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As part of a target simulator [1], a linearly polarized signal was required with a variable tilt angle that could be controlled electronically and changed at a 1 kHz rate. However, microwave components available in the 33.4 – 36 GHz operating range were inadequate to achieve the desired performance. A novel approach was developed to downconvert the input signal to a lower frequency range and use vector modulators available in this band to produce the appropriate phase and amplitude changes in each path, then upconvert back to the desired operating frequency to drive an orthomode transducer. A calibration and measurement procedure was developed to determine the vector modulator input settings that produced the most accurate tilt angles and best cross-polarization performance. By iteratively measuring cross-polarization and tilt angle, then adjusting the vector modulator controls, a tilt angle accuracy of +/-1 degree was achieved with a crosspolarization of -25 dB, exceeding the required performance. This paper provides an overview of the concept, a block diagram of the design, discussion of the calibration and measurement procedure, and a summary of the results achieved.
This paper addresses the difficulties of achieving lower cross-polarization EM field transmission (or reception) levels by employing wideband electromagnetic polarization filters (EMPF). These EMPFs are applied as add-on screens to reduce the cross-polarization levels of standard gain horns (SGH) and diagonal horns (DH). Cross-polarization level reduction as much as 19 dB is presented for diagonal horns with add-on screens. Similarly, more than 9 dB cross-polarization reduction is shown for standard gain horns across the operational bandwidth. Later, an alteration is done on the add-on screens by making use of Ludwig's 3rd coordinate definition. This modification results in further cross-polarization suppression in the vicinity of boresight direction. For instance, on X-Band SGH, near boresight angular region where cross-polarization level keeps below -60 dB increases by 26% with use of this modified add-on screen.
Method of moments (MoM) codes have become increasingly capable and accurate for predicting the radiation and scattering from structures with dimensions up to several tens of wavelengths. In an earlier AMTA paper [1], we presented a network model (NM) algorithm that uses a Gauss-Newton iterative nonlinear estimation method in conjunction with a MoM model to estimate the “as-built” materials parameters of a target from a set of backscatter measurements. In this paper, we demonstrate how the NM algorithm, combined with the basis pursuits (BP) l1 minimization technique, can be used to locate unknown defects (dents, cracks, etc.) on a target from a limited set of RCS pattern measurements. The advantage of l1 minimization techniques such as BP is that they are capable of finding sparse solutions to underdetermined problems. As such, they reduce the requirement for a priori information regarding the location of the defects and do not require Nyquist sampling of the input pattern measurements. We will also show how the BP solutions can be used to interpolate RCS pattern data that is undersampled or has gaps.
We present exact solutions to antenna holography problems based on planar, spherical, or cylindrical nearfield data. Full field distribution information in the source region is determined exactly, from two tangential field components over a planar, spherical, or cylindrical surface. Stated in so many words, all three components of both electric and magnetic fields in the antenna aperture are obtained exactly from two-component near-field data. Conventional antenna holography relies upon back transformation for planar near-field data, and upon optimization schemes for both spherical and cylindrical near-field data. It is both acknowledged and accepted that the back transform is only an approximate solution due to its far-field nature, whereas optimization algorithms are vulnerable to convergence instability and, moreover, are computationally intensive. Our approach tackles holography by solving an inverse scattering problem, with exact solutions derived on the basis of three common types of near-field data. A mapping algorithm is proposed herein which determines the field everywhere, in both interior and exterior regions, based on a single-slice nearfield data capture. It provides exact antenna holography solutions analytically, with the full electric and magnetic fields disclosed throughout the source region. The field mapping algorithm is a direct, closed-form solution which is numerically straightforward and efficient. Verification is carried out and demonstrated by analytic examples and numerical simulations, as well as by hardware measurements. Nine test examples are given. Analytic examples include dipole arrays deployed across planar, spherical, and cylindrical regions, and a narrow azimuthal slot on a conducting sphere. The simulation example exposes the structure of a slotted array antenna based upon its near-field data as generated by a commercial software package. The hardware measurements address themselves to a concrete embodiment of that same slotted array antenna, an elongated sector antenna, and to a patch antenna. Excellent agreement is found in all test cases.
