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In wireless communication technology, the growth of 5G and MIMO (multiple- input and multiple-output) systems has revealed a gap in the methods to characterize and calibrate hardware for high frequency and coherent MIMO applications. For coherent array configurations and ad hoc systems we need to measure transmission loss and phase/delay over every element. We demonstrate the use of standard RF hardware to generate and receive multiple signals in a system that is a tabletop analogy for an ad hoc system. The initial test system consists of using a single WR-15 VNA extender to detect two separate modulated signals. As our sources, we individually modulate WR-15 VNA extenders to generate continuous waveform, modulated signals around 60 GHz. On the receive side, our IF signal is first measured with a high-dynamic- range spectrum analyzer and then later collected in a digital oscilloscope. All the signal generators for the receiver LO and transmitter(s) RF IN are tied together with a common 10 MHz reference. Characterizing this initial 2x1 system is then extensible to multiple-receiver applications. We will use these coherent sources to get full complex waveform characterization element-by-element in a receiving array. We report on measurement and calibration methods to characterize the response of these systems for continuous waveforms, modulated signals, and multi-frequency applications needed for next generation coherent MIMO systems.
This contribution presents a universal antenna construction toolkit with slotted waveguide elements that can flexibly combined to form a reconfigurable antenna array capable of providing arbitrary symmetric radiation patterns. The design and the arrangement of radiating elements allow adjusting arbitrary real amplitudes of single radiating elements in a solely mechanical way without any electrical feeding network. Additional modular connecting elements even allow two dimensional and conformal antenna designs with circular and multiple polarizations. With a single toolkit in the Ku-band several design and measurement examples are presented, such as a linear array forming a desired main lobe down to -20dB, and a universal two dimensional antenna array that can switch between vertical, horizontal, LHC and RHC polarization. Given a desired antenna pattern the design procedure allows an automated generation of the physical antenna layout that can mechanically be combined without the need of additional full wave simulations. The waveguide toolkit is easily scalable to any other frequency band just being limited in the upper frequency by manufacturing issues. Another major benefit is that the modular concept of connecting and radiating elements eases the manufacturing where otherwise integral waveguide antennas require much more demanding processes. Different physical realizations of the modular waveguide concept are presented and discussed in the paper and related to the antenna performance. Beside several applications for the universal antenna toolkit, such as investigating illumination issues in scattering theory, educational aspects of teaching group antenna theory are also discussed in this contribution.
Electro-optic (EO) probes provide an ultra-wideband, high-resolution, non-invasive technique for polarimetric near-field scanning of antennas and phased arrays. Unlike conventional near field scanning systems which typically involve metallic components, the small footprint all-dielectric EO probes can get extremely close to an RF device under test (DUT) without perturbing its fields. In this paper, we discuss and present measurement results for EO field mapping of a dual-band circularly polarized active phased array that operates at two different S and C bands: 2.1GHz and 4.8GHz. The array uses probe-fed, cross-shaped, patch antenna elements at the S-band and dual-slot-fed rectangular patch elements at the C-band. At each frequency band, the array works both as transmitting and receiving antennas. The antenna elements have been configured as scalable array tiles that are arranged together to create larger apertures. Near-field scan maps and far-field radiation patterns of the dual-band active phased array will be presented at the bore sight and at different scan angles and the results will be validated with simulation data and measurement results from an anechoic chamber.
Current and future beam-steerable phased array antennas require broadband frequency range, multiple-beam operation and fast switching speeds. Near-field antenna testing is an efficient tool to rapidly and securely test antenna array performance, but many of the features of current and next-generation electronically steerable antennas require advances in near-field techniques so as to fully characterize and optimize advanced antenna arrays. For example, system requirements often dictate broadband frequency operation, which presents challenges in terms of probe antenna choices and probe-to-test antenna distances to properly characterize and optimize test antennas with a minimal number of scans and thus satisfy stringent customer requirements in a cost- and time-effective manner. Raytheon is developing near-field antenna test measurement techniques tailored to measure the radiation patterns of multiple beams over wide frequency ranges, to expand the range of test data collected for antenna optimization and customer review. Key test design considerations faced in developing advanced near field characterization techniques will be presented. Custom software to integrate antenna control with the near field measurement system is necessary to provide enhanced capability of characterizing multiple beams. Specialized data processing and analysis tools are needed to process thousands of datasets collected from a single scan, in a timely manner.
