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There are different applications where the radiation level of the electromagnetic waves are needed to be controlled or reduced. One way to achieve a functional passive control of the radiation level is by the use of electromagnetic-wave absorbers. The absorption efficiency is not only gained by the electromagnetic characteristics of the base material but also by the geometrical shape of the absorber specifically for wideband absorbers. One of the main applications of wideband absorbers is in anechoic chambers. In anechoic chambers, the walls of the chamber are lined with different absorbing panels each of which have different geometrical shapes. Two major groups of wideband absorbers are the wedge and pyramidal absorbers. When an infinite wall is lined completely with one type of these absorbers, the resulting electromagnetic problem will be a 1-dimensional (for the case of wedge absorber) or a 2-dimensional (in the case of pyramidal absorber) periodic-boundary-condition problem. A semi-analytical method based on a multi-conductor-transmission-line model has been previously introduced to solve the 1-dimesional problem (wedge absorbers) [1]. A modified method has been developed and will be introduced for the 2-dimensional problem (pyramidal absorbers). Some examples comparing the simulation results with the measurements ones will show the efficiency of the proposed method for the pyramidal absorbers. [1] A. Enayati, and A. Fallahi,“ Full-wave modeling of wedge absorbers”, ATMS 2014, Chennai, India.
There is an increasing interest in the use of adaptive antenna arrays for applications such as interference suppression, beamforming, and direction of arrival estimation. However, optimal use of an antenna array requires precise knowledge of the relative gain and phase responses of all elements in the array for all directions of interest (the antenna manifold). One generally obtains the antenna manifold through carefully controlled indoor measurements in an antenna test range. While these measurements are very precise and may include a range of frequencies, this approach has drawbacks in that it is time consuming and costly to perform for a large number of antenna arrays. One may also measure an antenna array's manifold outdoors using signals of opportunity. For Global Navigation Satellite Signal (GNSS) antennas, the satellite signals are the signals of opportunity. These measurements are quick and inexpensive if one has access to the digitized samples of the antenna outputs. In this paper, we discuss and compare our measurements of a multiple element antenna array using the indoor and outdoor approach. We show that there is a very good agreement between the two approaches and that outdoor measurements may be a viable substitute for indoor measurements in many applications.
Electrically small antennas (ESAs) are neither efficient nor good radiators because their radiation quality factor is considerably high. It is therefore critical to add appropriate matching networks (MNs) to the antenna to enhance its realized gain and therefore its performance over a large frequency range. For receiver applications, the important factor for the electrically small antenna is the signal-to-noise ratio (SNR). In this paper, the design of stable non-Foster circuits (NFCs) to improve the performance of the ESA in terms of the realized gain and the SNR has been achieved. Measurements of the signal and noise of the electrically small antenna with and without non-Foster circuits has been performed in an outdoor environment. Key steps of the measurements will be shown including the post-processing of the data, which is an important step to reduce the effect of undesired signals. Based on the measured data, it is shown that the Non-Foster circuits improve both antenna gain and SNR by more than 15dB over a wide frequency range, namely, 100MHz to 700MHz, with respect to the case without a NFC. To the best knowledge of the authors, this improvement is maintained over the widest frequency band among all the published work. Excellent agreement between simulation and measurement results in terms of gain and signal improvements is obtained and will be highlighted in our presentation.
Applications using millimeter-wave antennas have taken off in recent years. Examples include wireless HDTV, automotive radar, imaging and space communications. NSI has delivered dozens of antenna measurement systems operating at mm-wave frequencies. These systems are capable of measuring a wide variety of antenna types, including antennas with waveguide inputs, coaxial inputs and wafer antennas that require a probing station. The NSI systems are all based on standard mm-wave modules from vendors such as OML, Rohde & Schwarz and Virginia Diodes. This paper will present considerations for implementation of these systems, including providing the correct RF and LO power levels, the impact of harmonics, and interoperability with coaxial solutions. It will also investigate mechanical aspects such as application of waveguide rotary joints, size and weight reduction, and scanner geometries for spherical near-field and far-field measurements. The paper will also compare the performance of the various mm-wave solutions. Radiation patterns acquired using some of these near-field test systems will be shared, along with some of the challenges encountered when performing mm-wave measurements in the near-field.
