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Planar near-field probing is used in the optimisation of the quiet-zone of a hologram-based compact antenna test range (CATR). In this paper, the measurement instrumentation for 650 GHz operation is introduced and the potential measurement errors in the quiet-zone measurements are identified. Applicable error correction and compensation methods are discussed and the total measurement accuracy is calculated.
An efficient algorithm for calculating the position of the phase center of an antenna from a measurement is derived and implemented in software. Application of the algorithm to actual measurements shows that the success of the algorithm depends on characteristics of the antenna and a weighing parameter derived from the amplitude pattern.
This paper deals with characterization of passive ultra-high frequency (UHF) radio frequency identification (RFID) tag performance. Tag’s energy harvesting properties and the significance of the backscattered signal strength and radar cross section (RCS) of the tag are discussed using two examples: dipole tag antennas of various widths and identification of industrial paper reels.
Space qualification of antennas imposes stringent RF testing to assure on-orbit reliability and environmental testing to assure the antennas can withstand launch and on-orbit conditions. The qualification testing requirements are reviewed for antenna systems. Specialized RF tests specific to satellite applications are described. Development recommendations for future testing are also described.
This paper shall discuss antenna range measurements performed upon a prototype Ultra Wide Band communication system. The measurements required the evaluation of both wideband RF pulses (5 MHz) and an active transmit antenna at the NUWC Fishers Island facility including the Mile Site Overwater Range. The measurement technique employed will be discussed along with choice of equipment, approach used for data collection and test results. Funding is provided by the Office of Naval Research.
The development and implementation of the radome measurement Range 12 at the Raytheon Advanced Product Center, (APC) indoor range complex at McKinney, Texas will be covered. A cooperative relationship between Raytheon and the vendor allowed the realization of a very demanding set of requirements to be built, installed, and verified. Very precise simultaneous multi-axis motion was achieved. Range performance after installation was verified with planar probe techniques pioneered by another vendor. Repeatability studies with antenna removal, radome placement, and RF drift have been performed to verify long-term stability. All of this brought up a number of lessons learned resulting in better reliability and improved knowledge for the next implementation.
This paper describes the development of a test procedure for OMNI directional antenna pattern measurements in Compact Antenna Test Facility (CATF). This study is also of importance as it was presumed that OMNI directional antennas can not be tested in ISAC-CATF due to reflections coming from high-rise metallic structure of DUT positioner. As in ISAC-CATF, DUT positioner is not at all covered with the RF absorbers. Further, effect of Spacecraft body on radiation pattern is also studied. In addition to that effect of high-rise metallic structure of DUT positioner is also presented. It was observed that due to spacecraft body ripples were generated in the radiation pattern of OMNI directional antenna. It was also observed that effect of high-rise metallic structure of DUT positioner was not as significant as of Spacecraft body. At the end of this study, to exactly simulate the integrated spacecraft level condition a 33 dB coupler was connected at antenna output port and measurements were performed with the help of coupled port. Those results are also presented in this paper.
A probe-compensated near-field-to-far-field transform algorithm has been developed that can generate far-field patterns from near-field measurements made on an arbitrary surface. We present the concept, the algorithm, and computer simulated and measured test results for measurements on a conical surface. The prototype conical near-field measurements were made in a planar near-field range on a horn antenna under test (AUT) mounted on an azimuth-over-elevation positioner to produce a conical measurement surface. This system is especially applicable for producing full-hemisphere far-field patterns for antennas mounted on vehicles where other standard measurement systems may not adapt to the profile well, may not provide full-hemisphere coverage, or may require large, mechanically complex systems.
This paper presented a theoretical and numerical investigation of the performance comparison of Compact Antenna Test Range (CATR) equipped with Hybrid and Super Hybrid modulated serrations. The performance of the quiet zone will be degraded for a traditional CATR without both an edge treatment of the reflector antenna and a high quality anechoic chamber. Usually, the ripples in both the phase and magnitude of the field intensity inside the quiet zone are caused by stray signals, which come from edge diffraction. In order to solve the edge diffraction problems, edge treatments such as a different shaped serrated edge are often applied along the edge of the reflector antenna. The quiet zone field analysis of such reflectors has traditionally taken the form of ray tracing using numerical integration of the reflector surface currents called physical optics (PO). PO technique is used to obtain Fresnel Zone field of a plane square aperture embedded with a hybrid and super hybrid serrated CATRs. It is observed that super hybrid serrated CATR gives lesser ripples and enhanced quiet zone width than hybrid serrated CATR.
