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Although In the 1970’s and 1980’s the near-field technology was proven to work properly for antenna characterization. It was until the late 1990’s that antenna communities begun to trust this technology and depend heavily on it. This same scenario could happen to the phase-less near-field technologies. It is true that there is still much to be done in the sense of reliability of these techniques. Nevertheless there are still situations where these techniques must be applied. This paper will be dealing with the phase-less near-field antenna measurement technique. The well-known iterative Fourier transformation (IFT) technique is used. The amplitude of the field distribution on concentric spheres surrounding the antenna under test (AUT) is used to reconstruct the phase information necessary for the spherical near-field to far-field transformation (SNFFF). It will be shown that despite its geometrical and computational complexity this technique can be applied on the spherical case achieving very good accuracy. In addition this paper makes use of global optimization techniques especially genetic algorithm (GA) to establish an initial estimate of the phase distribution necessary for the algorithm which is later on fine-tuned using the local optimization i.e. IFT to retrieve a closer estimate of the solution. It will be shown that except for the null positions the far-field accuracy can be enhanced. The implementation of the GA will be shortly given and the concept of masks, which simplifies the implementation, will be discussed.
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.
This paper describes an mm-wave extrapolation range installed at KRISS, which may be used for testing standard gain antennas by using the three-antenna extrapolation technique in the frequency range from 110 GHz to 325 GHz. It consists of a precision linear slide and an mm-wave S-parameters measurement system. The precision linear slide for changing the separation distance between transmitting and receiving antennas is realized with a linear motor with 1.6 meter long on a precision stone surface plate. The mm-wave measurement system for measuring S-parameters at extrapolation antenna measurements consists of a 67 GHz vector network analyzer used as a main frame and three frequency extenders which are operating at three frequency bands (D-band (110 -170 GHz), G-band (140-220 GHz) and J-band (220-325 GHz)). The S-parameters measurement system is calibrated with TRL/LRL method. The general procedure of the extrapolation technique is as follows; 1) The effect of multiple reflections between transmitting and receiving antennas is removed from data measured at a reduced distance. 2) A polynomial is determined for curve-fitting the data removed the effect of multiple reflections. 3) Finally, far-field antenna properties are calculated from the polynomial. In this paper, a method using measured S-parameters for reducing multiple reflections between transmitting and receiving antennas is used. Power gain of D-band standard gain horn antennas is measured with the mm-wave extrapolation range. Description of detailed measurement system and measurement result will be presented at the symposium.
One of the most useful metrics for a wireless device is Total Radiated Power, or TRP as it is commonly abbreviated. The total radiated power of a wireless device is determined by measuring the radiated power at a number of sample points (typically 264) over a spherical surface surrounding the device under test and integrating the results to get the total power radiated by the device. A measurement of a single channel typically takes between one and two minutes. This paper presents a method of measuring TRP with only a single data point measurement which can be made in less than one second. This method uses a conductive ellipsoid surface. The device under test is placed at one focal point and the measurement antenna is placed at the other. The surface of the ellipsoid performs the integration of the radiated power and only a single measurement is needed to determine the total radiated power. A proof of concept model was built and measurements made on both active and passive devices. These same devices were then measured in a classical anechoic over-the-air (OTA) chamber and the results compared. The comparison of the two measurement methods, although not perfect, is encouraging and supports a conclusion that this is a viable technique for quickly determining the total radiated power of a wireless device. The method can be expanded to measure the Total Isotropic Sensitivity (TIS) of a wireless device. Although not as fast as a TRP measurement, the sensitivity measurement is still many times faster than the same measurement in an anechoic chamber. The design of the proof of concept model is presented along with the data taken both in the ellipsoid and in the anechoic chamber.
Precise determination of antenna phase centers is crucial to reduce the uncertainty in gain when employing the three-antenna method, particularly operated over a short range-such as a 3-m radio anechoic chamber, where the distance between the phase centers and the open ends of an aperture antenna (the most commonly-used reference) is not negligible, compared with the propagation distance. An automatic system to determine the phase centers of aperture antennas in a radio anechoic chamber has been developed and the absolute gain of horn antennas have been thereby evaluated with the three-antenna method. The phase center of an X-band horn was found to migrate up to 55 mm from the open end. Uncertainties in the gain were evaluated in accordance with ISO/IEC Guide 93-3: 2008. The 95% confidence interval of the horn antenna gain was reduced from 0.39 to 0.25 dB, when using the phase center location instead of the open end. Then the gains, polarization, and radiation pattern of space-borne antennas were measured: low-, medium-, and high-gain X-band antennas for an ultra small deep space probe employing the polarization pattern method with use of the horn antenna. Comparison between the radiation properties with and without the effect of spacecraft bus was carried out for low-gain antennas. The 95% confidence interval in the antenna gain decreased from 0.60 to 0.39 dB.
