Optimized 90° Polarization Shift Step Twists for Ku, K and Ka Bands Vasilis G. Salis & Sotirios A. Mallios & Ioannis G. Tigelis & Aristidis S. Theodorou Received: 17 August 2006 / Accepted: 19 February 2007 / Published online: 3 March 2007 # Springer Science + Business Media, LLC 2007 Abstract Optimized models for 90° polarization shift step twists for Ku, K and Ka bands are presented. The cross-section of the waveguide employed is similar to that of a rectangular one, with the difference that the walls of the shorter side are part of a circular one with the proper diameter. The optimized models have been found using the CST Microwave Studio simulation tool and in all cases the return loss is kept below -20 dB for a wide range of frequency spectrum. Two examples are given, one for Ku band and the other for K and Ka ones. Keywords 90° polarization twists . Rectangular waveguide twists . Waveguide discontinuities . Broadband twists 1 Introduction Linear polarization rotation is often required in the RF telecommunication systems and a number of appropriate devices have been proposed in the past [1–6]. In most cases the rotation is achieved with the mechanical transformation and interconnection of rectangular wave- guides in order to convert the propagating mode TE 10 to TE 01 or vise versa. The simplest way to perform such an action is by mechanically twisting a rectangular waveguide. However, the limitations of these components, considering their bandwidth and mainly their length, are well known, since there are several commercially available products [7, 8]. A different approach is to disrupt the continuity of the waveguide by inserting discontinuities in the structure. In [2, 3] a cascaded connection of rectangular waveguides of different cross-sections is proposed, with the gradual transformation of the mode TE 10 to TE 01 . These structures give only 90° rotations and present the advantage to be very short in Int J Infrared Milli Waves (2007) 28:291–298 DOI 10.1007/s10762-007-9209-9 V. G. Salis : S. A. Mallios : I. G. Tigelis (*) Department of Physics, Applied Physics Division, Electronics Laboratory, National and Kapodistrian University of Athens, Building V, Panepistimiopolis, Zografou, 157 84 Athens, Greece e-mail: itigelis@phys.uoa.gr A. S. Theodorou INTRACOM S.A., Defense Sector, 19.2 km Markopoulou Avenue, 19002 Peania, Athens, Greece