The measurement of the dielectric constant of a sample of unknown material is the sort of measurement that occurs frequently in the laboratory environment. At low frequencies, simple methods are well established, such as the parallel plate method. However at microwave frequencies, the methods for measuring the dielectric constant can be cumbersome and often require accurate knowledge of the dimensions of the sample being tested and the fixture used, as in the case of the well-known perturbation method. This paper shall present some observations on a simpler method based on a modest sample of the unknown dielectric material. The method employs a rectangular waveguide fixture in which the portion of the waveguide containing the sample to be measured is deliberately narrowed to half the guide width in order to increase its cutoff frequency. It turns out that this approach yields a measurement method that is insensitive to the length of the sample and that allows accurate determination of the real portion of the dielectric constant.
This paper presents a novel method to evaluate very small stray signals in compact range. The ripples of signals probed by an omni-directional antenna along the orthogonal direction of the bore sight could be treated as signals in time domain. Transforming the probed data with fast Fourier transform (FFT), the direction and amplitude (relative to the test signal) of each stray signal could be obtained. To improve the accuracy, time domain software gating should also be used in calibrating the measurement error of amplitude and phase. The presented method has the ability to measure very small stray signals with good angle resolution. The method has been tested by both simulation using MATLAB and experiment in the compensated compact range CCR120/100 in CAST using a monopole antenna centered on a circular ground plane as a probe. Good results were obtained.
Traditional passive antenna measurements result in well-known quantities like Directivity, Efficiency, and Gain. However, when testing over-the-air (OTA) performance of active devices, there are additional effects that cannot be lumped together as part of the antenna performance. Terms like gain and efficiency are defined based on transmit or receive signal levels at the antenna port relative to the radiation pattern of the device. Thus, OTA performance is often assumed to be equivalent to the conducted performance of the device combined with the passive radiation pattern. However, when that antenna port is attached to an active radio in a typical wireless device, interactions between the circuitry and the antenna can produce results that do not match that predicted by the conducted performance and the passive radiation pattern. The difference between the predicted and actual performance of a device can be quantified in terms of "interaction factors", which represent the often non-linear behavior of the active circuitry when operating in an OTA environment. These factors include such effects as variation in amplifier gain due to heating caused by antenna mismatch, and receiver desensitization due to platform noise that couples through the antenna of the device. This paper will discuss the concept of interaction factors and define a number of sub-components of these factors that may be useful in predicting the level of some interaction factors.
This paper presents the results of an intensive investigation for trading off size vs. frequency for a large bandwidth antenna. Theoretical limits were established to determine minimum size as a function of gain and frequency. Bandwidth for the antenna developed was 50 MHz to 2000 MHz; stimulation was done with 50 ohm input impedance. The antenna broadband elements were located in a unique cavity, 6 inches in depth and 15 inches in diameter. The unique ground plane was composed of a combination of a Ferrite Region and Perfect Electric Conductor region which was implemented using Silver particles embedded in MEK. The cavity was fabricated using Carbon Composites to reduce weight. FireFly Opus antenna is in the testing phases.
A material measurement technique is developed to simultaneously characterize electric and magnetic properties for homogeneous lossy material in a parallel-plate region. The material is excited by a rectangular waveguide which interacts with the parallel-plate region through a slot. In order to extract the complex constitutive parameters from the material two independent measurements are required. If the material is attached to a PEC surface and is unable to be removed, the most obvious manner to characterize the material is a parallel-plate region. This paper demonstrates through the use of a magnetic field integral equation (MFIE) how a rectangular waveguide interacting through a slot with a parallel-plate region can be used to obtain two independent measurements, which are necessary for characterizing the homogeneous lossy material. At last year proceedings, the formulation of this technique was presented assuming an infinitely thin wall-thickness. The formulation has now been altered to include the effects of finite wall-thickness, for which theoretical and experimental results are shown to validate the formulation. Thus, the focus of this paper is on the crucial influence of finite wall thickness, future results will focus on the material extraction process.
Calibration of planar near field probes is generally required to obtain accurate cross-polarization measurements of satellite antennas; however, probe calibration is costly and time consuming. One way to avoid probe calibration is to ignore the probe cross-polarization and use the probe co-polarized patterns alone for probe correction. Then the probe can be easily characterized by standard, in-house measurements or by analytical models. Of course, if the probe cross-polarization is ignored, additional errors are introduced in the co- and cross-polarized pattern measurements, but the errors can be manageable, depending on the probe and Antenna-Under-Test (AUT) polarization properties. Complete formulas and/or tables for near field measurement errors for three popular measurement configurations are presented, along with experimental verification of the error estimates for one case.