This paper will investigate practical aspects of measuring antennas operating with pulsed RF signals of very narrow width, down to 100 ns. Modern network analyzers provide very high IF bandwidth, theoretically allowing measurement of very narrow pulses. But in practice there are several factors that limit the minimum pulse width that can be measured accurately. These include lowpass filtering in the IF path, limited receiver dynamic range, and trigger synchronization issues. On large near-field scanners, the RF path length change with probe motion becomes significant when the pulses are short. If the RF system uses a pulsed reference signal, a delay line may be required to align the test and reference pulses arriving at the receiver. Even with a CW reference, the varying propagation delay in the test channel places a limit on the minimum pulse width. The paper will present a detailed investigation of these issues along with measurement examples. It will compare measured performance of a standalone VNA, a VNA with remote mixers, and the NSI Panther receiver.
Radome enclose antennas to protect them from environmental influences. Radomes are ideally electrically transparent, but in reality, radomes introduce transmission loss, pattern distortion, beam deflection, etc. Radome diagnostics are acquired in the design process, the delivery control, and in performance verification of repaired and newly developed radome. A measured near or far-field may indicate deviations, e.g., increased side-lobe levels or boresight errors, but the origin of the flaws are not revealed. In this presentation, source reconstruction from measured data is used for radome diagnostics. Source reconstruction is a useful tool in applications such as non-destructive diagnostics of antennas and radomes. The radome diagnostics is performed by visualizing the equivalent currents on the surface of the radome. Defects caused by metallic and dielectric patches are imaged from far-field data. The measured far-field is related to the equivalent surface current on the radome surface by using a surface integral representation together with the extinction theorem. The problem is solved by a body of revolution method of moment (MoM) code utilizing a singular value decomposition (SVD) for regularization. Phase shifts, an effective insertion phase delay (IPD), caused by patches of dielectric tape attached to the radome surface, are localized. Imaging results from three different far-field measurement series at 10 GHz are presented. Specifically, patches of various edge sizes (0.5?2.0 wavelengths), and with the smallest thickness corresponding to a phase shift of a couple of degrees are imaged. The IPD of one layer dielectric tape, 0.15 mm, is detected. The dielectric patches model deviations in the electrical thickness of the radome wall. The results from the measurements can be utilized to produce a trimming mask, which is a map of the surface with instructions how the surface should be altered to obtain the desired properties for the radome. Diagnosis of the IPD on the radome surface is also significant in the delivery control to guarantee manufacturing tolerances of radomes.
RCS measurements are often comprised of a combination of the coherent summation of many things in addition to the desired target. Those other things contribute to error in RCS measurements and include noise, clutter and background, which can be further characterized according to specific types. An approach has been developed that is capable of capturing and separating certain types of noise, clutter and background based on specific forward models to include RFI, target support (e.g., pylon), and many others, such that engineers can clearly see the separated components and selectively choose to include, exclude, or edit as the case may be. This approach affords far more flexibility than classic image edit reconstruct (IER), and offers more editing accuracy than Fourier-based approaches including entire phase history based approaches. This paper describes the basic approach and shows examples with measured data.
The Space Communications and Navigation (SCaN) Testbed was developed to investigate the applicability of software defined radios (SDR) to NASA space missions, study the operation of SDRs and their waveform applications in an operational space environment, and reduce cost and risk for future space missions using SDRs. The SCaN Testbed, developed at NASA’s Glenn Research Center, is currently installed on the International Space Station and has line-of-sight connection to NASA’s Space Network and compatible ground stations. To characterize the operation of the SDRs and their waveforms, a new and unique capability was developed at GRC, which uses purposeful antenna off-pointing to provide a wide range of power levels to the input of the SDR. With this capability, a radio can be more fully tested and characterized on-orbit. This paper describes the new antenna off-pointing capability and methodology, and how it was applied to characterize the on-orbit performance of an S-Band radio in the SCaN Testbed. It provides details of the antenna pointing system control algorithm, gimbal articulation limitations, medium gain antenna pattern profile, and phase limitations associated with the medium gain antenna. Finally, the paper presents test results and lessons learned.
