Showing papers by "Per-Simon Kildal published in 2006"

The eleven antenna: a compact low-profile decade bandwidth dual polarized feed for reflector antennas

Abstract: A novel dual polarized ultrawide-band (UWB) feed with a decade bandwidth is presented for use in both single and dual reflector antennas. The feed has nearly constant beam width and 11 dBi directivity over at least a decade bandwidth. The feed gives an aperture efficiency of the reflector of 66% or better over a decade bandwidth when the subtended angle toward the sub or main reflector is about 53/spl deg/, and an overall efficiency better than 47% including mismatch. The return loss is better than 5 dB over a decade bandwidth. The calculated results have been verified with measurements on a linearly polarized lab model. The feed has no balun as it is intended to be integrated with an active 180/spl deg/ balun and receiver. The feed is referred to as the Eleven antenna because its basic configuration is two parallel dipoles 0.5 wavelengths apart and because it can be used over more than a decade bandwidth with 11 dBi directivity. We also believe that 11 dB return loss is achievable in the near future.

Measurements of total isotropic sensitivity and average fading sensitivity of mobile phones in reverberation chambers

Abstract: The authors describe two ways to measure receive performance of active terminals by using a reverberation chamber, referred to as total isotropic sensitivity (TIS) and average fading sensitivity. The latter is a new method which can be measured very fast in a reverberation chamber. It is also more representative of the actual performance of a terminal in a real fading environment than the former. Based on measured results, they conclude that the average fading sensitivity is a promising alternative to TIS measurements for characterizing receive performance of mobile terminals. The reverberation chamber is well suited for both these measurements. Average fading sensitivity measurements can be done faster than TIS and give similar relative results i.e. the average fading sensitivity shows similar difference between the different phones as the TIS results, when they read the sensitivity levels at 0.5% error level.

Analysis of dispersion in dipole-FSS loaded hard rectangular waveguide

Abstract: We investigate the properties of the dipole frequency selective surfaces-loaded rectangular waveguide. The analysis is carried out by using the method of moments together with an algorithm that solves for a multilayer structure in the spectral domain. The eigenmodes are determined by searching for resonant solutions. Dispersion diagrams obtained from this approach are compared with those generated by commercial software simulations. Experimental validation is also performed

Investigation of Heavily Loaded Reverberation Chamber for Testing of Wideband Wireless Units

Abstract: Traditionally, the reverberation chamber has been used as a low-loss cavity to gain high signal levels. For testing of the radiated properties of wireless terminals and their antennas, this is not an issue, and lossy objects like for instance a head phantom can be introduced in the chamber without problem. However, for testing of active units, the bandwidth of the system itself plays an important role. In order to avoid distortion of the signal transmitted in the chamber, the bandwidth of the chamber must be larger than the bandwidth of the signal. This is one reason for loading the reverberation chamber. Another reason is a potential increase in the measurement accuracy, since an increased bandwidth makes more modes excited at a particular frequency. The purpose of this paper is to investigate the effect of loading on the statistics of the chamber and its bandwidth

Analysis of spherical arrays of microstrip antennas using moment method in spectral domain

Abstract: Arrays of rectangular single- and stacked-patch antennas embedded in a multilayer spherical structure are analysed using the spectral-domain approach and the moment method. The patch current is transformed to the spectral domain using the vector-Legendre transformation. This simplifies the analysis procedure, because the electromagnetic field excited by one spectral source component has the same angular variation as the source. To avoid numerical difficulties appearing when analysing structures with large radii, a modified vector-Legendre transformation and normalised Legendre functions are defined and applied to the solution procedure. Furthermore, the asymptotic formulas for the field distribution of higher-order spectral modes are implemented into the algorithm for calculating Green's functions. The effect of deviation from the spherical symmetry and the influence of the structure radius on self and mutual impedance are studied. A laboratory model is built to test different configurations of spherical patch antennas and to validate the developed program.

Single- and dual-band multimode hard horn antennas with partly corrugated walls

Abstract: We introduce a partly corrugated hard horn, consisting of a smooth-walled horn with an attached longitudinally corrugated outer section. This alleviates the problems with the manufacturing when the longitudinal corrugations extend into the throat of the horn. The transition between the inner smooth walled part and the outer corrugated part is abrupt. This is used and controlled to design better and shorter single-band horns than otherwise possible. Furthermore, it enables the design of dual-band horns with low cross-polarization and high gain, for multifunction use at Ka-band with transmit and receive frequencies in the same antenna. Measurements on a model of such a dual-band horn are presented and discussed.

