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2011-06-19 PIER Vol. 117, 495-509, 2011. doi:10.2528/PIER11042703

Ultra-Broadband Directional Couplers Using Microstrip with Dielectric Overlay in Millimeter-Wave Band

A. M. Peláez-Pérez, Pablo Almorox-Gonzalez, Jose I. Alonso, and J. González-Martín

Nowadays, millimeter-wave systems are being a key factor to develop wide band applications. In this paper, a directional coupler in millimeter-wave band using dielectric overlay is presented. This leads us to technology aspects, in directional coupler design, are key points to achieve the proper response of the circuit. The coupler proposed in this paper covers the 15-45 GHz band and its response has 15-dB coupling-level, 1-dB coupling-ripple and a reflection coefficient better than 10 dB.

2011-06-18 PIER Vol. 117, 479-494, 2011. doi:10.2528/PIER11051206

Near-Field and Particle Size Effects in Coherent Raman Scattering

Chong Heng Raymond Ooi

Nonlinear optical processes have been used for sensitive detection of chemicals, optical imaging and spectral analysis of small particles. We have developed an exact theoretical framework to study the angular dependence of coherent anti-Stokes Raman scattering (CARS) intensity in the near field and far field for nanoparticle and microparticle. We obtain exact analytical solution for the CARS signal valid for arbitrary detection distance. Interesting angular dependence is found for nanoparticle, especially with near field detection. The study includes the effects of focused lasers and particle size on the CARS intensity distribution. We find that the detection distance and particle size do not affect the spectroscopic peaks of CARS. However, interference of reflected waves in nanoparticle can produce a dip in the backscattered spectrum.

2011-06-17 PIER Vol. 117, 449-477, 2011. doi:10.2528/PIER11040801

Rubber Tire Dust-Rice Husk Pyramidal Microwave Absorber

Mohd Fareq Bin Abd Malek, Ee Meng Cheng, O. Nadiah, Hassan Nornikman, Manjur Ahmed, Mohamad Zoinol Abidin Abdul Aziz, Abdul Rani Othman, Ping Jack Soh, Azremi Abdullah Al-Hadi, A. Hasnain, and M. N. Taib

Rubber tire dust-rice husk is an innovation in improving the design of pyramidal microwave absorbers to be used in radio frequency (RF) anechoic chambers. An RF anechoic chamber is a shielded room covered with absorbers to eliminate unwanted reflection signals. To design the pyramidal microwave absorber, rice husk will be added to rubber tire dust since the study shows that both have high percentages of carbon. This innovative material combination will be investigated to determine the best reflectivity or reflection loss performance of pyramidal microwave absorbers. Carbon is the most important element that must be in the absorber in order to help the absorption of unwanted microwave signals. In the commercial market, polyurethane and polystyrene are the most popular foam-based material that has been used in pyramidal microwave absorber fabrication. Instead of using chemical material, this study shows that agricultural waste is more environmentally friendly and has much lower cost. In this paper, three combinations of rubber tire dust and rice husk are fabricated to investigate the performance of microwave absorber reflection loss in operating in the frequency range from 7 GHz to 12 GHz.

2011-06-16 PIER Vol. 117, 435-448, 2011. doi:10.2528/PIER11043001

Iterative Hybrid Method for Electromagnetic Scattering from a 3-D Object Above a 2-D Random Dielectric Rough Surface

Wei Yang, Zhiqin Zhao, Conghui Qi, Wei Liu, and Zai-Ping Nie

An iterative hybrid method combining the Kirchhoff approximation (KA) and the multilevel fast multipole algorithm (MLFMA) is studied for electromagnetic scattering from a three-dimensional (3-D) object above a two-dimensional (2-D) random dielectric rough surface. In order to reduce the computational costs, some treatments have been studied. Firstly, the fast far-field approximation (FAFFA) is utilized to speed up the electromagnetic coupling interaction process between the rough surface and the object. Secondly, based on the scattering mechanism of the rough surface, a truncation rule on moderate rough surface for bi-static scattering is proposed under the plane wave illumination, which can further speed up the iteration. Compared with the conventional methods, the hybrid method with the above treatments is very efficient to analyze the scattering of a 3-D object above random rough surfaces. Simulation results validate the effectiveness and accuracy of the iterative hybrid method.

