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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.
Multiple-Input Multiple-Output (MIMO) systems have been introduced as a solution to improve channel capacity and link reliability. Several MIMO real implementations have been developed and reported in the literature. Some of the implemented MIMO systems are channel sounders, used to perform channel measurements, and do not include any MIMO algorithm. As an improvement of reported testbeds, this paper summarizes a MIMO demonstrator that offers a number of features that make it especially suitable for research and education. Its main advantage is the possibility of testing MIMO algorithms under real channel conditions with different antenna array schemes and antenna configurations in a straightforward way. Other possible applications are channel measurements on different MIMO schemes. The basic configuration is a M x N MIMO (max(M,N)=4) scheme where the antenna module have been designed to allow the user easily change several physical features, such as the spacing and the type of antenna elements, offering the possibility to test the effect of such parameters in the algorithm under study.
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.
ABSTRACT The article discusses the performance and design of a SCARA type robot with counter balanced arms for portable near-field antenna testing. An X-band 43” by 93” antenna on its’ system trailer was tested. A SCARA robot uses rotating joints with parallel axis on linked arms to achieve straight line (or arbitrary) probe movement in a plane. For a horizontal movement plane counterbalanced arms allow movement without change in stress in the scanner structure or foundation, therefore probe movement stays in a plane and structure and foundations can be lightweight and more portable. Probe movement stayed within .004” of a flat surface. Graphite-epoxy tubular arms were used for lightweight, stiffness, and vibration damping. A clockspring like cable carrier was used for each rotary axis. This design kept the center axis free for a directly connected rotary encoder (providing greater accuracy). The diameter of the cable carrier housing at the rotary joint, between arms, enhanced safety by reducing the hazard of a scissoring effect. A dimension touch probe mounted in place of the RF probe was used to align the scanner to the antenna while on its’ system trailer.
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.
The gain and efficiency of electrically small antennas at long wavelengths can be difficult to measure. On the other hand, it can be shown that both the gain and efficiency of such antennas behave in a predictable asymptotic manner as the antenna becomes electrically smaller. Specifically, in free-space, electric-type antennas have an asymptotic frequency behavior given by f 3/2 and magnetic-type antennas behave as f 7/2. On a Bode plot, the break-point for the gain and efficiency asymptotes occurs when the gain or efficiency is 3 dB down from their electrically small maximum values. This occurs at the frequency where the efficiency is 50% which is where the radiation resistance equals the ohmic loss resistance. It is proposed in this paper that a knowledge of the asymptotic behavior could be of use in extending
The measurement uncertainties for base station antenna gain measurement are in general very high, ± 1dB could normally be expected and there are examples of much higher uncertainties. Applying the uncertainties above to the cell planning tools gives at the end a very large uncertainty on the number of cells needed to cover an area. The extra cost for this uncertainty could be an extra 15-20% of the site costs or 10-20% less coverage than expected. This paper identifies the different uncertainty sources and suggests how to optimize the measurement set-up to reduce uncertainties as much as possible during the measurement and compensate for the remaining uncertainties after the measurement.
This paper describes the design and testing of a feed network for a transparent flat plate array antenna. This antenna is the top of a stack of three antennas that must occupy the same volume while pointing in different directions. At many pointing angles, the antenna will create blockage for the antennas underneath. In order to minimize the blockage, the array and its transmission lines must be as transparent as possible to the antennas underneath. The flat plate array consists of active elements over a frequency selective surface (FSS) ground plane that is transparent at the frequencies of the antennas below. The feed lines must also be transparent to the antennas below. This is achieved by minimizing the total area occupied by the feed lines. Rather than the traditional corporate feed network, a series feed network was designed. Such a network requires that each individual feed point must be fed with a coupler where the coupling coefficient is adjusted to distribute the same power to each array element. We will show the details of the design of the network as well as a set of measurements that show the performance.
