A New Approach to Suppress the Effect of Machining Error for Waveguide Septum Circular Polarizer at 230 GHz Band in Radio Astronomy

A new stepped septum-type waveguide circular polarizer (SST-CP) was developed to operate in the 230 GHz band for radio astronomy, especially submillimeter-band VLBI observations. For previously reported SST-CP models, the 230 GHz band is too high to achieve the design characteristics in manufactured devices because of unexpected machining errors. To realize a functional SST-CP that can operate in the submillimeter band, a new method was developed, in which the division surface is shifted from the top step of the septum to the second step from the top, and we simulated the expected machining error. The SST-CP using this method can compensate for specified machining errors and suppress serious deterioration. To verify the proposed method, several test pieces were manufactured, and their characteristics were measured using a VNA. These results indicated that the insertion losses were approximately 0.75 dB, and the input return losses and the crosstalk of the left- and right-hand circular polarization were greater than 20 dB at 220–245 GHz on 300 K. Moreover, a 230 GHz SST-CP was developed by the proposed method and installed in a 1.85-m radio telescope receiver systems, and then had used for scientific observations during one observation season without any problems. These achievements demonstrate the successful development of a 230 GHz SST-CP for radio astronomical observations. Furthermore, the proposed method can be applicable for observations in higher frequency bands, such as 345 GHz.

[1]  A. Miyazaki,et al.  The Hitachi and Takahagi 32 m radio telescopes: Upgrade of the antennas from satellite communication to radio astronomy , 2016 .

[2]  P. Brachat,et al.  Compact duplexer-polarizer with semicircular waveguide (antenna feed) , 1991 .

[3]  Jens Bornemann,et al.  Ridge waveguide polarizer with finite and stepped-thickness septum , 1995 .

[4]  Tokyo,et al.  REVEALING THE PHYSICAL PROPERTIES OF MOLECULAR GAS IN ORION WITH A LARGE-SCALE SURVEY IN J = 2–1 LINES OF 12CO, 13CO, AND C18O , 2014, 1412.0790.

[5]  Sami G. Tantawi,et al.  NOVEL COMPACT WAVEGUIDE DUAL CIRCULAR POLARIZER , 2013 .

[6]  Ming Chen,et al.  A wide-band square-waveguide array polarizer , 1973 .

[7]  A. E. Martynyuk,et al.  A Multilayer Circular Polarizer Based on Bisected Split-Ring Frequency Selective Surfaces , 2014, IEEE Antennas and Wireless Propagation Letters.

[8]  Yoshiharu Kojima,et al.  A 1.85-m mm-submm Telescope for Large-Scale Molecular Gas Surveys in 12CO, 13CO, and C18O (J = 2–1) , 2013 .

[9]  P. M. Koch,et al.  Greenland telescope project: Direct confirmation of black hole with sub‐millimeter VLBI , 2014, 1407.2450.

[10]  Mauro Mongiardo,et al.  Full-wave design and optimization of circular waveguide polarizers with elliptical irises , 2002 .

[11]  J. Sombrin,et al.  Approximation by Gegenbauer polynomials in the study of a rectangular ridged waveguide. Application to the analysis of a waveguide septum polarizer , 2003 .

[12]  Jens Bornemann,et al.  Analysis and design of circular ridged waveguide components , 1999 .

[13]  Sami Tantawi,et al.  Theory and Experiment of a Compact Waveguide Dual Circular Polarizer , 2012 .

[14]  J. R. Montejo-Garai,et al.  A 225 GHz Circular Polarization Waveguide Duplexer Based on a Septum Orthomode Transducer Polarizer , 2013, IEEE Transactions on Terahertz Science and Technology.

[15]  Y. Murata,et al.  Septum Polarizer for Ka-Band H-Shaped Rotary Joint , 2009 .

[16]  R. Tascone,et al.  A novel design tool for waveguide polarizers , 2005, IEEE Transactions on Microwave Theory and Techniques.

[17]  M. Miyazaki,et al.  A design of novel grooved circular waveguide polarizers , 2000, IMS 2000.

[18]  Kimihiro Kimura,et al.  MOLECULAR CLUMPS AND INFRARED CLUSTERS IN THE S247, S252, AND BFS52 REGIONS , 2013 .

[19]  Wolfgang J. R. Hoefer,et al.  Closed-Form Expressions for the Parameters of Finned and Ridged Waveguides , 1982 .

[20]  Subbarao,et al.  Compact coaxial-fed CP polarizer , 2004, IEEE Antennas and Wireless Propagation Letters.

[21]  Ruey-Beei Wu,et al.  A circular polarizer designed with a dielectric septum loading , 2004 .

[22]  N. Albertsen,et al.  A Compact Septum Polarizer , 1983 .

[23]  P. Raffin,et al.  Greenland Telescope (GLT) Project: "A Direct Confirmation of Black Hole with Submillimeter VLBI" , 2013, 1310.1665.

[24]  M. J. Franco,et al.  A High-Performance Dual-Mode Feed Horn for Parabolic Reflectors with a Stepped-Septum Polarizer in a Circular Waveguide [Antenna Designer's Notebook] , 2011, IEEE Antennas and Propagation Magazine.