2011-06-16 PIER Vol. 117, 425-434, 2011. doi:10.2528/PIER11051301

A Printed 2.4 GHz /5.8 GHz Dual-Band Monopole Antenna with a Protruding Stub in the Ground Plane for WLAN and RFID Applications

Jyoti Ranjan Panda and Rakhesh Singh Kshetrimayum

The design of a simple microstrip fed folded strip monopole antenna (FSMA) with a protruding stub in the ground plane for the application in WLAN and RFID is presented. The antenna has two resonant paths, one in the radiating element (folded strip) and the other in the protruding stub of the ground plane. It supports two resonances at 2.4 GHz and 5.81 GHz, which are the center frequencies of WLAN and RFID. Effectively consistent radiation pattern and large percentage bandwidth have been observed. The measured percentage fractional bandwidth at 2.4 GHz (2.05 GHz to 2.86 GHz) is 32.99, and the percentage fractional bandwidth at 5.81 GHz (5.55 GHz to 6.14 GHz) is 10.11. The proposed antenna is simple and compact in size, providing broadband impedance matching, consistent radiation pattern and appropriate gain characteristics in the WLAN and RFID frequency regions.

2011-06-15 PIER Vol. 117, 409-423, 2011. doi:10.2528/PIER11042603

Coupling Matrix Decomposition in Designs and Applications of Microwave Filters

Ke Xiao, Liang Feng Ye, Fei Zhao, Shun-Lian Chai, and Joshua Le-Wei Li

The relationship between the immittance inverter coefficients and the coupling coefficients is obtained under the non-resonating coupling condition. With the relationship and the determinant properties of the transformation matrix, the coupling matrix could be decomposed to many sub-matrixes for filter designs. The physical significance of the decomposition is discussed. Using this idea, a filter can be decomposed to a number of sub-filters, which could be connected by sections of transmission lines with the same characteristics kept.

2011-06-15 PIER Vol. 117, 393-407, 2011. doi:10.2528/PIER11051601

A Novel Quasi-Elliptic Waveguide Transmit Reject Filter for Ku-Band Vsat Transceivers

Zhengbin Xu, Jian Guo, Cheng Qian, and Wen-Bin Dou

In this paper, a novel compact quasi-elliptic waveguide low-pass transmit reject filter (TRF) by using T-shape units is proposed for Ku-band very small aperture terminal (VSAT) transceivers. The equivalent circuit model of the T-shape unit is investigated and shows a topology similar to that of the elliptic low-pass filter. In order to reduce the difficulty in physical realization, which is commonly encountered with a standard elliptic low-pass filter, an approximate elliptic low-pass filter prototype is presented. Accordingly, a synthesis approach is developed to obtain the initial dimensions of the filter. To optimize the performance of the filter, full-wave electromagnetic simulation is used to fine-tune the dimensions of the filter. An eleven-order Ku-band low-pass TRF is designed and fabricated using a WR-75 waveguide. Measured results show it has a low insertion loss of less than 0.3\,dB in the pass band and a high attenuation slope of 78 dB/GHz. Moreover, the miniaturized size of the filter is only 38 mm × 38 mm × 42 mm (WR-75 flange size is 38 mm × 38 mm).

2011-06-15 PIER Vol. 117, 379-392, 2011. doi:10.2528/PIER11051403

A Multichanneled Filter in a Photonic Crystal Containing Coupled Defects

Heng-Tung Hsu, Min-Hung Lee, Tzong-Jer Yang, Yu-Chao Wang, and Chien-Jang Wu

ℜOptical filtering properties in a multichanneled transmission filter based on one-dimensional photonic crystal containing the coupled defects are theoretically investigated. The resonant transmission peaks are designed to be located within the photonic band gap of a defect-free photonic crystal. The number of peaks is directly equal to the number of the coupled defects. The positions of resonant peaks can be tuned by varying the refractive index of the defect layer. In addition, extremely resonant peaks can be produced by adding the Bragg mirrors at the front and rear sides of the structure.