The automotive industry is changing rapidly through the evolution of on board and embedded components and systems. Many of these systems rely on the over the air performance of a communication link and the evaluation of these links is a key requirement in understanding both the real world performance, and associated operating limits of a particular system. The operating frequency range of the installed communication systems now extends from the traditional AM bands from 540KHz to almost 6GHz for WiFi. There are several different antenna design options available to cover this range and in many cases, the performance of an antenna when installed on a vehicle differs from a measurement of the same antenna in isolation. There is also a growing use of high frequency RADAR systems operating at frequencies approaching 80GHz that also need to be included in the performance analysis. The behavior of the individual components using conducted methods for example, is an important step but the direct measurement of antenna pattern and data throughput under ideal steady state and also varying spatial and operating conditions is likely to be the most robust method of channel evaluation. There is a steady march toward vehicle autonomy that is pushing the development of increasingly complex and sophisticated sensors, receivers, transmitters and firmware, all installed on an already well populated platform. The interoperability and EMC performance of these embedded systems is an extension to the need for a fundamental understanding of performance. This paper will present some of the available measurement and evaluation options that could be used as part of an integrated test environment which takes advantages of a number of established techniques.
RCS and Antenna measurement accuracy critically depends on the quality of the incident field. Both compact and far field ranges can suffer from a variety of contaminating factors including phenomena such as atmospheric perturbation, clutter, multi-path, as well as Radio Frequency Interference (RFI). Each of these can play a role in distorting the incident field from the ideal plane wave necessary for an accurate measurement. Methods exist to mitigate or at least estimate the measurement uncertainty caused by these effects. However, many of these methods rely on knowledge of the incident field amplitude and phase over the test region. Traditionally the incident field quality is measured directly using an electromagnetic probe antenna which is scanned through the test region. Alternately, a scattering object such as a sphere or corner reflector is used and the scattered field measured as the object is moved through the field. In both cases the probe/scatterer must be mounted on a structure to move and report the position in the field. This support structure itself acts as a moving clutter source that perturbs the incident field being measured. Researchers at the Air Force Institute of Technology (AFIT) have recently investigated a concept that aims to eliminate this clutter source entirely. The idea is to leverage the advances in drone technology to create a free flying field probe that doesn’t require any support structure. We explore this concept in our paper, detailing the design, hardware, and software developments required to perform a concept demonstration measurement in AFIT’s RCS measurement facility. Measured data from several characterization tests will be presented to validate the method. The analysis will include an estimate of the applicability of the technique to a large outdoor RCS measurement facility.
Direction Finding (DF) Antennas are usually designed and tested in controlled environments. However, antenna far field response may change significantly in its operational environment. In such perturbing or not -controlled close context, the antennas calibration validity becomes a major issue which can lead to DF performance degradation and to a costly re-calibration process. Even if in-situ re-calibration is still complicated; the DF antenna response can be monitored, during the mission, in order to ensure the DOA accuracy. This paper presents an innovative design and the performance of a low-disturbing solution to detect the near field antenna response deviations from a nominal case. The proposed system is based on an array of transmitting miniature dipoles deployed all around the DF antennas. These probes are optically fed through a non-biased photodiode that carries the direct conversion into a RF signal at the desired frequency. The detection re-used the DF receiving RF chains to analyze any deviation (complex values) of the antennas array manifold. Compared to the Optically Modulated Scatterer (OMS) technique, the benefits of the proposed approach are demonstrated experimentally over a frequency decade (UHF band). First a better sensitivity is shown (higher than 80 dB on the monitored link), and secondly the phase detection is made really simple compared to the OMS technique. Finally, a relation between this in-situ diagnosis mode and the DF angular direction accuracy is established. Thus the capacity to detect, on the near field response, the presence of various types of closed obstacles (open trap on the carrier, additional antenna…) which perturb significantly the far field antenna response, is evaluated.
The radiated efficiency is a key performance indicator for multi-standards frequency agile electrically small antennas (ESA) that are mounted on wireless IoT sensors. One of the techniques to estimate it, consists to integrate, over all the angular directions, the gain measured in the far field condition. The gain-comparison method is usually implemented in the CEA LETI testbench ; which requires an accurate knowledge of the standard horn gain. The introduction of a new RF-optical link to remove coaxial cable perturbation on ESA radiation, in our test bench has raised the opportunity to proceed to an error budget analysis. This paper delivers the main results of this study where the impact of several parameters such as the optical fiber movement, the horn position, the received power level, chamber imperfection… have been evaluated. We have carried on the three antennas method (one Vivaldi and two TEM standard horns) to estimate the complex transfer function of the three antennas. The overall goal is to estimate the detailed uncertainty analysis of the ESA efficiency measurement over a large band of frequencies. This work aims to identify the most impacting effects on uncertainty and to initiate the discussion with the AMTA community how to decrease them.
