Stopband singlet: A novel structure implementing resonating couplings

In this letter a new type of singlet is introduced, called stopband singlet. The new singlet is implemented in rectangular waveguide, exploiting TE301 as resonating mode and TE10 mode as nonresonating bypass coupling. Unlike the previously introduced singlets [which produce one transmission zero (TZ) and one reflection zero (RZ)], the stopband singlet generates one TZ alone (the RZ is pushed to infinity). The novel structure allows designing filters with resonating couplings introducing TZs very close to the passband (difficult to implement with other resonating waveguide discontinuities). A prototype two-pole filter with one TZ has been designed and fabricated to validate experimentally the novel singlet configuration.