Designing reverberation chambers for measurements of small antennas and wireless terminals: Accuracy, frequency resolution, lowest frequency of operation, loading and shielding of chamber

Abstract: The last five years the reverberation chamber has been developed to an accurate instrument for measuring the performance of small antennas and active mobile terminals in Rayleigh fading. The present paper gives an overview of the research done by the authors in relation to achieving an accuracy of 0.5 dB RMS or better, when measuring efficiency and radiated power. The accuracy has been verified by comparison with measurements in anechoic chambers, and between reverberation chambers of different size, and from participation in benchmarking of measurement ranges done within ACE (Antenna Center of Excellence, a European Network of Excellence). There have also been developed procedures for measuring quantities that are specific for the Rayleigh environment, such as diversity gain, MIMO capacity, and static as well as dynamic receiver sensitivity at certain data error rate (BER or FER). The paper will describe important topics related to the mode stirring and loading of the chamber, such as the accuracy, frequency resolution, average transfer function, and the system bandwidth when measuring active terminals. Numerical simulations play an important role in controlling the chamber performance.

Analysis of spherical arrays of microstrip antennas using moment method in spectral domain

Abstract: Arrays of rectangular single- and stacked-patch antennas embedded in a multilayer spherical structure are analysed using the spectral-domain approach and the moment method. The patch current is transformed to the spectral domain using the vector-Legendre transformation. This simplifies the analysis procedure, because the electromagnetic field excited by one spectral source component has the same angular variation as the source. To avoid numerical difficulties appearing when analysing structures with large radii, a modified vector-Legendre transformation and normalised Legendre functions are defined and applied to the solution procedure. Furthermore, the asymptotic formulas for the field distribution of higher-order spectral modes are implemented into the algorithm for calculating Green's functions. The effect of deviation from the spherical symmetry and the influence of the structure radius on self and mutual impedance are studied. A laboratory model is built to test different configurations of spherical patch antennas and to validate the developed program.

Measurements of a 150 to 1700 MHz low loss Eleven feed for the 42 m radio telescope at Green Bank

Abstract: We present measured results for a dual polarized 150 to 1700 MHz Eleven feed for use in the 42 m radio telescope in Green Bank. The feed is manufactured from a 3 mm thick aluminium plate and located inside a steel container with a soft radome over its opening. The feed provides dual polarization and more than a decade bandwidth. The aperture efficiency in a primary feed reflector system is better than -2.25 dB over the entire band, and the input reflection coefficient is better than -7.0 dB. The losses have been computed and measured and are lower than the measurement accuracy of -0.5 dB over the entire band. The coupling between the two polarizations is lower than -29 dB across the entire band. The results agree well with computed values.

Maximizing the effective diversity gain of two parallel dipoles by optimizing the source impedances

Abstract: The embedded element patterns of two parallel half-wavelength dipoles are calculated for various source impedances and dipole spacings by using classical formulas for self and mutual impedances. These are used to calculate the effective diversity gain, which is shown to vary with source impedances and dipole spacing. The results are verified using a method of moments (MoM) code for wire antennas and via measurements in a reverberation chamber. The numerical model is used to find the source impedances that maximize the effective diversity gain, which has a maximum for the computed cases when the source impedances are conjugate-matched to the input impedances of each of the embedded dipole elements. Then the two antenna ports are uncorrelated. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 532–535, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21400

Control of reflection and mutual coupling losses in maximizing efficiency of dense focal plane arrays

Abstract: The FOV of a radio telescope fed by a cluster of conventional horns in a one-horn-per-beam configuration is limited to a few beamwidths due to the field distortions which appear for off-axis directions of observation. To overcome this limitation, it has been suggested to use dense focal plane arrays (FPAs) of electrically small elements in which several of these elements contribute to each beam. The primary goal of the paper is to investigate the impact of reflection, coupling and dissipation losses in dense FPAs on the total aperture efficiency of the reflector antenna. We present and discuss results obtained for two dense array realizations: one reference realization of miniaturized open-ended hard waveguides, and another practical FPA of Vivaldi elements.