The performance of a typical narrowband antenna array is reduced by mutual coupling between radiating elements. The degree to which this inter-element coupling occurs may be correlated with the resonant characteristics and tendency for late time ringing of an individual element. The parabolic reflector impulse radiating antenna (IRA) is an ultra-wideband (UWB) antenna which by virtue of its design and aim to radiate a very short time-domain signal demonstrates significantly decreased late time ringing. Given this quality, the suitability and performance of the reflector IRA in an array configuration is examined. Modeling and simulation of the reflector IRA is accomplished using commercially available software and single antenna results are compared to measured data. Full-wave simulation of arrayed reflector IRAs in varying physical configurations and excitation modes is performed The relative levels of coupling and degradation of radiation pattern and signal quality are discussed.
The 3D reconstruction algorithm of DIATOOL, with its higher-order Method of Moments-based implementation, reconstructs extreme near fields and surface currents on arbitrary 3D surfaces enclosing the antenna under test (AUT) from its measured radiated field. This is a valuable analysis and diagnostics tool for the antenna engineer to speed up the antenna prototyping cycle and identify errors in the manufactured AUTs, since the 3D reconstruction can solve a number of problems which traditional microwave holography cannot handle, namely: Accurate and detailed identification of array malfunctioning due to the enhanced spatial resolution of the reconstructed fields and currents Filtering of the scattering from support structures and feed network leakage A number of papers published over the past four years have shown these features in detail. At the same time it was observed that the spherical wave expansion (SWE) of the field radiated by the currents reconstructed by DIATOOL always provides a SWE power spectrum that looks noise-free. This phenomenon was observed for all the antennas on which the 3D reconstruction was applied, and it was explained as being an effect of the 3D reconstruction algorithm, which uses the a-priori information that all sources are contained inside the reconstruction surface. However, since real measured data were always used as input, it was not possible to prove that the SWE power spectrum of the reconstructed currents coincided with the one that would be obtained from noise-free measurements. The purpose of the present paper is thus to investigate in detail the noise filtering capabilities of the 3D reconstruction algorithm of DIATOOL. Models of several antennas, differing in size and type, were set up in GRASP with noise at different levels added to the radiated field. The noisy field was then given as input to DIATOOL and the SWE coefficients and the power spectra of the reconstructed currents were compared with the noise-free results coming from GRASP. Moreover, the effect of the varying noise level on the obtainable resolution was investigated.
Typical RF cables found in most labs have an expanded PTFE dielectric material, commonly known as Teflon. This material works well for most RF applications, however as engineers we know there’s always a “gotcha.” The Teflon Knee is a very old problem that is manifested as a phase variation in a very small temperature range. Unfortunately this occurs close to room temperature, 19 to 23 degrees Celsius in particular. This makes accurate and repeatable phase measurements a daunting task near those temperatures.???? The phenomena is caused at the molecular level where the material goes through a phase state change (long molecule chains change their twisting slightly). A recently developed network analyzer accessory, Agilent CalPods, makes accurate observations of the effects of Teflon Knee possible. The author was the first to use a CalPods system in Raytheon and experiment with various RF cables in an environmental chamber. Teflon is a registered trademark of DuPont Co. 5/12/2014 Copyright © 2014 Raytheon Company. All rights reserved. Customer Success Is Our Mission is a registered trademark of Raytheon Company.???????????
In late 2013, the Federal Aviation Administration (FAA) announced that airline passengers would be allowed to use personal electronic devices (PEDs) during all phases of commercial flights. However, to gain FAA approval for PED usage, airlines were required to demonstrate that their aircraft were sufficiently immune to potential interference from PEDs. As a result of the FAA requirement, Delta Air Lines (DAL) and the Georgia Tech Research Institute (GTRI) collaborated to develop and implement a certification testing program based on the industry accepted standard for PED testing, RTCA/DO-307 “Aircraft Design and Certification for Portable Electronic Device (PED) Tolerance”. Delta and GTRI accomplished certification of the Delta fleet by tailoring DO-307 to meet Delta’s needs of testing eleven flight active aircraft within a short timeframe. GTRI was able to identify ways to improve test efficiency and implement changes to the test program in response to different aircraft configurations and active flight schedules. This paper will discuss the program requirements, test system architecture, component selection, test methodology and test results for two critical components of aircraft Instrument Landing System (ILS); the Localizer and Glide Slope systems.
