of the nominal filter bandwidth. Shunt L and/or stray capacitance are easily taken into account in the design; in particular, crystals as well as lumped LC have been used. The procedures can accommodate any amount of series resistance in inductors at the expense of flat loss, without any essential change in the computed values of inductors, capacitors, or resonant frequencies. The sensitivity of the network transmission to component errors is modest; discrepancies in the impedance level or tuning of a given constituent resonance in the network branches affect the characteristic mainly in the vicinity of that resonance.