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In Compact Antenna Test Range (CATR) applications, better cross polar discrimination is often the main motivation for choosing the more complex and expensive compensated dual reflector system as opposed to the simpler and cheaper single reflector system. Other than reflector geometry adjustment, different options have been presented in the literature to improve the cross polar performance of the single reflector CATR [1-4]. One solution is the insertion of a polarization selective grid between the feed and the reflector. The shape of the grids curved strip geometry is determined from the geometry of the reflector and each polarization has a different shape. This approach has been demonstrated to provide Quit Zone (QZ) cross polar performances similar to the dual reflector system on a decade bandwidth. The drawback of this solution is that orthogonal polarizations components cannot be measured simultaneously since a different polarizer grid is required for each polarization [1-2]. Other techniques aim at improving both amplitude/phase taper and cross polarization are based on measurement post processing. Processing techniques have been proposed based on numerical modelling of the range [3] or by de-convoluting the measured pattern with a predetermined range response based on QZ probing [4]. The drawback of these methods are the finite accuracy of the post processing, increased measurement complexity and the difficulty to measure active antenna systems. Recently, the application of conjugated matched feeds for reflector systems aimed at cross polar reduction in space application have received attention in the literature [5-10]. Recognizing, that the cross polar contribution induced by the offset reflector geometry has a focal plane distribution very similar to the higher order modes in feed horns, various techniques have been devised to excite compensating feed modes. Although a very elegant technique, the achievable bandwidth is limited and only single polarized solutions have been presented. A different concept of conjugated matched excitation, overcoming the dual polarization limitation has been introduced in [11-12] based on a patch array feed system. However, this implementation is aimed at applications with different beam-width in the principle planes. In this paper we will introduce a new feed horn concept, based on conjugate matched feeding, aiming at cross polar cancellation in single reflectors CATR systems. The proposed feed system is dual polarized and has an operational bandwidth of 1:1.5. The feed concept is introduced and the demonstrator hardware described. The target QZ <40dB cross polar discrimination is demonstrated by QZ probing of a standard single reflector CATR. References: [1] C. Dragone, "New grids for improved polarization diplexing of microwaves in reflector antennas," Antennas and Propagation, IEEE Transactions on , vol.26, no.3, pp.459-463, May 1978 [2] M.A.J. Griendt, V.J. Vokurka, “Polarization grids for applications in compact antenna test ranges”, 15th Annual Antenna Measurement Techniques Association Symposium, AMTA, October 1993, Dallas, Texas [3] W. D. Burnside, I. J. Gupta, "A method to remove GO taper and cross-polarization errors from compact range scattering measurements," ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM (APSURSI), June 1989, San Jose, California [4] D. N. Black and E. B. Joy, “Test zone eld compensation,” IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, vol. 43, no. 4, pp. 362–368, Apr. 1995. [5] K. K. Shee, and W. T. Smith, “Optimizing Multimode Horn Feed Arrays for Offset Reflector Antennas Using a Constrained Minimization Algorithm to Reduce Cross Polarization”, IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 45, No. 12, December 1997, pp. 1883-1885. [6] S. B. Sharma, D. Pujara, Member, S. B. Chakrabarty,r. Dey, "Cross-Polarization Cancellation in an Offset Parabolic Reflector Antenna Using a Corrugated Matched Feed", IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009, pp. 861-864. [7] S. B. Sharma, D. A. Pujara, S. B. Chakrabarty, and V. K. Singh, “Improving the Cross-Polar Performance of an Offset Parabolic Reflector Antenna Using a Rectangular Matched Feed”, IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009, pp. 513-516. [8] S. K. Sharma, and A. Tuteja, “Investigations on a triple mode waveguide horn capable of providing scanned radiation patterns”, ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM (APSURSI), July 11-17, 2010 [9] K. Bahadori, and Y. Rahmat-Samii, “Tri-Mode Horn Feeds Revisited: Cross-Pol Reduction in Compact Offset Reflector Antennas”, IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, No. 9, September 2009. [10] Z. Allahgholi Pour, and L. Shafai, “A Simplified Feed Model for Investigating the Cross Polarization Reduction in Circular- and Elliptical-Rim Offset Reflector Antennas”, IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, No. 3, March 2012, pp. 1261-1268. [11] R. Mizzoni, G. Orlando, and P. Valle, “Unfurlable Reflector SAR Antenna at P-Band”, Proc. of EuCAP 2009, Berlin, Germany. [12] P. Valle, G. Orlando, R. Mizzoni, F. Heliere, K. van ’t Klooster, “P-Band Feedarray for BIOMASS”, Proc. of EuCAP 2012, Prague, Czech Republic.
