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Cable ringing is a concern in all short range Radar Cross Section (RCS) measurements. The standard method to reduce the RCS return from cable ringing is to minimize the cable length and add additional attenuation at either end of the cable. For VHF to L-band measurements, where the overall longer system ringdown times from both the antenna and cable can dominant the measurement background, this paper demonstrates another solution to eliminate the cable ringdown from the target measurement area for short range RCS measurements. This paper describes how using a cable length that is at least the same physical length of the range you want to measure can eliminate the cable ring down from the target measurement area. The cable length, which has the same physical length as the measurement range, provides a clean measurement target area with an additional margin depending on the group velocity of the cable used. Since the cable loss can be minimized with lower loss coaxial cables from VHF and L-band frequencies, using a longer single cable is a very viable solution to eliminate cable ring down from the target measurement area.
Korea Research Institute of Standards and Science (KRISS) has upgraded antenna measurement system to W-band (75 GHz ~ 110 GHz). This paper describes the antenna measurement facility that consists of a planar near-field scanner, a microwave subsystem and an extrapolation range, and measurement results. The microwave subsystem is adjusted to meet system power budget. Comparison result of on-axis horn antenna gains from extrapolation method based on three-antenna technique with those from planar near-field measurement shows good agreement within 0.15 dB.
A broad band interferometer antenna was designed and manufactured by Saab Avitronics. Saab Aerotech has installed a test facility for calibration of the interferometer antenna. The main purpose of the facility is to measure the interferometric function of the antenna. The interferometric function of the antenna can be measured directly but this method puts very high demands on the test range performance. An alternative method where each element is centered on a short far-field range is evaluated and compared by measurement with a large compact range at Saab Microwave Systems. The paper also describes the design aspects when measuring broad band, broad beam interferometer elements together with the actual design of critical components such as positioners, RF-system and absorber treatment.
This paper analyzes the reduction of the noise effect in spherical near-field antenna measurements. Two techniques have been evaluated: the first one is based on the mode truncation and the second one consists of a spatial filtering after a diagnosis process. The antenna under test (AUT) used for this evaluation is the 12 GHz Validation Standard antenna (VAST12). The VAST12 measurements have been performed in the Spherical Near-Field Antenna Test Facility of the Technical University of Madrid (UPM). These measurements have been corrupted adding a White Gaussian Noise (WGN) with different levels. First, the effect of the number of spherical modes considered in the near-to-far-field transformation has been evaluated, analyzing also the error due to the mode truncation versus the reduction of the noise uncertainty associated to each spherical mode. Second, a diagnosis process based on a holographic technique has been carried out. A spatial filtering including the AUT aperture has been applied and then, the far-field is reconstructed and compared with the uncorrupted far-field. Several results illustrate the signal In this paper, the effect of White Gaussian Noise (WGN) in spherical near-field measurements and the improvement of the signal to noise ratio (SNR) through mode truncation and spatial filtering are evaluated employing simulations and measurements. Section 2 and 3 respectively explain the mode truncation and spatial filtering to minimize the noise. In section 4 and 5 the results achieved when applying both techniques are illustrated. Finally, section 6 summarizes the conclusions drawn.
The laser based Molded Interconnect Device technology offers the potential of designing electrical and mechanical components on three-dimensional surfaces to increase functionality,level ofintegration and to reduce costs.To utilize this technology especiallyfor thedesign ofRFdevices, the electromagnetic parameters of the substrate materials as the complex permeability and permittivity have to be known precisely, as these quantities strongly in.uence the device performance. This paper therefore presents a broadband characterization of the dielectric properties of two Molded Interconnect Device materials. Based on this parameter characterization, two simple antennas are designed and their simulated and measured input re.ection coef.cients are compared.