2011-06-13 PIER Vol. 117, 365-378, 2011. doi:10.2528/PIER11050501

Improving Silicon Integrated Antennas by Substrate Micromachining: a Study of Etching Patterns

Joan Gemio, Josep Parron, Pedro de Paco, J. Sacristan, and Antonio Baldi

One of the main drawbacks of antenna integration on standard CMOS silicon substrates are the low radiation efficiency levels obtained due to the high silicon losses. This paper studies the use of micromachining techniques to remove silicon beneath the antenna as a solution to improve radiation efficiency. Several etching patterns are analyzed for different etching depths through simulations and measurements in order to find out which are the best ones for the micromachining process. Results are verified in two operating scenarios.

2011-06-13 PIER Vol. 117, 357-364, 2011. doi:10.2528/PIER11040201

Compact Dual-Band Bandpass Filter Using Folded SIR with Two Stubs for WLAN

Dechen Ma, Zhong Yin Xiao, Liangliang Xiang, Xiaohuan Wu, Chunyan Huang, and Xin Kou

A novel compact dual-band bandpass filter using tri-section stepped impedance resonators (SIRs) is presented for Wireless Local Area Network (WLAN). SIRs and one stub between parallel couple line are employed to realize two satisfactory passbands. Meanwhile, one transmission zero is generated between the two passbands to achieve a high out-of-band rejection. Simulated results show that two central frequencies are located at desired 2.4 and 5.2 GHz with 3 dB fractional bandwidths of 6.3% and 3.4% respectively. The measured results are in agreement well with the simulated ones.

2011-06-10 PIER Vol. 117, 339-355, 2011. doi:10.2528/PIER11050504

On the Analytic-Numeric Treatment of Weakly Singular Integrals on Arbitrary Polygonal Domains

Sergio Lopez-Pena, Athanasios G. Polimeridis, and Juan Mosig

An alternative analytical approach to calculate the weakly singular free-space static potential integral associated to uniform sources is presented. Arbitrary oriented flat polygons are considered as integration domains. The technique stands out by its mathematical simplicity and it is based on a novel integral transformation. The presented formula is equivalent to others existing in literature, being also concise and suitable within a singularity subtraction framework. Generalized Cartesian product rules built on the double exponential formula are utilized to integrate numerically the resulting analytical 2D potential integral. As a consequence, drawbacks associated to endpoint singularities in the derivative of the potential are tempered. Numerical examples within a surface integral equation-Method of Moments framework are finally provided.

2011-06-10 PIER Vol. 117, 321-337, 2011. doi:10.2528/PIER11041208

Embroidered Fully Textile Wearable Antenna for Medical Monitoring Applications

Mai A. R. Osman, Mohamad Kamal Abd Rahim, Noor Asmawati Samsuri, Hashim Ali M. Salim, and Mohammed F. Ali

Telecommunication systems integrated within garments and wearable products are such methods by which medical devices are making an impact on enhancing healthcare provisions around the clock. These garments when fully developed will be capable of alerting and demanding attention if and when required along with minimizing hospital resources and labour. Furthermore, they can play a major role in preventative ailments, health irregularities and unforeseen heart or brain disorders in apparently healthy individuals. This work presents the feasibility of investigating an Ultra-WideBand(UWB) antenna made from fully textile materials that were used for the substrate as well as the conducting parts of the designed antenna. Simulated and measured results show that the proposed antenna design meets the requirements of wide working bandwidth and provides 17 GHz bandwidth with compact size, washable and flexible materials. Results in terms of return loss, bandwidth, radiation pattern, current distribution as well as gain and efficiency are presented to validate the usefulness of the current manuscript design. The work presented here has profound implicationsfor future studies of a standalone suite that may one day help to provide wearer (patient) with such reliable and comfortable medical monitoring techniques.

