In this paper, a planar monopole antenna for Ultra-Wideband (UWB) communications with a notched behavior in the two sub-bands UNII1 and UNII2 of the Wireless Local Area Network (WLAN) band is presented. The antenna geometry is described by means of a spline curve and a rectangular slot. Numerical and experimental results are reported to assess the effectiveness of the proposed design in terms of impedance matching and radiation characteristics.

A new reflectarray configuration is proposed for low-loss applications at millimeter waves. It is based on the use of dielectric resonator antennas (DRA) as radiating unit-cells. The phase response of the elementary cell is controlled by adjusting the length of a parasitic narrow metal strip printed on the top of each DRA. A 330° phase dynamic range is obtained for DRAs made in rigid thermosetting plastic (ε_r=10). As the antenna radiating aperture is non flat, an original low-cost fabrication process is also introduced in order to fabricate the parasitic strips on the DRA surface. A 24×24-element array radiating at broadside has been designed at 30 GHz and characterized between 29 and 31 GHz. The antenna gain reaches 28.3 dBi at 31 GHz, and the measured -1 dB-gain radiation bandwidth is 5.2%. The 3.2 dB loss observed between the measured gain and theoretical directivity is mainly due to the spillover loss (2.3 dB). The total dielectric and conductor loss is less than 0.9 dB.

In recent years, location determination systems have gained a high importance due to its rule in the context aware systems. In this paper, we will design a multi-floor indoor positioning system based on Bayesian Graphical Models (BGM). Graphical models have a great flexibility on visualizing the relationships between random variables. Rather of using one sampling technique, we are going to use multiple sets each set contains a collection of sampling techniques, the accuracy of each set will be compared with each other.

A compact 9-21 GHz monolithic image reject mixer (IRM) with a chip dimension of 0.9×0.74 mm² has been designed and fabricated using a standard 0.18 μm CMOS technology. The compact configuration is composed of a 90°coupler for local oscillator (LO) and two doubly balanced ring mixers for mixing core. Particularly, a radio frequency (RF) dual balun with advanced intermediate frequency (IF) extraction technique can not only eliminate the use of power divider in IRM design, and simultaneously provide balanced signals for ring mixing, but also obtain high side band suppression without any additional IF low-pass filter. Moreover, the entire passive circuits are constructed by utilizing broad side coupling structure to achieve high-level integration further. From the measured results, the IRM exhibits a 19.4-22.4 dB conversion loss, a maximum image rejection ratio (IRR) of 34 dB, all port-to-port isolations better than 28 dB over RF frequency range of 9 to 21 GHz, and an input 1 dB compression power of 14 dBm.

In this paper, a new ultra wideband circular antenna array (UCAA) combining genetic algorithm (GA) to minimize the bit error rate (BER) is proposed. The ultra wideband (UWB) impulse responses of the indoor channel for any transmitter-receiver location are computed by SBR/Image techniques, inverse fast Fourier transform and Hermitian processing. By using the impulse response of multipath channel, the BER performance of the binary pulse amplitude modulation (B-PAM) impulse radio (IR) UWB system with circular antenna array can be calculated. Based on the topography of the antenna and the BER formula, the array pattern synthesis problem can be reformulated into an optimization problem and solved by the genetic algorithm. The novelties of our approach is not only choosing BER as the object function instead of sidelobe level of the antenna pattern, but also considering the antenna feed length effect of each array element. The strong point of the genetic algorithm is that it can find out the solution even if the performance index cannot be formulated by simple equations. Simulation results show that the synthesized antenna array pattern is effective to focus maximum gain to the multiusers.