Near field Radar Cross Section (RCS) measurements and Inverse Synthetic Aperture Radar (ISAR) are used in this study to obtain geometrically correct images and far field RCS. The methods and the developed algorithms required for the imaging and the RCS extraction are described and evaluated in terms of performance in this paper. Most of the RCS measurements on full scale objects that are performed at our measurement ranges are set up at distances shorter than those given by the far field criterion. The reasons for this are e.g., constraints in terms of budget, available equipment and ranges but also technical considerations such as maximizing the signal to noise in the measurements. The calibrated near-field data can often be used as recorded for diagnostic measurements. However, in many cases the far field RCS is also required. Data processing is then needed to transform the near field data to far field RCS in those cases. A straightforward way to image the RCS data recorded in the near field is to use the backprojection algorithm. The amplitudes and locations for the scatterers are then determined in a pixel by pixel imaging process. The most complicated part of the processing is due to the near field geometry of the measurement. This is the correction that is required to give the correct incidence angles in all parts of the imaged area. This correction has to be applied on a pixel by pixel basis taking care to weigh the samples correctly. The images obtained show the geometrically correct locations of the target scatterers with exceptions for some target features e.g., when there is multiple or resonance scattering. Separate features in the images can be gated and an inverse processing step can be performed to obtain the far field RCS of the full target or selected parts of the target, as a function of angle and frequency. Examples of images and far field RCS extracted from measurements on full scale targets using the ISAR processing techniques described in this paper will be given.
Equivalent isotropically radiated power (EIRP) and Saturating flux density (SFD) are two system level parameters often sought during characterizing of spacecraft systems. The EIRP quantity is the power that an isotropic radiator will have to transmit to lead to the same power density that the AUT will effect at a specific angle of interest. A convenient measurement technique is to set up a standard gain antenna as receiver in the far-field of an AUT and to then determine EIRP by measuring the power at the port of the standard gain receiving antenna. Since the distance is known the EIRP can be calculated. SFD is the flux required to saturate the receiver of the antenna under test and is also usually determined on a far-field range. The philosophy of this measurement is to determine the saturation level of the receiver and this is typically achieved by gradually increasing the input power level of the transmitter. This process continues as long as the receiver response linearly tracks the increase in power of the transmitter and is terminated once the receiver is saturated. Thus, SFD can be interpreted as being the receive system parameter analogy of the transmit system parameter EIRP. There is a common misconception that these parameters cannot be measured on a near-field range and that they require far-field (or far-field equivalent, i.e. compact range) conditions for a valid measurement to be made. However, the principles for measuring both of these parameters in a planar near-field range (PNF) were presented in [1]: An EIRP technique is presented in [1] equation 32 and this approach relies on a complex integration of the measured near-field power, the near-field probe gain and a single power measurement at a reference location. A SFD technique is presented in [1] equation 39. This technique also relies on a complex integration of the measured near-field power, the near-field probe gain and a single transmitting probe power measurement at a reference location. Although these descriptions are theoretically concise their execution is not obvious [2] and as a result, there still seems to be hesitation in making (and trusting) these measurements in industry. This paper intends to provide further insight into measuring these two parameters in a PNF range and offers test procedures outlining the steps involved in doing so. The principle goal is to offer further explanation to illuminate the underlying principles. The work presented here is not new, but is presented as a tutorial on this illusive subject. [1] Newell, Ward and McFarlane, “Gain and Power Parameter Measurements Using Planar Near-Field Techniques”, IEE APS Transactions, Vol 36, No. 6, June 1988. [2] Masters & Young, “Automated EIRP measurements on a near-field range”, Antenna Measurement Techniques Association Conference, September 30 - October 3, 1996.