In the late 1990’s, Maloney et al. began investigating the design of highly pixelated apertures whose physical shape and size are optimized using genetic algorithms (GA) and full-wave computational electromagnetic simulation tools (i.e. FDTD) to best meet the required antenna performance specification; i.e. gain, bandwidth, polarization, pattern, etc. [1-3]. Visual inspection of the optimal designs showed that the metallic pixels formed many connected and disconnected fragments. Hence, they coined the term Fragmented Aperture Antennas for this new class of antennas. A detailed description of the Georgia Tech design approach is disclosed in [4]. Since then, other research groups have been successfully designing fragmented aperture antennas for other applications, see [5-6] for two examples. However, the original fragmented design approach suffers from two major deficiencies. First, the placement of pixels on a generalized, rectilinear grid leads to the problem of diagonal touching. That is, pixels that touch diagonally lead to poor measurement/model agreement. Other research groups are also grappling with this diagonal touching issue [7]. Second, the convergence in the GA stage of the design process is poor for high pixel count apertures (>>100). This paper will present solutions to both of these shortcomings. First, alternate approaches to the discretization of the aperture area that inherently avoid diagonal touching will be presented. Second, an improvement to the usual GA mutation step that improves convergence for large pixel count fragmented aperture designs will be presented. Over the last few years, the authors have been involved with developing the use of the focused beam measurement system to measure antenna properties such as gain and pattern [8]. A series of improved, fragmented aperture antenna designs will be measured with the Compass Tech Focused Beam System and compared with the design predictions to validate the designs. References: [1] J. G. Maloney, M. P. Kesler, P. H. Harms, T. L. Fountain and G. S. Smith, “The fragmented aperture antenna: FDTD analysis and measurement”, Proc. ICAP/JINA Conf. Antennas and Propagation, 2000, pg. 93. [2] J. G. Maloney, M. P. Kesler, L. M. Lust, L. N. Pringle, T. L. Fountain, and P. H. Harms, “Switched Fragmented Aperture Antennas”, in Proc. 2000 IEEE Antennas and Propagations Symposium, Salt Lake City, 2000, pp. 310-313. [3] P. Friederich, L. Pringle, L. Fountain, P. Harms, D. Denison, E. Kuster, S. Blalock, G. Smith, J. Maloney and M. Kesler, “A new class of broadband planar apertures,” Proc. 2001 Antenna Applications Symp, Sep 19, 2001, pp. 561-587. [4] J. G. Maloney, M. P. Kesler, P. H. Harms and G. S. Smith, “Fragmented aperture antennas and broadband antenna ground planes,” U. S. Patent # 6323809, Nov 27, 2001. [5] N. Herscovici, J. Ginn, T. Donisi, B. Tomasic, “A fragmented aperture-coupled microstrip antenna,” Proc. 2008 Antennas and Propagation Symp, July 2008, pp. 1-4. [6] B. Thors, H. Steyskal, H. Holter, “Broad-band fragmented aperture phased array element design using genetic algorithms,” IEEE Trans. Antennas Propagation, Vol. 53.10, 2005, pp. 3280-3287. [7] A. Ellgardt, P. Persson, “Characteristics of a broad-band wide-scan fragmented aperture phased array antenna”, EuCAP 2006, Nov 2006, pp. 1-5. [8] J. Maloney, J. Fraley, M. Habib, J. Schultz, K. C. Maloney, “Focused Beam Measurement of Antenna Gain Patterns”, AMTA, 2012
The smart plasma antenna based on opening and closing antenna windows to create antenna beam steering. It can steer 360 degrees in the azimuthal direction and 180 degrees in the z direction. The smart plasma antenna RFID reader can scan and read both passive and active RFID tags. Furthermore the smart plasma antenna is very compact compared to a phased array because plasma physics is used to steer and shape the antenna beam. The smart plasma antenna can easily fit in a small room where tags are to be read. It meets most SWaP criteria. The smart plasma antenna can have an omnidirectional metal antenna along the central axis such as a dipole or biconical antenna and is surrounded by a cylindrical ring of plasma tubes to shape and steer the antenna beam. The diameter of the smart plasma antenna is approximately one wavelength. When one of the plasma tubes has the plasma extinguished, it creates an aperture for the antenna beam. This is an open plasma window. The other plasma tubes are on with the plasma not extinguished. These plasma tubes with closed plasma windows protect the inside antenna from EMI. EMI is reflected from the closed plasma windows of the smart plasma antenna if the plasma density is high enough so that the plasma frequency is greater than the frequencies of the external EMI. The plasma frequency is proportional to the square root of the unbound electrons and is a measure of the amount of ionization of the plasma. If the inside antenna is a plasma antenna then not only is the beamwidth reconfigurable but the bandwidth is reconfigurable with a reconfigurable center line frequency. The reconfigurable bandwidth is equal to the difference in plasma frequencies from the inside plasma antenna and the plasma frequency of the outside cylindrical ring of plasma tubes. Thus by reconfiguring the relative plasma densities of the inside plasma antenna and the outside ring of plasma tubes, the bandwidth and centerline frequencies get reconfigured. This is useful in an RFID reading when some tags need to be read and others ignored through reconfigurable frequency filtering.