Recent advances in the design of orthomode junction (OMJ) have created new devices capable of achieving as much as 1:4 bandwidth while maintaining the high performance of traditional OMJ designs [1–6]. The new OMJ technology is based on inverted ridge structure with four symmetrical feeding points for external balanced feeding stabilizing the frequency dependence of the OMJ. Probes with one or more corrugations on the aperture can greatly enhance the radiated performance in terms of return loss, pattern symmetry, stability with frequency and minimizing the cross polar levels within the main beam of the probe. In the standard corrugated horn literature [7] the upper limit on achievable bandwidth for corrugated horns is often stated to be somewhere between the 1:1.5 and 1:1.8 ratio depending on the performance requirements. New strategies in corrugated horn design and optimization are therefore required in order to take advantage of the increased bandwidth of the wideband OMJ technology. This paper discusses the achievable performances and limitations of wide band probes with multiple corrugated apertures and show measured and predicted design examples of apertures covering up to 1:2 bandwidth in the L to Ka band range.
This paper describes how to use reverberation chambers for characterization of radiated performance for wireless units with multiple antennas. Recently, there has been a rapid growth in the interest within the wireless industry for units with multi-antenna configurations. Therefore, there has also been an urgent need for efficient and accessible measurement methods which can capture multi-antenna performance. The reverberation chamber natively supports a rich and uniform multipath scattering environment due to its reflective walls and mode-stirrers. The way of creating the fading statistics with uncomplicated hardware (e.g. a standard shielded enclosure without absorbers) makes the solution easy to handle and cost-effective. Due to the fading properties existing by default in the chamber multi-antenna properties can be directly, accurately and quickly measured in the reverberation chamber.
We describe two theoretical bases for an algorithm for back-projection. The first is (1) Fourier inversion of the mathematical expression for the far electric field components in terms of the aperture electric field. The second is (2) Fourier inversion of the complete vectorial transmitting characteristic of Kerns' scattering matrix. It is this characteristic that results from the standard process of planar near-field (PNF) scanning and the ensuing reduction of the PNF transmission equation. We demonstrate that the theoretical approaches (1) and (2) yield identical back-projection algorithms. We report on back-projection measurements of an 18 inch X-band flat plate phased array using the far-field obtained from both planar and spherical near-field scanning. The spherical measurements were made on a large arch range.
A new simple approach is presented to calibrate the gain of standard gain horn antennas operating in the millimeter-wave frequency band. In terms of calibration, it is difficult to accurately measure the gain of standard gain horn antennas in the far-field region due to the space limitation. Therefore, near-field measurement methods are generally used to calibrate the gain of standard horn antennas. The extrapolation range method is one of the most accurate measurement methods in the near-field region. In the conventional extrapolation range method, a moving average process is applied to remove multiple reflections between antennas. Moving average can only remove multiple reflections between antennas. Therefore, electromagnetic absorbers are required to remove other reflections increasing measurement uncertainties. The time-domain gating method in extrapolation range allows us to remove all reflection waves, and achieve accurate antenna gain calibration without absorbers. The time-domain gating also reduces the number of measurement positions in the extrapolation ranges and obtains the gain of antennas in wide frequency ranges. In this paper, we compare the theoretical value with the time-domain gating method without absorbers by measuring three W-band standard gain horn antennas.
Thermal and other random noise sources give rise to an error contribution in spherical near field measurement systems [12]. With modern receivers and sufficient amplification in the system this term often give an insignificant contribution in the overall measurement uncertainty. However, in special cases the uncertainty linked to random noise may be more significant and the proper treatment of this term is needed to evaluate the impact on overall measurement uncertainty. The motivation for this paper comes from observations on spherical near field (SNF) measurement of relatively small antennas using a high degree of oversampling. In a multiprobe system this is generally the case particularly in measurements of small antennas like dipoles as shown in Figure 1. In these cases the near field to far field (NF/FF) processing is performed with data collected from all probes and some truncation of the spherical mode spectrum depending on the antenna size. The term modal filtering is often used to describe the deliberate truncation of the mode spectrum. What can be observed is that the effective signal to noise ratio (S/N) in small antenna measurements in which modal filtering is applied during NF/FF processing are often much better than the apparent S/N in the “raw” near field (NF) data. Parseval’s theorem, which states that power computed in either domains equals the power in the other explains this difference. The “noise power” is spread out on all available spherical modes and therefore reduced when the mode spectrum is truncated by modal filtering at the appropriate order/distance depending on the size of the antenna. In this paper we present a formal discussion on how the residual noise power after NF/FF processing is affected by the processing parameters. It will be shown that the “effective S/N” can be calculated directly from simple formulas from the applied sampling and filtering. The formulas will be validated by an experimental setup.
