Virtual negative coupling in folded waveguide cavity filter for space applications

This paper describes the design of a folded rectangular waveguide cavity band pass filter, incorporating virtual negative coupling (VNC) by means of circular iris, at X-band. Thus, the filter is robust from mechanical aspects, and hence apt for space application. The filter realized at 8310 MHz with 1.2 percent fractional bandwidth, has a sharp roll-off due to VNC. As a result, rejection better than 40 dBc is achieved at just 100 MHz offset from band centre. Compared to traditional all pole filter, introduction of VNC has resulted in around 20% size reduction.