Numerical modeling within Computational Electromagnetics (CEM) solvers is an important engineering tool for supporting the evaluation and optimization of antenna placement on larger complex platforms. While measurements are still required for final validation due to the conclusiveness and high reliability of measured data, numerical modeling is increasingly used in the initial stages of antenna placement investigation, optimization and to ensure that final testing, often a complex procedure, has a positive outcome. In some cases, the full-wave representation of the source antenna is unavailable to the designer in the format required by the CEM solver. This is often the case if the source antenna is from a third party. To overcome this problem, an equivalent computational model of the antenna must be constructed, bearing in mind that CEM solvers require an accurate source representation to achieve reliable results. Equivalent sources or currents implemented in the commercial tool INSIGHT have been adopted as an efficient diagnostics and echo reduction tool in general antenna measurement scenarios as discussed in [1-6]. The INSIGHT processing of measured antenna data was initially developed as a numerical representation of antennas in complex environment analysis for CEM solvers [7-10]. The main obstacle for widespread use of this method was the handling of the proprietary format of the equivalent currents. Commercial CEM providers are currently investigating and implementing domain decomposition techniques based on the near field description of the local domain. This development also provides a direct link between INSIGHT processing of measured antenna data and numerical simulation opening a range of interesting applications for using measured antennas in commercial numerical simulation tools as discussed in [11-12]. In flush-mounted antenna applications the measurement and subsequent INSIGHT processing has to be carefully performed. This paper discusses guidelines for the correct source antenna measurement, post processing and successive link to the commercial numerical tools for simulation. Application examples of the link using CST STUDIO SUITE® software [14-17] with flush mounted antennas and comparison with measurements of the full structure will be provided. [1] http://www.satimo.com/software/insight [2] J. L. Araque Quijano, G. Vecchi. Improved accuracy source reconstruction on arbitrary 3-D surfaces. Antennas and Wireless Propagation Letters, IEEE, 8:1046–1049, 2009. [3] J. L. A. Quijano, G. Vecchi, L. Li, M. Sabbadini, L. Scialacqua, B. Bencivenga, F. Mioc, L. J. Foged "3D spatial filtering applications in spherical near field antenna measurements", AMTA 2010 Symposium, October, Atlanta, Georgia, USA. [4] L. Scialacqua, F. Saccardi, L. J. Foged, J. L. Araque Quijano, G. Vecchi, M. Sabbadini, “Practical Application of the Equivalent Source Method as an Antenna Diagnostics Tool”, AMTA Symposium, October 2011, Englewood, Colorado, USA [5] J. L. Araque Quijano, L. Scialacqua, J. Zackrisson, L. J. Foged, M. Sabbadini, G. Vecchi “Suppression of undesired radiated fields based on equivalent currents reconstruction from measured data”, IEEE Antenna and wireless propagation letters, vol. 10, 2011 p314-317. [6] L. J. Foged, L. Scialacqua, F. Mioc,F. Saccardi, P. O. Iversen, L. Shmidov, R. Braun, J. L. Araque Quijano, G. Vecchi" Echo Suppresion by Spatial Filtering Techniques in Advanced Planar and Spherical NF Antenna Measurements ", AMTA Symposium, October 2012, Seattle, Washington, USA [7] E. Di Giampaolo, F. Mioc, M. Sabbadini, F. Bardati, G. Marrocco, J. Monclard , L. Foged, “Numerical modeling using fast antenna measurements”, 28th ESA Antenna Workshop on Space Antenna Systems and Technologies, June 2005 [8] L. J. Foged, F. Mioc, B. Bencivenga, E. Di Giampaolo, M. Sabbadini “High frequency numerical modeling using measured sources”, IEEE Antennas and Propagation Society International Symposium, July 9-14, 2006. [9] F. Mioc, J. Araque Quijano, G. Vecchi, E. Martini, F. Milani, R. Guidi, L. J. Foged, M. Sabbadini, “Source Modelling and Pattern Enhancement for Antenna Farm Analysis”, 30th ESA Antenna Workshop on Antennas for Earth Observation, Science, Telecommunication and Navigation Space Missions, May 2008 ESA/ESTEC Noordwijk, The Netherlands [10] L. J. Foged, B. Bencivenga, F. Saccardi, L. Scialacqua, F. Mioc, G. Arcidiacono, M. Sabbadini, S. Filippone, E. di Giampaolo, “Characterisation of small Antennas on Electrically Large Structures using Measured Sources