Precise Design of Coaxial Low-Pass Filters

The coaxial low-pass filters described are of the conventional stepped impedance type consisting of a cascade of alternating low and high impedance sections of line. Exact prototype filters having Chebyshev equal-ripple characteristics are obtained from published tables giving the characteristic impedances of the sections. The capacitive discontinuities at the junctions are compensated by a new method which is exact at the cutoff frequency, and nearly exact in the region of this frequency. The production of low-pass filters with a passband VSWR of 1.05 or less is feasible and experimental results are described for such designs.