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ABSTRACT We have developed a new compact spherical near-field measurement system using a photonic sensor as a probe and successfully measured the 3D antenna patterns of a double-ridged horn antenna from 1 GHz to 10 GHz. This system consists of a compact spherical scanner and a photonic sensor that is used for the probe of the spherical near-field measurements. In our system, only one probe can be used for the wide frequency range measurements and the probe compensation is not needed in the measurements. For the system, we propose a simple calibration method using a double-ridged horn antenna for our system. We calibrate the system by measuring the double-ridged horn antenna on the reasonable assumption that the antenna efficiency is 100 %. Comparing the absolute gain obtained by the proposed calibration method with the one decided by using three-antenna method at far-field range, we show that the agreement is good within 1 dB over the whole frequency range.
In this paper is presented an experimental investigation of conventional array calibration in the presence of various kinds of joint discontinuities between array panels. Two rigid array panels were positioned such that the element lattice was continuous across a narrow joint. Three kinds of discontinuities were applied to the joint: (1) an angle, (2) a gap (including an edge), and (3) a step between panels. Each type was investigated for joints oriented in the E-plane and the H-plane. Each discontinuity was also varied in magnitude so as to observe parametric effects. Planar near-field-range (NFR) measurements were made in a conventional array calibration mode and a near-field pattern mode. Processing included separating the pattern component due to element transmission (impedance) change from that due to pattern shape change. Results show that conventional calibration methods quickly become inadequate to calibrate these discontinuities because they change element pattern shapes.
A system for measuring large linear arrays of antennas has been developed, fabricated and tested. The system consists on a 12 meters structure where the antenna under test (a L band array of dipoles in this case) is positioned. The measurement probe (another dipole) moves on a linear slide and stops in front of each element of the array to acquire the electric field. All the system is installed on an semi-anechoic chamber, that can be lifted (with two synchronized stepped motors). This semi-anechoic chamber covers the top and side parts of the structure. The bottom part consists on a metallic reflector, that controls the reflections from each antenna element. Once the data is acquired, the data are processed to obtain the far field patterns and parameters of the antenna array (element amplitude and phase, beam width, side level, beam pointing …) All the results are presented in a windows environment, and all the system is integrated in a friendly user interface.
For many years now, GDAIS has described the development, characterization, and performance of an image-based circular near field-to-far field transformation (CNFFFT) for predicting far-field radar cross-section (RCS) from near-field measurements collected on a circular path around the target. In this paper, we present an improved version of the algorithm that avoids a stationary phase approximation inherent in earlier versions of the technique. The improvement is realized by modifying the range-domain weighting used to implement the frequency derivative in the existing method. A similar modification was presented in the context of linear near-field measurements in an earlier AMTA paper. Numerical simulations are presented that demonstrate the improvement afforded by the technique in predicting far-field RCS patterns from near-field data collected using typical bandwidths and standoff distances. An additional benefit of the revised algorithm is that it readily admits a formulation that includes antenna pattern compensation, as described in a companion paper.
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 Electronic devices designed for purposes other than transmitting and receiving electromagnetic fields nonetheless act as unintentional antennas. Measurements methods are needed to characterize these antennas for electromagnetic compatibility tests; however, the rigor of precision antenna measurements is typically too costly and time consuming for electromagnetic compatibility applications. Alternate approaches are needed. This paper presents analytical estimates for the directivity of unintentional antennas based on the assumption that unintentional antennas will only randomly excite the available propagating spherical modes at a given frequency. This directivity estimate is then compared to simulated and measured data. Good agreement is shown. Directivity estimates combined with simple total radiated power measurements represent a useful alternative to direct antenna measurements for electromagnetic compatibility tests.
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.
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.
An antenna measurement system was developed to complement a new rectangular anechoic chamber (20’L x 10’W x 9’7”H) that has been established at California Polytechnic State University (Cal Poly) through donations and financial support from industry and Cal Poly departments and programs. Software algorithms were written to provide four data acquisition methods: continual sweep and step mode for both single and multiple frequencies. Log magnitude and phase information for an antenna under test is captured over a user-specified angular position range and the antenna's radiation pattern is obtained after post processing. Pattern comparisons against theoretical predictions are performed. Finally an RF link budget is calculated to evaluate the performance of the antenna measurement system.
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.
At the Institut Fresnel in Marseille (France), we created an original experimental setup in order to test antennas and carry out scattering measurements in both monostatic and bistatic configurations. The main advantage of this setup is, of course, the multipurpose feature. Two main mechanical systems are installed in a large anechoic chamber. The first system is a spherical positioning setup which allows measurements of antennas and scattered fields for both bi-dimensional (2D) and three-dimensional (3D) targets. This setup consists of two carriages moving on a circular vertical arch and a third carriage which follows a circular path on a horizontal plane. A transmitter and a receiver can be fixed on any of these three carriages. A fourth rotating stage in the center of the spherical setup fixes the angular position of the antenna under test or of the scattering target. The second system is a far-field positioner which allows the measurement antenna patterns and RCS. To illustrate our activities with this original setup, we first show measurements of a metamaterial antenna prototype and then some results of scattered fields obtained on 2D and 3D targets used in studies of electromagnetic direct and inverse problems.
Abstract This paper describes the development of an inexpensive high-precision Compact Antenna Test Range (CATR) located at CSIRO, Australia, for the measurement of electrically large aperture antennas (>250.) at 200GHz. The CSIRO designed CATR is based on a single parabolic offset reflector that has been machined from a single billet of cast aluminum plate to provide a RMS error of better than 16 µm as determined from photogrammetry. The design is unique as it leverages CSIRO’s ability to accurately design and manufacture feed horns with highly optimized radiation patterns; in this case corrugated feed horns with flat amplitude tapers at the beam maximum and fast amplitude roll-off at the edge illumination angle of the reflector. The advantage of using this type of feed horn is that it eliminates the need to specially treat the edges of the CATR reflector and therefore greatly reduces the cost of the system.