As a result of recent technical and regulatory developments, the millimeter wave frequency band (30GHz – 300 GHz) is being adopted for wide range of applications. Based on array signal processing technologies used for 4G and MIMO, companies are developing small active array antennas operating throughout the millimeter-wave bands. These arrays may include radiating elements and feed structures that are fraction of a millimeter in size and cannot be fed via a coaxial cable. Connection to the antenna is instead performed through a micro-probe more commonly used in the chip industry. MVG-Orbit/FR has developed a compact antenna measurement system which integrates hardware and software necessary to provide antenna gain and radiation patterns of antennas fed with such a micro-probe. To evaluate uncertainties in the measurements of the Antenna Under Test (AUT) gain, directivity, efficiency, pattern, or VSWR, reference antennas are an invaluable tool. The authors have recently driven the development of a micro-probed chip reference antenna. This reference antenna was designed to be mechanically and electrically stable and with reduced sensitive to its mounting fixture and feeding method. Close agreement between measured and simulated characteristics has been achieved. With low losses, the antenna provides good dynamic range and confidence in the measured antenna efficiency and gain. Without chip antenna gain standards, a micro-probed antenna test system requires the use of the insertion loss method for gain calibration. This method requires correction for additional losses such as cables, attenuators, or adaptors that are included in the calibration but not in the subsequent measurement of the AUT. In addition, the micro-probe (which is in the measurement but not in the calibration) should be calibrated and de-embedded from the measurement. Each of these measurements and associated connections and related processing, increases uncertainty and chance of mistakes by the user. It is therefore essential to validate the calibration using a well characterized reference antenna. This paper will outline design requirements and present test results of 60 GHz Chip Reference antennas. Several dozen antennas have been tested. The related uncertainties in the micro-probed antenna measurements will be evaluated with particular emphasis on the gain calibration uncertainty. The paper will also describe the next steps towards developing a chip antenna gain standard, that should reduce gain uncertainties while also significantly simplifying the calibration process.
A guided-wave setup has been introduced for evaluating the high-power capability of the pyramidal absorbers. The details of the setup has been explained and its pros and cons has been noted. The major benefit of the proposed setup compared to the ones found in the literature is its need for lower amount of power when a pyramidal absorber is to be illuminated by a specific power density. That means, the high-power tests done using the proposed setup are cheaper compared to the tests performed with the setups formerly proposed in the literature.
A specific set-up for probe-fed antenna with an articulated arm has been developed by NSI with a 500mm AUT-probe distance. This paper will give an example of far-field measurement and highlight its limitations. A near field approach to filter the probe effect is investigated. First measurement results, including amplitude and phase, will be presented. Phase data will be leveraged to develop post-processing technique to filter probe and environmental effect.
For a compact antenna test range (CATR) there exists a low frequency limit as to difficultly achieve an acceptable planar characteristic of the field in the test zone. In this paper some techniques are recommended to improve the low frequency performance, including in the serration ratio, the location of the quiet zone and the focal ratio. And the mirror reflection bouncing from the ground usually disturbs the quiet zone especially at the low frequencies, which can be reduced by the optimized layout of the absorber. As a successful example, a dimension of 5.5 m ´ 5.5 m parabolic reflector (about 16 wave lengths at 0.9 GHz) is designed and manufactured in the year of 2012. The quiet-zone quality is measured to verify the consideration for the optimized design process. The measured maximum peak-to-peak variations are 1.3 dB (amplitude) and 10.4° (phase) over the 2.0 m quiet zone at 0.9 GHz.