The design of active electronically steered arrays (AESA) is a challenging, time-consuming and costly endeavor. The design process becomes much more sophisticated in the case of dual-band circularly polarized active phased arrays, in which CP radiating elements at two different frequency bands occupy a common shared aperture. A design process that takes into account various inter-element and intra-element coupling effects at different frequency bands currently relies solely on computer simulations. The conventional near-field scanning systems have serious limitations for quantifying these coupling effects mainly due to the invasive nature of their metallic probes, which indeed act as receiving antennas and have to be placed far enough from the antenna under test (AUT) to avoid perturbing the latter’s near fields. In recent years, a unique, versatile, near-field mapping/scanning technique has been introduced that circumvents most of such measurement limitations thanks to the non-invasive nature of the optical probes. This technique uses the linear Pockels effect in certain electro-optic crystals to modulate the polarization state of a propagating optical beam with the RF electric field penetrating and present inside the crystal. In this paper, we will present near-field and far-field measurement data for a dual-band circularly polarized active phased array that operates at two different S and C bands: 2.1GHz and 4.8GHz. The array uses probe-fed, cross-shaped, patch antenna elements at the S-band and dual-slot-fed rectangular patch elements at the C-band. At each frequency band, the array works both as transmitting and receiving antennas. The antenna elements have been configured as scalable array tiles that are patched together to create larger apertures.
Calibrating a passive, space-fed, phased array antenna is more difficult and time consuming then calibrating corporate-fed arrays because individual elements cannot be activated or deactivated. We will present our method of determining element state-phase curves and insertion phase bias between elements. We will also explain this method’s theoretical basis and validate it by comparing data measured in an anechoic chamber with data measured in a planar near field range. The anechoic chamber data will be compared with the typical, proven, but more time-consuming planar near field calibration method.
The cost of quality is critical to all industrial processes including microwave device production. Microwave device production is often labor intensive and subject to many production defects. Early detection of these defects can markedly improve production quality and reduce cost. A novel approach to industrial defect detection has been demonstrated using a random noise radar (RNR), coupled with Radio Frequency Distinctive Native Attributes (RF-DNA) fingerprinting processing algorithms to non-destructively interrogate microwave devices. The RNR is uniquely suitable since it uses an Ultra Wideband (UWB) noise waveform as an active interrogation method that will not cause damage to sensitive microwave components and multiple RNRs can operate simultaneously in close proximity, allowing for significant parallelization of defect detection systems. The ability to classify defective microwave antennas and phased array elements (prior to RF system assembly) has been successfully demonstrated and presented at the 36th AMTA symposium. This paper expands on the prior research by focusing on the effects of altering interrogation signal characteristics to include operational bandwidth and signal frequency while actively interrogating similar antennas using an UWB noise signal. The focus of the experimental variation was to optimize classifier performance since unique device characteristics will be excited by various interrogation signal traits that can be exploited by the fingerprint generation and classifier algorithms. Experimentation with several typical UWB antennas and a phased array antenna is demonstrated. The effects of signal bandwidth on classifier performance on simulated fault conditions was performed using various antenna terminations and attenuators. Interrogation of the phased array was demonstrated using the array “backend” for signal down-conversion enabling a quick quality check control method with a simple back-end connection. The ability to wirelessly discriminate multiple fault conditions on individual phased array elements and discern phased array operational range of motion, both in pristine and heavy RFI environments is also shown. This method ensures that each produced phased array meets quality and operational requirements.