Hologram-based compact antenna test range (CATR) is a promising way to measure submm wave antennas. The hologram quality and the measurement accuracy of the hologram-based CATR is limited by the hologram manufacturing process. The measurement accuracy can be improved using pattern correction techniques. However, at submm wavelengths only the antenna pattern comparison (APC) technique is able to correct the effects of the spurious signals originating from the residual inaccuracies of the hologram pattern. A problem with the APC technique is that it is time consuming. This paper introduces a pattern correction technique for hologram-based CATRs. The technique is based on averaging in the frequency domain, and it is able to correct spurious signals originating from the hologram. Proposed technique is also faster than the APC technique. The proposed method is verified with a combination of measurements and simulations.
ABSTRACT The proposed system is aimed at offering a simple and cost-effective solution for antenna radiation pattern measurements coherently in the higher millimeter-wave range, particularly at the 77 GHz and 120 GHz frequency bands, using harmonic mixers and the multi-source option of the ordinary Vector Network Analyzers (VNAs). Within this paper, the detailed design procedures of every module of the harmonic mixers as well as the block diagram of the modified measurement setup are to be illustrated, in addition to the simulation and experimental results of every submodule in the system. Finally the link budget calculations of the whole arrangement will be demonstrated so as to show the relevant dynamic range of the measurements.
In previously reported work, the groundwave correction approach was presented for measurement of the gain of vertically polarized antennas in the presence of a seawater groundplane. This approach was limited to application in the commercial HF (2-30 MHz) band due to a variety of factors, including the geometry of the test range, and so can not always be applied at higher frequencies. This paper will discuss a method for measuring the gain and azimuthal pattern performance of antennas operating in the commercial VHF band (50-175 MHz) that has been developed at the NUWC Fishers Island Antenna Range, and will discuss its application and implementation.
The electromagnetic field as projected by a 12 ft. prime focus offset fed compact range reflector with r-card edge terminations located in an existing chamber 20 ft. high, 30 ft. wide and 66 ft. long was probed using a broadband antenna to sample the field at 12 inch increments from the center line to the anechoic chamber wall. The purpose of the test was to evaluate the field roll off in dB to see if a narrower room would significantly impact the performance of the existing reflector system. The new chamber is 20 ft. high, 20 ft. wide and 40 ft. long. The probe data at six frequencies from 2.1 to 17.8 GHz indicated that 10 ft. off the center line the measured field level was -20 dB or greater below the level of the test region, which was our maximum acceptable field level goal. It is expected that the sidewall absorber will provide over 20 dB of bistatic attenuation for a total reflected field level of -40 dB, and is sufficient for conducting antenna pattern measurements in an anechoic chamber. Key Words: Compact Range, R-Card Terminations, Absorber Performance
The present paper introduces a new antenna design to be used in anechoic chambers. When measuring 3D patterns the receiving antenna in the anechoic chamber must be able to sense the two orthogonal components of the field that exist in the far field. This can be accomplished by mechanically rotating the source horn in the chamber. A better and faster approach is to use a dual polarized antenna and electronically switch between polarizations. This new design is a broadband (2-18GHz) antenna with dual polarization. The antenna is a ridged guide horn. The novel part is that the sides have been omitted. Numerical analysis and measurements show that this open-sided or open-boundary horn provides a better and more stable pattern behavior for the entire band of operation as well as good directivity for its compact design. The radiation and input parameters of the antenna are analyzed in this paper for the novel design as well as for some of the early prototypes to show some of the ill effects of bounded quadridge horn designs for broadband applications. Mechanically the antenna is built so that it can be mounted onto the shield of an anechoic room without compromising the shield integrity of the chamber.
In this paper, we study the possibility to use an amplitude hologram as a reflection-type collimating element to produce a plane wave in the compact antenna test range (CATR). So far, we have used holograms as transmission-type elements only. The hologram studied here has a diameter of 600 mm and it operates at the frequency of 310 GHz. It is a computer-generated slot pattern etched on a thin metal-plated dielectric film. We have simulated and measured the plane wave field reflected from the hologram. The maximum measured ripples are only 1.6 dB and 20°, peak-to-peak. The reflection-type hologram has some advantages over the transmission-type one. For example, the power loss is about 4 dB lower for the reflection-type hologram. In addition, a CATR based on the reflection-type hologram can be situated in a much smaller space. To demonstrate the capability of the reflection-type hologram in actual antenna testing, the radiation pattern of a small reflector antenna was measured at 310 GHz.
A strong interest exists in the commercial and military sectors for small and broadband antennas. For instance, in the automotive industry there is a need for a single antenna operating in the frequency range of 825-2500 MHz (AMPS, DAB, GPS, PCS, SDARS). For military applications, there is also a need to have a single aperture which permits operation in different communication bands and can be also used for imaging and guidance applications. These needs require wide band antennas, such as the miniaturized spiral antenna. In this paper we present the implementation of a spiral antenna situated on a ground plane that is fully functional at the size of 0.16 wavelength onward. Low profile (0.05 wavelength) and broadband operation design goals bring unique challenges, which must be confronted with multiple-front techniques. A combination of antenna geometry design and material loading results in the desired miniaturization effect. Further techniques, including the use of distributed resistors ensure good axial ratio and VSWR. Pattern uniformity and phase linearity of the antenna was also improved. In addition, we also examine the effectiveness of broadband spiral antenna miniaturization as a function of loading material’s dielectric constant.