and Advanced Numerical Modelling”, 35th Annual Symposium of the Antenna Measurement Techniques Association, AMTA, October 2013, Columbus, Ohio, USA [11] L. J. Foged, L. Scialacqua, F. Saccardi, F. Mioc, D. Tallini, E. Leroux, U. Becker, J. L. Araque Quijano, G. Vecchi, “Bringing Numerical Simulation and Antenna Measurements Together”, 8th European Conference on Antennas and Propagation, EuCAP, April 2014, Den Haag, Netherlands [12] L. J. Foged, L. Scialacqua, F. Saccardi, F. Mioc, D. Tallini, E. Leroux, U. Becker, J. L. Araque Quijano, G. Vecchi “Innovative Representation of Antenna Measured Sources for Numerical Simulations”, IEEE International Symposium on Antennas and Propagation and USNC/URSI, July 2014, Memphis, Tennese, USA [13] L. J. Foged, B. Bencivenga, F. Saccardi, L. Scialacqua, F. Mioc, G. Arcidiacono, M. Sabbadini, S. Filippone, E. di Giampaolo, “Characterisation of small Antennas on Electrically Large Structures using Measured Sources and Advanced Numerical Modelling”, 35th Annual Symposium of the Antenna Measurement Techniques Association, AMTA, October 2013, Columbus, Ohio, USA [14] CST STUDIO SUITE™, CST AG, Germany, www.cst.com [15] T. Weiland: "RF & Microwave Simulators - From Component to System Design" Proceedings of the European Microwave Week (EUMW 2003), München, Oktober 2003, Vol. 2, pp. 591 - 596. [16] B. Krietenstein, R. Schuhmann, P. Thoma, T. Weiland: "The Perfect Boundary Approximation Technique facing the big challenge of High Precision Field Computation" Proc. of the XIX International Linear Accelerator Conference (LINAC 98), Chicago, USA, 1998, pp. 860-862. [17] D. Reinecke, P. Thoma, T. Weiland: "Treatment of thin, arbitrary curved PEC sheets with FDTD" IEEE Antennas and Propagation, Salt Lake City, USA, 2000, p. 26.
In this paper the inverse-source technique or source reconstruction technique has been applied as diagnostic tool to determine the complex excitation at sub array and single element level of a measured array antenna [1-5]. The inverse-source technique, implemented in the commercially available tool “INSIGHT” [5], allows to compute equivalent electric and magnetic currents providing exclusive diagnostic information about the measured antenna. By additional processing of the equivalent currents the user can gain insight to the realized excitation law at single element and sub-array level to identify possible errors. The array investigated in this paper is intended as part of the European Navigation System GALILEO and is a pre-development model flying on the In-Orbit Validation Element the GIOVE-B satellite. The antenna, developed by EADS-CASA Espacio, consists of 42 patch elements, divided into six sectors and is fed by a two level beam forming network (BFN). The BFN provide complex excitation coefficients of each array element to obtain the desired iso-flux shaped beam pattern [6-7]. The measurements have been performed in the new hybrid (Near Field and Compact Range) facility in the ESTEC CPTR as part of the installation and validation procedure [8]. The investigation has been performed without any prior information of the array and intended excitation. The input data for the analysis is the measured spherical NF data and the array topology and reference coordinate system. References [1] J. L. Araque Quijano, G. Vecchi. Improved accuracy source reconstruction on arbitrary 3-D surfaces. Antennas and Wireless Propagation Letters, IEEE, 8:1046–1049, 2009. [2] L. Scialacqua, F. Saccardi, L. J. Foged, J. L. Araque Quijano, G. Vecchi, M. Sabbadini, “Practical Application of the Equivalent Source Method as an Antenna Diagnostics Tool”, AMTA Symposium, October 2011, Englewood, Colorado, USA [3] J. L. Araque Quijano, L. Scialacqua, J. Zackrisson, L. J. Foged, M. Sabbadini, G. Vecchi “Suppression of undesired radiated fields based on equivalent currents reconstruction from measured data”, IEEE Antenna and wireless propagation letters, vol. 10, 2011 p314-317. [4] L. J. Foged, L. Scialacqua, F. Mioc,F. Saccardi, P. O. Iversen, L. Shmidov, R. Braun, J. L. Araque Quijano, G. Vecchi " Echo Suppresion by Spatial Filtering Techniques in Advanced Planar and Spherical NF Antenna Measurements ", AMTA Symposium, October 2012, Seattle, Washington, USA [5] http://www.satimo.com/software/insight [6] A. Montesano, F. Monjas, L.E. Cuesta, A. Olea, “GALILEO System Navigation Antenna for Global Positioning”, 28th ESA Antenna Workshop on Space [7] L.S. Drioli, C. Mangenot, “Microwave holography as a diagnostic tools: an application to the galileo navigation antenna”, 30th Annual Antenna Measurement Techniques Association Symposium, AMTA 2008, Boston, Massachusetts November 2008 [8] S. Burgos, M. Boumans, P. O. Iversen, C. Veiglhuber, U. Wagner, P. Miller, “Hybrid test range in the ESTEC compact payload test range”, 35th ESA Antenna Workshop on Antenna and Free Space RF Measurements ESA/ESTEC, The Netherlands, September 2013