Inverse synthetic aperture radar (ISAR) images represent the two-dimensional (2-D) spatial distribution of the radar cross-section (RCS) of an object and, thus, they can be applied to the problem of target identification. The traditional approach to ISAR imaging is the range-Doppler algorithm based on the 2-D Fourier transform. However, the 2-D Fourier transform often results in poor resolution ISAR images, especially when the measured frequency bandwidth and angular region are limited. Instead of the Fourier transform, high resolution spectral estimation techniques can be adopted to improve the resolution of ISAR images. These are the autoregressive (AR) model, multiple signal classification (MUSIC), and matrix enhancement and matrix pencil MUSIC (MEMP-MUSIC). In this study, the ISAR images from these high-resolution spectral estimators, as well as the FFT approach, are identified using a recently developed identification algorithm based on the polar mapping of ISAR images. In addition, each ISAR imaging algorithm is analyzed and compared in the framework of radar target identification. The results show that the dynamic range as well as the resolution of the ISAR images plays an important role in the identification performance. Moreover, the optimum size of the subarray (i.e. covariance matrix) for MUSIC and MEMP-MUSIC in terms of target identification is experimentally derived.

A novel dual-wideband microstrip bandpass filter (BPF) with improved upper-stopband performance is presented. With the use of some special structures such as E-shaped microstrip Stepped-Impedance Resonator (SIR) and input-output cross-coupling feed structure, this filter can generate five transmission zeros which are beneficial for improving its frequency selectivity and upper-stopband performance. Finally the microstrip dual-wideband BPF has been simulated, fabricated and measured. Measurement results show that the two passbands are centered at 3.7 GHz and 5.8 GHz with the fractional bandwidth of 31% and 13% respectively. Meanwhile more than 50% relative upper stopband bandwidth with 20 dB rejection has been realized. The simulated and measured results are in good agreement.

In this paper, a new hybrid classification method using both range profile (RP) and time-frequency image is proposed. The time-frequency image is obtained using the short-time Fourier transform before calculating the RP and this image is used for classification. 2-Dimensional Principal Components Analysis (2DPCA) is used to further compress the time-frequency image and to derive useful features from the image. The proposed method achieves a higher correct classification ratio than existing methods, especially when the signal-to-noise ratio is low.

Novel, dual band, single and double negative metamaterials composed of nonconcentric and different sized delta loop resonators are presented. The proposed structures provide two distinct resonant frequencies in the microwave region. Effective medium parameters of these metamaterial structures are extracted using retrieval method to demonstrate the presence of the mentioned frequencies. In addition, equivalent circuit model for the individual magnetic resonator and wire strip is presented to give a clear explanation for the resonance behavior of the structures and to validate the proposed designs. The results show that the proposed metamaterials can be used as an alternative to the known counterparts especially when a dual band operation is needed at the frequency region of interest.

In this paper, a jamming cancelation approach based on the concept of pulse diversity is proposed to suppress some newer complicated digital radio frequency memory (DRFM) range false targets (RFT). Just repeating the intercepted radar electromagnetic signal, as done in the conventional re-transmitting jammer, is not effective because only one range false target is produced. In contrast, the newer DRFM-based RFT generation methods, especially chopping and interleaving (C&I) and smeared spectrum (SMSP) can yield a multi-lobe filter output by transforming the internal structure of the intercepted radar signal. The presented approach to overcome this challenge is based on the temporal pulse diversity technique, and it does not require parameter estimation of the jamming signal. By transmitting pulses with specific transmission pulse block and the following proper processing, it can cancel out the protruding spikes of the jammer at the price of an acceptable performance loss. Particularly, this method is applicable to broad DRFM repeat jammer in electronic warfare (EW) area.

Non-invasive termite detection avoids damage to the structure under investigation. In this paper, we present the design and simulation of a hybrid radar array, with sub-arrays designed for both close range imaging and wide-area direction of arrival (DOA) processing for non-invasive termite detection. This radar array achieves wide area detection via novel modifications to the Matrix Enhanced Matrix Pencil algorithm and array transformation and achieves high resolution imaging through near field beam-steering from a large random array. The array hardware is designed to be implemented using available technology and low cost electronics.

