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Ground Plane

Nearfield Antenna Measurements over Seawater – Some Preliminary Thoughts
David Tonn, October 2017

The principles of near-field antenna measurements and scanning in Cartesian and spherical coordinates are well established and documented in the literature, and in standards used on antenna ranges throughout government, industry, and academic applications. However the measurement methods used and the mathematics that are applied to compute the gain and radiation of the pattern of the test antenna from the near-field data assume typically that the antenna is operating in free space. This leaves several questions open when dealing with antennas operating over a lossy ground plane, such as the ocean damp soil, etc. In this paper, we shall discuss some of the motivation behind an examination of the physics and mathematics involved in performing a near-field antenna measurement over a seawater ground plane. Examples of past work in this are shall be discussed along with some of the challenges of performing far field antenna measurements in the presence of the air-sea interface. These discussions lead to some fundamental questions about how one defines gain in this environment and whether or not a near field approach could be beneficial. This will lead to some discussion of when and how the existing modal field expansions used in near-field measurements may need to be adjusted to account for the presence of the ground plane created by the ocean surface. An example of the limiting case of an antenna operating over a metallic ground plane will be discussed as a stepping stone to the more general problem of an antenna operating over a lossy ground plane.

A Cylindrical Reconfigurable Antenna Technology with Full Hemispherical Coverage
Gregory Kiesel, Efstrateos Strates, October 2017

Reconfigurable antennas provide the ability to electronically change the antenna’s performance, which allows the antenna’s band of operation and gain pattern to be rapidly adapted to meet system requirements. A cylindrical, conformal reconfigurable antenna is presented which tunes over a wide band and provides full 360° azimuth coverage. The antenna maintains a realized gain (with mismatch and loss) better than a dipole from 800 MHz to 3 GHz, using the antenna’s gain to compensate for losses in the antenna. The antenna is designed and characterized with the cylinder’s bottom over a finite ground plane (no other antenna ground planes are used). The antenna is constructed using a modular approach out of a series of identical boards which act as antenna pixels. Each pixel contain four RF switches (one for each side of the board) along with contacts for control and ground wires. By fragmenting the reconfigurable antenna into individual pixel boards, one can construct elements of arbitrary size and shape with the primary physical constraint being how densely the electronics can be fabricated. By providing flexibility to scale in size, the antenna implementation can be optimized for more gain or for a smaller footprint. Two scaled versions of the same architecture have been constructed out of the same pixels to demonstrate the flexibility of the approach. In this paper we present data demonstrating more than 2 dBi gain from 1.2 GHz to 2.5 GHz band with beamwidths as narrow as 60°. Beam patterns are presented for GSM-900, GMS-1900, and WiFi frequencies. Finally, we will show the antenna element’s ability to maintain gain in a specific direction while forming a null over a series of offset angles.

Truncation Error Mitigation in Free-Space Automotive Partial Spherical Near Field Measurements
Francesco Saccardi, Francesca Rossi, Lucia Scialacqua, Lars Foged, October 2017

Modern cars are equipped with a large number of antennas which are strongly integrated with the car. A full characterization of the radiating properties of the entire vehicle is thus typically required. In order to characterize the radiating properties of the installed antennas, large measurement systems accommodating the full vehicle are required. As in standard antenna measurements, a full spherical near field (NF) scanning around the car is desirable in order to perform an accurate NF/FF transformation. However, due to size and weight of the Device Under Test (DUT) and/or economic factors a full spherical scan is often unfeasible. For this reason, truncated spherical scanners (such as hemispherical) are typically involved. A classic solution is to combine hemispherical scanning with a metallic ground plane which is assumed to be a Perfect Electric Conductor (PEC) in the NF/FF transformation. However, the PEC ground-plane is less representative of realistic automotive environments such as asphalt that is strongly dielectric. A further drawback is the strong scattering from the large metallic ground-plane which highly compromises the NF measurements at low frequencies. In many situations, it is thus desirable to perform the NF measurements in a condition similar to free-space by using absorber materials on the floor. It is well-known that standard NF/FF transformations applied to partial spherical acquisitions generates the so called truncation errors. Such errors are stronger at lower frequencies due to the lower number of spherical modes for fixed DUT size. Moreover, typical antennas for automotive applications are generally low directive thus, the impact of the truncation on the measured pattern is often non-negligible. In such cases advanced post-processing techniques must be involved to mitigate the effect of the truncation errors. In this paper two truncation error mitigation techniques will be compared when applied to automotive measurements performed in free-space conditions. The first technique is an iterative process which at each iteration applies a modal filtering based on the size of the DUT. The second technique is based on the computation of the equivalent currents of the DUT over an equivalent surface which acts as spatial filter. Both techniques give excellent mitigation performance with different computational effort. The good agreement between two different techniques effectively defining the lower bound for what can be successfully mitigated by post processing techniques.

