System Equivalent Flux Density of a Polarimetric Tripole Radio Interferometer
Abstract
Electromagnetic and information properties of tripole antennas have been studied since the 1980s. In radio astronomy, tripole antennas find an application in space telescopes. More recently, a radio interferometer with satelliteborne tripole antennas is being considered for a lunar orbiting radio telescope to observe very long wavelengths. System equivalent flux density (SEFD) is an important figure of merit of a radio telescope. This paper aims to derive a general expression for SEFD of a polarimetric tripole interferometer. The derivation makes only two basic and reasonable assumptions. First, the noise under consideration is zero mean and when expressed in complex phasor domain, has independent and identically distributed (iid) real and imaginary components. Correlated and nonidentically distributed noise sources are allowed as long as the real and imaginary components remain iid. Second, the system noise is uncorrelated between the elements separated by a baseline distance. The SEFD expression is derived from first principles, that is the standard deviation of the noisy flux estimate in a target direction due to system noise. The resulting SEFD expression is expressed as a simple matrix operation that involves a mixture of the system temperatures of each antenna and the Jones matrix elements. It is not limited to tripoles, but rather, fully extensible to multipole antennas; it is not limited to mutually orthogonal antennas. To illustrate the usefulness of the expression and how the formula is applied, we discuss an example calculation based on a tripole interferometer on lunar orbit for ultralong wavelengths observation. We compared the SEFD results based on a formula assuming short dipoles and the general expression. As expected, the SEFDs converge at the ultralong wavelengths where the dipoles are wellapproximated as short dipoles. The general SEFD expression can be applied to any multipole antenna systems with arbitrary shapes.
 Publication:

Publications of the Astronomical Society of the Pacific
 Pub Date:
 January 2022
 DOI:
 10.1088/15383873/ac4383
 arXiv:
 arXiv:2112.07147
 Bibcode:
 2022PASP..134a4502S
 Keywords:

 Astronomical instrumentation;
 Interferometers;
 Polarimetry;
 Radio interferometers;
 Radio interferometry;
 Radio receivers;
 Radio telescopes;
 Space telescopes;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 doi:10.1088/15383873/ac4383