A broadband Orthomode Transducer for the new ALMA band 2+3 (67–116 GHz)

In this paper we present the design, construction and characterization of a broadband Orthomode Transducer (OMT) for the new Band 2+3 of the Atacama Large Millimeter/Submillimeter Array (ALMA). The term Band 2+3 (67-116 GHz) refers to the recent proposal of covering current Bands 2 and 3 with a single dual-polarization broadband receiver. One of the key components of the future receiver is the polarizer, also known as orthomode transducer (OMT). For this work we have selected the turnstile architecture since it presents low cross polarization leakage in a large wideband. We have obtained an OMT with reflection losses below -15 dB, an isolation between output ports below -26 dB, and a cross polar transmission better than -20 dB.