Free-Space Antenna Far-Field Extraction from Near-Field Measurements Above Metallic Ground
Raimund Mauermayer, Thomas Eibert, October 2017

Antenna measurements above a material half-space are becoming an interesting aspect of near-field measurements especially for automotive antenna tests. Upcoming measurement facilities will be equipped with a dielectric or metallic ground. The near-field is sampled on a measurement surface in the vicinity of the device under test (DUT) above the ground, e.g. on a hemisphere. Thus, the effect of the ground has to be considered in the subsequent near-field to far-field transformation in order to obtain the far-field of the DUT above the ground plane. Assuming the metallic ground of the facility to be perfectly conducting, the ground effects are considered by introducing image sources below the ground plane in addition to the primary sources of the DUT above the ground plane. If coupling effects between the DUT and the ground plane are negligible, the primary sources correspond to the sources of the DUT in free-space. As a consequence, by separating the primary sources from the image sources, the free-space far-field of the DUT can be obtained from near-field measurements above ground. This means that measurement ranges with a ground plane can also be used to obtain free-space far-fields. In electromagnetic simulations, the primary sources can be placed in arbitrary environments, e.g. for communication channel evaluations. The quality of the primary sources extraction process mainly depends on the distance of the DUT sources from the ground plane as well as on the localization property of the employed equivalent sources which e.g. can be electric and/or magnetic surface currents or spherical modes. In this contribution, the numerical properties of the forward operator describing the relation between the DUT sources and the signal of the probe antenna above ground are analyzed in detail. The requirements for the unique determination of the primary sources from the near-field observations by inverting the operator are identified. Based on numerical investigations and real measurements obtained in a hemispherical near-field measurement facility, it will be shown that dependent on the ratio of the geometrical extensions of the DUT and its height above the ground as wells as on the strength of the coupling between the DUT and the ground, the free-space DUT far-field can be extracted with high quality.

Multi-Band Compact MIMO Antenna System for LTE and WLAN Communications
Jiukun Che, Chi-Chih Chen, October 2017

In this paper, a novel compact 2-channel MIMO antenna design for all cellular and Wi-Fi communication needs from vehicular is discussed. The entire antenna system fits within the 13cm (diameter) by 9cm (height) volume. It consists of 2 vertical multi-band cellular antenna elements and two vertical multi-band Wi-Fi antenna elements. All four antennas share a 13cm diameter circular ground plane. Each antenna element design is a PCB based slot-loaded multi-band monopole. This particular element design as well as their mounting positions were chosen to minimize mutual coupling and blockage in order to maximize MIMO performance, i.e. diversity gain. In addition, the center region of the antenna volume also accommodates a raised L1-band GPS antenna. A prototype antenna was subsequently fabricated. The measured antenna performance compared well with simulated results before and after being mounted on a 4 feet diameter ground plane. The effect of the radome was also assessed and was found to be insignificant. The cellular antenna produced realized gain of over 2 dBi in lower cellular band (0.7 GHz to 1 GHz), and over 5dBi in the higher cellular band (1.7-2.1GHz and 2.3GHz-2.5GHz). The Wi-Fi antenna produced realized gain of over 5dBi in both 2.4 GHz and 5.8 GHz bands. The far-field pattern correlation coefficient was also calculated to evaluate the diversity gain performance of antenna system. For the cellular band, the correlation number is lower than 0.55 for 0.7 to 1 GHz, and lower than 0.35 for all the other band. For the entire Wi-Fi band, the correlation number is lower than 0.4.

