Rotating Element Electric Field Vector Research Articles

Low complexity on-board vector calibration network for optimal microwave wireless power transmission and enhanced RF-to-DC conversion efficiency

A low complexity on-board vector calibration network for optimal microwave wireless power transmission (MWPT) efficiency is proposed in this work. The proposed technique is based on sequentially tracking the minimum power level of two antenna elements in an array for both phase and amplitude error discrimination. Unlike conventional vector calibration networks based on a down-conversion topology, the proposed architecture can perform vector calibration by only monitoring the magnitude of each antenna element. Thus, high system efficiency can be achieved by reducing hardware costs and eliminating any unnecessary power consumption by extra active devices. Further, phase and amplitude imbalances between antenna elements in an array can be accurately captured with higher precision compared to the conventional rotating-element electric-field vector (REV) method. The proposed technique achieved higher resolutions for both amplitude and phase error detection than REV, which suffers from low resolution near the maximum or minimum field crests. To verify the MWPT efficiency improvement based on the proposed calibration network, a 1 × 4 phased array MWPT system was fabricated and tested at 5.8 GHz with a reference rectenna. With the calibrated power transmission, the total RF-DC conversion efficiencies at ± 45° beamforming angles were improved by up to a maximum of 138.79%.

Phased array calibration system with high accuracy and low complexity

This paper presents a highly efficient phased array calibration system for phase and magnitude error correction. The proposed calibration system is based on far-field scanning of the array antenna under test at factory level. Since the proposed structure requires a magnitude detection only for vector calibration, low circuit complexity can be achieved. Unlike the conventional far-field calibration based on rotating-element electric-field vector (REV) method to find maximum vector-sum point, the proposed system detects the minimum vector-sum point and tracks the behavior of the null point. To verify the feasibility of the proposed system for large-scale array antenna, 4 × 4 phased array antenna is implemented at 5.8 GHz. Then, the proposed method is applied to the phased array antenna and compared with the conventional REV method.

Phased Array Antenna Calibration Method Experimental Validation and Comparison

This paper investigates the calibration methods appropriate to the phased array calibration in practical measurement setups. The rotating element electric field vector (REV) method, fast amplitude-only calibration method, and complex amplitude calibration method are compared and analyzed in the same measurement setup. The objective is to investigate the robustness of the discussed algorithms with different measurement ranges, with or without the support of array element on/off operation. A 4×8 uniform rectangular array (URA) is used to validate the three different calibration methods. The measurement results indicate that array element on/off measurement in the far field is suitable to be a reference calibration method in practical setup. The REV and complex amplitude calibration methods present comparable accuracy while fast amplitude-only calibration method provides less accurate calibration results in this measurement. Further, it was demonstrated that with element on/off data available, same calibration accuracy can be achieved either in small or large measurement ranges for the three different calibration methods. However, when the element on/off data is not available, the array calibration accuracy deteriorates with small measurement range. This paper presents the method to calibrate the phased array antenna in near-field by using the element on/off data. This is a very useful method in massive production line calibration. The calibration errors of different calibration methods are analyzed. Furthermore, this paper also analyzes the uncertainty of each method.

Improved Rotating-Element Electric-Field Vector Method for Fast Far-Field Phased Array Calibration

We present a fast far-field phased array calibration/beamforming method. An improved version of the rotating-element electric-field vector (REV) method, which is used to calibrate array antennas by measuring the power received at a far-field point while varying the phase of each element, is proposed. Two major improvements were made. First, a simpler algorithm was used to determine the calibration value of the conventional REV method, without disconnecting an antenna element during the calibration process. Second, a solution for a specific case was added for a more accurate categorization to use the correct formula. This improved rotating-element electric-field vector (IREV) is experimentally verified. Curve fitting and sinusoidal regression were used to reduce the number of measurements required for fast calibration/beamforming. Arrays of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 6$ </tex-math></inline-formula> phased array system comprising a 4-bit phase shifter and a 6-bit variable-gain attenuator (VGA) were calibrated using only measurements of the far-field received power. Calibrations were performed when the horn and array antennas were perfectly aligned with each other and when the latter was tilted at an angle of 12° relative to the former.

Over-the-Air Array Calibration of mmWave Phased Array in Beam-Steering Mode Based on Measured Complex Signals

Accurate knowledge of initial complex excitation coefficients for phased-array elements is essential to ensure accurate array performance. In the literature, many array calibration algorithms have been proposed for this purpose, which generally requires customized phase setting for individual phase shifters connected to array elements. In this article, a new array calibration method is proposed for phased array operating in beam-steering mode only, that is, phase shifts of elements are only simultaneously set according to the beam-steering directions, and therefore, there is no need for dedicated individual element phase tuning. The proposed method requires a minimum number of complex-signal measurements in principle, which enables fast measurement. Furthermore, it is found that the performance of the proposed method is determined by the beam-steering matrix, whose condition number is mainly ruled by the beam-steering angle interval. The proposed method is numerically simulated and experimentally validated in a millimeter-wave (mmWave) phased-array antenna-in-package (AiP) platform at 28 GHz. The proposed method presents good agreement with the well-known rotating element electric field vector (REV) array calibration method, with an amplitude error and phase error within ±0.5 dB and ±5°, respectively. Furthermore, the reconstructed array pattern with the proposed method offers excellent match with the measured array pattern.

A Novel Amplitude-Only Measurement Method to Determine Element Fields in Phased Arrays

A novel amplitude-only measurement method is proposed for phased array calibrations. The proposed method can determine a complex element field at every phase shift of a digital phase shifter in phased arrays. The method can be realized using higher order Fourier coefficients of one array-power response measured with the conventional rotating element electric field vector (REV) method. Simulations and experiments were carried out, including transmission errors from the phase shifters, which validated the proposed method. More accurate calibration and beam forming can be achieved by using the precise element fields at all phase shifts determined by the proposed method.

