T. Zervos

Sum of Non-Identical Independent Squared η-μ Variates and Applications in the Performance Analysis of DS-CDMA Systems

In this paper, new expressions for the probability density function (pdf) of the sum of non-identical independent squared η-μ random variables are derived. Based on our newly derived results, we provide a pdf-based approach for the performance analysis of 1-D and 2-D RAKE receivers in the context of an asynchronous direct sequence code division multiple access system operating over η-μ fading channels. For the considered system, useful performance metrics such as the outage probability, the channel capacity and the average bit error probability are investigated. Extensive numerical and computer simulation results are presented that illustrate the proposed mathematical analysis.

Statistical Analysis for On-Body Spatial Diversity Communications at 2.45 GHz

An investigation of the fading experienced by on-body diversity channels at 2.45 GHz is presented by focusing on the effects of the receive antennas position and the human body movement. This investigation is based on the conduction and analysis of signal measurements in an indoor office environment using bodyworn antennas. Three principal combining techniques, namely selection combining (SC), equal gain combining (EGC) and maximal ratio combining (MRC) are considered. A statistical characterization of the fading experienced by dual diversity on-body channels is performed in terms of first and second order statistics. Our investigations have shown that among several distributions tested, the α - μ distribution provides sufficient fit to measured combined signal envelopes and also offers a good approximation to second order statistics for the majority of test cases.

On-body channel modelling: Measurements and statistical analysis

This paper investigates the propagation phenomena and the fading experienced by on-body channels at 2.45 GHz, focusing on the effect of the human body. This investigation is based on signal measurements conducted for both stationary and mobile user cases using bodyworn antennas placed in various positions on the human body. The effect of the antenna location and the human body movement on the fading characteristics of the on-body channels is extensively studied through statistical analysis of the measurement data.

Patch antenna with polarization agility using ferrimagnetic materials

In this paper we propose the use of the ferrimagnetic compound, Yttrium Iron Garnet (YIG), as a substrate part of a patch antenna operating in Ku band (YIG-Patch). We investigate its influence on the antennas polarization properties under the application of an external magnetic field. It is proved that the axial ratio and also the sense and the tilt of the antenna polarization ellipse are strongly influenced by the YIG substrate since they change in respect to the direction and the magnitude of the external magnetic field. Also the presence of this material arises non reciprocal properties in the antenna operation, changing the antenna properties in respect to receiving or transmitting mode.

The Impact of the Position of MIMO Terminal User's Hand on Channel Capacity

In this paper the impact of the position of users hand holding a multiple-input-multiple-output (MIMO) terminal on system performance and more specifically on channel capacity is investigated. We consider a 4times4 MIMO system with a personal digital assistant (PDA) equipped with a compact array of 4 patch elements. Radiation field patterns of the antenna elements in the presence of the other elements as well as in the presence of a users hand are simulated. Different positions of the users hand are taken into account. The covariance matrix of the receiving antennas is evaluated by means of the obtained patterns. A correlation-based channel model is considered, where the antenna patterns are incorporated. Extensive simulations showed that the performance of the MIMO systems varies significantly with the position of the users hand.

Mobile Phone Antenna Performance and Power Absorption in Terms of Handset Size and Distance from User's Head

In this work numerical simulation and measurements of three-dimensional radiation patterns of a mobile handset model in the presence of a human head phantom were performed at 1800 MHz. Based on theoretical and experimental results, the influence of the human head on the radiation efficiency of the handset has been investigated as a function of the handset size and the distance between the head and the handset during its operation. Furthermore, the relative amount of the electromagnetic power absorbed in the head has been obtained. It was found that significant reduction of the absorbed power (about 50%) with proportional increment of the handset radiation efficiency could be achieved by moving the phone for 1 cm only away from the head. Agreement between theoretical and experimental results was found to be very good.

Experimental verification of a dual band CP patch antenna using a biased YIG compound

In this paper, we present a patch antenna design and fabrication that uses a ferrimagnetic compound, Yttrium Iron Garnet (YIG), as part of its substrate. It is proved via both numerical simulations and experimental measurements, that with suitable application of an external magnetic field, a reconfigurable behavior in terms of the polarization characteristics can be achieved. The antenna is reconfigured from a single band linear polarized to a dual band circular polarized one, with different polarization sense in each resonance band. Mixtures containing YIG and epoxy resin in various consistencies have been examined.

Reconfigurable proximity coupled patch antenna using magnetic bias

In this paper, we present the design, fabrication and characterization measurements of a proximity-coupled fed patch antenna that uses a ferrimagnetic compound, Yttrium Iron Garnet (YIG), as part of its substrate. External magnetic field is applied in order to achieve reconfigurability. Specifically, by applying a suitable external magnetic field, the linearly polarized single-band antenna exhibits dual-band behavior. Furthermore, it is proved via simulation and experimental measurements that we can achieve antenna polarization reconfigurability.

Properties of aluminum-substituted YIG with applications in tunable notched UWB antennas

Reconfigurable antennas based on ferrite materials require lower values of saturation magnetization than that of YIG to operate properly below 5 GHz. To this end, we turned to aluminum-substituted YIG. Six Y3Fe5-xAlxO12 samples, with x = 0.0, 0.25, 0.5, 0.7, 0.8 and 0.9, were synthesized with the standard solid state reaction method. Isothermal magnetization measurements at T = 295°K showed ferrimagnetic behaviour with ferromagnetic saturation magnetic moment which diminishes linearly with x. Ferromagnetic resonance measurements revealed that the mixed compounds exhibit approximately half the losses of pure YIG. The YIG-Al compound was then applied in the design of a tunable notched UWB antenna operating in the 1.7-8 GHz range. The ferrite was biased by small permanent magnets. The biased and unbiased states of the YIG-Al block produce isolated stopbands. Moreover, in these stopbands, the notched antenna is not only reflective, but also very inefficient.

Investigation of wearable antennas performance in static LOS and NLOS on-body channels

In this paper modelling of specific on-body channels is conducted by using three different antenna types. Our goal is to investigate antennas performance in different on-body contexts and examine antennas propagation mechanisms. For this purpose, a measurement campaign is performed. Results will be provided in terms of channel gain, slow and fast fading modelling by performing statistical analysis of received signal envelope.