The Measurement of Horizontal Magnetic Dipole Moment at a Conducting Ground Plane Using a Modified Van Veen Loop
James McLean, Robert Sutton, November 2016

Magnetic Field Wireless Power Transfer (MF-WPT) systems such as those used in vehicular applications produce extraneous emissions not only at the fundamental frequency (typically in the LF range) but also, due to rectifier harmonics and short-time-scale ringing in the H-bridge and rectifier circuits, over a broad spectrum which extends well up into the HF frequency range.  Thus, characterization of the emissions from such a system must cover this broad frequency range.  The Van Veen Loop or Loop Antenna System has been successfully used to characterize some MF-WPT systems.  However, typically the couplers in such a system are situated essentially at ground level.  One problem with using the conventional Van Veen Loop to characterize an MF-WPT system is that there is some possibility that removing the couplers from the ground will modify the current distribution in them and hence change the extraneous field.  Thus, it would be useful to determine the net magnetic dipole moment of an MF-WPT system in situ.  In the case of conducting ground, the vertical magnetic dipole moment is nearly completely canceled by its image.  The net horizontal magnetic dipole moment is thus the predominant source of the far electromagnetic field.  Therefore, we consider measuring the two orthogonal components of the net horizontal dipole moment of an MF-WPT system situated at conducting ground. The Van Veen Loop can be adapted to operation at a conducting ground plane by taking advantage of the images of the two component loops with horizontal axes. With this in mind, a system has been developed which is essentially half of a Van Veen loop.  That is, it consists of two orthogonal shielded “half” loops which terminate at the ground plane. We analyze this unconventional Van Veen Loop and also provide experimental verification of its performance in the time and frequency domains.  Finally, we provide details of the design which is similar to, but not the same as, that given in the CISPR 16-1-4 standard.

Spherical Field Transformation for Hemispherical Antenna Measurements above Perfectly Conducting Ground Planes
Raimund Mauermayer, Thomas Eibert, November 2016

The spherical multipole based near-field far-field transformation is extended to near-field antenna measurements above a perfectly electrically conducting (PEC) ground plane. As the effect of the ground plane is considered in the transformation by applying the image principle to the spherical modes radiated by the device under test (DUT), the near-field measurement points above the ground plane are sufficient to fully characterize the radiation behavior of the DUT above PEC ground. The nonequispaced fast Fourier transform (NFFT) is employed in the forward operator of the inverse problem in order to apply the transformation to e.g. spiral scans which are favorable to large and heavy scanner systems. If the elevation axis is located above or below the ground plane, an additional translation operator is integrated into the transformation to consider such an offset in the mechanical system. The proposed method is applied to synthetic and simulated automotive antenna near-field data in order to show its effectiveness.

Compact First-Order Probe for Spherical Near-Field Antenna Measurements at P-band
Oleksiy Kim, November 2016