A balanced PIFA-inspired antenna design is presented for use with the 2:45 GHz ear-to-ear radio channel. The antenna is designed such that the radiated electric fields are primarily polarized normal to the surface of the head, in order to obtain a high on-body path gain (jS21 j). The antenna structure can be made conformal to the outer surface of a hearing instrument, such that the bandwidth of the antenna is optimized given the available volume. The radiation patterns, ear-to-ear path gain and available bandwidth is measured and compared to the simulated results. It is found that the antenna obtains a relatively high ear-to-ear on-body path gain, as well as a bandwidth that is large enough to cover the entire 2:45 GHz ISMband.
A fast algorithm is presented for the generation of 3D current density images of antennas utilizing arbitrary antenna measurement data. The images represent a broadband equivalent current distribution which radiates the same fields as the true current distribution on the antenna structure in a broad frequency band. These equivalent currents convey important information about the antenna. The imaging algorithm can efficiently handle arbitrary measurement geometries and probe characteristics. It is inspired by the Multi-Level Fast Multipole Method (MLFMM). The near-field compensation and probe correction is realized using a modified adjoint operator based on adaptive fast multipole translations. Due to the modifications, a priori knowledge about the field observation density can be exploited and the generated image becomes more accurate. The complexity of the proposed approach is identical to a fast Fourier transform (FFT) based imaging algorithm. Numerical examples are given to prove
Over-the-air (OTA) testing is an established technique used to measure the wireless system performance of mobile devices in addition to characterizing the antenna subsystem. 3D radiation patterns of transmit power and receive sensitivity are used to determine a figure of merit (FOM) for the transmitter and the receiver performance, i.e., Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS), respectively. For LTE, most attention is focused on the MIMO receiver chain evaluation. Discussions have been ongoing for quite some time on how OTA testing can be updated to support LTE MIMO. The MIMO OTA decomposition approach [1], [2] determines separate FOMs for the key MIMO receiver chain subsystems. The conducted MIMO test is utilizing a fading simulator to introduce dynamic fading and is used to determine a FOM for the MIMO receiver performance. The radiated test is performed without the introduction of fading profiles inside the anechoic chamber and is used to determine a FOM for the MIMO receive antenna pair. The FOM for the overall MIMO performance of the DUT is a combination of the FOMs from each test (conducted and OTA). Splitting up the MIMO wireless system performance testing into two straightforward and cost effective tests provides more information about the DUT performance than performing a complex single test. The presented approach differentiates itself from competitive MIMO OTA approaches due to its simplicity, reduced complexity, and low cost.
The Electronic Proving Ground's Antenna Test Facility at Fort Huachuca, Arizona has some of the most interesting testing structures in the world. These structures include a wooden Arc measurements system with a 23 m radius, a 30 m tower, and a compact range with an 18 m quiet zone. All of these structures are outdoors and support testing from UHF to mm frequencies on antenna systems mounted on large land and air vehicles. This paper describes the ranges supported by these structures (some of which were built in the late 1960’s) and the efforts made to keep these ranges current. This paper also describes an economical approach to arc range design which moves the arc instead of the vehicles. This paper discusses plans to build one of these systems outdoors at EPG within a limited budget.
This paper details a systematic procedure of the evolution of an electromagnetic band-gap (EBG) meta-surface from a simple ground plane. The main aspect of the paper is to understand the behavior of these EBG surfaces for low profile antenna design solutions. Reflection phase diagrams are used as a criterion to understand the flat reflection phase response of these surfaces for all angles of incidences and all polarizations. The evolution of EBG from a PEC ground plane to a via-loaded PEC ground plane to a planar patch-type surface and finally to a Mushroom-EBG surface is presented in a novel way. In addition, uniplanar compact-EBG (UC-EBG) properties are also investigated. It is observed that the EBG structures are most robust to different incident angles and polarizations making it a powerful candidate for low profile antenna design solutions. Additionally, the band-gap properties of planar patchtype, Mushroom-EBG and UC-EBG are studied and representative designs are provided.
A dual-band GPS L1/L2 (1.575/1.227 GHz) RHCP antenna is presented for small cylindrical platforms where the antenna must have small size and height. The antenna is a single-layer, dual probe-fed patch with meandered slots and is 4cm 4cm 5.08mm (?/6 ?/6 ?/50 at 1.227 GHz). The antenna was recess mounted on the circumference of various diameter metal cylinders (60-160 mm) and its performance was simulated. For all cylinders, it was found that the antenna has good gain bandwidth performance (1.2-2.7 dBi peak RHCP gain and 25 MHz 3 dB bandwidth) to receive C/A-, P(Y)-, and M-coded GPS satellite signals. Importantly, the antenna does not need to be retuned when placed on different diameter cylinders. Finally, the performance of the antenna is measured when the antenna is mounted on a 117 mm diameter cylinder. The measured performance shows very good agreement with the simulated results.
