As part of NASA's Beyond Einstein Program, the characterization of the Cosmic Background polarization has become a high priority for NASA. Since 2002, the efforts in which NASA is engaged are the first steps in the development of the instrumentation to achieve this vision. The critical systems that have previously caused the most losses have to be replaced. Microwave waveguide components are ideal to replaces old systems, improving accuracy of measurement and reducing the losses. In this work, a novel microwave waveguide filter and transformer are presented and discussed. The filter has been designed with 30% fractional bandwidth, guaranteeing extreme stop-band performances by using a quadruple ridge waveguide cross section. The waveguide component exhibits four-fold-symmetry preserving the dual polarization state of the electromagnetic field and resulting ideal for astronomical detections. Moreover, the important suppression of the fundamental mode re-resonance by using attenuation zeros is also discussed.