RF guided missile developers require flight simulation of their target engagements to develop their RF seeker. This usually involves the seeker mounted on a Flight Motion Simulator (FMS) as well as an RF target simulator that simulates the signature and motion of the target. Missile intercept engagements are unique in that they involve highly dynamic relative motion in a short period of time. This puts demanding requirements on the RF target simulator to adequately present the desired phase slope, amplitude, and polarization to the seeker antenna and electronics under test. This paper describes a newly installed RF Target Simulator that addresses these requirements in a unique fashion. The design utilizes a compact range reflector, dynamically rotated in two axes as commanded by the flight simulation computer, to produce the desired changing phase slope and an RF feed network dynamically controlled to produce the desired changing polarization and amplitude. Physical optics analysis establishes an accurate correlation between reflector physical rotation and resulting angle-of-arrival of the wave front in the quiet zone. The RF Target Simulator is self contained in a two-man portable anechoic chamber that can be disengaged from the FMS and rolled to and from the FMS as needed. Measurements are presented showing the performance of the RF Target Simulator.
In a search and rescue effort following a natural disaster, rubble and debris within the search environment can obscure human victims. A digital noise radar operating at UHF can penetrate the types of materials typically found in these situations with relatively little loss. This paper compares and contrasts measured correlation values of human and non-human objects taken from a digital noise radar. A noise radar works by cross correlating the received signal with a replica of the transmit signal. A high correlation indicates range to the target. Measured results with the noise radar show that patterns of peaks and valleys exist near the range of the targeted object. This paper looks at the correlation patterns generated by two different sized hollow metal tubes and a human at various look angles. The results show that the correlation patterns of the tubes are similar, but the correlation patterns of the human differ. Full characterization of human and non-human noise radar correlation patterns could confirm the presence of a human victim and information about his location within the rubble.
The models governing ground-bounce illumination have been well-understood for decades. Previous ref-erenced work examined the application of these mod-els to three-dimensional geometries and showed that illumination variation is a spatially-dependent func-tion of frequency which requires knowledge of the target geometry and scattering characteristics in order to evaluate uncertainty. This paper leverages that work and further develops a Short-Time Fourier Transform (STFT) method to extract frequency do-main scattering characteristics from target data di-rectly. By utilizing at least two antenna heights in two separate measurements, ground-bounce geometries allow for useful target feature characterization. This enables an assessment of spatial target uncertainty in the image domain as well as for RCS; it further shows promise for illumination error mitigation. This paper demonstrates this potential in simulation to support measurements collected at the National RCS Test Fa-cility (NRTF), Holloman AFB NM.
In this paper, we propose an approach to the design of 2D Generalized Plane Wave Synthesizers (GPWS), i.e., of PWS with radiating elements located on non-uniform grids and for which the Quiet Zone (QZ) specifications are enforced at non-uniformly spaced sampling locations. The approach, based on a singular values optimization process, allows to dimensioning the size of the GPWS to meeting the QZ specifications, to defining the number and locations of the QZ sampling points and of the radiators to control the ill-conditioning when searching for the excitation coefficients, to dramatically reducing the number of radiating elements, and to finding the excitations by a Singular Value Decomposition approach. The performance is numerical pointed out and experimentally and successfully verified.
