S. W. Leung

Electromagnetic Interference Immunity Testing of Medical Equipment to Second- and Third-Generation Mobile Phones

There has been concern regarding the effect of electromagnetic interference (EMI) on medical equipment from portable wireless communication devices in hospitals in Hong Kong. The latest third-generation (3G) mobile communication system was fully implemented in 2004. As a result, an investigation to examine the EMI issues surrounding medical equipment, due to interference from communication devices, including GSM900, PCS1800, and 3G digital mobile phones, has been carried out. A statistical analysis has shown that the cumulative distribution function of base station signals within the hospitals environment follows the Weibull distribution for all three mobile phone systems in Hong Kong and that the percentage of failed medical equipment increases with a correlation of an increase in the radiated power level of the mobile phone. This is a direct result of a weakening in base station signals. The EMI effect from 3G mobile phones is also found to be four to eight times lower than that of the GSM900 and PCS1800, in locations inside the hospitals with weak base station signal strength, such as a basement or in operation theaters.

Single-Layer Microstrip High-Directivity Coupled-Line Coupler With Tight Coupling

A novel symmetrical coupled-line circuit structure without patterned ground plane is proposed to design tight-coupling high-directivity couplers, which would be found in numerous applications in a microstrip RF front end because of its simple structure and inherent excellent compatibility. Based on a traditional even- and odd-mode technique, closed-form mathematical equations for both circuit electrical parameters and scattering parameters are obtained. Due to the use of two coupled-line sections placed in the vertical direction, the directivity of this novel coupler without any other compensation techniques can be enhanced while maintaining tight-coupling performance of almost 3 dB. For demonstrative purposes, three typical full-wave simulation examples with realized physical dimensions in microstrip technology are presented, indicating high directivity and tight coupling coefficient. Finally, a practical microstrip coupled-line coupler is designed and fabricated to operate at approximately 2 GHz. The measured results show good return loss, quadrature phase characteristics, high directivity, and strong coupling performances.

An Analytical Design Method for a Novel Dual-Band Unequal Coupler With Four Arbitrary Terminated Resistances

A new design concept of a generalized dual-band branch-line coupler with unequal power division and four arbitrary terminated resistances is proposed in this paper. By using an external frequency-dependent impedance transformer, a novel dual-band branch-line coupler is obtained with a detailed analytical design method. For ease of design, maximum power-dividing ratio with varying frequency ratio for different terminated impedance values is provided. Owing to the additional design freedom, the calculation of parameters becomes much more flexible. Finally, for experimental validation and convenient measurement, a dual-band unequal microstrip branch-line coupler with four standard ports is designed, fabricated, and measured. Good agreement between the simulated and measured results can be observed.

An investigation of the SAR reduction methods in mobile phone applications

Due to the rapid growth in the use of wireless communication systems, there has been a recent increase in public concern regarding the exposure of humans to radio frequency (RF) electromagnetic radiation. This is particularly evident in the case of mobile telephone handsets. This paper aims to provide an investigation of the effectiveness of various commercially available Specific Absorption Rate (SAR) reduction products and shielding materials that can be externally attached to the handsets in Hong Kong. Also, the SAR values of different mobile phones are measured. Results are compared to the USA and European standards and then characterized for SAR reduction applications.

A fuzzy approach to signal integration

A new fuzzy concept for postdetection signal integration is presented. The fuzzy integrator is developed as a simple extension of the classic binary integrator by replacing the crisp binary threshold, which quantizes the observed data, with a fuzzy threshold. The performance of the fuzzy integrator is illustrated for detection of a simple nonfluctuating signal in Gaussian noise and is shown to exceed that of the binary integrator, approaching that of the optimal detector with Neyman-Pearson decision rule. Furthermore, the fuzzy integrator has the characteristic that the false alarm rate can be tuned using a single threshold, more easily than that of the dual-threshold binary integrator.

Adaptive non-uniform sampling delta modulation for audio/image processing

Adaptive non-uniform sampling delta modulation (ANS-DM), a modification of the non-uniform sampling delta modulation (NS-DM) technique, is proposed and examined. The proposed technique has been applied to audio and image processing; simulation results have shown that the ANS-DM technique has good improvement over linear delta modulation (LDM), adaptive delta modulation (ADM) and NS-DM on the compression ratio, the SQNR, and the dynamic range.

The use of fuzzy spaces in signal detection

The fuzzy constant false alarm rate (CFAR) detector, which is based on the M-out-of-N binary detector, is characterized and compared with the optimal Neyman–Pearson detector. It replaces the crisp M-out-of-N binary threshold with a soft, continuous threshold, implemented as a membership function. This function is chosen so that the output is equal to the false alarm rate of the binary detector, and therefore maps the observation set to a false alarm space corresponding to the false alarm rate, PFA. An analogous membership function is also developed mapping observations to a detection space which corresponds to the detection rate, PD. These two spaces allow different detectors to be compared directly with respect to the two important detection performance indices, PFA and PD. Comparison of the false alarm space and detection space indicates that the fuzzy CFAR detector and Neyman–Pearson detector detect signals in a different manner and have different detection properties. Nevertheless, performance results illustrate that the fuzzy CFAR detector achieves detection performance comparable to the optimal Neyman–Pearson detector.

Miniaturized Arbitrary Phase-Difference Couplers for Arbitrary Coupling Coefficients

In this paper, a planar miniaturized arbitrary phase-difference coupler with arbitrary coupling coefficients is proposed. The proposed coupler consists of three coupled-line sections which achieves a compact circuit layout in microstrip implementation. The circuit parameters of this novel coupler can be easily determined by the derived closed-form equations and the corresponding performance analysis in terms of the bandwidth and miniaturization requirement is provided. Two prototypes with this proposed structure, operating at 2 GHz, have been designed and implemented using microstrip technology. One has a 45° phase difference with - 3-dB coupling coefficient and the other demonstrates a 60° phase difference with - 4.77-dB coupling coefficient. In addition, over 20% fractional bandwidth, which is defined as 5° phase error and 0.5-dB magnitude imbalance, is obtained in both of the two prototypes.

A digital audio processing system based on nonuniform sampling delta modulation

A new digital audio recording and reproduction system based on a nonuniform sampling delta modulation (NSDM) technique is presented. Theoretical analysis and experimental results have shown that the NSDM technique has a higher coding efficiency, a larger signal-to-quantization-noise ratio and wider dynamic range than those of conventional linear delta modulation (LDM).

A NOVEL COMPACT DUAL-FREQUENCY COUPLED- LINE TRANSFORMER WITH SIMPLE ANALYTICAL DESIGN EQUATIONS FOR FREQUENCY-DEPENDENT COMPLEX LOAD IMPEDANCE

In order to perfectly match arbitrary frequency-dependent complex load impedances at two uncorrelated frequencies, a novel coupled-line impedance transformer without transmission-line stubs is proposed in this paper. This transformer mainly features small size, wide bandwidth, simple analytical design method, and easy planar implementation. The transformer simply consists of a coupled- line section and an additional transmission-line section. Due to the usage of a coupled-line section, the theoretical synthesis of the proposed transformer becomes very simple when compared with previous transformers and the total size of the planar circuit without deterioration of operating bandwidth becomes small. Furthermore, several numerical examples are presented to demonstrate the ∞exible dual-frequency matching performance. Finally, the proflle of matching frequency-dependent complex load impedance at two arbitrary frequencies has been examined by simulation and measurement of two microstrip generalized T-junction power dividers. Good agreement between the calculated results and measured ones justifles this proposed transformer and the design theory.