In this paper, an L-band wideband quad-ridged waveguide orthomode transducer (OMT) for the Five hundred meter Aperture Spherical radio Telescope (FAST) is presented with a simple design principle. By designing two critical parts of the OMT separately and introducing matching rings into two orthogonal probes, an improved wideband performance has been realized successfully. The OMT is designed to operate across the 0.95 GHz-1.9 GHz band, and the simulation shows a return loss better than -20 dB for both polarizations, cross-polarized isolation levels over 45 dB and insertion loss lower than 0.15 dB over the entire bandwidth. The measured results are in good agreement with the simulations.
2. Reck, T. J. and G. Chattopadhyay, "A 600 GHz asymmetrical orthogonal mode transducer," IEEE Microw. Wireless Compon. Lett., Vol. 23, No. 11, 569-571, Nov. 2013.
3. Robertson, S. D., "Recent advances in finline circuits," IRE Trans. Microwave Theory Tech., Vol. 4, 263-267, 1956.
4. Skinner, S. J. and G. L. James, "Wide-band orthomode transducers," IEEE Trans. Microwave Theory Tech., Vol. 39, 294-300, Feb. 1991.
5. Grimes, P. K., O. G. King, G. Yassin, and M. E. Jones, "Compact broadband planar orthomode transducer," Electron. Lett., Vol. 43, No. 21, 1146-1147, Oct. 2007.
6. Yu, J. L., C. J. Jin, Y. Cao, and H. S. Chen, "Broad-band orthomode transducers," Proc. Int. Conf. Microwave and Millimeter Wave Technology, Vol. 1, 320-322, Apr. 2008.
7. Zhuang, Z., B. Li, and Q. Y. Fan, "Design of improved quad-ridged orthomode transducer," Proc. Int. Conf. Microwave and Millimeter Wave Technology, 867-870, Jul. 2010.
8. Coutts, G. M., "Octave bandwidth orthomode transducers for the expanded very large array," IEEE Trans. Antennas Propag., Vol. 59, No. 6, 1910-1917, Jun. 2011.
9. De Villiers, D. I. L., P. Meyer, and K. D. Palmer, "Design of a wideband orthomode transducer," AFRICON 2009, 1-6, 2009.
10. Dunning, A., M. Bowen, and Y. Chung, "Offset quad ridged ortho-mode transducer with a 3.4 : 1 bandwidth," 2013 Asia-Pacific Microwave Conference Proceedings (APMC), 146-148, 2013.
11. Stennes, M., "L-band OMT test report,", http://www.nrao.edu/.
12. Nan, R., "Five hundred meter aperture spherical radio telescope (FAST)," Sci. China Ser. G, Vol. 49, No. 2, 129-148, 2006.
13. Pozar, D. M., Microwave Engineering, 3rd Ed., John Wiley & Sons Inc., 2005.