A number of European Space Agency's (ESA) initiatives planned for the current decade require metrology level accuracy antenna measurements at frequencies extending from L-band to as low as 400 MHz. The BIOMASS radar, the Galileo navigation and search and rescue services could be mentioned among others. To address the needs, the Technical University of Denmark (DTU), who operates ESA’s external reference laboratory “DTU-ESA Spherical Near-Field (SNF) Antenna Test Facility”, in years 2009-2011 developed a 0.4-1.2 GHz wide-band higher-order probe. Even though the probe was manufactured of light-weight materials -- aluminium and carbon-fibre-reinforced polymer (CFRP) -- it still weighs 22.5 kg and cannot be handled by a single person without proper lifting tools. Besides that, a higher-order probe correction technique necessary to process the measurement data obtained with such a probe is by far more demanding in terms of the computational complexity as well as in terms of calibration and post- processing time than the first-order probe correction. On the other hand, conventional first-order probes for SNF antenna measurements utilizing open-ended cylindrical waveguides or conical horns fed by cylindrical waveguides operating in the fundamental TE11-mode regime also become excessively bulky and heavy as frequency decreases, and already at 1 GHz an open-ended cylindrical waveguide probe is challengingly large. For example, the largest first-order probe at the DTU-ESA SNF Antenna Test Facility operates in the frequency band 1.4–1.65 GHz and weighs 12 kg. At 400 MHz, a classical first-order probe can easily exceed 1 cubic meter in size and reach 25-30 kg in weight. In this contribution, a compact P-band dual-polarized first-order probe is presented. The probe is based on a concept of a superdirective linear array of electrically small resonant magnetic dipole radiators. The height of the probe is just 365 mm over a 720-mm circular ground plane and it weighs less than 5 kg. The probe covers the bandwidth 421-444 MHz with more than 9 dBi directivity and |µ| ? 1 modes suppressed below -35 dB. The probe design, fabrication, and test results will be discussed.

Experimental Validation of Improved Fragmented Aperture Antennas Using Focused Beam Measurement Techniques
James Maloney,John Schultz, Brian Shirley, November 2015

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

Scattered Fields from a Panel
Teh-Hong Lee,Inder J. Gupta, November 2015

There is a lot of interest in measuring the scattered fields from a panel. The panel could be a frequency selective surface (FSS), could consist of lossy dielectric material, resistive material, etc. For these measurements, the panel is mounted in a large ground plane (perfectly conducting) that mimics an infinite ground plane and the back scattered/bistatic scattered fields are measured. These measured fields contain the scattering from the panel under test as well as the diffracted fields from the junction between the panel and the ground plane, and it is quite difficult to discern the two field components. Alternatively, one can measure the scattered fields over a frequency band in the near zone using a fixed transmitting antenna while the receiving antenna is displaced to scan a planar surface or a linear scan. Note that the measurements are similar to one-way probing. The total measured scattered fields can be processed to isolate the scattering from the panel of interest. In this paper, we will present various signal processing techniques that can be applied to the measured scattered field data. These techniques include high resolution down range processing (tie domain), time domain near field focusing, etc. We will also show that it is straight forward to obtain the reflection and transmission coefficient of the panel from the near field measured data.

Size Reduction of Patch Antenna Based on Complementary Rose Curve Resonators
Betty Savitri,Larbi Talbi, Khelifa Hettak, November 2015

In this paper, a patch antenna has been designed based on the complementary split ring resonator (CSRRs), complementary rose curve resonators (CRCRs) and without using these inclusions. Complementary rose curve resonators (CRCRs) are used in design of patch antenna. The Patch antenna based on the complementary rose curve resonators (CRCRs) are achieved by patterning the ground plane under the conductor trace. The perimeter of the Rose curve can be adjusted by tuning the amplitude of the sine function and the radius of the base circle.  With the order of CRCRs, the loading effect of the complementary resonators on the patch antenna is controlled. This works demonstrated that higher order CRCRs allows more compactness of the design and higher miniaturization factor. We proposed a compact patch antenna based on the complementary split ring resonator (CSRRs) and the complementary Rose curve resonator (CRCRs). The proposed patch antenna shows good performances which is designed to operate at 2.4 GHz. The results demonstrate the configurability of the design for a specific size. The results show the effectiveness of using metamaterials in microwave circuit can obtain from n to n+1 of the CRCRs order will result in 0.3 % miniaturization. IndexTerms:  Patch Antenna, Metamaterial, Size Reduction, split ring Resonators, Rose Curve Resonators

Earth-Facing Antenna Characterization in Complex Ground Plane/Multipath Rich Environment
Bryan Welch,Marie Piasecki, November 2015