The increasing complexity and stringent performances in RF instruments and payloads often demands that the final RF functional verification is performed on the integrated satellite. In order to minimize the overall time and cost of future Antenna Integration Verification and Test campaigns (AIV/AIT) it is necessary to investigate and develop advanced test methodologies to minimize the test duration. This paper reports the preliminary results of a functional testing solutions for RF end-to-end antenna testing. The proposed approach is based on the intelligent and innovative use of existing measurement capabilities and advanced numerical modeling tools. The scope of the activity is to demonstrate through the implementation of a demonstrator and measurement on suitable hardware the possibility to achieve accurate and fast measurement results using a radical measurement under-sampling with respect to the conventional Nyquist criteria.
In this paper, a broadband EM wave absorptive structure using a periodic structure is proposed and its reflectivity characteristic examined. Based on the proposed structure, the design technique for improving absorption bandwidth of original structure is additionally proposed. Finally, the method for measuring the reflectivity of the absorber is presented, and the measured results of the absorbers, which show a broadband reflectivity response with a fractional bandwidth of approximately 76% below -10 dB and an increase of 17% of the bandwidth because of the proposed design technique, are presented.
IDS has developed a RCS measurement solution capable to operate both in indoor and outdoor test ranges. The solution is based on the Agilent PNA series of network analyzers, whose performance are enhanced by a dedicated RF front end (named "Pulser"), resulting in a low-cost, compact and flexible system covering the frequency band from 2GHz to 18GHz. At first, the capability of the measurement solution was verified in a near field test range, demonstrating sensitivity compliant with low observable platform requirements (typical values of Noise Equivalent RCS can be in the order of -50 dBsm indoor at 30 m). Recently the RF front end has been upgraded to be usable for outdoor dynamic RCS measurements as well, being the upgraded solution named "Pulser_EV". This paper describes the performance of the Pulser_EV, its application field and possible developments.
We present a test procedure and results that compare RF performance of traditional pyramidal absorber to that with latex coating. Measurements were performed from 5 to 15 GHz, but the same measurement methodology can be applied to other frequency bands. Absorber with protective coating is being used in place of traditional absorber for outdoor antenna measurement facilities to reduce degradation of the absorber performance in harsh environments. Knowledge of the RF performance characteristics of coated absorber is especially necessary when it is used to replace uncoated absorber in an operational antenna measurement facility. Measurements are performed with a simple measurement setup based on a vector network analyzer and broadband horn antennas. Results from bi-static and mono-static measurements are presented.
The focused beam measurement technique has proven to be a solid technique for free space measurement of electromagnetic material properties. This paper presents the use of the focused beam method to measure swept frequency antenna gain as well as antenna patterns. A calibration and signal processing procedure has been developed to properly handle the range of incident waves inherent in the Gaussian beam illumination. One disadvantage of this technique is that the size of the antenna under test is limited by the spot size of the focused beam. However, the GTRI focused beam system uses lenses that are easily reconfigured to realize various spot sizes. The advantage of the focused beam illumination is that the number of measurements and thus measurement time is reduced by roughly an order of magnitude when compared to spherical near-field scanning techniques. More importantly, focused beam systems can be used in a lab environment and do not require large dedicated chambers. We present both model/theory predictions and measured data of how a too-small spot size of the focused beam leads to systematically lower peak gain measurements and wider beam widths.
Over-the-air performance testing of MIMO wireless devices requires the simulation of an RF environment similar to that experienced in the real world. There are a number of standardized spatial channel models that are considered acceptable for evaluating MIMO performance of LTE devices. A number of different methods have been proposed for generating MIMO test environments, but the ability of those methods to reproduce a target wireless channel, and the results they produce, vary. There are several methods for evaluating a spatial channel that are useful validation tools if the goal is to produce a specific known environment. This paper will present the results from several of those for different test cases. In addition, a set of reference device antenna systems have been developed to allow one MIMO radio to be tested with antennas designed for "good", "nominal", and "bad" performance. In this way, the ability of a MIMO test system to provide a relative distinction between different levels of device performance may be assessed. This presentation will show results of this comparison for different system configurations and channel models and provide an indication of the suitability of these systems for evaluating MIMO device performance."
