Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
For satellite applications payload measurements are a crucial part of the radio frequency validation campaign before the launch. Parameters like Equivalent Isotropic Radiated Power (EIRP), Input Power Flux Density (IPFD), Gain over Noise Temperature (G/T), Gain over Frequency (G/F), Group Delay, and Passive Intermodulation (PIM) are to be measured in suitable facilities on satellite level. State-of-the-art payload measurements are conducted in compensated compact range facilities which offer a real-time test capability which is easy to setup and use. Closed link tests are straightforward to realize with two compact range feeds employing feed scanning. The measurement techniques as well as the error budgets are well known. Near-field facilities are widely used for antenna pattern measurements. However, there is not much literature available discussing in particular measurements of G/T, G/F, and Group Delay in the near field. Measurements of the above parameters in the near field seem to be feasible, however, the processing of the measured data has to be adapted and further calibration measurements are required. In this paper methodologies for payload parameter measurements in compact range and near field facilities will be described. A comparison of payload measurement campaigns in near field and compact range facilities will be drawn. The techniques will be compared in terms of measurement timing and effort, practicability for satellite applications, and achievable accuracies.
In this paper an advanced analysis regarding the interaction between antennas installed on a spacecraft is presented. In particular, data coming from a GNSS satellite near field measurement campaign have been considered and the MV-INSIGHT software has been used to perform the analysis. Such a software, starting from the measured field of a DUT, computes equivalent currents on a surface conformal to the test object. The availability of the equivalent currents is a key point for an in depth analysis of DUT such as a spacecrafts since it allows to obtain exclusive diagnostic information like coupling between antennas and satellite structure. The near-field data have been collected in the Hybrid ESA RF and antenna Test Zone (HERTZ) at ESTEC. Such a hybrid NF/FF system has recently been installed in the existing dual reflector CPTR. The installed system has been designed to perform spherical, cylindrical and planar NF measurements in the broad frequencies range 0.4-50 GHz.
Recently, the 5 GHz bands have become increasingly attractive for the wireless industry due to the large amount of unlicensed spectrum available and less congested than the 2.4 GHz band. For this reason, WiFi standards 802.11a/h/j/n/ac operate in the 5 GHz band and its use is also being proposed for LTE-U (LTE-Unlicensed), which will use the unlicensed spectrum in this band for increasing the capacity of LTE (Long-Term Evolution) networks. However, this band is allocated on a primary basis to aeronautical and satellite services, meteorological and military radars and other federal and non-federal uses. In this context, it is necessary to perform additional propagation and interference studies in order to characterize the 5 GHz mobile radio channel considering its current uses and future applications. This work contains measurements and characterization of 5 GHz mobile radio channel along indoor and indoor to outdoor paths using a novel narrowband propagation measurement system. This system, developed at the Institute for Telecommunications Sciences (NTIA/ITS), consists of a vector signal analyzer and highly stable oscillators. The stability, precision and flexibility of the system permit post-processing the baseband complex received signals in order to analyze the channel characteristics. We have performed narrowband measurements on the 5.41 GHz mobile radio channel in four different scenarios: indoor with line of sight, indoor through walls, indoor through different floors and indoor to outdoor. The data collected has been processed for estimating the path loss (including the attenuation factors and path loss exponents), fading statistics and Doppler power spectrum for each scenario. We also show that the processing permits the extraction of accurate information about the scattering environment. The results permit characterizing the 5 GHz mobile radio channel for future spectrum sharing designs, as well as for network planning and capacity planning for WiFi and cellular applications in this band.
To determine the proper moisture content in the soil is critical to get maximum grow in plants and crops and its estimation it is used to regulate the amount of irrigation that it is needed. For this reason, many sensors that measure water content have been developed to give the grower some feedback of the water content. Some methods such as the ones based in gravimetric properties are accurate but labor consuming, other such as the tension meters require periodic service, the neutron probe is also accurate but expensive. The more popular sensor is based in electrical resistance measurement that gives acceptable accuracy and it is not expensive. However, this sensor has the disadvantage that needs to be buried in the soil. Here, we are exploring the characteristics of electromagnetic propagation and its scattering properties as a tool to identify the physical soil composition. The presence of water changes drastically the dielectric properties of the soil affecting the reflected signal. In this research, we are assessing the viability of a sensor based in FMCW radar technology for water detection with the advantage of being portable and low cost. The research involves the fabrication of a directive antenna operating in a broadband regimen, transmitter/ receiver circuit and the signal processing of the return signal adjusted to the detection of moisture in soil. We present the calibration methods and graphic results of the intensity of the reflected signal of dry bare soil, wet soil, and soil covered by plants.