The Space Communications and Navigation (SCAN) Testbed was a Software Defined Radio (SDR)-based payload launched to the International Space Station (ISS) in July of 2012.  The purpose of the SCAN Testbed payload was to investigate the applicability of SDRs to NASA space missions in an operational space environment, which means that a proper model for system performance in said operational space environment is a necessary condition.  The SCAN Testbed has line-of-sight connections to various ground stations with its S-Band Earth-facing Near-Earth Network Low Gain Antenna (NEN-LGA).  Any previous efforts to characterize the NEN-LGA proved difficult, therefore, the NASA Glenn Research Center built its own S-Band ground station, which became operational in 2015, and has been successfully used to characterize the NEN-LGA’s in-situ pattern measurements.  This methodology allows for a more realistic characterization of the antenna performance, where the pattern oscillation induced by the complex ISS ground plane, as well as shadowing effects due to ISS structural blockage are included into the final performance model.  This paper describes the challenges of characterizing an antenna pattern in this environment.  It will also discuss the data processing, present the final antenna pattern measurements and derived model, as well as discuss various lessons learned.

Research on Unwanted Reflections in an OATS for Precise Omni Antenna Measurement
Donglin Meng,Xiao Liu, Dabo Li, November 2015

Open-area test site (OATS) is a basic range for measuring omni antennas at VHF/HUF band. Reflections from the trees nearby, from the edge of the metal ground plane of an OATS are researched with the aid of ultra-broadband calculable dipole antennas (CDAs). Usually, these reflections are detrimental to precise antenna measurements from 20 MHz to 1 GHz; however they are very difficult to analyze accurately, since no rigorous theory exists on the relationship between the reflections and the configurations of an OATS. For this difficulty, a pair of very accurate and broadband CDAs are manufactured and verified with a slightly modified near-field method, whose site-insertion-loss deviation (?SIL) between measurements and simulation is less than 0.3 dB over 10 MHz to 340 MHz for a single pair of dipole elements resonated at 90 MHz. Based on the optimized CDAs, the effects of ground plane sizes, wire mesh shapes around the edge of the metal ground plane, trees nearby and especially masts are researched. The research shows that the reflections from the edge of an optimized ground plane is less than 0.1 dB at 10 m range. Finally, the performance of an OATS with these optimizations is verified: for 10 m separation, ?SIL is within 0.26 dB at horizontal polarization (HP) and within 0.34 dB at vertical polarization (VP) for the typical 24 frequencies from 30 MHz to 1 GHz; at 20 m separation, ?SIL is within 0.59 dB (HP) and 0.85 dB (VP) from 20 MHz to 500 MHz. An example for the uncertainty of calibration the free-space antenna factor of tuned dipole antennas are provided, too.

Scaled Model Measurements of HF Antenna for Vehicular Platforms
Saurabh Sanghai,Maxim Ignatenko, Kim Hassett, Dejan Filipovic, November 2014

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.

Gain and Phase Center Calibration of Log Periodic Dipole Arrays using Complex Fit Algorithm
Zhong Chen, November 2014

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.

Compact Microstrip Defected Ground Structured Antenna for Reduction of Harmonics and Cross Polarized Radiations
Sarat Kumar Kotramraju,B T P Madhav, Ram Krishna TV, Khan Habibulla, November 2013

Abstract: A novel Inset fed microstrip patch antenna is designed on defected ground structure (DGS) to reduce the higher order harmonics and cross polarized radiations. Square rings, and square shaped slots are placed on the ground plane of the microstrip patch antenna to get the desired operation. These annular ring and arc DGS appears to be highly efficient in terms of suppressing the cross polarization. Relative suppression of radiated field is observed by placing and without placing the defected ground structures. The stop band property exhibited by the DGS is used to filter out the harmonics. The current model successfully reduced the DGS size and by comparing with the well known design, size reduction of 20% is achieved. Instead of normal square patch, a slotted aperture patch model is considered in the current design to reduce the overall size of the antenna.

