Direct-coupled, band-pass filters with λ_{o}/4 resonators

Filters can be designed with resonators approximately
\lambda_{0}/4
long using, alternately, series and shunt coupling discontinuities. Advantages over filters with
\lambda_{0}/2
resonators include: shorter length, second pass band is centered at
3f_{0}
instead of
2f_{0}
(
f_{0}
is design band center), mid-stop-band attenuation is higher, precision design for a prescribed insertion loss characteristic is tractable to greater bandwidths, can be made in "bar transmission line" form without dielectric supports. The design procedure used is on the insertion loss basis and incorporates an improved low-pass to band-pass transformation due to Cohn. The results of an experimental design are presented. Use of
\lambda_{0}/4
direct-coupled resonators for mounting crystal diodes on strip transmission line bandpass filters is also dicussed. Experimental results obtained with a wide-band mixer-filter unit designed in this manner are presented. In these experiments the unit was operated so as to translate a wide-band of relatively low frequency microwave signals up to a higher microwave frequency band.