Reverberation chamber evaluation of multi-antenna handset having low mutual coupling and high efficiencies

Abstract: This paper presents the evaluation of the diversity performances of several multi-antenna structures in a reverberation chamber Firstly, a two-antenna system having low isolation between the radiators is measured Its performances are compared with a second structure which uses a neutralization technique to enhance the radiating element's isolation Then the performances of a four-antenna system with and without the neutralization method are measured and presented Particularly, the total antenna efficiencies, the envelope correlation coefficients and the diversity gain of these systems are presented and discussed We especially focus on the advantages of the neutralization technique

Comments on "Application of double negative materials to increase the power radiated by electrically small antennas"

Abstract: For original paper see Ziolkowski and Kipple (IEEE Trans. Antennas Propag., vol.51, no.10, p.2626-40, 2003 October). The results of the commented paper are of no value for evaluating the performance of small antennas surrounded by double negative material. The characterizing parameter "radiated power gain" is misleading and turns out to be a relative input resistance rather than a gain.

Realized diversity gain of active DECT phones in talk position measured in reverberation chamber

Abstract: The reverberation chamber is a rectangular metal cavity that supports several modes. Each mode can be interpreted as eight plane waves propagating in different directions. To simulate a rich scattering environment, the modes are stirred. The net effect is fading with Rayleigh statistics, being very similar to what handheld units experience in indoor and urban areas. DECT is an acronym for Digital Enhanced Cordless Telecommunications. The cordless units receive and transmit on the same frequency, which in Europe lies in the band 1880-1900 MHz, and this makes it easy to implement antenna diversity on transmit. The maximum output power from a DECT unit is limited to 24 dBm.

Fundamental Limitations of Focal Plane Arrays Characterized in Terms of Radiation Efficiencies of Their Embedded Element Patterns

Abstract: This paper investigates the prospects of using an array of open-ended miniaturized rectangular hard waveguide elements to realize a dense focal plane array (FPA) feed illuminated according to the desired Airy-disc aperture illumination function. The investigation employed an existing computer program code that analyzes an infinite planar "active" array of such open ended dielectric-loaded hard rectangular waveguides which are uniformly excited and linearly phase-steered to give a certain beam direction. Upon further processing and manipulation of the results generated by this array code, any kind of array aperture illumination (in both amplitude and phase) can be studied, with all self and mutual coupling effects taken into account. Hence, this permits the study of the Airy-illuminated FPA feed. The objective of this paper is to ascertain the effects of element size on radiation efficiency of the FPA feed

Relations between radiation characteristics of small antennas located in free space and close to lossy phantom

Abstract: The characterization of small terminal antennas close to head phantoms and other lossy objects is time-consuming, and in particular if the radiation patterns are to be measured for many positions close to the phantom. The main effect of a lossy object is absorption and a corresponding reduction in the radiation efficiency of the antenna. For operation in multipath environments with Rayleigh fading the radiation efficiency is the most significant performance parameter; the radiation pattern plays a minor role. Therefore, characterization could be based on only the radiation efficiency, which can be measured fast and accurately in e.g. a reverberation chamber. It has been proposed (and is also practiced some places) to determine the absorption in the head phantom and the corresponding radiation efficiency by simply using the free space radiation pattern to calculate the relative power shadowed by the phantom. The purpose of the present work is to investigate the relevance and accuracy of such an approach, compared to an actual measurement of radiation efficiency

Fast numerical model of reverberation chambers with metal stirrers using moment method and cavity Green's function calculated by Ewald summation

Abstract: Reverberation chambers (RC) are metal cavities used for measuring electronic devices. When designing RCs it might be useful to have a numerical model of them. Since a RC is large in terms of wavelength this is challenging. A numerical model of a rectangular metal cavity is developed using method of moments (MoM) and a cavity Green's function (GF). In this way, unknowns at the walls or in the volume of the cavity are not needed. Since movable parts have to be modeled, extensive computations are needed to cover all possible positions of these parts, and statistical analysis has to be used. Therefore, computational speed is very important. In the present paper, various methods used to reduce the computation time of the code and how it is implemented for perfect electric conducting thin wires and plates located inside the chamber are described.

Overview of the software integration activities within ACE

Abstract: The ACE project initiated the start of several integration activities between European institutions involved in electromagnetic modeling of antennas with planar or conformal topologies. The goal of the integration activities was / is not to create a global software package that integrates the software of all partners, but to initiate a long term process for antenna software integration activities within the European antenna community. During the first two years of ACE the integration activities were performed in several groups with a rather small number of partners in each group. The groups were formed by partners who wanted to integrate a specific approach developed by one partner into the software code of another partner. This allows increasing the capability and efficiency of a software code. In this paper a short overview of all integration activities is given.

Dyadic GO reflection coefficient for PEC/PMC strip surface and application to the planar case for dipole radiation

Abstract: The dyadic reflection coefficient of a planar surface consisting of parallel PEC and PMC strips is derived and used to study radiation patterns of dipoles located over the surface. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 583–587 2006; Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.21414