Antenna alignment for near-field scanning was typically done at NIST with multiple instruments (theodolites, electronic levels, motor encoders) to align multiple stacked motion stages (linear, rotation). Many labs and systems are now using laser trackers to measure ranges and perform periodic compensation across the scan geometry. We are now seeing the use of laser trackers with 3D coordinate metrology to align ranges and take positional data. We present the alignment techniques and positional accuracy and uncertainty results of a mmWave antenna scanning system at 183 GHz. We are using six degree-of-freedom (6DOF) AUT and Probe measurements (x, y, z, yaw, pitch, roll) to align the AUT and then to align the scan geometry to the AUT. We are using a combination of 3DOF laser tracker measurements with a combined 6DOF laser tracker/photogrammetry sensor. We combine these measurements using coordinated spatial metrology to assess the quality of each motion stage in the system, tie the measurements of each individual alignment together, and to assess scan geometry errors for position and pointing. Finally we take in-situ 6DOF position measurements to assess the positional accuracy to allow for positional error correction in the final pattern analysis. The knowledge of the position and errors allow for the correction of position and alignment of the probe at every point in the scan geometry to within the repeatability of the motion components (~30 µm). The in-situ position knowledge will eventually allow us to correct to the uncertainty of the measurement (~15 µm). Our final results show positioning errors on the spherical scan surface have an average error of ~30 µm with peak excursions of ~100 µm. This robust positioning allows for accurate analysis of the RF system stability. Our results show that at 183 GHz, our RF repeatability with movement over 180° orientation change with a 600 mm offset to be less than ±0.05 dB and ±5°.
Performance requirements for compact ranges are typically specified as metrics describing the quiet zone's electromagnetic-field quality. The typical metrics are amplitude taper and ripple, phase variation, and cross polarization. Acceptance testing of compact ranges involves phase probing of the quiet zone to confirm that these metrics are within their specified limits. It is expected that if the metrics are met, then measurements of an antenna placed within that quiet zone will have acceptably low uncertainty. However, a literature search on the relationship of these parameters to resultant errors in antenna measurement yields limited published documentation on the subject. Various methods for determining the uncertainty in antenna measurements have been previously developed and presented for far-field and near-field antenna measurements. An uncertainty analysis for a compact range would include, as one of its terms, the quality of the field illuminating on the antenna of interest. In a compact range, the illumination is non-ideal in amplitude, phase and polarization. Error sources such as reflector surface inaccuracies, chamber-induced stray signals, reflector and edge treatment geometry, and instrumentation RF leakage, perturb the illumination from ideal.
The measurement community can use advanced simulation techniques to minimize both the time and financial investment necessary to design a custom compact antenna test range (CATR), while simultaneously optimizing performance. Traditionally, engineers have analyzed parabolic reflectors, a collimating device installed in CATRs, with approximate methods similar to ray-tracing, physical optics and physical theory of diffraction due to the practical limitations of the available resources. However, recent technological advances facilitate the rigorous analysis of electrically large parabolic reflectors. Computational resources (i.e. processors and memory) continue to offer improved performance at reduced cost. In addition, rigorous numerical solvers (i.e. the Multilevel Fast Multipole Method (MLFMM)), have become available in commercial software such as FEKO. Simulations employing these numerical solvers extend previous research by characterizing the quiet zone when operating offset-fed parabolic reflectors. The gain-transfer method is then emulated with an antenna under test (AUT). Several reflector edge treatments (e.g. serrated, blended-rolled) are considered to better understand performance trade-offs. Simulating an antenna measurement technique provides the insight necessary to identify and quantify potential error sources. The convergence between measured and simulated antenna performance characteristics can therefore be expedited with improved reliability.
