Bessel low pass filter in mixed planar waveguide techniques

This paper describes the design and results of a Bessel low pass filter at 7.5 GHz for high speed (optical) communication applications. The equivalent circuit of a lumped element filter is transformed into a planar circuit mounted in a rectangular waveguide channel Each reactance of the filter is realized by an electrically short transm on line. To this end, a combianation of microstrip line and suspended stripline had to be used to cope with the widely varying impedance levels and to achieve a compact low loss filter.