The concept of using plasma physics to create antenna array characteristics with or without multiple elements is to surround a plasma antenna or even a metal antenna by a plasma blanket in which the plasma density can be varied. In regions where the plasma frequency is much less than the antenna frequency, the antenna radiation passes through as if a window exists in the plasma blanket. In regions where the plasma frequency is high, the plasma behaves like a perfect reflector with a reactive skin depth. Hence, by opening and closing a sequence of these plasma windows, we electronically steer or direct the antenna beam into any and all directions. During transmission of the inside antenna of the smart plasma antenna design, the signal can pass through an open plasma window by turning off the plasma in the plasma window or sufficiently decreasing the density of the plasma in the plasma window to allow the signal to pass through. A smart plasma antenna prototype has already been built and demonstrated using these physical principles. A faster technique to steer the smart plasma antenna beam, is to increase the plasma density in the plasma tubes so that Fabry-Perot-Etalon effects are met and the signal will pass through. The Fabry-Perot-Etalon effects are well known in optics. The smart plasma antenna has been programmed to meet the Fabry-Perot-Etalon conditions. The characteristic decay time of the plasma after power turn-off is typically in milliseconds, so the opening time of such a barrier generally is predicted also to be in milliseconds. However such a barrier can be opened on a time scale of microseconds by using Fabry-Perot-Etalon effects. This is done by increasing the plasma density rather than waiting for it to decay. The annular cylindrical ring of plasma of the smart plasma antenna creates a Fabry-Perot-Etalon cavity under the proper conditions.
Crystallographic sample design of complex media influences material tensor properties. These properties offer amplitude, phase and polarization control of the electromagnetic (EM) fields. Previous works have evaluated crystallographic sample designs for isotropic, uniaxial and biaxial anisotropic media, each respective design offering more ways to control the fields. The tensor elements for these designs are all aligned along the main diagonal of the permittivity and/or permeability tensors. Additional field control can be obtained by producing materials that have off-diagonal tensor elements in addition to the aforementioned main diagonal elements. A monoclinic crystal sample design supports the existence of two off-diagonal elements and offers more field control than biaxial anisotropic media. In this work, field analysis is performed on media that possesses a monoclinic tensor element arrangement, demonstrating the additional control over EM fields as compared to biaxial anisotropic media. A monoclinic sample is then constituted using crystallographic symmetry. Future work will yield the development and analysis of a monoclinic sample material measurement capability.
Antenna measurement accuracies or error budgets are related to the signal-to-noise ratio of the measurement receiver. Signal-to-noise can be modelled taking two vectors, the intended signal and an interfering signal (i.e. from unwanted multipath propagation or simple noise), which superpose to the actual measured quantity. Although this approach is widely used, it is rarely discussed to its full extent. Instead, the error of the measured quantity is often estimated for high signal-to-noise ratios by applying worst case assumptions to the unwanted part. This excludes not only any statistical nature of the interfering signal but also the probability of the error appearance represented by its standard deviation. Especially when considering several error contributions in a total budget the adequate combination of different error probabilities yields a much more realistic result than adding single worst cases. Within this paper probability functions are analytically derived for measurement errors depending on the signal-to-noise ratio according to the aforementioned model. This yields a more sophisticated analysis of amplitude and phase errors having standard deviations for measured quantities. The confidence intervals of measurement errors are given with respect to varying signal-to-noise ratios. Limitations of the white noise synthesis with uniform phase and amplitude distributions are explained. Further, the applicability of worst case assumptions to the analytical solutions is discussed in the presence of high and low dynamic ranges. The derived expressions are statistically tested using Matlab calculations and compared to measurements with a vector network analyzer. The results are interpreted with respect to practical applications.
