Antenna Calibration Method Research Articles

A Relative Field Antenna Calibration Method Designed for Low-Cost GNSS Antennas by Exploiting Triple-Differenced Measurements

Performing the high-precision Global Navigation Satellite System (GNSS) applications with low-cost antennas is an up-and-coming research field. However, the antenna-induced phase biases, i.e., phase center corrections (PCCs), of the low-cost antennas can be up to centimeters and need to be calibrated in advance. The relative field antenna calibration method is easy to conduct, but the classical procedure entails integer ambiguity resolution, which may face the problem of low success rate under the centimeter-level PCCs. In this contribution, we designed a relative field calibration method suitable for the low-cost GNSS antennas. The triple-differencing operations were utilized to eliminate the carrier-phase ambiguities and then construct PCC measurements; the time-differencing interval was set to a relatively long time span, such as one hour, and the reference satellite was selected according to the angular distance it passed over during a time-differencing interval. To reduce the effect of significant triple-differencing noise, a weight setting method based on the area of a spherical quadrilateral was proposed for the spherical harmonics fitting process. The duration of the data collection with respect to GPS and BDS was discussed. The performance of the proposed method was assessed with real GPS and BDS observations and a variety of simulated phase patterns, showing that calibration results could be obtained with millimeter-level accuracy. The impact of cycle slip and elevation mask angle on the calibration results was also analyzed.

A Fast and Efficient Calibration Method for Phased Array Antennas Using Fourier-Structured Excitation Matrix

This article presents a novel phased array antenna calibration method. Unlike conventional phased array calibration methods equipped with only one probe antenna in the far-field setup, multiple measurement probes are introduced in the proposed algorithm to significantly improve the measurement efficiency. Specifically, a novel construction method for an excitation matrix (which contains excitation coefficients for phased array elements) is proposed, where phase differences introduced by the spatial locations of the multiple probes are perfectly incorporated into the Fourier-structured excitation matrix, thereby presenting the best measurement efficiency without sacrificing the array calibration accuracy. The proposed method can offer robust array calibration results (guaranteed by the low condition number of the constructed excitation matrix with Fourier structure) and high measurement efficiency (offered by multiprobe setups). To experimentally validate the proposed algorithm, a multichannel (i.e., multiprobe) far-field measurement setup was utilized. A four-element open-ended waveguide array operating at 2.6 GHz and two-probe far-field systems were employed as the antenna under test (AUT) and multiple probes, respectively, to validate the effectiveness and robustness of the proposed phased array calibration algorithm. The proposed algorithm will be highly valuable for efficient phased array calibration, especially for future antenna systems equipped with large-scale antenna configurations.

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.

Antenna Excitation Optimization with Deep Learning for Microwave Breast Cancer Hyperthermia.

Microwave hyperthermia (MH) requires the effective calibration of antenna excitations for the selective focusing of the microwave energy on the target region, with a nominal effect on the surrounding tissue. To this end, many different antenna calibration methods, such as optimization techniques and look-up tables, have been proposed in the literature. These optimization procedures, however, do not consider the whole nature of the electric field, which is a complex vector field; instead, it is simplified to a real and scalar field component. Furthermore, most of the approaches in the literature are system-specific, limiting the applicability of the proposed methods to specific configurations. In this paper, we propose an antenna excitation optimization scheme applicable to a variety of configurations and present the results of a convolutional neural network (CNN)-based approach for two different configurations. The data set for CNN training is collected by superposing the information obtained from individual antenna elements. The results of the CNN models outperform the look-up table results. The proposed approach is promising, as the phase-only optimization and phase–power-combined optimization show a 27% and 4% lower hotspot-to-target energy ratio, respectively, than the look-up table results for the linear MH applicator. The proposed deep-learning-based optimization technique can be utilized as a protocol to be applied on any MH applicator for the optimization of the antenna excitations, as well as for a comparison of MH applicators.

Proposed Massive‐MIMO Antenna Calibration Method Using Near‐Field Measurement

Fifth‐generation mobile communications systems now being developed use antennas with large numbers of antenna elements and are decided to be massive‐MIMO technologies for flexibly changing the antenna beam (beam forming). Obtaining the required directivity for a multielement antenna requires control of the phase and amplitude of the variable phase shifter and variable amplifier built into each antenna element. Moreover, the variable phase shifter and variable gain amplifier settings must be obtained so that every antenna element radiates equiamplitude and equiphase radio waves. This process is called antenna calibration. This paper proposes a method using near‐field measurement and back‐projection processing to perform calibration. Moreover, actual calibration tests of a simulated massive‐MIMO base station were executed using the proposed method. The results reported here confirm that calibration can be implemented using the proposed method even when the phase shifter of the simulated base station suffers large variability. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

High Quality Zenith Tropospheric Delay Estimation Using a Low-Cost Dual-Frequency Receiver and Relative Antenna Calibration

