Ing. Vojtěch Neuman

The presented article proposes a theory for the optimization of multiple-input-multiple-output antenna performance by assessing feeding coefficients. Antenna clusters with multiple feeding ports are utilized, which brings additional degrees of freedom and improves the performance. This work considers fixed shape and matching networks. The method is based on quadratic programming and maximizes total efficiency constrained by channel correlation and channel power distribution. The formulation provided in the article enables establishing trade-offs between all mentioned metrics. Evaluating the performance in this manner provides comprehensive information about the chosen geometry and port placement. Selected examples demonstrate how efficiency and channel correlation can be both in agreement but also in significant conflict. The effect of frequency dispersion on feeding is also investigated.

We present a design approach for a long-distance optical camera communication (OCC) system using side-emitting fibers as distributed transmitters. We demonstrate our approach feasibility by increasing the transmission distance by two orders up to 40 m compared to previous works. Furthermore, we explore the effect of the light-emitting diode (LED) modulation frequency and rolling shutter camera exposure time on inter-symbol interference and its effective mitigation. Our proposed OCC-fiber link meets the forward-error-correction (FEC) limit of 3.8 · 10−3 of bit error rate (BER) for up to 35 m (with BER= 3.35 · 10−3) and 40 m (with BER=1.13 · 10−3) using 2-mm and 3-mm diameter side-emitting fibers, respectively. Our results at on-off keying modulation frequencies of 3.54 kHz and 5.28 kHz pave the way to moderate-distance outdoor and long-distance indoor highly-reliable applications in the Internet of Things and OCC using side-emitting fiber-based distributed transmitters.

An existing method for maximization of the total efficiency of antenna clusters is modified so that the correlation between the channels can be suppressed while maintaining good balance of powers in different channels. This is achieved by setting additional constraints based on matrix description which control the system radiated power by means of weighted feeding coefficients. The developed theory is demonstrated on the example of four parallel dipoles forming two antenna clusters.

We demonstrate for the first time the application of LED-based optical camera communication using a side-emitting fiber in wearable applications. A 1.2-m long plastic side-emitting fiber with a 4-mm outer diameter acts as a distributed transmitter. The side-emitting fiber is attached to a T-shirt over the shoulder with a 50-cm section of the fiber both on the front and back side of the T-shirt. This expands the possibilities of data detection by the rolling shutter camera. The light from a white LED is coupled into the side-emitting fiber with LED on-off keying (OOK) modulation frequencies of 2.64 kHz, 3.54 kHz, and 5.31 kHz. The results show bit error rate bellow 3.8 • 10 −3 for up to 200 cm fiber to camera distance.

The existent technique for shape optimization based on exact reanalysis of method-of-moments models is extended by symmetry operators. Their application is twofold: to prescribe a given symmetry and accelerate the optimization by reducing the number of unknowns, or to penalize unsymmetrical shapes, constraining thus the regularity and simplifying potential manufacturing.

The topology optimization based on iterative changes of discretization is introduced. The optimal solution on coarse discretization is translated and enhanced on dense discretization. The similarity matrix used for solution translation is defined. Two examples of Q-factor minimization are shown to depict improvements in evaluation spee

The existent framework for shape optimization of electrically small antennas is extended by a new set of geometrical operators. They are capable of operating over shapes directly, controlling their regularity, amount of used material, etc. The formulation is compatible with existent physical fitness functions and known fundamental bounds. A simple example of Q-factor minimization is presented.