?Radiation efficiency is an important attribute of an antenna that can be calculated from its gain and directivity. This paper focuses on investigating the effects of influence factors for antenna radiation efficiency measurement in an anechoic chamber (AC). The gain transfer method (GTM) is used widely during the gain measurement, but the results can be influenced by many factors. A comparison of gain measurement performed by GTM and the three-antenna method (TAM) is presented. All measurements were carried out between 1 GHz and 8 GHz in an anechoic chamber with a double-ridged waveguide horn antenna as the antenna under test (AUT), which has a relatively broad half-power beamwidth. The results show that the maximum difference between the two methods is about 1.5 dB and the GTM may bring greater measurement uncertainty. To evaluate the influence of directivity and its repeatability, two sets of directivity measurements were performed using four different antenna mounting brackets, namely: Rohacell foam, Tufnol, metal, and metal covered by radio frequency absorber. Amongst the antenna mounting brackets, the Tufnol bracket gives the best repeatability performance. The antenna axial symmetrical properties were also assessed for each antenna mounting bracket except for Rohacell foam. The results shows that the gain measurement has more influence over characterization of antenna radiation efficiency as compared with the directivity measurement. To improve accuracy for radiation efficiency measurement, one suggests to use TAM for the antenna gain measurement.
In this paper, we propose a calibration method for monostatic radar cross section (RCS) of simple radar targets (e.g. trihedral corner reflectors and square flat-plate reflectors) using extrapolation method. By the proposed method, we can calibrate the monostatic RCS of radar targets from 1-port S-parameter measurements. In our system, the applicable size of radar targets are 75 mm to 125 mm for corner reflectors and 40 mm to 75 mm for square flat-plate reflectors, respectively. The nominal RCS of reflector targets calculated by physical optics ranges from +3 dBsm to +15 dBsm in W-band. The measured results are agree well with simulation results calculated by method of moment (MoM).
In this paper, a patch antenna has been designed based on the complementary split ring resonator (CSRRs), complementary rose curve resonators (CRCRs) and without using these inclusions. Complementary rose curve resonators (CRCRs) are used in design of patch antenna. The Patch antenna based on the complementary rose curve resonators (CRCRs) are achieved by patterning the ground plane under the conductor trace. The perimeter of the Rose curve can be adjusted by tuning the amplitude of the sine function and the radius of the base circle. With the order of CRCRs, the loading effect of the complementary resonators on the patch antenna is controlled. This works demonstrated that higher order CRCRs allows more compactness of the design and higher miniaturization factor. We proposed a compact patch antenna based on the complementary split ring resonator (CSRRs) and the complementary Rose curve resonator (CRCRs). The proposed patch antenna shows good performances which is designed to operate at 2.4 GHz. The results demonstrate the configurability of the design for a specific size. The results show the effectiveness of using metamaterials in microwave circuit can obtain from n to n+1 of the CRCRs order will result in 0.3 % miniaturization. IndexTerms: Patch Antenna, Metamaterial, Size Reduction, split ring Resonators, Rose Curve Resonators
We have performed spherical and extrapolation scans of two antennas at 118 GHz using a commercial 6-axis robot. Unlike spherical scanning, linear extrapolations do not precisely conform to the natural circular movement about individual robot axes. To characterize the quality of the data, we performed dynamic position and orientation characterization of the robotic systems. A laser tracker is used to measure the probe antenna movement relative to the antenna under test, this information is used to continually update the position and posture of the probe during scanning. We correlated the laser tracker data with the mmWave insertion phase to validate dynamic measurement position results at speeds up to 11 mm/s. We previously demonstrated spherical measurements with this system. The extrapolation measurements presented here require more stringent accuracies for pointing that general pattern analysis
Inverse Synthetic Aperture Radar (ISAR) measurements are used in this study to obtain images of full scale targets placed on a turntable. The images of the targets are extracted using compressed sensing methods. The extracted target images are edited and merged into measured Synthetic Aperture Radar (SAR) images. Airborne SAR field trials are complicated and expensive. This means that it is important to use the acquired data efficiently when areas with different background characteristics are imaged. One would also like to evaluate the signature of targets in these background scenes. Ideally, each target should then be measured for many orientations as well as illumination angles which would result in a large number of measurement cases. A more efficient solution is to use ground based ISAR measurements of the desired targets and then blend these images into the SAR scene. We propose a SAR blending method where a noise free image of the target is extracted from the RCS measurement by using the compressed sensing method Basis pursuit denoise (BPDN) and then solving for a model consisting of point scatterers. The target signature point scatterers are then merged into a point scatterer representation of the SAR background scene. The total point scatterer RCS is evaluated in the frequency-angle domain followed by using that RCS for back projection to form a seamless SAR image containing the target with the desired orientation and aspect angle. A geometrically correct shadow, constructed from a CAD-model of the target, is edited into the background. The process is completed by adding noise to the image consistent with the estimated SNR of the SAR-system. The method is demonstrated with turntable measurements of a full scale target, with and without camouflage, signature extraction and blending into a SAR background. We find that the method provides an efficient way of evaluating measured target signatures in measured backgrounds.