2011-06-10 PIER Vol. 117, 299-319, 2011. doi:10.2528/PIER11033105

Linear Array SAR Imaging via Compressed Sensing

Shun-Jun Wei, Xiao-Ling Zhang, and Jun Shi

In recent years, various attempts have been undertaken to obtain three-dimensional (3-D) reflectivity of observed scene from synthetic aperture radar (SAR) technique. Linear array SAR (LASAR) has been demonstrated as a promising technique to achieve 3-D imaging of earth surface. The common methods used for LASAR imaging are usually based on matched filter (MF) which obeys the traditional Nyquist sampling theory. However, due to limitation in the length of linear array and the ``Rayleigh'' resolution, the standard MF-based methods suffer from low resolution and high sidelobes. Hence, high resolution imaging algorithms are desired. In LASAR images, dominating scatterers are always sparse compared with the total 3-D illuminated space cells. Combined with this prior knowledge of sparsity property, this paper presents a novel algorithm for LASAR imaging via compressed sensing (CS). The theory of CS indicates that sparse signal can be exactly reconstructed in high Signal-Noise-Ratio (SNR) level by solving a convex optimization problem with a very small number of samples. To overcome strong noise and clutter interference in LASAR raw echo, the new method firstly achieves range focussing by a pulse compression technique, which can greatly improve SNR level of signal in both azimuth and cross-track directions. Then, the resolution enhancement images of sparse targets are reconstructed by L1 norm regularization. High resolution properties and point localization accuracies are tested and verified by simulation and real experimental data. The results show that the CS method outperforms the conventional MF-based methods, even if very small random selected samples are used.

2011-06-10 PIER Vol. 117, 283-298, 2011. doi:10.2528/PIER11040706

Periodic Time-Varying Noise in Current-Commutating CMOS Mixers

Benqing Guo and Guangjun Wen

An analytical approach based on linear periodic time-varying theory, is developed to analyze the noise characteristics of current-commutating CMOS mixers. Based on the derived transfer functions with memory effect of tail capacitance, the frequency-dependent noise transforming factors for individual stages in the mixers are numerically computed to rigorously describe the noise output. A unified noise expression considering both the thermal noise and the flicker noise is proposed. It enables the noise analysis of the mixers particularly for a high LO frequency with different IF characteristics, and is verified by measurements.

2011-06-09 PIER Vol. 117, 267-281, 2011. doi:10.2528/PIER11051005

An Improved Cubic Polynomial Method for Interpolating/Extrapolating MoM Matrices Over a Frequency Band

Wei-Dong Li, Jun-Xia Miao, Jun Hu, Zhe Song, and Hou-Xing Zhou

The inter/extrapolation accuracy of the cubic polynomial method has been improved by optimizing three frequency samples for frequency-sweeping in the method of moments (MoM). In the method, the frequency samples are optimized by minimizing the global maximum of the polynomial component at the stationary points and two terminal points of the frequency band. The optimal frequency samples can be expressed as analytical forms of the two terminal points. Numerical examples are presented to validate the proposed method through comparison with the Pad\'{e} approximation.

2011-06-09 PIER Vol. 117, 253-265, 2011. doi:10.2528/PIER11042003

Enhancement of a Microwave Radiometry Imaging System's Performance Using Left Handed Materials

Melpomeni I. Giamalaki and Irene Karanasiou

Aiming at the enhancement of a non invasive Microwave Radiometry Imaging System's (MiRaIS) attributes, Left Handed Materials (LHM) with negative permittivity and negative permeability simultaneously, have been utilized. The optimization of the system focusing properties is being theoretically explored, implementing a semi-analytical Green's function technique and different matching structures. In the framework of this analysis the head is modeled by a double layered cylinder while a dielectric cylindrical layer consisting of LHM is placed on the surface of the human head model with a view to achieve focusing improvement inside the brain. Numerical code executions have been conducted for two different operating frequencies (0.5\,GHz and 1.0\,GHz) and for matching layers of various values of thicknesses and electromagnetic properties. The numerical results for the electric field distribution inside the head model, presented in this paper, verify that the LHM can provide an increased sensitivity of the system focusing properties and thus improve its overall performance.

