Element rotation tolerance in a low-frequency aperture array polarimeter

We present a rotation error tolerance analysis for dual-polarized dipole-like antennas commonly found in low-frequency radio astronomy. A concise Jones matrix expression for the phased array is derived which facilitates calculations of rotation error effects in polarimetry. As expected, for random rotation error and number of elements approaching infinity, the estimation error converges to that of the error-free case. However, as in practice large but finite number of antennas are involved, we present a simple analysis to estimate rotation error effects. An example calculation based on a “baseline” design for a low-frequency Square Kilometre Array (SKA) “station” is discussed

Antenna rotation error tolerance for a low-frequency aperture array polarimeter

We present antenna rotation error tolerance analysis for a polarimeter consisting of dual-linearly polarized dipole-like elements. Treating the elements as a phased array and expressing the measurement basis as circularly polarized (CP) results in a concise expression for the Jones matrix for the array. For the type of elements being considered, the matrix shows that the intrinsic cross-polarization ratio (IXR) of the array at the intended beam scanning direction is unaffected by small rotation errors. For random rotation error and very large number of elements, we further find that the relative Jones matrix estimation error converges to that of the error-free case at the intended beam scanning direction; however, the effect of element rotation error on array directivity and radiation pattern remains. Recasting the analysis with the array observing an unpolarized source, a relation between rotation error and cross-polarization “leakage” is obtained, wherein similar trends with very large number of elements hold true. Practical examples involving “large” number of elements such as the low frequency Square Kilometre Array are discussed

Intrinsic cross-polarization ratio of dual-linearly polarized antennas for low-frequency radio astronomy

This note discusses the intrinsic cross-polarization ratio (IXR) from an antenna engineering perspective in that we seek to identify an a priori (coordinate) system where IXR is well approximated by the raw cross-polarization numbers. We begin by establishing a special case where IXR is identical to the raw cross-polarization ratios for in-phase dual-linearly-polarized antennas when the Jones matrix is expressed using circular polarization bases. This insight allows physical interpretation of IXR which may be useful in antenna design and system calculations. In addition, we discuss comparisons between direct IXR calculations and circular polarization approximations for more realistic cases involving dual-polarized Murchison widefield array (MWA) bow-tie antennas

Evaluating Receiver Noise Temperature of a Radio Telescope in the Presence of Mutual Coupling: Comparison of Current Methodologies

© 2019 European Association on Antennas and Propagation. We present the computation of receiver noise temperature which includes the effects of mutual coupling of two different radio telescopes deployed in the Murchison Radio-astronomy Observatory, namely the Murchison Widefield Array and the prototype Engineering Development Array. We used three different formulations that only require information of measured noise parameters of the low noise amplifier as used in the radio telescope and simulated S-parameter of the array to perform the calculation. In addition, we show convergence in computed receiver noise temperature for various pointing angles and array configurations (uniform and pseudo-random) that indicate agreement with existing literature

Near-Field Analysis and Design of Inductively-Coupled Wireless Power Transfer System in FEKO

Inductively-coupled wireless power transfer (WPT) system is broadly adopted for charging batteries of mobile devices and electric vehicles. The performance of the WPT system is sensitively dependent on the strength of electromagnetic coupling between the coils, compensating topologies, loads and airgap variation. This paper aims to present a comprehensive characteristic analysis for the design of the WPT system with a numerical simulation tool. The electromagnetic field solver FEKO is mainly used for studying high-frequency devices. However, the computational tool is also applicable for not only the analysis of the electromagnetic characteristic but also the identification of the electrical parameters in the WPT system operating in the nearfield. In this paper, the self and mutual inductance of the wireless transfer windings over the various airgaps were inferred from the simulated S-parameter. Then, the formation of the magnetic coupling and the distribution of the magnetic fields between the coils in the seriesparallel model were examined through the near-field analysis for recognizing the efficient performance of the WPT system. Lastly, it was clarified that the FEKO simulation results showed good agreement with the practical measurements. When the input voltage of 10 V was supplied into the transmitting unit of the prototype, the power of 5.31 W is delivered with the transferring efficiency of 97.79% in FEKO. The actual measurements indicated 95.68% transferring efficiency. The electrical parameters; in , out, in , , in , and out, had a fair agreement with the FEKO results, and they are under 8.4% of error

Analysis of the polarization properties of dual polarized inverted vee dipole antennas over a ground plane

This paper presents the derivation of an explicit closed-form expression of dual-polarized inverted-vee dipole antenna behavior based upon electromagnetic theory and physical explanations. The expression is used to determine the intrinsic cross-polarization ratio (IXR) as function of the droop angle, position of the sky-vector, the height above a ground plane and frequency. The expression is verified using full-wave simulations with a Method-of-Moments solver, and shows excellent agreement with simulations. It explains the increase observed in IXR if an infinite perfect electric conductor ground plane is deployed

Impact of bandwidth on antenna-array noise matching

This letter expands the treatments of wideband noise analysis of antenna arrays by including bandwidth effects on beam-equivalent receiver noise temperature, (Formula presented.), and the active reflection coefficient, (Formula presented.). The particular focus of the letter is on receiver noise decorrelation in wideband systems having noise bandwidth (Formula presented.) 1 Hz. The new analysis and simulations show increase in (Formula presented.) and the departure of (Formula presented.) from that obtained using contemporary analyses for (Formula presented.) 1 Hz. Although the paper also shows that for many applications over moderate bandwidths and close connection between the receiver and array the influence of (Formula presented.) on (Formula presented.) is not significant, the simulations of a 71-element array demonstrate that the noise decorrelation due to wide (Formula presented.) can result in tens of percent (as much as 45.5% in simulations described in this letter) increase in (Formula presented.) above the low-noise amplifier minimum noise temperature, which should be taken into account at the design stage of ultra-wide band systems, such as those under investigation by, for example, the Defense Advanced Research Project Agency (DARPA) in its wideband adaptive RF protection (WARP) program and ultra-sensitive active electronically scanned array (AESA) radars for tracking stealth objects

Closed-form Jones matrix of dual-polarized inverted-vee dipole antennas over lossy ground

This paper presents a closed-form expression for the Jones matrix of a dual-polarized inverted-vee dipole antenna based on the Lorentz reciprocity theorem and the basic rules of electromagnetic refraction. The expression is used to determine the intrinsic cross-polarization ratio (IXR) as a function of droop angle, position of the source in the sky, antenna height, frequency, and reflection coefficient of the underlying ground. The expression is verified using full-wave simulations with a method-of-moments solver, showing very good agreement. It explains the increase in the IXR when the antenna is placed over a perfect electric ground plane. This result is used to explain the polarization properties of the Square Kilometre Array Log-periodic Antenna. Through the LOw-Frequency ARray Low-Band Antenna (LOFAR-LBA), the importance of the size of the ground plane is explained. Finally, design consideration for high polarization purity antennas is discussed