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A large rolled edge compact range system featuring a 12’H x 16’W quiet zone has been designed, fabricated, installed, and tested in a large aerospace test facility. During the program, a high precision alignment methodology was utilized in conjunction with electromagnetic prediction capability to verify both mechanical and electrical performance while still under trial assembly conditions at the factory. A coherent laser radar (CLR) was utilized to measure the reflector surface on a very fine grid, and the electromagnetic (EM) quiet zone performance was calculated from the raw CLR data using a Physical Optics (PO) model. Despite extremely high surface accuracy of the panels, this evaluation methodology highlighted systematic alignment errors in the reflector system, and guided the process of correcting these errors to achieve a final factory verification assembly for the entire 20’H x 24’W reflector system of better than 0.001” over the quiet zone section of the reflector, and 0.004” rms over the entire reflector. This procedure was also utilized for the on-site installation to achieve alignment of the reflector to an AUT positioning system using the CLR, as the positioning system and chamber were already existing and operational. Thus, it was required to align the reflector to the positioning system, and not the positioning system to the reflector as is usually the case. A unique vertical carousel feed system was also aligned using this procedure. Predicted EM results were again used to finalize alignment on site prior to quiet zone field probe evaluation. This paper summarizes the overall alignment and EM evaluation process, and presents results for the installed compact range reflector system.
A probe station based antenna measurement setup is presented. The setup allows for measurement of complex impedance and radiation patterns of an on-wafer planar antenna, henceforth referred to as the device under test (DUT), radiating at broadside and fed by a coplanar waveguide (CPW). The setup eliminates the need for wafer dicing and custom-built test fixtures with coaxial connectors or waveguide flanges by contacting the DUT with a coplanar RF probe. In addition, the DUT is probed exactly where it will be connected to a transceiver IC later on, such that no de-embedding of the measured data is required. The primary sources of measurement errors are related to calibration, insufficient dynamic range (DR), misalignment, scattering from nearby objects and vibrations. The performance of the setup will be demonstrated through measurement of an on-wafer electrically short slot antenna (.0/35 × .0/35, 5 mm2) radiating at 2.45 GHz.
An indoor localization and communication project is described that proposes to use RFID (radio-frequency identification) tags, placed in the building beforehand, as navigation waypoints for an inertial navigation system carried by a first responder. RFID devices commonly are attached to persons or to moveable objects so that the objects can be tracked by using fixed readers (special-purpose radio receivers) at different locations. In this project, we explore the “flip side” of this practice. Our concept is that detection of RFID devices in known, fixed locations by a moving reader provides a precise indication of location for tracking the person or moving object that is carrying the reader. This information can then be used to correct for any errors of an inertial tracking system.
Adaptive antenna has both the amplitude as well as phase (as weights) can be adapted optimally to get required Direction of Arrival (DOA) estimation or directed beam forming. This paper tries to analyze state of the art criteria for Adaptive antenna, suppressing the interference in directions other than desired. We model the Uniform Linear array (ULA) based on simulations of various adaptive and non-adaptive algorithms. We list possible types of errors in brief. Element spacing and mutual coupling influence each other and affect the antenna element pattern. We formulate the array antenna that tries to reduce the error by optimally adjusting the weights. We make an attempt to model mutual coupling. A high precision array antenna can be designed keeping in mind error factors, optimum adjustment of the element interval and mutual coupling. An adaptive antenna optimal weight adjustment is discussed here. Key words: ULA, DOA, DBF.
The potential transmit power, and hence dynamic range of monostatic millimeter wave RCS measurements may be limited by the feed coupling of the antenna. Time domain gating can be used to reduce the measurement errors caused by this signal, as well as other undesired signals from scattering sources in the range, but does not protect the receiver from compression. Hardware gating can allow increases in transmit power by protecting the receiver from the effects of the feed coupling return. Unfortunately, equipment capable of hardware gating at millimeter wave frequencies is difficult to obtain. In addition, the usefulness of hardware gating is limited by the duty cycle loss in the measured signal. We describe a practical system using gating of the low frequency intermediate frequency (IF) signal in the receiver and a microwave pulse modulator prior to the millimeter wave multiplier in a mono-static millimeter wave RCS measurement system. We also describe methods to minimize the loss of measurement dynamic range due to duty cycle losses in this system. We demonstrate the use of this system for RCS measurements of simple targets, and compare the results with those obtained using software gating alone.
Abstract. We present new RCS measurements from an 8-foot square flat plate for frequencies from 0.15 to 5.5 GHz. Guided by the theory, we study the peak RCS at normal incidence, the principal plane pattern, and the 3-dB beam-width in detail. The broadside echo from the plate is found to be extremely narrow at higher frequencies. From the errors, we estimate that the wave-field experienced by the plate is reasonably uniform to within +0.3 dB, over a wide dynamic range of 60 dB.