Active S-parameters represent reflection coefficients of elements in an active phased array antenna under various element excitations. Active S-parameters can be calculated for any array excitation if the S-parameter matrix is fully characterized. In practice, the entries of this matrix can usually be gathered through measurements with a 2-port vector network analyzer (VNA). However, depending on the number of elements in the phased array, the number of measurements can be extremely large in order to obtain a full S-matrix. For a phased array consisting of N elements, N(N-1)/2 measurements with a 2-port VNA are required to obtain N-by-N S-matrix, assuming the antenna elements are reciprocal. In order to avoid large number of measurements, a scenario consisting of S-parameter measurements for the center element and also some elements located at the edges and corners of the array is proposed under a flexible predefined error criterion. Then, measured S-parameters are used to obtain N-by-N S-matrix via exploitation of the array symmetry and periodicity which is required to calculate the active S-parameters of the whole array. A fabricated uniform planar Vivaldi array with 112 elements is measured with the proposed scenario and calculated active S-parameters are compared with those obtained from full-wave analysis.
In military applications, where low sidelobes and high precision in beam pointing are vital, a phased array antenna beamformer requires to be calibrated regarding the cabling that connects the beamformer to the antenna and mutual coupling between antenna elements. To avoid problems associated with mismatched phase transmission lines between the beamformer and the antenna and include the coupling effects, beamforming network characterization must be done with the antenna integrated to the beamformer. In this paper, a method to characterize the beamformer of a slotted waveguide array antenna in the antenna measurement range is introduced. The antenna is a travelling wave slotted waveguide array scanning in the elevation plane. The elevation pattern of the antenna is a shaped beam realized by a phase-only beamformer. The calibration channel includes serial cross-guide couplers fed by a single waveguide line. The channel is integrated to the waveguide lines of the antenna. In the first phase of the characterization, the far field pattern of each antenna element is obtained from the near field measurements at the “zero” states of the phase shifters. In the second stage, all states of the phase shifters are measured automatically using the calibration channel described above. The results of calibration channel measurements are used to determine the changes in phase and magnitude for different states of phase shifters. The phase and magnitude of the peak point of the far field pattern is referenced to the zero state measurement of the calibration channel. Phase only pattern synthesis is carried out using the results of both zero-state near field and calibration channel measurements and the required phase shifter states are determined accordingly. Measured patterns show good agreement with the theoretical patterns obtained in the synthesis phase.
Experimental measurement plays a key role for technology maturation in an R&D environment. In this paper we highlight the versatility of a new compact range at the Air Force Research Laboratory (AFRL), Sensors Directorate. In its first year of operation, the OneRY Range supported a wide variety of projects ranging from electrically small antennas to 20’ structures, spanning frequencies of 400 MHz to 45 GHz, and involving applications covering land, airborne, and space-based platforms. Here we present measured results from three different antenna development efforts for the Air Force. The first effort involves a UHF meta-material inspired antenna developed for an airborne application. In addition to successfully demonstrating relatively low frequency capability for a compact range, this effort met the challenge to measure antenna patterns from a physically large target. Results from OneRY are compared to those collected from a tapered chamber. Next we show experimental measurement of digital beam forming (DBF) in a large conformal phased array antenna operating at L and S bands. The DBF experimental testing is part of a follow-on effort to an Advance Technology Demonstration conformal array supporting satellite tracking, telemetry and command (TT&C). Finally, we present results from a “quick look” investigation into the operability of a COTS antenna system matched to a third party radome. The project supports airborne satellite communications at K, Ka, and Q bands. Performance of a high frequency extension (18-50 GHz) to the compact range is examined to include an inter-range comparison to planar near-field measurements. A description of the OneRY Indoor Range is also provided.
Abstract- Quality control is critical for all industrial processes, but often times defect detection is labor intensive. A novel approach to industrial defect detection is to use a random noise radar (RNR), coupled with Radio Frequency "Distinctive Native Attributes (RF-DNA)" fingerprinting processing algorithms to non-destructively interrogate microwave devices and classify defective units from properly functioning units. Example applications include assembly line inspection of automotive collision avoidance systems, wireless or cellular antenna defect detection during manufacture, and phased array element defect detection prior to RF system assembly. The RNR is uniquely suitable since it uses an Ultra Wideband noise waveform as an active interrogation method that will not cause destructive damage to microwave components. Additionally, it has been demonstrated that multiple RNRs can operate simultaneously in close proximity, allowing for significant parallelization of defect detection systems resulting in increased process throughput. Using this method, 100% sampling for quality control may be attainable in many cases. RF-DNA has previously demonstrated “serial number” discrimination of Orthogonal Frequency Division Multiplexed (OFDM), Direct Sequence Spread Spectrum (DSSS) network signals, GSM, WiMAX signals and others with classification accuracies above 80% using Multiple Discriminant Analysis and Generalized Relevance Learning Vector Quantification classification algorithms. Those cases all involved discrimination of passive emissions. This approach proposes to couple the classification successes of the RF-DNA fingerprinting with a non-destructive active interrogation waveform.
