In-Line Pure ${\rm E}$ -Plane Waveguide Band-Stop Filter With Wide Spurious-Free Response

A new compact pure E-plane waveguide structure is proposed for coupling band-rejection cavities to the main rectangular waveguide in bandstop in-line filters. This coupling structure reduces drastically the unwanted resonances in filters with a very large pass band requirement. Moreover, it has some additional advantages. First, unlike typical inductive irises, large coupling coefficients can be implemented. Second, a pure E-plane configuration is achieved, which simplifies the manufacturing and also reduces significantly the computational effort. Third, in the design, by means of distributed model circuits, the rejection cavities are individually designed and connected by phase shifters maintaining the E-plane layout. Experimental validation is demonstrated by a pseudoelliptic fifth-order bandstop filter centered at 28 GHz and 2% fractional stop band. It is free of spurious resonances in the full Ka-band.