Current antenna measurement techniques are based on the underlying idea that echoes generated by nearby structures should be avoided. Indeed, the absence of echoes allows a precise measurement of the line-of-sight radiation of the antenna under test (AUT), via mechanical rotation to span some or all spatial directions until the radiation pattern is formed. In this paper, this idea is challenged by introducing an alternative test approach that generates controlled echoes and use them as a useful source of information. Preliminary results are presented and it is shown how frequency diversity can be fruitfully used to retrieve the free space radiation pattern. A special care is given to the conditioning of the mathematical problem. Accordingly, it is shown how the different parameters involved in the set-up influence the feasibility of the technique. The proposed technique is expected to lead to a faster characterization of the AUT, as the need for mechanical rotation is cut down.
Broad band, dual polarized probes are becoming increasingly popular options for use in near-field antenna measurements. These probes allow one to reduce cost and setup time by replacing several narrowband probes like open-ended waveguides (OEWG) with a single device covering multiple waveguide bands. These probes are also ideal for production environments, where chamber throughput should be maximized. Unfortunately, these broadband probes have some disadvantages that must be quantified and corrected for in order to make them viable for high accuracy near-field measurements. Most of these broadband probes do not have low cross polarization levels across their full operating bandwidths and may also have undesirable artifacts in the main component of their patterns at some frequencies. Both of these factors will result in measurement errors when used as probes. Furthermore, the use of a dual port RF switch adds an additional level of uncertainty in the form of port-to-port channel balance errors that must be accounted for. This paper will describe procedures to calibrate the pattern and polarization properties of broad band, dual polarized probes with an emphasis on a newly developed polarization correction algorithm. A simple procedure to measure and correct for amplitude and phase imbalance entering the two ports of the near-field probe will also be presented. Measured results of the three calibration procedures (pattern, polarization, channel balance) will be presented for a dual-polarized, broad band quad-ridged horn antenna. Once calibrated, this probe was used to measure a standard gain horn (SGH) and will be compared to baseline measurements acquired using a good polarization standard open-ended waveguide (OEWG). Results with and without the various calibration algorithms will illustrate the advantage to using all three routines to yield high accuracy far-field pattern data.
Indoor RCS measurement facilities are usually dedicated to the characterization of only one azimuth cut and one elevation cut of the full spherical RCS target pattern. In order to perform more complete characterizations, a spherical experimental layout has been developed at CEA for indoor Near Field monostatic RCS assessment. This experimental layout is composed of a 4 meters radius motorized rotating arch (horizontal axis) holding the measurement antennas while the target is located on a mast (polystyrene or Plexiglas) mounted on a rotating positioning system (vertical axis). The combination of the two rotation capabilities allows full 3D near field monostatic RCS characterization. This paper investigates the influence of the material of the mast supporting the target under test. Across several measurement steps, we compare different RCS measurement results of canonical targets in order to eliminate the unwanted RCS measurement contribution due to the mast. The aim is to find out the mast which disturbs the least the RCS of the target under test but still compatible with the measurement facility ARCHE 3D. All these measurements are also compared to Near Field and Far Field calculations taking into account the material of the supporting mast.
