Michael Yan Wah Chia

Small planar UWB antennas in proximity of the human head

The effects of a human head on the performance of small planar ultra-wideband (UWB) antennas in proximity of the head are investigated numerically and experimentally. In simulation, a numerical head model is used in the XFDTD software package. The head model developed by REMCOM is with the frequency-dependent dielectric constant and conductivity obtained from the average data of anatomical human heads. Two types of planar antennas printed on printed circuit board (PCB) are designed to cover the UWB band. The impedance and radiation performance of the antennas are examined when the antennas are placed very close to the human head. The study shows that the human head slightly affects the impedance performance of the antennas. The radiated field distributions and the gain of the antennas demonstrate that the human head significantly blocks and absorbs the radiation from the antennas so that the radiation patterns are directional in the horizontal planes and the average gain greatly decreases. The information derived from the study is helpful to engineers who are applying UWB devices around/on human heads.

UWB characteristics of disc cone antenna

Recently, ultra-wideband (UWB) technology has attracted much attention and demands for UWB antennas with omnidirectional coverage are increasing. The conventional solution to achieve omnidirectional radiation in a horizontal plane is to use a thin wire dipole or monopole with a ground plane. However, these suffer from a narrow impedance bandwidth. Disc cone antennas have been employed for many years in the microwave frequency range because of their broadband characteristics. Their radiation is omnidirectional in azimuth. The disc cone antenna is a special case of biconical antenna; its impedance and radiation characteristics are mainly determined by the angle of the cone and the diameter of the disc. The length of the cone and the dimensions of the feeding structure limit the antennas lowest and highest frequencies. We characterize the disc cone antenna, not only by classical frequency domain parameters, such as impedance, gain and radiation patterns, but also by time domain parameters, such as transfer function and fidelity. The results show that the disc cone antenna has acceptable performance for UWB applications.

Broadband annular dual-slot antenna for WLAN applications

A novel annular dual-slot antenna is presented. The antenna consists of two concentric annular slots and an open-circuited microstrip feed line. The simulation and experimental results indicate broad operating bandwidth from 4.8 GHz to 6.2 GHz (VSWR 2:1). At these frequencies, the antenna displays a broadside bidirectional radiation pattern, with gain on the order of 2.5 dBi. It is suitable for 5 GHz WLAN applications.

Parametric Study of Ultra-Wideband Dual Elliptically Tapered Antipodal Slot Antenna

Parametric study of the impedance and radiation characteristics of a dual elliptically tapered antipodal slot antenna (DETASA) is undertaken in this paper. Usually, the performance of the DETASA is sensitive to the parameters, the effects of major geometry parameters of the radiators and feeding transition of the DETASA on antenna performance are investigated across the frequency range of 1–18 GHz. The information derived from this study provides guidelines for the design and optimization of the DETASAs which are widely used for UWB applications.

CCDF and Monte Carlo Analysis of a Digital Polar Transmitter for Ultra-Wideband System

Polar modulation has been adopted by modern wireless systems due to its high power efficiency. In this paper, a novel behavioral model for a digital polar transmitter is presented. The polar transmitter contains an array of amplifiers, which are controlled digitally. A system level simulator is used to model each amplifier. The effects of different number of stages on the mandatory data rates are studied with respect to the error vector magnitude, in conformance to the ultra-wideband standard. Next the complementary cumulative distribution function is studied for a four-stage digital polar transmitter in order to gain an understanding of when each individual stage is turned on. Lastly, nonlinearity, modeled as gain variation for the different parallel stages, is included for a four-stage digital polar transmitter when the data rate is 480 Mbps. Results demonstrate the feasibility of obtaining high efficiency using digital polar transmitters for multiband OFDM UWB systems.

Design of a CMOS UWB receiver front-end with noise-cancellation and current-reuse

The design of an ultra-wideband (UWB) CMOS receiver front-end that integrates a broadband single-ended low-noise amplifier (LNA) and a quadrature downconversion balun-mixer is presented. Noise-canceling technique is employed in the LNA to decouple input match from noise figure (NF). To be directly driven by the LNA, the balun-mixer has a single-ended input double-balanced topology. For low power consumption, both the LNA buffer and the active balun are embedded in the mixer design with bias current reused. Drawing 21 mA from 1.5V, the receiver front-end simulates a voltage conversion gain of 29 dB with an input IP3 of −14 dBm. Over the 3.1–10.6 GHz UWB band, an NF of 4–5.1 dB and an S11 <−10 dB are obtained.

Enhanced radiation performance of broadband suspended plate antenna

broadband suspended plate antenna is experimentally presented to enhance its radiation performance. A probe-fed narrow half-wavelength strip parallel to a ground plane is proposed to feed the antenna. The segments at the front and back end of strip are vertical to the plate and ground plane. The two vertical segments with the currents of a 180/spl deg/ phase shift act as the dual-probe feeding structure. The resultant cross-polarization levels in the H-planes come down on and the distortions of co-polarization patterns in the E-planes ease off. The experiments on the antenna were conducted. The measured impedance and radiation characteristics have shown that the design is capable of providing a 20% impedance bandwidth for 2:1 VSWR with cross-polarization levels of <-20 dB and stable radiation patterns in both E- and H-planes.

The effects of reinforced concrete walls/floors on wireless personal communications systems (PCS)

The reinforced concrete (RC) wall/door of a building is typically made up of a wire mesh embedded in a thick layer of concrete cement for structural reinforcement. The mesh may consists of straight wires joined perpendicularly to give a planar periodic array of square grid for structural reinforcement. When the array is illuminated by electromagnetic waves, its inherent periodicity would exhibit certain reflection characteristics depending on the size of the grid and the concrete properties. The paper shows that such a gridded RC structure would enhance the reflection in a wireless personal communications systems (PCS) environment. The present study gives a brief theoretical formulation for the gridded RC structure using the Floquet modal theorem and discusses its predicted reflective characteristics.

Design and performance of a digital polar transmitter system for multiband-OFDM Ultra-WideBand

A low-voltage 3-bit Digital Polar Amplifier for MB-OFDM UWB is proposed, which comprises 7 parallel RF amplifiers driven by a constant RF phase-modulated signal and 7 cascode transistors (connected in series) digitally controlled by a 3-bit digitized amplitude signal to reconstruct the UWB signal at the output. Our DPA was able to achieve an EVM of -22 dB and drain efficiency of 21.0% while delivering 5.5 dBm of output power and consuming 17 mW of power using IBM 130-nm CMOS technology.