The source reconstruction or equivalents source method provides an accurate near-field representation of any radiating device in terms of equivalent electric and magnetic currents. The equivalent currents can be determined from measured near or far field data through a post-processing step involving the solution of an integral equation. The currents constitutes an accurate 3D electromagnetic model, maintaining near and far field properties of the measured device. A newly created link, enable the export of the model to a number of commercial computational electromagnetic (CEM) solvers in the form of a near-field Huygens box. Of special interest to the EMC community, equivalent current representation of measured devices are directly applicable in diagnostics/hot-spot finding and in the determination of radiated emission at any distance. The Huygens box, derived from measurements, is applicable in the simulation of emission in different scenarios when the device is in vicinity of different objects such as shielding, cables etc. This papers shows examples of diagnostics and emission analysis of a representative printed circuit board (PCB) based on commercially available near field measurement systems, post-processing and CEM tools.
Among the near-field – far-field (NF–FF) transformation techniques, the one employing the plane-polar scanning has attracted a considerable attention [1]. In this framework, efficient sampling representations over a plane from a nonredundant number of plane-polar samples, which stays finite also for an unbounded scanning plane, have been developed, by applying the nonredundant sampling representations of the EM fields [2] and assuming the antenna under test (AUT) as enclosed in an oblate ellipsoid [3] or in a double bowl [4], namely, a surface formed by two circular bowls with the same aperture diameter but eventually different lateral bends. These effective representations make possible to accurately recover the NF data required by the plane-rectangular NF–FF transformation [5] from a nonredundant number of NF data acquired through the plane-polar scanning. A remarkable reduction of the number of the needed NF data and, as a consequence, of the measurement time is so obtainable. However, due to an imprecise control of the positioning systems and their finite resolution, it may be impossible to exactly locate the probe at the points fixed by the sampling representation, even though their position can be accurately read by optical devices. Therefore, it is very important to develop an effective algorithm for an accurate and stable reconstruction of the NF data needed by the NF–FF transformation from the acquired irregularly spaced ones. A viable and convenient strategy [6] is to retrieve the uniform samples from the nonuniform ones and then reconstruct the required NF data via an accurate and stable optimal sampling interpolation (OSI) expansion. In this framework, two different approaches have been proposed. The former is based on an iterative technique, which converges only if there is a biunique correspondence associating at each uniform sampling point the nearest nonuniform one, and has been applied in [6] to the uniform samples reconstruction in the case of cylindrical and spherical surfaces. The latter, based on the singular value decomposition method, does not exhibit this constraint and has been applied to the nonredundant plane-polar [7] scanning technique based on the oblate ellipsoidal modelling. However, it can be conveniently used only when the uniform samples recovery can be split in two independent one-dimensional problems. The goal of this work is to develop these two techniques for compensating known probe positioning errors in the case of the nonredundant plane-polar scanning technique using the double bowl modelling [4]. Experimental tests will be performed at the UNISA Antenna Characterization Lab in order to assess their effectiveness. [1] Y. Rahmat-Samii, V. Galindo Israel, and R. Mittra, “A plane-polar approach for far-field construction from near-field measurements,” IEEE Trans. Antennas Prop., vol. AP-28, pp. 216-230, 1980. [2] O.M. Bucci, C. Gennarelli, C. Savarese, “Representation of electromagnetic fields over arbitrary surfaces by a finite and nonredundant number of samples,” IEEE Trans. Antennas Prop., vol. 46, pp. 351-359, 1998. [3] O.M. Bucci, F. D’Agostino, C. Gennarelli, G. Riccio, and C. Savarese, “NF–FF transformation with plane-polar scanning: ellipsoidal modelling of the antenna,” Automatika, vol. 41, pp. 159-164, 2000. [4] O.M. Bucci, C. Gennarelli, G. Riccio, and C. Savarese, “Near-field–far-field transformation from nonredundant plane-polar data: effective modellings of the source,” IEE Proc. Microw. Antennas Prop., vol. 145, pp. 33-38, 1998. [5] E.B. Joy, W.M. Leach, Jr., G. P. Rodrigue and D.T. Paris, “Application of probe-compensated near-field measurements,” IEEE Trans. Antennas Prop., vol. AP-26, pp. 379-389, May 1978. [6] O.M. Bucci, C. Gennarelli, G. Riccio, C. Savarese, “Electromagnetic fields interpolation from nonuniform samples over spherical and cylindrical surfaces,” IEE Proc. Microw. Antennas Prop., vol. 141, pp. 77-84, 1994. [7] F. Ferrara, C. Gennarelli, G. Riccio, C. Savarese, “Far field reconstruction from nonuniform plane-polar data: a SVD based approach,” Electromagnetics, vol. 23, pp. 417-429, July 2003