The recent release of consumer-grade dual-frequency receivers sparked scientific interest into use of these cost-efficient devices for high precision positioning and tropospheric delay estimations. Previous analyses with low-cost single-frequency receivers showed promising results for the estimation of Zenith Tropospheric Delays (ZTDs). However, their application is limited by the need to account for the ionospheric delay. In this paper we investigate the potential of a low-cost dual-frequency receiver (U-blox ZED-F9P) in combination with a range of different quality antennas. We show that the receiver itself is very well capable of achieving high-quality ZTD estimations. The limiting factor is the quality of the receiving antenna. To improve the applicability of mass-market antennas, a relative antenna calibration is performed, and new absolute Antenna Exchange Format (ANTEX) entries are created using a geodetic antenna as base. The performance of ZTD estimation with the tested antennas is evaluated, with and without antenna Phase Center Variation (PCV) corrections, using Precise Point Positioning (PPP). Without applying PCVs for the low-cost antennas, the Root Mean Square Errors (RMSE) of the estimated ZTDs are between 15 mm and 24 mm. Using the newly generated PCVs, the RMSE is reduced significantly to about 4 mm, a level that is excellent for meteorological applications. The standard U-blox ANN-MB-00 patch antenna, with a circular ground plane, after correcting the phase pattern yields comparable results (0.47 mm bias and 4.02 mm RMSE) to those from geodetic quality antennas, providing an all-round low-cost solution. The relative antenna calibration method presented in this paper opens the way for wide-spread application of low-cost receiver and antennas.

Antenna Calibration for Near-Field Material Characterization

A novel antenna calibration method is presented for near-field problems, such as material characterization or inverse scattering. The procedure accurately accounts for differences between simulations of objects close to antennas and the equivalent experimental measurements. It is based on the method of moments (MoM) solution to surface integral scattering equations. An efficient choice of macrobasis functions (MBFs) is applied to the antenna, which reduces the computational costs by several orders of magnitude. The calibration involves scanning a target of known constitution through the antenna near field, assigning a tuning parameter to each MBF and optimizing said parameters, so as to reduce the error between antenna simulations and measurements. This adjusts the antenna’s simulated surface currents, so as to more accurately represent the currents on the experimental apparatus. Thus, an efficient antenna model is obtained, which more accurately represents the real-world antenna. The calibration technique is verified by applying it to the characterization of dielectric objects of known but arbitrary shape.

Antenna calibration technique based on channel prediction in time-varying TDD-MIMO system

The traditional antenna calibration for time division duplex multiple input multiple output (TDD-MIMO) systems assume that free-space channel keeps constant during calibration, which is unreasonable under the high-speed rail and other time-varying channel scenarios for time variability can cause calibration error. This paper analyzes the performance of traditional antenna calibration methods, and then proposes an antenna calibration method based on Wiener channel prediction for time-varying TDD-MIMO system. Through theoretical derivation, we get the capacity formula of the TDD-MIMO system using traditional antenna calibration and antenna calibration based on channel prediction. The theoretical analysis and simulation results both indicate that the performance degradation of antenna calibration can be caused by time-varying channel and the prediction algorithm proposed in the paper can well compensate for the performance loss and significantly improve the antenna calibration performance for time-varying TDD-MIMO system.

Antenna calibration using channel prediction for time-varying channels

Traditional antenna calibration methods for time division duplex (TDD) systems assume that the free-space channel remains the same during calibration, which is unreasonable under the high-speed rail and other time-varying channel scenarios, and will cause calibration error due to time variability. This paper proposes an antenna calibration method for time-varying channels. In the proposed method, the transceiver first sequentially sends a pilot signal to obtain equivalent downlink and uplink channel responses. Then, by predicting the downlink (uplink) channel response fed back from the receiver using the channel prediction algorithm, the transmitter obtains the channel response corresponding to the channel response on uplink (downlink). Finally, the transmitter calculates the transmission calibration factor through the prediction value. Compared with the traditional antenna calibration method, this method can improve the accuracy of the calibration factor. Simulation results show that the performance degradation of antenna calibration can be caused by time-varying channels and the proposed method can well compensate for the performance loss and significantly improve the antenna calibration performance for time-varying channels.

시간 영역에서 안테나 이득 측정 연구

There are several antenna calibration methods, so-called 3-Antenna Method, Standard Site Method, and Standard Antenna Method which measure the antenna gains or antenna factors. These methods yield the free space or quasi free space antenna gains in only the frequency domain. In this paper, an antenna calibration method using the time domain in the open area test site is discussed. The reflected waves due to the ground are traced in the time domain. After they are removed by the time gating function of network analyzer, the free space transmission coefficient is extracted. Such a way is applied to the broad band horn antenna ranging 1 GHz to 18 GHz, and the free space gains are obtained by Friis transmission equation. The method is checked by Standard Site Method in open area test site. The results show comparatively good agreement except for 18 GHz.