This paper presents results of planar near-field measurements at 16, 35 and 94 GHz using probe position correction algorithms. The algorithms correct for position errors of the probe near the scan plane. The probe’s actual position is measured using a laser tracker integrated into the planar-near-field scanning system at NIST. The laser tracker simultaneously obtains probe-position information at each point where amplitude and phase data are acquired during planar near-field antenna measurements.
A method is presented to measure the antenna pattern of an AUT where the antenna port is inaccessible. That means that it is not possible to connect a test cable, nor can the termination be changed physically. In some cases there is no test port at all. The only variation possible is to change the input impedance of the first receiver or LNA by switching it on and off. An RCS-technique can be used to retrieve the radiation pattern. By experimental comparison between the conventional pattern measurement technique and the RCS-technique it is shown that pattern determination via RCS-measurements is feasible. In addition, the measurement method offers the advantage of directly reducing the influence of systematic measurement errors. On the other hand, the penalty is put on power efficiency and a subsequent limited dynamic range.
We examine how accurately the transmit and receive parameters of a radar cross section measurement system can be determined by use of a rotating dihedral as the polarimetric calibration device. We derive expressions for the errors due to misalignment in the angle of rotation. We obtain expressions for the angles a0,hv and a0,vh for which the measured cross-polarization ratios of a target vanish. Since the theoretical cross-polarization of a cylinder is 0, we can .nd the calibration bias-correction angles. We use simulated and real data to demonstrate the robustness of this bias-angle correction technique. We derive expressions for the uncertainty in the polarimetric system parameters.
In previous work [1], we presented an antenna pattern compensation technique for linearly-scanned near field measurements. In this paper, we present a similar technique to mitigate the errors from uncompensated azimuthal antenna pattern effects in circular near-field monostatic radar measurements. The antenna pattern co mpensation is implemented as part of an improved algorithm for transforming the near-field measurements to the far-field RCS. A description of this improved circular near field-to-far field transformation CNFFFT technique for isotropic antennas is presented in a companion paper [2]. In this paper, we formulate the near-field signal model in the presence of an azimuthal antenna pattern under the same scattering approximation used in the isotropic CNFFFT. Using this model, we derive a modified version of the CNFFFT that includes antenna pattern compensation. Numerical simulations are presented that demonstrate the ability of the technique to remove antenna pattern errors and improve the accuracy of the far field RCS patterns and sector statistics.
ABSTRACT A fast and accurate technique is proposed in this work for the far field evaluation from a nonredundant number of voltage data collected by using the planar wide-mesh scanning (PWMS). It relies on the nonredundant sampling representations of the electromagnetic field and on the optimal sampling interpolation expansions of central type. By using a very flexible source modelling, which fits very well a lot of actual antennas, a new sampling technique is developed to recover the plane-rectangular data from the knowledge of the PWMS ones. It must be stressed that the so developed near-field–far-field transformation requires a number of data remarkably lower than that needed by the standard plane-rectangular scanning. Some numerical tests, assessing the accuracy of the technique and its stability with respect to random errors affecting the data, are reported.
Antenna systems are increasing in complexity at a rapid pace as advances are made in electronics, signal processing, communication, and navigation technologies. In the past, antenna design requirements have focused on parameters such as gain, efficiency, input impedance, and radiation pattern (e.g., beamwidth and sidelobe level). For some new systems, the group delay characteristics of the antenna are important, where the group delay is proportional to the derivative of the insertion phase as a function of frequency. The group delay is required to stay within certain bounds as a function of frequency and pattern angle. Unfortunately, there are not well established methods or standards for calibrating antenna group delay like the standard methods used for gain and input impedance. This paper presents a method for calibrating the group delay of three antennas based on an extension of the widely used three-antenna gain and polarization calibration methods. No prior knowledge of the gain or group delay of the three antennas is required. The method is demonstrated by a measurement example where it is shown that multipath errors and time gating can be critical for calibrating the group delay.
This paper presents a modification to the standard three-antenna polarization measurement method. The new technique solves for the sense, axial ratio, and tilt angle utilizing a least-squared errors routine and multiple measurements of the response at different roll angles between antennas. The paper compares the results of this method to Allan Newell’s well known modified three-antenna polarization measurement technique. Four antennas were measured two at a time and in several different arrangements to get twenty-four measures of the polarization parameters for each antenna. The work shows this method had a more repeatable measure of the axial ratio than the parameters determined using Newell’s technique.