We present experimental results for on platform (in-situ) calibration of an antenna array with signals that are treated as signals of opportunity. In-situ calibration is required for antenna arrays installed on vehicles as platform scattering significantly perturbs the radiation patterns of the antenna elements. In-situ measurement of the array response requires: determining location of the unknown signals; determining the array’s response in the direction of the signals; and synthesizing the array pattern from the measured data. For this work, a seven element L-band antenna array was mounted on a generic aircraft platform. The platform was mounted on a dual rotator setup and emitters were placed nearby. The platform was then rotated while the emitters transmitted, and the signals received by the antenna elements were digitized. The collected data was then post processed to obtain the array calibration. We found that the calibrated array manifold enables more accurate direction of arrival estimation and provides additional gain in direction constrained beamforming. The present work serves as experimental verification of earlier simulation studies on in-situ array calibration.
The Space Communications and Navigation (SCAN) Testbed was a Software Defined Radio (SDR)-based payload launched to the International Space Station (ISS) in July of 2012. The purpose of the SCAN Testbed payload was to investigate the applicability of SDRs to NASA space missions in an operational space environment, which means that a proper model for system performance in said operational space environment is a necessary condition. The SCAN Testbed has line-of-sight connections to various ground stations with its S-Band Earth-facing Near-Earth Network Low Gain Antenna (NEN-LGA). Any previous efforts to characterize the NEN-LGA proved difficult, therefore, the NASA Glenn Research Center built its own S-Band ground station, which became operational in 2015, and has been successfully used to characterize the NEN-LGA’s in-situ pattern measurements. This methodology allows for a more realistic characterization of the antenna performance, where the pattern oscillation induced by the complex ISS ground plane, as well as shadowing effects due to ISS structural blockage are included into the final performance model. This paper describes the challenges of characterizing an antenna pattern in this environment. It will also discuss the data processing, present the final antenna pattern measurements and derived model, as well as discuss various lessons learned.
Inter-comparisons of antenna test ranges serve the purpose of validating the measurement accuracy of a given range before it can be qualified to perform certain measurements, which is particularly important for space applications, where antenna specifications are very stringent. Moreover, by verifying the measurement procedures and identifying sources of errors and uncertainties, inter-comparison campaigns improve our understanding of strengths and limitations of different measurement techniques, which, in turn, leads to further improved measurement accuracies. The lesson learned from early comparison campaigns executed by the Technical University of Denmark (DTU) in early 80s on some readily available antennas says that proper inter-comparisons can only be done on dedicated antennas, whose design is driven by stringent requirements on their rigidity and mechanical stability. Furthermore, well-defined reference coordinate systems are essential. These principles have convincingly been proven valid by the VAST-12 antenna designed by DTU in late 80s, which in more than 20 years has demonstrated its usefulness and a long-term value. Currently, the satellite communication industry is actively commercializing the mm-wave frequency bands (K/Ka-bands) in its strive for wide frequency bandwidth and higher bit-rates. The next step is the exploration and exploitation of the Q/V-band. In this scenario, the European Space Agency (ESA) is expanding its portfolio of VAlidation STandard antennas (VAST) into mm-waves to ensure accurate measurements of the next generation communication antennas. This time, ESA demands all four bands (K/Ka/Q/V-bands) to be covered by a single VAST antenna. In this contribution, we report our efforts in designing, fabricating, and testing a new precision tool for antenna test range qualification and inter-comparisons at mm-waves -- the mm-VAST antenna. In particular, we present the details of the antenna mechanical design, fabrication and assembling procedures. The performance verification test plan as well as first measurement results will also be discussed.
