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A novel diagonal quadruple-ridge OMT with a compact geometry is proposed for detecting circularly polarized signals when used in conjunction with a 90 degree phase shifter. X-Band OMT prototypes, covering 8 GHz-12 GHz, have been fabricated and tested, and exceed specifications by a wide margin, with no evidence of trapped-mode resonances in the operating bandwidth. In addition to having good reflection and transmission performance, measured results show that the fabricated OMT performs well in separating orthogonal circularly polarized signal components. The OMT design is discussed in detail, focusing on impedance matching as well as the methods used to avoid in-band trapped-mode resonances. Since the OMT design focuses on performance, manufacturability and ease of tuning, the new design would be well suited to array applications. Furthermore, the new OMT design is amenable to multiple-pixel feeds as a result of its narrow geometry.