Showing papers by "Per-Simon Kildal published in 2005"

Radiation efficiency, correlation, diversity gain and capacity of a six-monopole antenna array for a MIMO system: theory, simulation and measurement in reverberation chamber

Abstract: A six-monopole circular antenna array for use in a MIMO system is considered. The authors show how to calculate the embedded element patterns, both by classical analytical modeling and by the method of moments. Thereafter, these are used to calculate the radiation efficiency of each embedded element, correlation and diversity gain, as well as the maximum average capacity of the MIMO system when the array is located in a rich scattering environment. The theoretical value for the capacity is obtained by numerically distributing many plane wave sources statistically uniformly over 4/spl pi/, letting them illuminate the calculated embedded element pattern and using Shannon's capacity formula on the received wave amplitudes. The calculated results are compared with measurement in a reverberation chamber, representing a similar scattering environment. The agreement is good.

Miniaturized rectangular hard waveguides for use in multifrequency phased arrays

Abstract: The elements of a multiband array need to be small to allow elements of other frequencies to be interlaced over the same array aperture. This paper investigates the use of miniaturized open-ended partially dielectric-loaded hard-walled rectangular waveguides for this purpose. Apart from studying its modal properties, we seek to find out how it performs in an infinite planar array environment. Specifically, we study how the various array parameters affect its radiation characteristics. Comparisons are also made with fully filled waveguides. The waveguides are matched at broadside. The results show a narrow-band solution.

Mode-matching modeling of a hard conical quasi-TEM horn realized by an EBG structure with strips and vias

Abstract: A conical horn with hard wall used for supporting the quasi-TEM-mode having a uniform field distribution over the cross section is modeled. The hard wall is realized as an electromagnetic bandgap (EBG) structure using a dielectric layer loaded with narrow longitudinal strips connected to the basic metallic wall by radial vias to prevent excitation of the strip-line mode. The modeling is based on a stepwise approximation of the horn surfaces by a set of cylindrical sections. Each section consists of a strip-loaded part and a longitudinally corrugated part representing the vias. The stepped horn characteristics are calculated by using the mode-matching method combined with the Winer-Hopf-Weinstein method for accurate account of the wave scattering at the aperture. The strip-line mode resonance effects are studied and demonstrated. It is shown that if the length of the strip part of each section sufficiently differs from the resonance value, the performance of the hard strip-loaded horn with vias is similar to high performance of the appropriate hard corrugated horn. Recommendations are given on appropriate choice of the maximum spacing between the vias providing the absence of resonance effects in the specified frequency band.

Study of High-Efficiency Corrugated Hard-Horn Antennas Using Classical Approaches: Hard Circular Waveguide Mode, Phase Factor, and Aperture Integration

Abstract: In this paper, a classical-type approach is used to analyze the hard horn antenna. The quasi-TEM mode in the longitudinally corrugated cylindrical waveguide is found by using the homogenized asymptotic boundary conditions. The finite horn length is accounted for by including a phase factor in the waveguide-aperture fields, and the radiation patterns are finally obtained by aperture integration. The bandwidth is found to be much wider than previously anticipated with respect to low cross-polarization. Also, an advanced mode-matching code has been used for verification of the aperture field and the radiation patterns obtained with the much faster classical model.

Comparison between bandgaps and bandwidths of back radiation of different narrow soft ground planes

Abstract: Size reduction is one of the most important considerations for wireless personal communication system antennas In many cases, the main problem is the reduction of ground plane size Such reduction means an increase in antenna back radiation EBG (electromagnetic bandgap) surfaces have been used as ground planes Soft and hard surfaces are defined in terms of surface impedance and boundary conditions in the E- and H-planes A soft surface behaves like a PEC in the H-plane and as a PMC in the E-plane, thereby providing ideally infinite bandgaps in both E- and H-planes Therefore, they also reduce antenna back radiation in the E-plane A study of different soft surface ground planes has been made All the analyzed structures have been demonstrated to work as expected A bandwidth study is presented The results show an important conclusion: although the theoretical bandgap of these structures can be very large, this does not mean that for a particular application (in this case ground plane) the bandwidth is large as well For strip-loaded surfaces with vias, it was only possible to get very low back radiation in a narrow frequency band around the best 'soft' frequency, ie the start of the bandgap This best 'soft' frequency is slightly lower than the theoretical 'soft' frequency

Numerical investigation of bandgaps of different soft surfaces: corrugations and strip loaded substrate with vias

Abstract: The present work focuses on the study of bandgaps of soft surfaces in the form of metal strips printed on grounded dielectric slabs when the strips are provided with a metal connection to the ground plane. We can refer to such a structure as a modern realization of cavity loaded corrugations. In particular, the dispersion properties of the surface wave are investigated in order to find the bandgap.

Comparison of efficiency measurement methods for small antennas

Abstract: The National Center for Scientific Research (CNRS) in France launched a number of specific actions (SA) in order to identify the most challenging issues to be investigated by the French research community. One of these specific actions is dedicated to antenna miniaturisation. The aim of this action is to provide a state of the art and new direction of studies in the following topics: antenna miniaturisation techniques and designs, evaluation of small antenna Q and fundamental limitation in miniaturisations, software issues: computing and benchmark, comparison of different small antennas efficiency measurement methods. This last part gathers three French university laboratories (IETR, IREENA, LEAT) and two French companies (CEA-LETI, SAGEM). Recently, three companies (TCL&ALCATEL Mobile Phones, Bluetest AB, IMST GmbH) and the Chalmers University of Technology have been interested to participate to the efficiency round robin measurements. This paper presents the work already done from January to December 2004.

On the odd-even property of functions for boundary currents over k/sub z/ in a spectrum of two-dimensional solutions

Abstract: When a spectrum of two-dimensional (2-D) solutions (S2DS) is applied to calculate the far-field functions or impedances of three-dimensional (3-D) elements in the vicinity of two-dimensional (2-D) structures, in general, the calculations have to be performed for both positive and negative values of k/sub z/. This letter analyzes the odd-even property of functions for boundary currents over k/sub z/. Therefore, by using this odd-even property, the calculations of the far-field functions and impedances are only needed to be performed for positive values of k/sub z/, which reduces the computation cost by a factor of 2. A verification case is also presented.

Efficient Computation of a High-Q Resonator Realized by a Thin-Film Multilayer Metal/Dielectric Structure

Abstract: We present the computer code for a full-vector analysis of the fields inside a multilayer structure with an arbitrary number of layers. The code is validated by the analysis of a microwave resonator realized with thin-film technology. The periodic boundary conditions in the multilayer structure are derived for the cavity resonator. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 48–51, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20543

A method of moments solution for wires inside a reverberation chamber using spectral domain techniques and asymptotic extraction

Abstract: A Method of Moments Solution for Wires inside a Reverberation Chamber Using Spectral Domain Techniques and Asymptotic Extraction