The single-offset compact antenna test range (CATR) is a widely deployed technique for broadband characterization of electrically large antennas at reduced range lengths [1]. The nature of the curvature and position of the offset parabolic reflector as well as the edge geometry ensures that the resulting collimated field is comprised of a pseudo transverse electric and magnetic (TEM) wave. Thus, by projecting an image of the feed at infinity, the CATR synthesizes the type of wave-front that would be incident on the antenna under test (AUT) if it were located very much further away from the feed than is actually the case with the coupling of the plane-wave into the aperture of the AUT creating the classical measured “far-field” radiation pattern. The accuracy of a pattern measured using a CATR is primarily determined by the phase and amplitude quality of the pseudo plane-wave with this being restricted by two main factors: amplitude taper (which is imposed by the pattern of the feed), and reflector edge diffraction, which usually manifests as a high spatial frequency ripple in the pseudo plane wave [2]. It has therefore become customary to specify CATR performance in terms of amplitude taper, and amplitude & phase ripple of this wave over a volume of space, termed the quiet-zone (QZ). Unfortunately, in most cases it is not directly apparent how a given QZ performance specification will manifest itself on the resulting antenna pattern measurement. However, with the advent of powerful digital computers and highly-accurate computational electromagnetic (CEM) models, it has now become possible to extend the CATR electromagnetic (EM) simulation to encompass the complete CATR AUT pattern measurement process thereby permitting quantifiable accuracies to be easily determined prior to actual measurement. As the accuracy of these models is paramount to both the design of the CATR and the subsequent determination of the uncertainty budget, this paper presents a quantitative accuracy evaluation of five different CEM simulations. We report results using methods of CATR modelling including: geometrical-optics with geometrical theory of diffraction [3], plane-wave spectrum [4], Kirchhoff-Huygens [4] and current element [3], before presenting results of their use in the antenna pattern measurement prediction for given CATR-AUT combinations. REFERENCES [1]C.G. Parini, S.F. Gregson, J. McCormick, D. Janse van Rensburg “Theory and Practice of Modern Antenna Range Measurements”, IET Press, 2014, ISBN 978-1-84919-560-7. [2]M. Philippakis, C.G. Parini, “Compact Antenna Range Performance Evaluation Uging Simulated Pattern Measurements”, IEE Proc. Microw. Antennas Propag., Vol. 143, No. 3, June 1996, pp. 200-206. [3]G.L. James, “Geometrical Theory of Diffraction for Electromagnetic Waves”, 3rd Edition, IET Press, 2007, ISBN 978-0-86341-062-8. [4]S.F. Gregson, J. McCormick, C.G. Parini, “Principles of Planar Near-Field Antenna Measurements”, IET Press, 2007.
The Space Communications and Navigation (SCaN) Testbed project completed installation and checkout testing of a new S-Band ground station at the NASA Glenn Research Center in Cleveland, Ohio in 2015. As with all ground stations, a key alignment process must be conducted to obtain offset angles in azimuth (AZ) and elevation (EL). In telescopes with AZ-EL gimbals, this is normally done with a two-star alignment process, where telescope-based pointing vectors are derived from catalogued locations with the AZ-EL bias angles derived from the pointing vector difference. For an antenna, the process is complicated without an optical asset. For the present study, the solution was to utilize the gimbal control algorithm’s closed-loop tracking capability to acquire the peak received power signal automatically from two distinct NASA Tracking and Data Relay Satellite (TDRS) spacecraft, without a human making the pointing adjustments. Briefly, the TDRS satellite acts as a simulated optical source and the alignment process proceeds exactly the same way as a one-star alignment. The data reduction process, which will be discussed in the paper, results in two bias angles which are retained for future pointing determination. Finally, the paper compares the test results and provides lessons learned from this activity.
Abstract Antenna far field phase pattern is important for some applications. It can be directly obtained in pattern measurement by far field test range (FFTR) or compact range (CR). However, it is found that the antenna far field phase pattern measured by current near field test range (NFTR) is not correct. For a uniform phase feeding plane array, its far field phase pattern should be near constant in 3dB beam width. However, the antenna phase pattern measured by current NFTR looks square curve vs angle. This paper found out that the root cause of the error is due to different reference planes. Both the amplitude pattern and the phase pattern obtained by current NFTR, in fact, refer to the probe scanner plane, not the antenna plane. This shifting of the reference plane has no effect on amplitude pattern, but has effect on phase pattern. After that, a correction method is proposed. One example is used for the root cause finding and correction technique explanation. According to this paper, if one wants to get phase pattern using NFTR, it is necessary to measure the distance between AUT and probe aperture accurately so as to correct it accurately after measurement and obtain accurate phase pattern.