Antenna and Radar Cross Section (RCS) measurements are often required for orientation sets (cuts) that are difficult or impossible to produce with the positioning instrumentation available in a given lab. This paper describes a general coordinate transform, combined with a general polarization rotation to correct for these orientation differences. The technique is general, and three specific examples from actual test programs are provided. The first is for an RCS measurement of a component mounted in a flat-top test fixture. The component is designed to be mounted in a platform at an orientation not feasible for the flat-top fixture, and the test matrix calls for conic angle cuts of the platform. The transforms result in a coordinated, simultaneous two-axis motion profile and corresponding polarization rotations yielding the same information as if the component had been mounted in the actual platform. The second example is for a pattern measurement of an antenna suite mounted on a cylindrical platform (such as a projectile). In this case, the test matrix calls for a roll-cut, but the range positioning system does not include a roll positioner. The transforms again result in a coordinated, simultaneous two-axis motion profile and corresponding polarization rotations to provide the same information as the required roll-cut but without the use of a roll positioner. Finally, the third example is for an antenna pattern measurement consisting of an extremely large number of cuts consisting of conic yaw cuts, roll cuts and pitch cuts. The chosen method involves the use of the Boeing string suspension system to produce great-circle cuts at various pitch angles combined with the use of the coordinate and polarization transforms to emulate, off-line, any arbitrary cut over any axis or even multiple axes. Keywords: Algorithm, Positioning, Polarization, Coordinates, RCS
Driven by the mobile data communications needs of market broadband antennas at the upper frequency bands are already state-of-the-art, e.g. at the Ka-Band. For the characterization of an antenna the antenna gain is one of the major test parameters. This measurement task is already challenging for standard applications at the Ka-Band. However, for the calibration of remote station antennas utilized in high precision test facilities, e.g. the compact range, even higher measurement accuracies are typically required in order to fulfil the overall system performance within the later test facility. Therefore the requirement for this investigation is to improve the measurement set-up and also the steps to get a failure budget which is better than ± 0.15 dB. Every antenna gain measurement technique is affected by required changes in the measurement setup, e.g. the Device under Test (DUT) or the remote station, respectively. This results for example in a variation of mismatch with resulting measurement errors. To determine and compensate the occurred mismatches, the scattering parameters of the involved components have to be measured and be evaluated with a corresponding correction formula. To quantify the effect for the gain measurement accuracy the remaining uncertainty of the mismatch correction values is examined. Another distortion is caused by multiple reflections between the antenna apertures. To reduce this error source, four additional measurements each with a decreased free space distance should be performed. In addition to the common methods, this paper explains in detail an advanced error correction method by using the singular value decomposition (SVD) and compares this to the standard mean value approach. Finally the restricted distance between both antennas within the applied anechoic far-field test chamber has to be analysed very critically and optionally corrected for the far-field gain at an infinite distance in case the measurement distance is fulfilling the minimum distance requirement, only. The paper will discuss all major error contributions addressed above, show correction approaches and verify these algorithms with exemplary gain measurements in comparison to the expected figures.
Compact Mini Vector Network Analyzer (VNA) frequency extension modules have been developed for all frequency bands from WR-15 though WR-5.1, with prototypes in development for higher bands. These modules are available in both Mini transmit-receive (Tx-Rx) for full two-port S-parameter measurements and smaller Micro receive-only (Rx) configurations. A common setup, for example, would be to combine a Mini Tx-Rx with a Micro Rx to provide S11 and S21 measurement capability. The modules are designed to be used up to 8m away from the VNA system with excellent amplitude and phase stability, making them well suited for antenna range applications. The WR-15/WR-12/WR-10 family of Mini and Micro extension modules each cover greater than the nominal waveguide band—46-79 GHz for WR-15, 55-95 GHz for WR-12, and 65-116 GHz for WR-10. The Mini Tx-Rx modules provide 120dB dynamic range, +/- 0.15 dB amplitude stability, +/- 2 degree phase stability, and +6dBm test port power. They measure 1.5” x 3.0” x 8.5” with 1.2kg mass and require only a single +9V supply. The Micro Rx module is a single 300g 2.5” x 1.0” x 0.7” block with two coaxial connections and a DC +5V pin while still providing the same dynamic range and stability as the Mini Tx-Rx modules. For antenna range applications or other high path loss environments, the attenuator can be removed from the Micro Rx input to give 150 dB effective dynamic range. A WR-8.0/WR-6.5/WR-5.1 (90-140 GHz / 110-170 GHz / 140-220 GHz) family of Mini Tx-Rx and Micro Rx extension modules has also been developed with the same form factor as the lower-frequency family—smaller Minis for these bands are currently being developed. The WR-8.0/6.5/5.1 extender family also provides 120 dB dynamic range and excellent stability. Standard-size Tx-Rx and Rx extension modules, still quite compact at 3” x 5” x 11”, are also available for all waveguide bands up through WR-1.0/WM-250 (750-1100 GHz). Mini and Micro extension modules for bands above WR-5.1 are currently in development, with some modules such as a WR-3.4 Micro Rx already available.