Parallax occurs in antenna measurements when the antenna under test (AUT) is located off the center of rotation (COR) of the test positioner axis. As the AUT is rotated while located off of the COR of the axis, the angle to the AUT as viewed from the source antenna is different than the angle to which the positioner is commanded. This results in a distortion of the antenna pattern, and can result in errors in beam shape and beam width. Knowledge of the test geometry allows for the determination of an appropriate mapping from the recorded test angles to the actual angles to the AUT as viewed from the source. This, in turn, allows for the possibility that the antenna pattern may either be corrected for the parallax error, or measured at the correct angles in order to avoid pattern distortion. ORBIT/FR has implemented a parallax correction in the 959Spectrum Antenna Measurement Workstation software that allows for flexibility in positioning angle correction, and in addition provides a useful tool for implementing unusual measurement test scenarios, such as measuring antenna data at a “list” of angles. This paper describes the parallax problem, the implemented solution, and provides examples of use of the implemented software feature.
Reflections in antenna test ranges can often be the largest source of measurement errors, dominating all other error sources. This paper will show the results of a new technique developed by NSI to suppress reflections from the radome and gantry of a large hemi-spherical automotive test range developed for Nippon Antenna in Itzehoe, Germany. The technique, named Mathematical Absorber Reflection Suppression (MARS), is a post-processing technique that involves analysis of the measured data and a special filtering process to suppress the undesirable scattered signals. The technique is a general technique that can be applied to any spherical near-field test range. It has also been applied to extend the useful frequency range of microwave absorber in a spherical near-field system in an anechoic chamber. The paper will show typical improvements in pattern performance and directivity measurements, and will show validation of the MARS technique using data measured on antennas in a conventional anechoic chamber.
ABSTRACT A unified theory of near-field spiral scans is proposed in this work by introducing a sampling representation of the radiated electromagnetic field on a rotational surface from the knowledge of a nonredundant number of its samples on a spiral wrapping the surface. The obtained results are general, since they are valid for spirals wrapping on quite arbitrary rotational surfaces, and can be directly applied to the pattern reconstruction via near-field–far-field transformation techniques. Some numerical tests, assessing the accuracy of the technique and its stability with respect to random errors affecting the data, are reported with reference to the case of the helicoidal scan.
Inversion of the material parameters for a sample usually requires that the sample fill the waveguide cross-section. Alternative methods require that a non-filling sample be aligned along the center-line of the waveguide. However, it is not known how errors in placement impact the accuracy of the inversion. Hence, a numerical simulation to assess these errors is beneficial to the community. The extraction of the S-parameters from a rectangulardielectric-filled waveguide is conducted numerically by means of the Finite Element Method (FEM) and the Thru-Reflect-Line (TRL) calibration technique. Three different ratios of dielectric sample width (d) to waveguide width (a) are primarily studied. The results are then validated with experimental data on the X-band. An assessment of error with respect to position will be presented at the meeting.
Standard Gain Horns (SGH) are normally used as reference antennas in antenna measurements. Gain charts for SGH are provided by the supplier. These charts give the gain of the SGH in dBi versus frequency but do not provide any information on the phase variations versus frequency. For complete antenna calibration, one needs the phase as well as gain data for SGH over the frequency band of interest. To obtain the gain and phase data, one can use the three-antenna method which requires three independent measurements and, therefore, is more susceptible to measurement errors. Note that if one has access to two identical antennas, the three-antenna method reduces to a single measurement which is more desirable. In practice, however, one does not have access to two identical antennas. In this paper, a novel method which mimics measurements with two identical antennas is described. In the method, one performs S11 type measurements on the antenna of interest by placing the antenna in front of a large conductive flat plate. The late term in the S11 measurements is then used to obtain the boresight gain and phase of the antenna under test. The measured gain and phase data of several antennas obtained using the proposed method is presented and compared with the results obtained using the three-antenna method as well as with analytical results.
Abstract Historically, most commercially available Local Oscillator (LO) distribution systems have used a closed loop control system to set LO power levels. As frequency switching times decrease, the time constant of the control loop can introduce errors to precision antenna measurements. This paper will discuss the basics of the remote mixing test system, and then discuss the limitations of various current approaches. Finally, it will introduce an open loop LO distribution system, and discuss the design considerations for the various components of the system.
ABSTRACT This paper describes a broadband radome measurement method that provides insertion loss performance referenced to circularly polarized radiation. The measurements are performed using linearly polarized sources and post processing is employed to convert to circular polarization. The method reduces measurement errors encountered using circularly polarized sources that traditionally have poor cross polarization isolation.