A Novel Method to Measure Array Manifolds of GNSS Adaptive Antennas

: We present a procedure for measuring the complete, in situ array manifold of a STAP-based adaptive antenna using only standard GNSS receiver measurements. Note that one needs in situ array manifolds in adaptive spatial processing as well as for estimation of the antenna induced biases in GNSS measurements. The proposed procedure is a straightforward extension of traditional outdoor GPS antenna calibration methods. The adaptive filter weights in the antenna electronics are carefully varied, and their effect on the GNSS receiver measurements are recorded. Using a system of equations derived in this paper, these receiver measurements are used to solve for the frequency response of each antenna element in each satellite direction. The accuracy of the proposed procedure is established using computer simulations. We also show that the measured array manifolds provide a very good estimate of the antenna induced biases in GNSS receiver measurements in the presence of interferers.

30 MHz에서 1 GHz 대역 EMI 측정용 다이폴안테나 교정의 측정 불확도

Measurement uncertainty assessment is very important in measurement and calibration. RRL provides antenna calibration services for EMI test. Reliability of EMI test depends on accurate antenna calibration. Antenna calibration results have to be accompanied with measurement uncertainty for its better reliability. In the late of 2005, CISPR issued the CISPR/A/644/C which describes the antenna calibration and measurement uncertainty. In this paper, on the basis of CISPR/A/644/C, we provide the measurement uncertainty values for dipole antenna calibration at the Calibration Test Site(CALTS) of Icheon. The antenna calibration method is 3-antenna height-scanning-averaging method, which measures the free-space antenna factor. We also considered all uncertainty sources that can affect measurement results during calibration.

Realistic calibration method for mobile base-station array antennas with multi-reflection of feed circuits and mutual couplings between radiating elements taken into account

When a feed circuit cannot assure isolation between terminals in a mobile communications base-station antenna, the excitation distribution deviates from the desired values due to multiple reflections between components. Therefore, the desired radiation characteristics cannot be obtained. Also, it is not easy to derive the lengths of the transmission lines adjusting the phase within the feed circuit (fine-tuning cables). In this paper, using the S parameters of each component and the antenna, the feed circuit is optimized by deriving the fine-tuning cable lengths based on a nonlinear optimization method, realizing a desired excitation profile. A simulation based on the newly derived theory and actual measurements confirmed the effectiveness of the proposed approach. The present method does not require several adjustments with the feed circuit. The method is promising as a real calibration method for array antenna feed systems. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(12): 12–19, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20315

Average of the Height-Dependent Antenna Factor

Theoretical analyses are carried out on the height dependence of the antenna factor of an EMI antenna to develop an antenna calibration method that can provide the free-space value of the antenna factor. It is found that the antenna factor in general varies with the antenna height in a quasi-periodic way with a period of about λ/2. Thus, the present paper proposes to take an average of the antenna factors over a height range of about λ/2 to obtain an accurate estimate of the free-space antenna factor. Effective antenna arrangements are also proposed for the antenna calibration. Deviations in the estimate from the free-space antenna factor are less than 0.1 dB for tuned dipoles in the frequency range above 50MHz. But the errors increase up to 0.3 dB at about 35 MHz. For broadband antennas, the free-space antenna factor can be accurately estimated by taking the average of the antenna factors. Errors are estimated to be less than 0.3 dB in the frequency range from 30 MHz to 1000 MHz.

Study of active antenna receivers and calibration method for digital beamforming

AbstractIn next‐generation high speed wireless communications, the development of digital beamforming (DBF) is indispensable for the creation of base stations and terminal antennas with high functionality, low cost. and small size. On the other hand, active antennas that combine a passive antenna and active devices are advantageous for use in DBF, because the feed line can be shortened and phase and amplitude imbalance among the array branch elements can be reduced. Further, if technologies to reduce the number of active devices, such as the direct conversion and Low IF schemes, are combined, it is possible to attempt miniaturization and reduction of individual differences. In this paper, a receiver of small size for DBF is proposed and experimentally studied by using an active integrated antenna containing an amplifier and a Low IF scheme. A calibration circuit for amplitude and phase corrections is discussed in which the error factors in the characteristics between the devices are taken into account. Further, experimental results on beam pattern generation by the test system in an anechoic chamber are presented. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(11): 20–29, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10119

Comparison of Absolute and Relative Antenna Phase Center Variations

Three major GPS antenna calibration methods are available toda: the relative field calibrations using the GPS data collected on short baselines, the absolute field calibrations, where the GPS antenna is rotated and tilted by a robot, and calibration measurements in an anechoic chamber. Mean antenna offsets and the elevation-dependent phase center variations of GPS antennas determined by all three techniques are compared to assess their accuracy. The analysis of global GPS data with these sets of calibration values reveals that the offsets and variations of the satellite antenna phase centers have to be considered, too, to obtain a consistent picture. © 2001 John Wiley & Sons, Inc.