The synthesis of a specific field distribution in a certain volume with a given set of sources is an issue which arises in acoustics as well as in electromagnetics. Field Synthesis is of increasing interest for over the air (OTA) testing of multiple input multiple output (MIMO) based communication devices as arbitrary multipath communication channels can be simulated synthesizing the corresponding field distribution around the device under test (DUT). Plane-wave Field Synthesis methods have already been applied to improve the quality and extents of the quiet zone region of compact antenna test ranges (CATR). Furthermore, by synthesizing a plane wave field in a test region for an antenna under test (AUT), using an array of probe antennas in its near-field region, near-field far-field transformations (NFFFT) can be performed. Since there exists a variety of important applications for electromagnetic Field Synthesis, a Field Synthesis approach with high flexibility and low computational complexity is presented in this contribution. Usually, depending on the application, a single moving probe antenna or an array of probe antennas is used to synthesize a desired field distribution in the test zone volume where the DUT will be placed. The challenge is to determine appropriate excitation signals for the individual probe antennas. For that purpose an equation system is iteratively solved which arises from the boundary condition for the tangential field components on the surface of the test volume. As a consequence of the uniqueness theorem, equality of the desired and synthesized tangential field components induces that the desired and synthesized field distribution are identical in the source free test volume. Field testing on the surface of the test volume is performed by vector testing functions defined on a triangular mesh of the test zone surface enabling field synthesis in arbitrarily shaped test volumes. For accelerated evaluation of the coupling between probe antennas and vector testing functions, principles of the fast multipole method (FMM) are adopted. The implied plane wave expansions enables to incorporate the radiation characteristic of the probe antenna sources just by directly employing its plane wave spectrum representation which is nothing else but its far-field pattern. Additionally, the multilevel approach minimizes the number of translation operations between source and receiver boxes organized in a hierarchical oct-tree. Altogether the approach is applicable to arbitrarily shaped test volumes and arbitrarily arranged probe antennas and still shows a linearithmic complexity. In this contribution, detailed insight in the Field Synthesis method is given. Results for synthesized field distributions for arbitrarily shaped test volumes are presented. Finally the application of plane-wave Field Synthesis to NFFFT is shown for synthetic as well as for real near-field antenna measurement data.
Within RF measurement systems, engineers commonly wish to know how much phase ripple will be present in a signal based on a given signal-to-noise ratio (SNR). In a past AMTA paper (Measurement Considerations for Antenna Pattern Accuracy, AMTA 1997), John Swanstrom presented an equation which demonstrated how the bound on the phase error could be calculated from the peak SNR value. However, it can be shown that the Swanstrom bound is broken when the signal has a peak SNR value of less than approximately 15 dB. This paper introduces a new equation that bounds the maximum phase error of a signal based on the signal’s peak SNR value. The derivation of this new bound is presented, and comparisons are made between the old Swanstrom bound and the new bound. In addition, the inverse relationship (i.e., calculating the SNR value of a signal from phase-only measurements) is investigated. In the past, analytical equations for this relationship have been presented by authors such as Robert Dybdal (Coherent RF Error Statistics in IEEE Trans. on Microwave Theory and Techniques) and Jim P.Y. Lee (I/Q Demodulation of Radar Signals with Calibration and Filtering in a Defense Research Establishment Ottawa publication). The analytical equations for calculating the SNR value using phase-only measurements are reviewed and discussed, and a brand new numerical relationship based on a polynomial curve fitting technique is proposed.
Electrically small antennas present tremendous design challenges. Plagued with a small radiation resistance and high quality factor (thus narrow bandwidth), these types of antennas are difficult to accurately measure. For use in HF communication applications, the problems associated with the entire development cycle become even more pronounced. This paper focuses on the development of two such electrically small HF antennas for a vehicular platform, specifically the Amphibious Assault Vehicle (AAV). The primary design objective is to develop antennas that operate over the entire near-vertical incidence (NVIS) band (2 – 10 MHz) with a minimum of 3kHz bandwidth. Additional design objectives are low profile, broadside directive pattern, and high power handling capability. The inverted L antenna and the half loop antenna were selected as probable candidates for this application. At 2 MHz, the antenna – vehicle system fits within the envelope ka < 0.2, where k is the free space wave number and a is the radius of a sphere completely enclosing the radiator. The full scale antenna design and performance were evaluated using method of moments and finite element method codes FEKO and HFSS respectfully. It is observed that the presence of the real ground plane poses a serious challenge for well established modeling techniques and considerable care must be exercised to obtain credible design data. For measurement validation and characterization of the antenna/vehicle interaction, a set of scaled antenna and vehicle prototypes were developed. Rapid prototyping and 3D printing were employed to build a scaled model (1:50 scale) of the complete antenna – vehicle system. The step-by-step process from the computational model to the measurement validation is discussed along with the description of the adopted fabrication techniques. In the concluding section of the paper, the measured results from the scaled model are presented alongside the simulated results. The good agreement between these results paves the way towards the successful use of such scaled model testing for more complicated antenna designs in the future.
