Design methodology and performance analysis of a wideband 90 degree phase switch for radiometer applications

• Published in: Review of scientific instruments 2013-01, Vol.84 (12)
• Main Authors: Villa, Enrique, Aja, Beatriz, Cagigas, Jaime, de la Fuente, Luisa, Artal, Eduardo
• Format: Article
• Language: English
• Subjects: Amplitudes; Bandpass filters; Design engineering; Insertion loss; Noise levels; Phase shift; Switches; Wideband
• ISSN: 0034-6748
• DOI: 10.1063/1.4849555

This paper presents the analysis, design, and characterization of a wideband 90 degree phase switch in Ka-band. The phase switch is based on two microstrip bandpass filters in which the commutation is performed by a novel single-pole double-throw (SPDT) switch. The analysis of pi -network bandpass filters is provided, obtaining the phase difference and amplitude imbalance between filters and their scattering parameters; tested results show an average phase difference of 88.9 degree plus or minus 5 degree and an amplitude imbalance of 0.15 dB from 24 to 37 GHz. The new broadband SPDT switch is based on a coplanar waveguide-to-slotline-to-microstrip structure, which enables a full planar integration with shifting branches. PIN diodes are used to perform the switching between outputs. The SPDT shows isolation better than 19 dB, insertion loss of around 1.8 dB, and return loss better than 15 dB. The full integration of the phase switch achieves a return loss better than 11 dB and insertion loss of around 4 dB over the band 26-36 GHz, with an average phase difference of 87.1 degree plus or minus 4 degree and an average amplitude imbalance of 0.3 dB. It provides an excellent performance for this frequency range, suitable for radio-astronomy receivers.