2011-06-07 PIER Vol. 117, 237-252, 2011. doi:10.2528/PIER11032913

Pattern Synthesis of Conformal Arrays by a Modified Particle Swarm Optimization

Wen-Tao Li, Yong-Qiang Hei, and Xiao-Wei Shi

A method of designing a cylindrical conformal array with shaped-beam and reconfigurable dual-beam using a modified particle swarm optimization algorithm is proposed in this paper. The proposed algorithm is easy to implement and efficient to be used in synthesizing conformal arrays with digital attenuators and digital phase shifters. Moreover, the proposed synthesis has taken the actual active element patterns into account, which can reduce the error between computation and realization. Good agreement can be obtained between the desired patterns and the synthesized patterns.

2011-06-06 PIER Vol. 117, 209-236, 2011. doi:10.2528/PIER11042103

Evaluation of Electromagnetic Fields Associated with Inclined Lightning Channel Using Second Order FDTD-Hybrid Methods

Mahdi Izadi, Mohd Zainal Abidin Ab Kadir, and Chandima Gomes

Evaluation of electromagnetic fields caused by the lightning channel is an appealing topic in order to consider the indirect effects of lightning on the power lines. A common assumption for the calculation of electromagnetic fields at the observation point is a vertical lightning channel, but the fact is that in reality the lightning channel is seldom vertical on the ground surface. In this study, the electromagnetic fields due to inclined lightning channel at various observation points with different angles and with respect to the image of lightning channel on the ground surface were explored. This study also proposes general equations that can estimate the electric fields due to inclined lightning channel through the 2nd FDTD method. The proposed method supports the notion of vertical lightning channel, while the channel angle, with respect to z-axis, is assumed to be zero. This method was validated through the data gathered from four fields: three at a close distance from inclined lightning channel and one at an intermediate distance from vertical lightning channel. Similarly, due to inclined lightning channel, the effects of geometrical and current parameters on the electromagnetic fields are considered. This study substantiates different coupling models with FDTD structure directly at the time domain without a need for extra converters.

2011-06-06 PIER Vol. 117, 195-208, 2011. doi:10.2528/PIER11041503

A Miniature CPW Balun Constructed with Length-Reduced 3db Couples and a Short Redundant Transmission Line

Zeu-Yuan Yeh and Yi-Chyun Chiang

This work presents a new type of CPW balun consisting of 3dB coupled-line sections, which are one eighth wavelength long, and a short redundant transmission line for the applications of the modern wireless communication systems. A set of design equations that can determine the values of the elements of balun is proposed. A new type of coupler constructed with a structure similar to the conventional step impedance resonator is developed to further reduce the size of the balun. An experimental prototype operated at 1.0 GHz was designed and fabricated to verify the proposed design method. The measurement results show quite good correspondences with the theoretical predictions and the EM simulations.

2011-06-06 PIER Vol. 117, 181-194, 2011. doi:10.2528/PIER11050902

An Unequal Coupled-Line Wilkinson Power Divider for Arbitrary Terminated Impedances

Yongle Wu and Yuan'an Liu

A unequal Wilkinson power divider based on asymmetrical coupled line section is presented in this paper. The proposed unequal Wilkinson power divider topology uses asymmetrical coupled-line section and two transmission-line transformers. For simplification, a section asymmetrical coupled line is applied to obtain front compact matching structure. For generalization, three ports terminated impedances are defined as arbitrary values. In particular, the output ports impedances are arbitrary complex values. Design parameters and analysis equations for scattering parameters are also provided. In addition, the theoretical external performances of several examples are illustrated. Finally, the EM simulated results are validated with the characterization of two microstrip unequal power dividers at 2 GHz.

2011-06-05 PIER Vol. 117, 165-179, 2011. doi:10.2528/PIER11041904

A Novel Adaptive Beamforming Technique Applied on Linear Antenna Arrays Using Adaptive Mutated Boolean PSO

Zaharias D. Zaharis and Traianos V. Yioultsis

The present work introduces a new optimization technique suitable for adaptive beamforming of linear antenna arrays. The proposed technique is a new PSO variant called Adaptive Mutated Boolean PSO (AMBPSO) where the update formulae are implemented exclusively in Boolean form by using an efficiently adaptive mutation process. The AMBPSO aims at estimating the excitation weights applied on the array elements considering that a desired signal and several interference signals are received by the array at respective directions of arrival. In order to exhibit the robustness of the technique, the optimization process does not take into account the interference correlation matrix. A certain power level of additive Gaussian noise is also considered by the technique. The AMBPSO has been applied in several cases of uniform linear antenna arrays with different spacing between adjacent elements and different noise power level and therefore seems to be quite promising in the smart antenna technology.