This paper reports the recent investigation of data-link strings as supporting structures for antennas used in a bistatic radar cross section (RCS) measurement system. Although several candidate strings exist, analysis of the strings’ scattering contribution needs a generic string model to make comprehensive comparisons. A simple theoretical two-dimensional (2D) dielectric coated cylindrical wire model is initially utilized to predict and compare scattering characteristics of various data-link string structures. In addition to the simple model, a non-destructive measurement method is proposed for extracting the material properties of the string material. Using the analytic 2D model of a dielectric clad wire as the generic string model, the unknown permittivity is computed from reflectivity measurements taken with a focused beam system. Extracted permittivity values are then used in a full-wave electromagnetic solver to validate the model. Measured and simulated results are shown to have excellent agreement for the 2D RCS, radar echo width, of different strings and polarization configurations.
The paper presents a new system, to be used in near-field antenna characterization, which (in its simplest implementation) automatically assists the alignment of the Antenna Under Test (AUT) and the definition of the uniform/non-uniform sampling and filtering procedures. The system, based on a very cheap hardware (3D, coded structured-light, digitalization device), is able to provide a complete description of the geometry of the measurement set-up and of the movements of its parts, probe included. In this paper the simplest case, the alignment of the AUT, is considered. In this case, the system determines the coordinates of the surface points of the AUT in the Laboratory Reference System (LRS), providing the position and the orientation of the AUT in the LRS. The acquisition of the geometrical data on the AUT requires only few seconds, with a negligible human intervention. The acquired data are then processed to provide the desired setting of the AUT either manually or by means of computer controlled actuators, ensuring the accuracy suited to millimetre-wave band. The geometrical information can be exploited also to make possible the correction via software, when movements of the AUT should be avoided. The accurate information on the AUT geometry can be fruitfully exploited in advanced, high-performance filtering and sampling approaches, again drastically reducing any human interaction with the system. The performance of the system is discussed by referring to a prototype working in the millimetre-wave band.
Abstract — The multipath richness typical of aircraft channels represents a potentially well-suited environment for multiuser multiple-input multiple output technology (MU-MIMO). This paper presents results from measurements of the achievable MU-MIMO data rates in small aircraft using an open-source software-de.ned radio (SDR) testbed. These results are then compared against values simulated using 3-D ray-tracing. We also compare the achievable capacity of dirty paper coding (DPC) against time-division multiple access (TDMA) to illustrate the potential gains from MU-MIMO in aircraft environments. For transmitters located near the ends of the aircraft, the error between simulated and measured capacity was on the order of 5% or less. For the more centralized transmitter location, simulated values tended to predict as much as 15% less capacity than what was actually measured.
Radio source techniques are a common means of measuring the G/T of user antennas. These techniques depend on measuring noise parameters and are invalid when interference is present. The error sources in G/T measurements are described. The measurement and error sources of system noise temperature values, T, are also discussed and are needed when antenna gain values are required or when antenna gain levels are determined by other means and G/T is required.
Allwave Corporation, 3860 Del Amo Blvd., #404, Torrance, CA 90503, USA
In dynamic RCS measurements, uncompensated motion induces artifacts and distortions, from moderate to severe, into any Fourier-based analysis. A quadratic term in the kernel of the underlying spectra (length L) will stretch the spectra into one of L2 configurations. Whether radial velocity for stepped-chirp HRR measurements, or acceleration for fixed-frequency Doppler measurements, spectra often become buried in noise – the quadratic term spreading the bandwidth. Even an approximation to the quadratic term in the spectral kernel allows a variety of signal processing techniques to further refine and remove residual uncompensated motion within the stepped-chirp or Doppler vector. This paper presents blind and semi-blind techniques making use of Fourier-based processing, entropy calculation, and bandlimited resampling to compensate for motion. Doing so restores the SNR available to the individual underlying spectra.