The development of a wideband, high-power capable 18-45 GHz quad-ridge horn antenna for a small towed decoy platform is discussed. Similarity between the system-driven antenna specifications and typical requirements for gain and probe standards in antenna measurements (that is, mechanical rigidity, null-free forward-hemisphere patterns, wide bandwidth, impedance match, polarization purity) is used to assess the quad-ridge horn as an alternative probe antenna to the typical open-ended rectangular waveguide probe for measurements of broadband, broad-beam antennas. Suitability for the spherical near-field measurements is evaluated through the finite element-based full-wave simulations and measurements using the in-house NSI 700S-30 system. Comparison with the near-field measurements using standard rectangular waveguide probes operating in 18-26.5 GHz, 26.5-40 GHz, and 33-50 GHz ranges is used to evaluate the quality of the data obtained (both amplitude and phase) as well as the overall time and labor needed to complete the measurements. It is found that, for AUTs subtending a sufficiently small solid angle of the probe’s field of view, the discussed antenna represents an alternative to typical OEWG probes for 18-45 GHz measurements.
For future NASA Manned Space Exploration of the Moon and Mars, a blunt body capsule, called the Orion Crew Exploration Vehicle (CEV), composed of a Crew Module (CM) and a Service Module (SM), with a parachute decent assembly is planned for reentry back to Earth. A Capsule Parachute Assembly System (CPAS) is being developed for preliminary parachute drop tests at the Yuma Proving Ground (YPG) to simulate high-speed reentry to Earth from beyond Low-Earth-Orbit (LEO) and to provide measurements of landing parameters and parachute loads. The avionics systems on CPAS also provide mission critical firing events to deploy, reef, and release the parachutes in three stages (extraction, drogues, mains) using mortars and pressure cartridge assemblies. In addition, a Mid-Air Delivery System (MDS) is used to separate the capsule from the sled that is used to eject the capsule from the back of the drop plane. Also, high-speed and high-definition cameras in a Video Camera System (VCS) are used to film the drop plane extraction and parachute landing events. To verify Electromagnetic Compatibility (EMC) of the CPAS system from unintentional radiation, Electromagnetic Interference (EMI) measurements are being made inside a semi-anechoic chamber at NASA/JSC at 1m from the electronic components of the CPAS system. In addition, EMI measurements of the integrated CPAS system are being made inside a hanger at YPG. These near-field B-Dot probe measurements on the surface of a parachute simulator (DART) are being extrapolated outward to the 1m standard distance for comparison to the MIL-STD radiated emissions limit.
ABSTRACT When the mechanical requirements are established for a spherical near-field scanner, it is desirable to estimate what effects the expected mechanical errors will have on the determination of the far field of potential antennas that will be measured on the proposed range. The National Institute of Standards and Technology (NIST) has investigated the effects of mechanical errors for a proposed outdoor spherical near-field range to be located at Ft. Huachuca, AZ. This investigation was performed by use of theoretical far-field patterns and introducing position errors into simulated spherical near-field measurements using software developed at NIST. Periodic and random radial and angular position errors were investigated. Far-field patterns were then calculated with and without probe-position correction to determine the effects of mechanical position errors. Periodic errors were found to have a larger effect than random errors. This paper reports the results of these investigations.
Although the square patch antenna is a well known printed circuit antenna, there are gaps in the publications that prevented accurate design for practical dual polarization patch antennas. This paper describes (without gaps) the steps that allow rapid design of the dual polarized square patch antenna with typical commercial RF materials. Given a patch laminate material, the design process proceeds by using the Matlab program which is given in Appendix A. Typical values for a 5 GHz patch antenna are given. Dual polarization square patch antennas were constructed. Measurements show the two ports are well isolated, and they provide polarization diversity which is useful in our MIMO array development program. The scattering matrix of the two port antenna was measured with an Agilent PNA network analyzer. The antenna patterns were measured in our anechoic chamber and on our far field range. The pattern widths provide hemispherical coverage. The results which are given imply good efficiency for the antenna ports. When combined with the other patch elements in the MIMO array, robust communications are achieved for all look angles.