An orthomode transducer with a circular waveguide input and two rectangular waveguide outputs is described. The design utilizes a turnstile junction and two E-plane power combiners. A K-band version of this device has been constructed and tested. From 18 to 26 GHz, the input reflection coefficient was less than -19 dB, the cross-polarization was less than -48 dB, and the transmission loss was ~0.15 dB. We estimate the mechanical tolerances that would be required to scale this device to the 200-270-GHz band for use in a dual-polarization radio-astronomy receiver

A turnstile junction waveguide orthomode transducer

In almost 30 years of operation, the Very Large Array (VLA) has proved to be a remarkably flexible and productive radio telescope. However, the basic capabilities of the VLA have changed little since it was designed. A major expansion utilizing modern technology is currently under way to improve the capabilities of the VLA by at least an order of magnitude in both sensitivity and in frequency coverage. The primary elements of the Expanded Very Large Array (EVLA) project include new or upgraded receivers for continuous frequency coverage from 1 to 50 GHz, new local oscillator, intermediate frequency, and wide bandwidth data transmission systems to carry signals with 16 GHz total bandwidth from each antenna, and a new digital correlator with the capability to process this bandwidth with an unprecedented number of frequency channels for an imaging array. Also included are a new monitor and control system and new software that will provide telescope ease of use. Scheduled for completion in 2012, the EVLA will provide the world research community with a flexible, powerful, general-purpose telescope to address current and future astronomical issues.

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The Expanded Very Large Array

The Very Large Array is undergoing a major upgrade that will attain an order of magnitude improvement in continuum sensitivity across 1 to 50 GHz with instantaneous bandwidths up to 8 GHz in both polarizations. The new WIDAR correlator provides a highly flexible spectrometer with up to 16 GHz of bandwidth and a minimum of 16k channels for each array baseline. The new capabilities revolutionize the scientific discovery potential of the telescope. Early science programs are now underway. We provide an update on the status of the project and a description of early science programs.

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Expanded Very Large Array

B-Pol is a medium-class space mission aimed at detecting the primordial gravitational waves generated during inflation through high accuracy measurements of the Cosmic Microwave Background polarization. We discuss the scientific background, feasibility of the experiment, and implementation developed in response to the ESA Cosmic Vision 2015-2025 Call for Proposals.

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B-Pol: detecting primordial gravitational waves generated during inflation

The design and test results of a compact C-band orthomode transducer are presented. The transducer comprises four rectangular probes orthogonally arranged in a circular waveguide, designed to work in the WG13 band. Measurements of the system in the frequency range 4.64–7.05 GHz agree very well with simulation results and show a cross-polarisation level below −58 dB, a return loss of about −20 dB, and an insertion loss difference of less than 0.18 dB between the orthogonal polarisation modes across the full waveguide band.

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Compact broadband planar orthomode transducer

This note describes tests made of a planar L-band orthomode transducer consisting of four probes symmetrically arranged in a circular waveguide and two wideband baluns, made from back-to-back slotline-to-microstrip transitions. We designed this device to model at large scale (>50:1) the performance of a compact millimeter wave transducer for use in an astronomical receiver where probes and baluns are microfabricated with SiON thin-film dielectric deposited on a quartz substrate. In the L-band model, probes and baluns are printed on 0.010-in.-thick Duroid 6006, mounted on a 0.25-in.-thick piece of fiberglass and placed flush against the waveguide. Each pair of opposite probes is coupled through a balun to a 50 Ω microstrip output. Measurements show that, from 1.2 to 1.9 GHz, the orthomode transducer has an output return loss less than −18 dB and cross polarization less than −35 dB. It should be possible to scale this design to cover bands of high atmospheric transparency at 100, 230, or 345 GHz.

R. L. Plambeck

Papers

Tests of a planar L-band orthomode transducer in circular waveguide