Paolo Nepa

Antennas and propagation for on-body communication systems

On-body communication channels are of increasing interest for a number of applications, such as medical-sensor networks, emergency-service workers, and personal communications. This paper describes investigations into channel characterization and antenna performance at 2.45 GHz. It is shown that significant channel fading occurs during normal activity, due primarily to the dynamic nature of the human body, but also due to multipath around the body and from scattering by the environment. This fading can be mitigated by the use of antenna diversity, and gains of up to 10 dB are obtained. Separation of the antennas performance from the channel characteristics is difficult, but results show that for many channels, an antenna polarized normal to the bodys surface gives the best path gain. Simulation and modeling present many challenges, particularly in terms of the problems scale, and the need for accurate modeling of the body and its movement.

A Focused Planar Microstrip Array for 2.4 GHz RFID Readers

The specific problems encountered in the design of near-field focused planar microstrip arrays for RFID (Radio Frequency IDentification) readers are described. In particular, the paper analyzes the case of a prototype operating at 2.4 GHz, which has been designed and characterized. Improvements with respect to conventional far-field focused arrays (equal phase arrays) are discussed and quantified.

Diversity Performance Analysis for On-Body Communication Channels at 2.45 GHz

Body-centric communications is an important part of fourth-generation personal communications systems. Like the mobile cellular communication channel, on-body communication channels are affected by fading. In this paper, the effect of diversity for on-body communication channels is investigated. Measurements were taken in both an anechoic and typical indoor environments, with random body movements. Three different types of antennas were used. The diversity gain was calculated by plotting the cumulative distribution functions (CDF) for five body channels. Significant diversity gain values are observed for the nonline-of-sight channels and dynamic channels involving large body movements. The uplink and downlink diversity performance was found to be similar.

Multiband PIFA for WLAN mobile terminals

A novel compact planar inverted-F antenna (PIFA) to be mounted on laptop computers is presented. The proposed multiband single-feed PIFA simultaneously operates in the IEEE 802.11a, IEEE 802.11b/g, and HIPERLAN2 frequency bands. The multiband behavior is obtained by combining a trapezoidal feed plate with two different resonance paths in the radiating structure. The overall size of the antenna renders it suitable to be installed at the border of the display of a notebook. Simulation results are compared with measurements performed on an antenna prototype.

A hybrid uniform geometrical theory of diffraction–moment method for efficient analysis of electromagnetic radiation/scattering from large finite planar arrays

A hybrid uniform geometrical theory of diffraction (UTD)-moment method (MOM) approach is introduced to provide an efficient analysis of the electromagnetic radiation/scattering from electrically large, finite, planar periodic arrays. This study is motivated by the fact that conventional numerical methods become rapidly inefficient and even intractable for the analysis of electrically large arrays containing many antenna or frequency-selective surface (FSS) elements. In the present hybrid UTD-MOM approach, the number of unknowns to be solved is drastically reduced as compared to that which is required in the conventional MOM approach. This substantial reduction in the MOM unknowns is essentially made possible by introducing relatively few, special ray-type (or UTD) basis functions to efficiently describe the unknown array currents. The utility of the present hybrid approach is demonstrated here for the simple case of a large rectangular phased array of short and thin metallic dipoles in air, which are excited with a uniform amplitude and linear phase distribution. Some numerical results are presented to illustrate the efficiency and accuracy of this hybrid method.

Design Criteria for Near-Field-Focused Planar Arrays

A detailed performance analysis of near-field-focused planar arrays is addressed. Design curves and performance data are shown for planar square arrays as a function of the array size, the inter-element distance, and the focal distance. The performance curves are compared with results presented in earlier studies relevant to continuous-aperture antennas, as well as with numerical results obtained from a full-wave analysis of planar microstrip arrays.

A Wide-Band Dual-Polarized Stacked Patch Antenna

A wideband dual-polarized slot-coupled stacked patch antenna operating in the UMTS (1920-2170 MHz), WLAN (2.4-2.484 GHz), and UMTS II (2500-2690 MHz) frequency bands is described. Measurements on a prototype of the proposed patch antenna confirm good performance in terms of both impedance matching and isolation

Diversity Measurements for On-Body Communication Systems

In this letter, preliminary measurements for the analysis of diversity techniques for on-body communication systems have been carried out, when both the transmitter and the receiver are placed on the body. A monopole antenna on a square ground plane has been used as a transmitting element and two monopoles on a common ground plane as a two-branch receiver. Measurements have been carried out in an anechoic chamber in order to verify the scattering and fading effects of the body itself on the radio communication channel. The acquired data have been postprocessed by resorting to different signal combining techniques, in order to evaluate the diversity performance. Measurement results in terms of diversity gain are shown for a number of typical on-body radio links, when different body postures are considered.

Design of a Near-Field Focused Reflectarray Antenna for 2.4 GHz RFID Reader Applications

The design of a reflectarray antenna is presented when the radiated field is focused in the near-zone of the array aperture. In particular, the reflectarray antenna is implemented for RFID reader applications at 2.4 GHz. Numerical investigations on the radiation characteristics of this reflectarray, as well as an experimental validation, are presented to demonstrate its feasibility.

A novel single base station location technique for microcellular wireless networks: description and validation by a deterministic propagation model

Positioning algorithms in cellular networks has become increasingly important as a means of supporting emerging services that require a sufficiently precise estimation of the position of the mobile terminal (MT) associated with a given base station (BS). Currently, even the most sophisticated positioning algorithms require at least three BSs to achieve satisfactory precision. This paper presents a novel algorithm that makes use of a single-BS antenna array to locate MTs in cellular networks. A triangulation technique is utilized and supported by some minimal information about the environment in the BS neighborhood. This algorithm is shown to perform well when operating in a microcellular environment with perfect channel-parameter estimation. The effect of finite resolution of the input parameters is also investigated. The performance is analyzed for a universal mobile telecommunications system microcellular scenario through a three-dimensional deterministic channel model. Finally, the performance of the proposed positioning technique is compared to the well-known location method based on the time-of-arrival measurements at three different BSs.