Fast Measurement Technique for Phased Array Calibration

A novel measurement method is proposed in order to measure the active electric fields of the individual antenna elements in a phased array antenna. Fast and accurate measurements can be realized by the proposed method because the electric fields of multiple elements can be obtained simultaneously and no phase measurements are required. Hence, it can be easily applied to the on-board diagnostics and re-calibration in the operating phased array antenna systems. In the first step with this method, the phases of multiple antenna elements are successively shifted with the specified phase intervals while the array power variations are measured. Next, the measured power variation is expanded into a Fourier series and the terms are rearranged to put them into the form of the rotating element electric field vector (REV) method. Finally, the REV solution is used to identify the electric fields of the individual elements. Additionally, a theoretical study is carried out on the accuracy of the proposed measurement method. Simple, closed-form equations have been successfully derived for the measurement errors and the calibration accuracy is theoretically estimated. The proposed measurement method is validated with experimental results and the measurement accuracy is compared with the theoretical prediction.

Theoretical study on measurement accuracy of rotating element electric field vector (REV) method

AbstractThe rotating element electric field vector (REV) method is an extremely effective measurement technique for calibration of a phased array. However, if there is any error in the excitation amplitude and phase of each element antenna, the measurements will contain an error. In this paper, the relationship between the error of the excitation amplitude and phase of each element and the measurement error of the REV method is obtained by means of probabilistic analysis theory. In the derivation of the theoretical equation, we study the error in the combined power of the array antenna (to be called the array combined power) when the excitation phase of the element is varied in accordance with the measurement principle of the REV method. Then, the error from the ideal condition without any error in the excitation amplitude and phase is expressed in terms of probability density profile. Next, the relationship between the error in the array combined power and the measurement error of the REV method is given by an approximate formula. As a result, it is clarified that the error of the excitation amplitude and phase of each element and the measurement error of the REV method can be related by a simple theoretical equation. The effectiveness of the derived theoretical formula is verified experimentally, indicating that the measurement accuracy of the REV method is amenable to analysis. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(1): 22–33, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20239

Development results of partial model of a Ka-band active phased array antenna for gigabit satellite

The high data rate and global satellite communication systems are expected to be an improvement agenda to the social and economic activities in the 21st century. The experimental high data rate (gigabit) communications satellite is required to face the technological challenges of the future growing multi-media applications. For this gigabit communications system, a Ka-band scanning spot beam antenna (SSBA) which realizes multiple beam forming is required. CRL and MELCO have been developing Ka-band active phased array antenna (APAA) for the SSBA as one of the most important and challenging technology. An APAA has been developed mainly for radar systems for many years. CRL and MELCO are investigating and developing the direct radiating APAA for communication satellites which can operate under wide frequency band in Ka-band. This paper describes the preliminary study results of the Ka-band APAA for gigabit satellite and the radiation performances of the partial experimental model of Ka-band APAA with two multiple beams to both transmit and receive signals. The partial model includes the active MMIC device such as HPA (high power amplifier), LNA (low noise amplifier) and PS (phase shifter), and multi-layered BFN (beam forming network) as key components. Performances such as radiation pattern, beam scanning performance and input–output performance have been measured. We also verified that the REV (rotating element electric-field vector) method was effective for pattern calibration. Copyright © 1999 John Wiley & Sons, Ltd.

On-orbit measurement of phased arrays in satellites by rotating element electric field vector method

This paper discusses the measurement of the excitation amplitude and phase of each element antenna of phased arrays in satellite orbit. In a phased array, the excitation amplitude and the phase of each element antenna deviate from the desired values, due to the nearby satellite structure, the error of attachment to the satellite, and thermal deformation in the orbit. The errors in the amplitude and the phase must be known for beam scanning and the synthesis of various antenna patterns. The rotating element electric field vector method is useful in measuring the amplitude and the phase of phased arrays. In this method, the amplitude and the phase of the element antenna can be determined simply by varying the phase of the element antenna by a phase-shifter and measuring the amplitude change of the electric field as a result of composition by the array. This is suited to the measurement of phased arrays in satellite orbit, where direct measurement of the phase is difficult. In this study, the above method is used to measure the excitation amplitude and phase of the phased array installed on Engineering Test Satellite VI in orbit. Based on the measured phase, the phase is corrected to realize the designed value. The accuracy of the beam directivity is examined and the validity of the measurements is evaluated. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(1): 1–13, 1998

On‐orbit measurement of phased arrays in satellites by rotating element electric field vector method

On‐orbit measurement of phased arrays in satellites by rotating element electric field vector method

A method for measuring amplitude and phase of each radiating element of a phased array antenna

AbstractIn the phased array system, excitation amplitudes and phases based on the design are specified for each antenna element in order to synthesize desired beam scannings and radiation patterns. However, due to fluctuations of antenna and feed network characteristics, the amplitude and phase of each antenna element deviate from the desired values. To correct these deviations, the amplitude and phase of each antenna element must be accurately measured under specific operating conditions. In this paper, we employ variable phase shifters connected to the antenna elements and measure only the amplitude variation of the composite electric field of the entire array when the phase of each element is modified. The rotating element electric field vector method in which the measured amplitude variation is numerically processed for obtaining the amplitude and phase of the particular element is theoretically discussed and experimentally tested for its usefulness. The present method can be easily attained by simply adding software to the computer‐controlled phased array system.