One design of a smart plasma antenna is to surround a plasma or metal antenna by a plasma blanket in which the plasma density can be varied. In regions where the plasma frequency is much less than the antenna frequency, the antenna radiation passes through as if a window exists in the plasma blanket. In regions where the plasma frequency is high the plasma behaves like a perfect reflector with a reactive skin depth. Hence by opening and closing a sequence of these plasma windows this design can be computerized to electronically steer or direct the antenna beam into any and all directions. The plasma windowing design is one approach to the smart plasma antenna design. The beamwidth can vary from an omnidirectional radiation pattern with all the plasma windows open or a very directional radiation pattern when only one plasma window is open. The advantages of the plasma blanket windowing design are: 1. Beam steering of one omnidirection antenna with the plasma physics of plasma windowing. 2. A reconfiguable directivity. 3. The beamwidth can vary from an omnidirectional radiation pattern with all the plasma windows open to a directional radiation pattern with less than all the plasma windows open.
Abstract – This paper introduces a method for calibrating the gain and the frequency dependent phase center locations of Log Periodic Dipole Arrays (LPDAs). The method builds upon the three antenna method, but is conducted over a PEC ground plane in an Open Area Test Site (OATS). Similar to the traditional three antenna method, three pairings of transmission measurements are taken. In each measurement, one antenna is set at a fixed height above the ground plane, while the other antenna is scanned in height over 1 to 4 m heights. Magnitude and phase responses between the two antennas are taken at multiple heights. Measured results are fit to a theoretical model using a complex fit algorithm. From this process, the gain and frequency dependent phase center locations of each antenna can be solved. Measurement data show that it is effective in reducing systematic uncertainties associated with assuming fixed phase center locations. In addition, unlike other calibration methods over a conducting ground plane, no assumptions are made about the antenna patterns. This method provides an accurate, versatile and fast method for calibrating LPDAs from as low as 100 MHz.
Abstract—In this paper, a novel feeding method of microstrip line array is presented, with which every line array can be fed from the side part instead of from the center part .At the same time a novel compact slot patch antenna loaded with a pair of spirals is proposed, which is 66% smaller than the conventional half-wave patch antenna. The simulated and measured radiation patterns at center frequency are both presented. The -18dB side-lobe level for the sum pattern and -37dB null depth for the difference pattern have achieved in the experiment.
Abstract—Nowadays, radar retro-reflector has been widely applied as a decoy, to seduce an incoming assault away from the target, or towards a less vulnerable part of it to communication systems and remote identification as their characteristics of low-profile, low-cost and Radar Cross Section(RCS) enhancement. A passive retro-reflector is a device which can be used to be reflected most of the energy incident upon it in the direction of the in-going wave. The Luneberg lens and a sphere are widely used as their self characteristics. In this paper one of the retro-reflector, is paid more attention as time goes by, is introduced. The retroreflector is consist of patch antenna arrays and feeding system and can be defined as Retro-directive arrays (RDA). It has a very simple structure and can focus outgoing waves back at the direction of incident waves. The character of the re-radiation pattern affected by the size and type of patch and width and length of feeding network related are optimized by the HFSS. The final results are validated experimentally.
Abstract—When antennas are measured in echoic environments, there is usually a need to process the measured data in order to remove multipath contributions. Traditional measurement set-ups involving a single probe antenna provide limited information for the purpose of this separation. A multi-probe measurement technique whereby the AUT is measured with two sets of probe antennas is presented. One set of probe antennas are oriented such that they radiate mainly toward the AUT and the other set radiate away from it. This measurement technique allows for the separation of the direct AUT contribution from the multipath contributions. The acquired data is processed using a well-suited near-.eld far-.eld transformation algorithm with the echo sources considered as they were independent sources. The performance of the measurement technique is also evaluated for traditional spherical mode near-.eld far-.eld transformation whereby both incoming and outgoing spherical waves are considered. The results show a substantial improvement in the obtained far-.eld patterns when compared with non-compensated far-.eld results.