Recently, the Rapid Scatterometer (RapidScat) instrument was developed to sense ocean winds while being housed onboard the International Space Station (ISS). This latest addition to the ISS, launched and mounted in September 2014, significantly improves the detection and sensing capabilities of the current satellite constellation. The dual-beam Ku-band reflector antenna autonomously rotates at 18 rpm and acquires scientific data over a circular scan during typical ISS operations. Mounting such an antenna on the ISS, however, gives rise to many engineering challenges. An important consideration for any antenna onboard the ISS is the interference generated towards nearby ISS systems, space vehicles and humans due to the possible exposure to high RF power. To avoid this issue, this work aimed to characterize the antenna's absolute near-field distribution, whose knowledge was required for a blanker circuit design to shut off the RF power for certain time slots during the scan period. Computation of these absolute near-fields is not a straightforward task and can require extensive computational resources. The initial computation of those fields was done using GRASP; however, an independent validation of the GRASP results was necessary because of safety concerns. A customized plane wave spectrum back projection method was developed to recover the absolute electric field magnitudes from the knowledge of the measured far-field patterns. The customized technique exploits the rapid computation of the Fast Fourier Transform alongside the proper normalization. The procedure starts by scaling the normalized (measured or simulated) far-field patterns appropriately to manifest the desired total radiated power. This was followed by transforming the vectors into the desired rectangular coordinate system and interpolating those components onto a regularized spectral grid. The FFT of the resulting Plane Wave spectrum was properly scaled using the sampling lengths to determine the absolute near-field distributions. The procedure was initially validated by comparing the results with analytical aperture distributions with known far-field patterns. The properly normalized PWS approach was subsequently applied to the RapidScat Antenna using measured patterns from JPL’s cylindrical near-field range. The resulting near-fields compare quite well between the plane wave spectrum technique and GRASP, thus validating the calculations. This work provided significant enabling guidelines for the safe operation of the ISS-RapidScat instrument.
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.
This paper summarizes the design, fabrication and characterization of a coplanar waveguide fed modified aperture bowtie antenna operating in the 60 to 90 GHz range. Modifications to the bowtie edges extend the bandwidth up to 40% without increasing radiator area. The antenna was initially designed and measured in the 3-8 GHz frequency band and then frequency scaled to 60-90 GHz. The millimeter wave antenna is implemented on FR408 (er=3.65) and a multilayer laminate. Both substrates can be used in millimeter-wave system design where efficient antennas are needed. Return loss measurements of the antennas are made on a Cascade probe station. The results agree well with simulations in ANSYS HFSS. Until recently, only simulated radiation patterns were available illustrating broadside gain of 5 to 7 dB for these antennas. With the acquisition of a spherical scanner, near-field measurements have been taken of the three antennas from 67 to 110 GHz. The broadside radiation pattern results are compared with simulation. The NSI 700S-360 spherical near-field measurement system used in conjunction with an Agilent network analyzer, GGB Picoprobes and Cascade manipulator allow for on-wafer measurements of the antenna under test.
For high speed digital data connection such as WiMAX or WLAN, a good signal to noise ratio (S/N) is required. One way to keep up a good S/N-value while moving is the use of high gain antennas with a directive antenna beam. However, there is insufficient room to place high gain antennas in a vehicle. On top if this, it is becoming increasingly difficult and more packed in the car, so that progressive antenna approaches are enforced. As a vehicle can move towards and away from the transmitter site in any azimuth angle, the antenna shall offer some omni-directionality. In this paper, an antenna for 2.45 GHz WLAN is described which is very thin of 4 mm, offers 12 dBi antenna gain with almost omni-directional but very beneficial radiation characteristics with “rabbit-ear” shaped double-lobes. The flat antenna is easily implemented into the plastic spoiler on a hatchback vehicle. Experiments proof that this flat WLAN antenna structure in a spoiler outperforms monopoles and patch antennas on rooftop in any respect. When tuning to the right frequency, this antenna is ideally suited for Car2X-applications and Wireless Internet utilization such as WiMAX and WLAN.
On-chip antennas operating at mm-wave frequencies have led to the development of spherical near-field test systems that allow the antenna to remain stationary [1]. These test systems, although simple conceptually, introduce very unique and challenging mechanical constraints. The approach taken by NSI is to construct a dual rotary stage articulating arm [2] design that moves the near-field probe on a spherical surface around the antenna. This structure experiences the gravitational force as a function of location angles theta & phi, resulting in structural deformation which is therefore variable. This further introduces radial distance variation of the probe. The unintended effect is therefore to introduce cross-coupling between the spherical near-field (SNF) position variables and this in turn perturbs the ideal spherical surface that is assumed. In this paper we describe the structural perturbation observed on such a scanner and assess to what extent this limits high frequency application for SNF testing. We also describe techniques to correct for radial distance variation and show how this extends the upper frequency limit of the system for SNF applications. We will present structural data acquired using a laser tracker and show to what extent these results differ for the two orthogonal spheres. It will be shown how angular positioning can be corrected for using a real-time controller. Measured RF results will be presented for the case of no radial distance correction and it will be shown how this can be addressed through post processing. An assessment of the suitability of the system for mm-wave testing will also be presented.
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.