Abstract—Mutual coupling is a major issue in phased array antennas, especially when steering the beam to low angles, causing bandwidth and gain reduction. Such coupling arises from the presence of adjacent elements that produce scattering and absorption effects during low-angle beam steering. The scattering effect comprises of structure-mode scattering and antenna-mode scattering. The absorption effect happens when the EM energy received by an adjacent element is dissipated into the system. In addition, lattice scattering from the periodic structures of antenna elements and feed lines in phased arrays also produces undesired scattering modes that limit the frequency upper bound and maximum scan angles.
This paper will discuss a highly customizable and integrated waveform generator (WFG) subsystem used to coordinate the phased array test process. The WFG subsystem is an automated digital pattern generator that orchestrates the command and triggering interface between the NSI measurement system and a phased array beam steering computer. The WFG subsystem is controlled directly by the NSI 2000 software and allows the test designer to select and generate a sequence of up to sixteen unique synchronized timing waveforms. Test scenarios, results and data for the WFG subsystem will be presented along with plots showing the key timing characteristics of the system.
More complex antennas with higher transmit power levels are being tested in compact range environments. AESA's and other phased array antennas can transmit significant power levels from a relatively small volume. Without consideration of the impact of the transmitted power levels for a given test article, human and facility safety could be at risk. This paper addresses designing a test chamber in light of these power handling considerations for high power antennas on two fronts: 1) A methodology is presented to determine the power levels seen by surfaces in the chamber that are covered with absorber material and 2) Calculating the power levels seen at the compact range feed due to the focusing effect of the compact range itself. A test case is presented to show the application of the methods.
NOVEL PHASED ARRAY SCANNING EMPLOYING A SINGLE FEED WITHOUT USING INDIVIDUAL PHASE SHIFTERS Dipole Elements Reconfigurable transmission line Signal Transmission_line.bmpField mostly in air, so low ........ Field mostly in dielectric, so high ........ .... .... Nicholas K. Host, Chi-Chih Chen, and John L. Volakis Varied t .375mm Air Gap, g er=25
The Air Force Research Laboratory (AFRL), Information Directorate, has served as an Air Force center for antenna measurements for over thirty years. AFRL's Newport Research Facility consists of multiple far field outdoor test ranges with 3-axis positioner towers. The range supports a wide variety of test activities including measurements on simple antennas, complex active phased arrays, avionics, communications and electronic countermeasure systems. The trend towards increasingly complex antenna systems led to a requirement for a faster, more adaptable data acquisition system. To support the changing test requirements, AFRL developed a multi-port 16-RF-switch controller as part of our data acquisition system. In a typical antenna test at Newport, multiple aircraft antennas are multiplexed into a single RF output through a programmable matrix of solid state RF switches. The switch controller is installed inside the aircraft under test which is mounted on a 3-axis positioner. We can then configure and reconfigure each aircraft for a variety of antenna tests at Newport.
In addition to steady state performance, antennas also have transient responses that need to be characterized. As antennas become more complex, such as active phased arrays, the transient responses of the antennas also become more complex. Transient responses are a function of internal antenna interactions such as coupling and VSWR, active circuitry, and components such as phase shifters and attenuators. This paper will show techniques for measuring antenna transient responses. The first measurements utilize standard instrumentation capable of sampling at up to 4 MHz, giving 250 nS time resolution of the transient effect. Recognizing that some transient measurements require finer time resolution, a higher sampling rate prototype receiver was developed with 1 nS time resolution. After verification of its performance, the prototype receiver was used to measure the transient effects of a 50 nS pulse through a broadband antenna. The spectrum of the pulse yields information on the time and frequency domain responses of the antenna. Phased arrays may exhibit transient signals when switching between beam directions as well as switching between frequencies. The methods presented in this paper are applicable to both.
A spherical array designed for hemispherical coverage of satellite communications at S-band that is approximated by hexagonal and pentagonal planar panels. Ball Aerospace built a segment of a 10m diameter spherical array that has one center pentagonal panel and five surrounding hexagonal panels. This paper describes our efforts at testing one large hexagonal panel in a compact range.