Abstract: In order to characterize the Boeing 9-77 compact range, the empty chamber background was measured as a function of frequency, polarization, and the azimuth angle of the upper turn-table (UTT). The results exhibited a near-field diffraction pattern with enlarged hot-spots on a 4-fold symmetry [1]. A 2-D FFT on the diffraction pattern yielded a mapping on the relative arrangement of the absorbers on the UTT [2]. In this paper, we take a closer look at the scattering geometry of the UTT as illuminated by the residual field above and beyond the quiet zone (QZ). The different responses in VV and HH are discussed. The enhanced diffraction due to a “blazed grating” condition is identified and analyzed.
Abstract— Measurements and strategies for the calculation of radar cross-sections in the shorter millimeter wave region, especially of objects that include rough surfaces, are discussed. Because of decreasing wavelength, roughness becomes more significant in this spectral region, but also more difficult to characterize. A tabletop radar cross-section measurement system was set up to measure scattering from canonical objects and rough objects with regular or random patterns using a swept frequency continuous wave system. Random, rough objects of different surface roughnesses were measured and fit to statistical distributions governed by optical speckle theory. In this paper we consider the inclusion of optical speckle theory in the electromagnetic codes to address both issues associated with the characterization of target surfaces and the time required for numerical calculations.
Abstract— A special X-band PEC-backed dipole with integrated split coaxial balun was designed, fabricated, and tested for feeding a low-profile parabolic reflector. The aperture size and height of the reflector is 7.876” and 2.0315”, respectively. The reflector is covered with a 1/16” Teflon sheet radome for weather protection. The antenna has a measured peak gain of 23.72dB and first side lobe level of less than –25dB at 10.2GHz in both E and H planes. The worst case 3dB beamwidth is 11.09o in the H-plane. The -10 dB reflection coefficient bandwidth of this design is from 9.5 to 11 GHz. The E and H plane patterns were designed to have similar tapering and minimum coupling between TX and RX reflector antennas in an array configuration. Within an array configuration the measured coupling level is less than -66dB from 9.5 to 11 GHz.
Abstract— In order to achieve precise antenna pattern measurement in mm-wave frequency region, we propose a cylindrical near-field antenna measurement system using photomixing technique with UTC-PD. Due to this system, we can use an optical fiber as the transmission line of mm-wave signal and downsize the mm-wave signal source. Accordingly, we can achieve flexible cable movement and suppress the disturbance from the waveguide components. In this paper, we will show the measured near-field distribution on cylindrical coordinate by the proposed system and calculated far-field antenna pattern of standard gain horn antenna in W-band.
Abstract— This paper presents an original way for the design simulation, implementation, and measurement of a multiband flexible textile antenna. The aim is to realize an antenna with a dipolar radiation at several resonance frequencies. The radiating element is a monopole antenna. This antenna naturally exhibits a dipole and a quadripole radiation pattern for the first and second resonance frequency respectively. This behavior is due to the current distribution on the antenna. To constrain the second mode to change into a dipolar radiation pattern, two decorrelated and non-radiating parasitic elements are added to the antenna. At this second resonance frequency, the current distribution is different from the one of the quadripolar mode by the parasitic elements. The dimensions of these parasitic elements are defined by electromagnetic simulations and measurements. To validate this method, the monopole antenna is studied. The radiating element of the antenna is sewn on the textile flexible substrate. This substrate was previously characterized in terms of relative permittivity and losses. The near-field magnetic field and the far-field radiation pattern are studied in simulations and measurements.
Abstract—Four arm Log-Periodic (LP) antennas are frequency independent antennas that are capable of producing dual circular polarizations from the same aperture and over the same bandwidth making them more versatile than commonly used spiral antennas. In this paper we present a four arm LP that is capable of being a high power radiator. Each pair of arms of the LP is fed with a microstrip line that functions as both an impedance transformer and a 180° balun, thereby greatly simplifying the required beamformer. The antenna is tested successfully up to 500W of input CW power. Post high power characterizations of the antenna (far-field gain, radiation patterns, and VSWR) for linear polarization are presented and the stable high power performance of the antenna is demonstrated. With an appropriate beamformer, good quality circular polarization can be expected. Presented results should pave the way for use of the LP in relevant wideband high power applications.