This paper presents the method of determination of the amplitude and phase distribution in antenna plane aperture. This method is based on homodyne one, where the initial microwave oscillation is heterodyne one. The mobile probe unit consists of proper antenna probe, controlled phase shifter, high-frequency receiver. The initial microwave oscillation is shifted on low frequency with controlled phase shifter. The phase shifter is fed with low frequency modulating signal with modulation of carrier in high frequency band. The initial phase of low-frequency oscillations is transferred on microwave. The initial phase and frequency of microwave oscillations are eliminated in mixer. Low-frequency measurements of amplitude and phase difference are carried out.
Serrations are often applied at the edges of compact-range reflectors in order to reduce the scattering from the edges into the quiet zone. At low frequencies the serrations show different scattering of the field at the two polarisations: parallel to and perpendicular to the serration teeth. This has been verified by modelling a range by the Method of Moments (MoM). The size of the range reflectors is about 7.5 m by 10 m which make the re-flectors difficult to handle by MoM even at a fre-quency which is low for the range, viz. 1.7 GHz, in which case the reflectors are each 2400 wavelengths squared. A narrow strip, horizontal or vertical, across the re-flector and closed by a single serration tooth at each end is shown to give a good prediction of the field along a line parallel to the strip in the quiet zone. By this simple model of the range it has been demon-strated that the quiet-zone field depends highly on the polarisation. When the polarisation is parallel to the teeth the quiet-zone field has ripples which are 0.3 dB peak-to-peak, but for the perpendicular polarisation the field variations are 0.8 dB peak-to-peak. The results are compared to quiet-zone fields deter-mined by Physical Optics (PO).
This paper describes the Rectangular Coaxial 40’ long measurement system recently designed and installed at AEMI with the primary purpose of measuring the reflectivity of its high performance VHF/UHF absorbing materials in the frequency range 30 – 510 MHz. The basic principles of the system are described in detail in [1] and are based on S11 – measurements of absorbing material reflectivity by a Vector Network Analyzer (VNA). In order to improve the system productivity and measurement accuracy it was enhanced by the time-gating software option – the standard option of ORBIT/FR Spectrum 959 automated measurement software package [2].The measurement system performance was thoroughly evaluated and validated by a number of tests performed in the “empty” coaxial line, and in the line loaded by absorbing materials. The list of RF uncertainties – various measurement error sources - was generated, the main measurement error contributors were identified, the corresponding errors – estimated and the overall RSS measurement errors were calculated for the absorber reflectivity varying in the range of -30dB to – 40dB.
Commercial windmill driven power turbines (“Wind Turbines”) are expanding in popularity and use in the commercial power industry since they can generate significant electricity without using fuel or emitting carbon dioxide “greenhouse gas”. In-country and near-off shore wind turbines are becoming more common on the European continent, and the United States has recently set long term goals to generate 10% of national electric power using renewable sources. In order to make such turbines efficient, current 1.5 MW wind turbine towers and rotors are very large, with blades exceeding 67 meters in diameter, and tower heights exceeding 55 meters. Newer 4.5 MW designs are expected to be even larger. The problem with such large, moving metallic devices is the potential interference such structures present to an array of civilian air traffic control radars. A recent study by the Undersecretary of Defense for Space and Sensor Technology acknowledged the potential performance impact wind turbines introduce when sited within line of site of air traffic control or air route radars. [1]. In the Spring of 2006, the Air Force Research Laboratory embarked on a rigorous measurement and prediction program to provide credible data to national decision makers on the magnitude of the signatures, so the interference issues could be credibly studied. This paper, the first of two parts, will discuss the calibrated RCS measurement of the turbines and compare this data (with uncertainty) to modeled data.
The DGA/CELAR (France) (Centre d'Electronique de l'Armement: French Center for Armament Electronics) is able to measure targets in order to get their RCS (Radar Cross Section). Yet CELAR RCS measurement facilities are not compact bases and therefore the measured field is a near field. This article proposes a solution allowing the transformation of this near field to a far field and this in the three dimensions of space without limiting any dimension with Fraunhöfer criterion. Thanks to this method the RCS of a target is able to be known in any direction of space and moreover the calculation of a three-dimensional ISAR (Inverse Synthetic Aperture Radar) picture is thus possible. At first the theoretic part of our work is presented. Then a fast method in order to calculate the transformation of a near field to a far field by optimising the calculation time thanks to signal processing theory is given. Finally obtained results from simulated bright points are presented.