This paper reports design and development of an innovative compact Stepped Truncated-Circular Waveguide Branching Ortho-Mode Transducer (STCWB-OMT) operating at 4.5-4.8 GHz for horizontal and vertical polarizations. STCWB-OMT is derived by introducing branch waveguide via coupling slot on a stepped truncated-circular waveguide. This configuration possesses inbuilt rectangular-to-circular transition; therefore it does not require any additional square-to-circular transition to combine it with horn antenna. The challenge in the design incorporated is to obtain a mechanically compact design with low mass while compliant with the specified electrical performances; since this device is developed for space-borne application. Achieved return losses at both direct and coupled ports are >17 dB, insertion losses <0.08 dB for both polarizations, isolation is <-60 dB and cross-polarization discrimination >40 dB with the OMT length = 1.98λ atcenter frequency and weight = 250 gm The agreement between measured and computed results provides a validation of the proposed OMT configuration.
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