Radovan Zentner

Theoretical and experimental study of mutual coupling between microstrip stacked patch antennas

One of the major challenges that appears in the design of microstrip arrays is the impact of mutual coupling on radiation properties. The mutual coupling between array elements can be calculated using the standard moment method procedure in spectral domain. However, with increased distance between elements, the high-oscillating part of the sub-integral in method of moments (MoM) matrix elements makes standard integration procedures inapplicable. A convenient method for overcoming this problem is to change the integration path towards imaginary values in the complex plane, thus transforming the oscillatory behaviour to an exponentially decaying one. The challenge consists in careful management of the loci of the poles and branch cuts of the Greens function in the spectral domain (Garino, M.S. et al., 2000; Kitchener, D. et al., 1987), which generally differs for each MoM matrix element and must be tailored differently. A method for calculating these high-oscillating integrals is developed, implemented and compared with experimental results. The developed software can handle either single or stacked rectangular patch configurations with arbitrary number of dielectric layers.

Benefits and Challenges of Deterministic Reference Channel Models

The paper introduces a new paradigm for reference channel models. Current reference channel models are designed as platforms that generate radio channels for testing using random values for their parameters. These parameters follow some pre-established distribution based on process called parameterization, i.e. statistical processing of previous real measurements or accurate ray tracing simulations. The paper argues that random generated channels give either no new insight or even delusive information and should be replaced with the initial set of radio channels that was used for parameterization. Therefore a deterministic reference channel model, as an emulator of previously recorded real radio channels, is proposed and its potential elaborated.

Benefits of MIMO Systems in Practice: Increased Capacity, Reliability and Spectrum Efficiency

This work deals with multiple input multiple output (MIMO) systems in current and future wireless telecommunications systems. Advantages of adaptive antenna arrays, diversity techniques and waterfilling techniques are described. Possibilities of MIMO systems for the increase of channel capacity, reliability and spectrum efficiency is presented

Omnidirectional stacked patch antenna printed on circular cylindrical structure

A circular cylindrical multilayer stacked patch antenna with omnidirectional radiation pattern is considered. The antenna is rigorously analyzed using a moment method program, where the antenna structure is rigorously taken into account by using proper Greens functions and where the elements needed for the moment method procedure are calculated in the spectral domain. In order to obtain an omnidirectional radiation pattern and impedance matching, the patch dimensions and the coax feed position are optimized. The antenna has been built and its input impedance, gain and radiation pattern measured. The measurement results presented, including the radiation pattern with approximately 4 dB omnidirectionality, proves the idea of applying a stacked patch configuration for the wideband operation of circular omnidirectional cylindrical patch antennas.

Time domain analysis of mutual coupling measurements between stacked patches

The measurement of mutual coupling between stacked patch antennas was performed in presence of distant reflections. Time domain analysis and processing were used for canceling out reflection influence on the measurements. Thus, actual values of measured mutual coupling parameter are obtained. These measurements were used for verification of theoretical model and developed software, where both amplitude and phase of the coupling parameter were compared.

Validity of approximate boundary conditions for periodic strips on cylindrical substrates

The strip gratings on dielectric cylinders are analyzed by using two types of approximate boundary conditions and by the moment method (MoM). The used approximate boundary conditions are the boundary conditions obtained by the homogenization method (BCHM), where the local planar approximation was applied, and the asymptotic strip boundary conditions (ASBC). The results show that the both approximate boundary conditions give good results when the period of the strips is small compared to the wavelength. However, BCHM gives more accurate results, and practically there is no difference between the MoM results and the results obtained by BCHM method if the periodicity is small enough. Furthermore, the ASBC cannot predict the coupling of the incident wave to the waveguide modes of the strip-loaded dielectric cylinder, which is predicted both by the MoM and the BCHM methods. The numerical results are also compared to measurements showing a very good agreement.

Comparison of DoA Estimation Algorithms in SDMA System

With Space Division Multiple Access (SDMA) schemes employing digital signal processing algorithms in its smart antenna systems, it is possible to improve the system capacity of modern wireless communication systems by enabling users angular separation. Angular separation ability enhances reception in Signal-of-Interest direction and minimizes interference in Signal-of-Not-Interest direction. Direction of Arrival (DoA) algorithms are used for estimation of a number of incident plane waves on the antenna array and their incidence angles. This paper compares performance of three DoA algorithms: MUSIC, root-MUSIC and Capon applied on the uniform linear array in the presence of uncorrelated white noise. The simulation results show that MUSIC outperformed root-MUSIC and Capon in both required number of snapshots and number of array elements as well as in signal-to-noise ratio requirements.

Derivation and application of ray entity concept

The concept of ray entity would enable compact presentation and interpolation of ray tracing data. Moreover, ray entity concept should enable ray tracing based deterministic reference channel models that would enable obtaining double directional channel matrix for arbitrary user movement in realistic propagation environment. In this paper recording of ray entities is presented, for entities with rays formed due to different series of propagation phenomena on various interaction objects.

Ray tracing interpolation for continuous modeling of double directional radio channel

The paper investigates size of an area where a certain propagation phenomenon is visible in an urban setting, using post-processing of ray tracing (RT) data. The propagation phenomenon is distinctive from its counterparts by unique series of interactions that the radio signal encounters while traveling from transmitter to the receiver. Interactions are uniquely defined by their nature, i.e. diffraction or reflection, and by the object where they occur, i.e. specific building edge, or building side, respectively. The analysis of phenomenon visibility is performed on a set of data along an urban route, obtained from rigorous 3D ray tracing simulations. The rays along the route are divided into “ray entities” (RE), based on the affiliation to unique propagation phenomena. Introduction of REs along the route enables interpolation of the RT results between RT receiver points, thus enabling continuous radio channel model with significantly reduced computational burden. Additionally, based on each RE visibility along the route, the results give an insight into the dynamics of change of propagation modes in a multipath environment. This information provides the conditions under which it is reasonable to decrease the sample rate in ray tracing tools while using interpolation instead.

Open issues for practical implementation of MIMO systems

This paper deals with some of the open issues in the area of MIMO systems from a practical point of view. Theoretical capacity in several channel models and the difference between theoretical and realistic channel are described. Limitations of possible number of antenna elements and antenna topologies are presented. Trade-off between maximum capacity and cost/complexity is discussed.