A low-profile, high efficiency sixteen-element stacked patch microstrip array operating in the L-band frequencies of 1.26GHz and 1.413GHz was designed, fabricated and tested for use in applications to airborne sensors operating on small aircrafts. The array was optimized for element spacing, excitation amplitude taper, low cross-polarization and high beam-efficiency using Particle-Swarm Optimization (PSO) and Finite-Difference Time Domain (FDTD) methods. The design and measurement of sixteen-element array topology, stacked patch elements, and power-divider beam forming network are presented in detail. The study highlights the repeatability measurements and characterization of array with the effect of dielectric radomes in a spherical near-field test facility at UCLA. The results met the requirements of center-frequencies and frequencybands(1.26GHz ± 10MHz, 1.413GHz ± 15MHz), side-lobes, very good beam-efficiency (>90%) and low-cross polarization (<-40dB) in main-beam region of array. The measured results compared well with simulations for the two frequencies. Based on measurement results, the microstrip array design has a potential to be used as a feed for deployable mesh antennas for future spaceborne L-band passive and active sensing systems that can operate at integrated active radar (1.26GHz) and passive radiometer (1.413GHz) frequencies with dual polarization capabilities to study soil-moisture and sea-surface salinity.
Abstract The undergoing development of GPS system requires the integration of all three GPS bands: L1 (1575MHz), L2 (1227MHz), and L5 (1176MHz) into one miniature antenna. The objective of work is to develop a small GPS antenna (less than 1/10 wavelength) to cover all the three GPS bands with a minimum bandwidth of 24MHz in each band and a minimum gain of 0 dBic (RHCP). Three novel miniature antenna designs: Quad-F antenna (QF), proximity-fed stacked patch (PFSP) antenna and channel fed ring (CFR) antenna were investigated. These antennas utilize high-index inhomogeneous dielectric materials to achieve antenna miniaturization, mode excitation and mode control. The full-wave simulation (HFSS) and measurement results are presented and discussed in this paper.
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.
Measurements of the insertion loss and impedance in antenna characterization are very important and should be traced back to national attenuation and impedance standards. Vector network analyzers commonly used to measure the impedance are not suitable for millimeter-wave antenna measurements because movement of DUT (Device Under Test) during measurement is required and long cable of high loss for connection between the network analyzer and the DUT mounted high above the floor increases measurement uncertainty. In this paper, a conventional microwave subsystem based on external mixer configuration is modified to measure the impedance of DUT without using the vector network analyzer in millimeter-wave frequency range.
We propose a novel microwave measurement system that consists of transmitting and receiving optical-fiber link systems. The system can measure parameters of S11 and S21 of an antenna under test (AUT) by the procedure of OSLT 1-pass and 2-port calibration, due to the simultaneous measurement of its relevant signals going into, reflected and transmitted from the AUT. It is shown by some experiments that the S11 and S21 of the two log-periodic antennas measured by the optical link system agree very well with those by a conventional system using metal coaxial cables. It is proved that the optical system can be used to evaluate the S11 and S21 of the AUT in broad frequency range without using coaxial cable.
Polymers are generally characterized in two broad characters: thermoplastic and thermoset. The former, including many of the plastics used in everyday life – such as containers, Frisbees, etc. – have their polymer chains formed prior to use in commercial applications. The latter, and the subject of this paper, have polymer chains that are formed during a curing process. Examples of commonly thermoset polymers are epoxies commonly available in hardware stores. Curing is often accelerated by heating. Curing is also exothermic with a compositional change. It is important to measure the changes in the material properties in order to correctly assess the state of the cure and the resulting material. This final state is critical for antenna applications where the antenna is conformally mounted in a structure, such as fiberglass, that involves a thermoset polymer. In this paper, improvements to Michigan State’s characterization system will be described along with underlying numerical modeling used to investigate thermoset curing.
Electromagnetic material characterization is the process of determining the complex permittivity and permeability of a material sample. One common method uses measured scattering parameters from a sample mounted in a coaxial transmission line to calculate the material’s permittivity and permeability. If the material uniformly fills the cross-sectional area of the transmission line, then the standard Nicolson-Ross-Weir (NRW) algorithm [1][5] can be used since only a single dominant TEM mode will be supported. However, if gaps exist between the material sample and the coaxial conducting boundaries, higher-order modes are excited which introduce error into material characterization measurements since these modes are not accommodated in the NRW algorithm. This paper proposes two techniques for mitigating the air gap error in coaxial test fixtures. The first method utilizes a quasi-TEM approach whereas the second method invokes a more rigorous mode-matching analysis. In either case, expressions for the theoretical scattering parameters are obtained and are subsequently compared to the scattering parameters obtained via measurement. For both methods, the resulting error between the theoretical and measured scattering parameters is iteratively minimized until the material’s properties are calculated within a specified tolerance.