Sharp-rejection highpass and dual-band bandpass planar filters with multi-transmission-zero-generation transversal cell

A method to produce multiple transmission zeros (TZs) is applied to design sharp-rejection planar highpass filters (HPFs) and dual-passband filters (BPFs). It consists of adding an external transversal cell to a basic filter to create TZs in its response without damaging its in-band amplitude and group-delay variation. Thus, contrary to other filter design techniques, in-band requisites and stopband TZ creation can be separately addressed in the entire filter synthesis process. Such technique could have great potential in other technologies, such as waveguide filters for satellite communications, in which low in-band group-delay variation and adjustable high selectivity are necessary. Measurements for a microstrip HPF and simulations for a stripline dual-band BPF are shown.