has a limited frequency range of operation for example x band wr 90 waveguide has a good operating frequency range of 8 0 to 12 4 ghz its upper frequency range of operation is limited because the second mode undesired can occur at 13 4 ghz where its use is not possible single and double ridge waveguide was then developed to improve the operating frequency range of waveguide by placing a ridge of the proper dimensions in the center of the guide the low frequency cut off can be lowered because of the capacitive loading effect and the upper range is also increased since the second resonance is moved higher by the presence and location of the capacitive loading with the general use of ridge waveguide for high power aircraft radar systems the undesired spurious response produced by the filter described in fig1 a and 1b and illustrated in fig2 is often unacceptable an alternate solution would be to use a strip line or coaxial reject filter coaxial input and output connectors if waveguide input and output is required then transitions to waveguide could be employed however if the later approach is taken it will result in a relatively large insertion loss in the.