2011-06-01 PIER Vol. 117, 149-164, 2011. doi:10.2528/PIER11042406

Impedance Measurements of Nonuniform Transmission Lines in Time Domain Using an Improved Recursive Multiple Reflection Computation Method

Yu Liu, Ling Tong, Wenxue Zhu, Yu Tian, and Bo Gao

In this paper, a recursive computation method is developed to derive the multiple reflections of nonuniform transmission lines. The true impedance profiles of the nonuniform transmission lines are then reconstructed with the help of this method. This method is more efficient than other algorithm. To validate this method, two nonuniform microstrip lines are designed and measured using Agilent vector network analyzer E8363B from 10 MHz to 20 GHz with 10 MHz interval. The reflection coefficients of these nonuniform microstrip lines in time domain are attained from the scattering parameters using inverse Chirp-Z transform. The reconstructed characteristic impedance profiles of the nonuniform lines are compared with those reconstructed by Izydorczyk's algorithm. The agreements of the results illustrate the validity of the recursive multiple reflection computation method in this paper.

2011-06-01 PIER Vol. 117, 121-147, 2011. doi:10.2528/PIER11041905

Efficient Cluster Identification for Measured Ultra-Wideband Channel Impulse Response in Vehicle Cabin

Bin Li, Zheng Zhou, Dejian Li, and Shijun Zhai

Although the automatic and robust cluster identification is crucial for ultra-wideband propagation modeling, the existing schemes may either require interactions with analyst, or fail to produce reasonable clustering results in more universal propagation environments. In this article, we suggest a novel cluster identification algorithm. Rather than assuming the limited exponential power decay characteristics on UWB channels, from a novel perspective cluster identification is formulated as the local discontinuity detection based on wavelet analysis. Firstly, in order to comprehensively reflect the prevailing amplitude changes induced by new clusters, the moving averaging ratio is extracted from the measured UWB channel impulse responses. Subsequently, the appealing local-transient analysis ability of wavelet transform is properly exploited, and a computationally efficient cluster extraction method is developed. Distinguished from the subjective visual inspection and excluding any analyst interaction, the presented scheme can automatically discover multiple clusters. Our algorithm is premised on the general amplitude discontinuity, and hence is applicable to various complicated operation environments. Moreover, the produced clustering results, essentially depicting realistic physical propagations, are also independent of parameter configurations. Experiments on both simulated channels and the measured data in typical vehicle cabin further validate the proposed method.

2011-05-30 PIER Vol. 117, 103-119, 2011. doi:10.2528/PIER11040103

On the Influence of Coupling AMC Resonances for RCS Reduction in the SHF Band

María Elena de Cos, Yuri Alvarez-Lopez, and Fernando Las Heras Andres

A novel approach to Radar Cross-Section reduction using a thin Artificial Magnetic Conductor (AMC) structure is presented. The novel AMC structure combines two unit-cell metallization sizes and so it presents two resonant frequencies. RCS reduction is based on destructive interference of two partial reflections. Taking as starting point a previous work showing significant RCS reduction based on the combination of two AMC surfaces with overlapped AMC operation bandwidths (so that they have similar reflection coefficient amplitude) without a 180º-phaseshift, the key point of this contribution is to analyze the influence of the degree of the aforementioned overlapping on RCS reduction and to show that this achievement is based on coupling phenomena. A comparison of the achieved RCS reduction when combining two AMCs whose AMC operation bandwidth overlaps, two AMCs with non-overlapped AMC operation bandwidths, and PEC-AMC is presented. Prototypes of these three combinations have been manufactured (having them the same size) and their RCS has been measured in an anechoic chamber.

