Compact W-Band “Swan Neck” Turnstile Junction Orthomode Transducer Implemented by 3-D Printing

A turnstile junction orthomode transducer (OMT) provides polarization separation/combining on a full waveguide bandwidth; however, it bears a complex connecting structure, which accordingly leads to a bulky volume. We present a compact W-band (75-110 GHz) OMT using a “swan neck” twist for the connection between a turnstile junction and an E-plane Y-junction, for minimizing the overall OMT structure. The core volume for the proposed OMT is 9× less than the previously reported stacked-layer OMT. The compact W-band OMT was built by digital light processing (DLP) 3-D printing technology and was postmetallized by silver electroless plating. The return loss of the vertical-polarized port (V-port) and the horizontal-polarized port (H-port) is characterized, as averagely 17 and 15 dB, respectively. The measured average insertion loss from H- and V-ports to the common port is 0.5 and 0.6 dB. The measured isolation between V- and H-ports is averagely 28 dB. Furthermore, the turnstile junction asymmetry along the central axis was revealed in computed tomography (CT) scanned images. The simulation shows a negative effect of the asymmetric structure on the OMT isolation. In addition, the dual-polarized (dual-pol) antenna combining such OMT and a corrugated horn was realized in a compact size. The cross-polarization level of the OMT, characterized in a far-field test of this dual-pol antenna, is averagely -18 dB at the W-band.