ABSTRACT
The use of the electromagnetic fields at different frequencies and intensities, like mobile phones, wireless communications and wearable communications, received a lot of attention from many researchers from different fields.
The development of mobile phones and the miniaturization of portable electronic devices also stimulated many related research studies, like biological effects of electromagnetic fields, design of proper antennas for mobile terminals of satellite broadband communication systems, on-body communications.
The purpose of the first part of this thesis is to provide an understanding of the non thermal biological effects of electromagnetic fields. The objective was to evaluate the intensity of the electric field within different geometrical biological cells. The cell models have been simulated using CST MWS, and they have been exposed to a linearly polarized electromagnetic plane wave. Evaluations of the mutual interaction and transmembrane potential have been performed.
On the second part of this thesis the attention has been focused on a different application which regards the design of a rectangular dielectric resonator antenna operating in Ku frequency band. This new antenna is proposed to be used as a radiating element of a TX phased array of active integrated antennas (AIAs). Since in a transmitting AIA, the radiator has to provide a proper load for the power amplifier, two new techniques have been implemented in order to optimize the system performance at the fundamental frequency and first harmonics as well. The first technique is based on the use of the two additional slots. These two slots have been introduced parallel to the main coupling slot. The second harmonic tuning technique is based on a proper choice of the rectangular dielectric resonator dimensions, namely the shape factor. By using these techniques it is possible to control the input impedance at the second and third harmonic without influencing the impedance behaviour at the fundamental frequency. The antenna has been designed by using Ansoft HFSS. Simulations have been carried out to determine the features of the antenna and the capabilities of the two new harmonic tuning techniques.
In the third part of the thesis an analysis of the space diversity performance for on- body communication channels at 2.45 GHz has been addressed. Measurements have been carried out in the anechoic chamber for different body postures and antenna placements. A transmitting monopole has been always mounted at the belt. A receiving system of two monopole antennas located on a common ground plane has been mounted on five different positions, in order to form five different on-body links: belt-ankle, belt-back, belt-chest, belt-head and belt-wrist. The main objective of this chapter is to verify the consistency and the reliability of the diversity measurements. The received signals have been properly combined through Selection combining, Equal Gain combining and Maximum Ratio combining techniques. Cumulative distribution functions have been calculated and illustrated. The repeatability study has been based on the analysis of the diversity gain as a function of the power imbalance between the two receiving branches and the envelope correlation coefficient.
Finally, the last part of this thesis regards the design of a low profile antenna for on- body communication systems. The antenna proposed is a dual pattern/dual polarization annular ring slot antenna which operates in the IEEE 802.11a frequency band at 5.725-5.825 GHz. The antenna has been simulated by using Ansoft Designer software. The antenna presents triplet feeding, namely Port 1, Port 2 and Port 3. When the Port 1 is fed, a dipole-like radiation pattern is achieved.
When Port 2 and Port 3 are fed, broadside radiation patterns are obtained. A few prototypes have been realized and measurements have been performed to evaluate the antenna characteristics.