2011-05-30 PIER Vol. 117, 83-101, 2011. doi:10.2528/PIER10122208

Non-Invasive Microwave Radiometric System for Intracranial Applications: a Study Using the Conformal L-Notch Microstrip Patch Antenna

Nikolaos P. Asimakis, Irene Karanasiou, and Nikolaos Uzunoglu

Temperature variations in tissues inside the body have been measured using microwave radiometry for more than three decades in a variety of passive body monitoring applications. In this paper we study a non-invasive prototype system for passive intracranial monitoring using microwave radiometry. It comprises one or two (two-element array) L-notch microstrip patch antennas in conjunction with a sensitive multiband receiver for detection. The particular design characteristics of the antenna are its conformality and a special L cut on its upper left edge, features that make it suitable for human biomedical applications and lead to its multiband operation in the frequency range of 2-3 GHz. The theoretical electromagnetic study indicates that the radiometric contact system in question operates well at two frequencies, with satisfying detection depths and adequate portability (small dimensions). In order to verify the findings of these simulations, experimental measurements with phantoms and various setups were carried out, resulting in the definition of the actual temperature detection level and the spatial resolution of the system. Theoretical and experimental results conclude that with the appropriate combination of conformal patch antennas and microwave receiver it is possible to monitor areas of interest inside human head models with a variety of temperature resolutions and detection depths.

2011-05-30 PIER Vol. 117, 67-81, 2011. doi:10.2528/PIER11031908

Second-Order Scattering Induced Reflection Divergence and Nonlinear Depolarization on Randomly Corrugated Semiconductor Nano-Pillars

Gong-Ru Lin, Fan-Shuen Meng, and Yung-Hsiang Lin

Second-order scattering induced reflection divergence and nonlinear depolarization on randomly sub-wavelength corrugated semiconductor nano-pillar surface is observed, which explains the nonlinear transverse electric (TE)/transverse magnetic (TM) mode transformation of the nano-pillar surface reflection with diminishing Brewster angle. The reflected polarization ratios are degraded from 97.5% to 53% and from 96.8% to 40% under TM- and TE-mode incidences by increasing Si nano-pillar height from 30 to 240 nm. A small-perturbation modeling corroborates the scattering induced second-order polarization transformation to depolarize the reflection from highly corrugated Si nano-pillar surface. The lower polarization ratio at TE-mode reflection caused by a severer inhomogeneous Si nano-pillars oriented in parallel with surface normal is concluded. With field polarization ratio under TM-mode incidence, the angular dependent reflectance spectra with a gradually diminished and shifted Brewster angle from 74o to 45o can be simulated. The nano-roughened surface induced second-order scattering model correlates the diminishing Brewster angle with the surface depolarized reflection.

2011-05-27 PIER Vol. 117, 51-65, 2011. doi:10.2528/PIER11032805

The Effects of Compression on Ultra Wideband Radar Signals

Brian McGinley, Martin O'Halloran, Raquel Cruz Conceicao, Garry Higgins, Edward Jones, and Martin Glavin

Over the past ten years, Ultra Wideband (UWB) Radar has been widely investigated as a biomedical imaging modality, used to detect early-stage breast cancer and to continuously monitor vital signs using both wearable and contactless devices. The advantages of the technology in terms of low-power requirements and non-ionising radiation are well recognised, with the technology being applied to a range of non-invasive medical applications, from respiration to heart monitoring. Across all these applications, there is a strong necessity to efficiently manage the large quantities of UWB data which will be captured. For wearable devices in particular, the efficient compression of UWB data allows the monitoring system to conserve limited resources such as memory and battery capacity, by reducing data storage and in some cases transmission requirements. In contrast to lossless compression techniques, lossy compression algorithms can achieve higher compression ratios and consequently greater power savings, at the expense of a marginal degradation of the reconstructed signal. This paper compares the lossy JPEG2000 and Set Partitioning In Hierarchical Trees (SPIHT) algorithms for UWB signal compression. This study examines the effects of lossy signal compression on an UWB breast cancer classification algorithm. This particular application was chosen because the classification algorithm relies heavily on shape and surface texture detail embedded in the Radar Target Signature (RTS) of the tumour, and therefore will provide both a robust and easily quantifiable test platform for the compression algorithms. The study will evaluate the performance of the classification algorithm as a function of Compression Ratio (CR) and Percentage Root-mean-square Difference (PRD) between the original and reconstructed UWB signals.