Positioner Effects in Measurements of Low-Medium Gain Antennas
Alford Chauraya,Terence West, Rob Seager, Will Whittow, Shiyu Zhang, Yiannis Vardaxoglou, November 2013

Abstract—In this paper, a bespoke, fully automated anechoic chamber is discussed and the positioner effects on measurements of antennas are investigated. Antenna measurements performed in this robust anechoic chamber are undertaken in two parts namely; acquisition and analysis, with the aid of low cost positioner hardware and low level software language. In order to get a measure of validation of our measuring system only the important parts of the chamber have been modelled and measurements carried out using a balanced sleeved dipole and a microstrip patch antenna, which have well-known characteristics. It was noticed from the results that the positioner, exaggerates the performance of some antennas particularly small antennas without a ground plane at certain distances and frequencies. The positioner has a tendency to reflect energy, and distort radiation patterns; hence, it was important to ensure that such antennas are placed at an appropriate distance away from the positioner. The comparison between the simulated and measured efficiency of a balanced sleeved dipole is good. The predicted and measured peak efficiency at 2.49 GHz was 95% and 94% respectively. It was also observed that the variability in efficiency measurements was less than 3% for measurements with different angular resolutions on different days.

A Microstrip Fed Slot Antenna with a Dual Band Frequency Response for WiMAX Applications
Gökhan Murat Eryilmaz and Mustafa Turkmen, October 2013

In this study, a novel and compact microstrip-fed slot antenna, which has a dual-band resonance characteristic, is proposed for wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications. The proposed antenna has a simple geometry. It has a microstrip feed line on one side and a ground plane having simple slots on the other side of the substrate. The prototype is fabricated by using mechanical mill-etching technique on a 1.27 mm thick RT/duroid 6006 substrate with the relative permittivity of 6.15, and a loss tangent of 0.0027. The return loss (dB) characteristics of the proposed antennas are measured. The results show that the antenna can provide dual impedance bandwidths of 180 MHz centered at 2.44 GHz, 200 MHz centered at 5.56 GHz, which covers the 2.4 GHz (2400-2484 MHz) WLAN band, 2.3 GHz (2300-2500 MHz) and 5.5 GHz (5250-5850 MHz) WiMAX bands. A good agreement between the results of the numerical and experimental studies has been observed. Consequently, the proposed antenna with simple structure and dual-band frequency response can be suitable for WLAN/WiMAX applications.

An Extremely Low Profile Ferrite-Loaded Wideband VHF Antenna Design
Chi-Chih Chen,The Ohio State University ElectroScience Laboratory, November 2012

A low profile UWB VHF antenna with a maximum diameter of 60.96cm and height of 5.08cm is presented. The top of this antenna is made of a wide conducting plate top which is shorted to ground at one end and a 50-ohm coaxial feed at the other end. Specially selected and shaped ferrite bars are strategically placed between the top plate and ground plane for achieving good antenna performance for wide angle coverage in the upper hemisphere from 30 to 300 MHz. Minimal amount of ferrite was used to keep the antenna’s weight at below 9.07 kg. Simulated and measured results will be discussed.

Understanding The Evolution Of An Ebg Meta-Surface From A Pec Ground Plane
Yahya Rahmat-Samii and Harish Rajagopalan, November 2012

This paper details a systematic procedure of the evolution of an electromagnetic band-gap (EBG) meta-surface from a simple ground plane. The main aspect of the paper is to understand the behavior of these EBG surfaces for low profile antenna design solutions. Reflection phase diagrams are used as a criterion to understand the flat reflection phase response of these surfaces for all angles of incidences and all polarizations. The evolution of EBG from a PEC ground plane to a via-loaded PEC ground plane to a planar patch-type surface and finally to a Mushroom-EBG surface is presented in a novel way. In addition, uniplanar compact-EBG (UC-EBG) properties are also investigated. It is observed that the EBG structures are most robust to different incident angles and polarizations making it a powerful candidate for low profile antenna design solutions. Additionally, the band-gap properties of planar patchtype, Mushroom-EBG and UC-EBG are studied and representative designs are provided.
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