2011-05-25 PIER Vol. 117, 35-50, 2011. doi:10.2528/PIER11041107

A Holly-Leaf-Shaped Monopole Antenna with Low RCS for UWB Application

Hai-Yang Xu, Hou Zhang, Ke Lu, and Xian-Feng Zeng

As to low observable platform, one of the major contributing sources of target RCS is the scattering due to onboard antennas. So the research on RCS reduction of the antenna is important. In this paper, a holly-leaf-shaped monopole antenna with low RCS is designed. A square notch is etched to improve impedance matching and expand the bandwidth in the ground. The measured -10 dB bandwidth is from 2.1 to 15.4 GHz (only a little higher than -10 dB around 7.5 GHz). The radiation patterns retain symmetry and are relatively stable at 2.5, 8 and 11 GHz. The monostatic RCS performance in four different incident cases is studied to obtain some helpful conclusions for the RCS reduction of the UWB antenna. The RCS achieves effective reduction in comparison with that of the reference antenna. The largest reduction is 4.1, 19.8, 3.9dBsm in three different incident cases, respectively, while the largest loss of gain is only about -1.3 dB. The antenna suits the occasion of desiring UWB antenna with low RCS.

2011-05-25 PIER Vol. 117, 19-33, 2011. doi:10.2528/PIER11041304

Iterative Time-Reversal Mirror Method for Imaging the Buried Object Beneath Rough Ground Surface

Xiaozhang Zhu, Zhiqin Zhao, Wei Yang, Yin Zhang, Zai-Ping Nie, and Qing Huo Liu

An iterative Time-Reversal Mirror (TRM) method is proposed to Detect and Image the buried target beneath ground surface. Unlike the conventional TRM methods which treat the information of the ground as clutters and directly delete them, the iterative TRM imaging method proposed in this paper utilizes the information of rough ground surface as a useful knowledge. The new approach is consisted of two TRM procedures. In the first TRM procedure, it aims to image the rough surface where the propagation environment for electromagnetic wave is free space. The second TRM procedure aims to image the buried target. In this step, the information of the rough surface estimated by the first TRM procedure will be treated as newly updated propagation environment. Then conventional TRM is applied to image the buried target. By applying this iterative TRM method, the information of the rough ground can be well considered in the whole TRM procedure. Numerical simulations prove that this method performs significantly better image contrast comparing with the results obtained by using conventional TRM. 4-5 dB improvement on the imaging SNR has been achieved. Furthermore, the target can be located more accurately.

2011-05-25 PIER Vol. 117, 1-18, 2011. doi:10.2528/PIER11040405

A Late-Time Analysis Procedure for Extracting Weak Resonances. Application to the Schumann Resonances Obtained with the TLM Method

Juan Antonio Morente, Enrique A. Navarro, Jorge Andres Porti, Alfonso Salinas, Juan A. Morente-Molinera, Sergio Toledo-Redondo, Williams J. O'Connor, Bruno P. Besser, Herbert I. M. Lichtenegger, Jesús F. Fornieles, and Antonio Méndez

The sequence of Schumann resonances is unique for each celestial body with an ionosphere, since these resonances are determined by the dimensions of the planet/satellite and the corresponding atmospheric conductivity profile. Detecting these frequencies in an atmosphere is a clear proof of electrical activity, since it implies the existence of an electromagnetic energy source, which is essential for their creation and maintenance. In this paper, an analysis procedure for extracting weak resonances from the responses of electromagnetic systems excited by electric discharges is shown. The procedure, based on analysis of the late-time system response, is first checked using an analytical function and later applied to the vertical electric field generated by the computational simulation of Earth's atmosphere using the TLM (Transmission Line Matrix) method in order to extract the weak Schumann resonances contained in this electric field component.