Obtaining higher efficiency during the development of space Traveling Wave Tubes (TWTs) is always one of the most important goals for scientists. In this paper, a scheme of obtaining the maximum theoretical overall efficiency is explored by optimizing the helix pitch profile of a TWT based on the collectability of spent beam. The collectability of the spent beam was evaluated by the maximum collector efficiency, and this maximum collector efficiency was employed to calculate the maximum theoretical overall efficiency. The energy distribution of the spent beam and the output power of TWTs were calculated by the 3-D large signal Beam-Wave Interaction Simulator (BWIS) of MTSS. The detailed design of a Ku-band helix TWT is described according to three optimization goals (theoretical overall efficiency, theoretical collector efficiency and electronic efficiency). The simulation results indicate that the optimization for high interaction circuit efficiency or collector efficiency by itself is not adequate to obtain maximum overall efficiency. The maximum theoretical overall efficiency of 77% was achieved via the optimization of slow wave structure for theoretical overall efficiency.

A comprehensive review has been done on the types of electromagnetic transients that may affect low voltage electrical systems. The paper discusses various characteristics of lightning, switching, nuclear and intentional microwave impulses giving special attention to their impact on equipment and systems. The analysis shows that transients have a wide range of rise time, half peak width, action integral etc. with respect to both source and coupling mechanism. Hence, transient protection technology should be more specific with regard to the capabilities of the protection devices. Furthermore, we discuss the components and techniques available for the protection of low voltage systems from lightning generated electrical transients and the adequacy of International Standards in addressing the transient protection issues. The outcome of our analysis questions the suitability of 8/20 μs test current impulse in representing characteristics such as the time derivative and the energy content of lightning impulses. The 10/350 μs test current impulse better represents the integrated effects of the energy content of impulse component and long continuing current. A new waveform is required to be specified for testing the ability of protective devices to respond to the fast leading edges of subsequent strokes that may appear 100s of millisecond after the preceding stroke. The test voltage waveform 1.2/50 μs should also be modified to evaluate the response of protective devices for fast leading edges of induced voltage transients. A surge protective device that is tested for lightning transients may not be able to provide defense against other transients.

We present fast and accurate solutions of electromagnetics problems involving realistic metamaterial structures using a lowfrequency multilevel fast multipole algorithm (LF-MLFMA). Accelerating iterative solutions using robust preconditioning techniques may not be sufficient to reduce the overall processing time when the ordinary high-frequency MLFMA is applied to metamaterial problems. The major bottleneck, i.e., the low-frequency breakdown, should be eliminated for efficient solutions. We show that the combination of an LF-MLFMA implementation based on the multipole expansion with the sparse-approximate-inverse preconditioner enables efficient and accurate analysis of realistic metamaterial structures. Using the robust LF-MLFMA implementation, we demonstrate how the transmission properties of metamaterial walls can be enhanced with randomlyoriented unit cells.

A form of a novel adaptive antenna system that combines radio frequency identification (RFID) technology, programmable intelligent computer (PIC) microcontroller and reconfigurable beam steering antenna is proposed. Localization and adaptive response are the most challenging issues in smart antenna system. In this research, the localization technique relying on the received signal strength (RSS) signals has been done intensively where the capability of the RFID tag in producing certain level of signal strength has been exploited as a stimulator for the system to adaptively activate certain PIN diode switches of reconfigurable beam steering antenna. It is found that the detecting ability of the RSSI signals is extremely influenced by the 45°angle of the RFID reader's directive antenna. The combination of four 90°triangles which have 'adjacent' and 'opposite' angle of 45°forming pyramid antenna which has four sections; 1, 2, 3 and 4 enable the RFID readers to receive the RSS signals from the angles of 0°/360°, 90°, 180°and 270°respectively. When the RFID tag is directly facing a certain section, certain RSS signals will 'flow' from particular section into their respected RFID readers to automatically detect the range and angles' location of the RFID tag through the input ports of PIC microcontroller: A1, A4, C4 and C7. The PIN diode switches of the reconfigurable beam steering antenna are then activated by the output ports of PIC microcontroller: B0 up to B4, to steer the beam adaptively towards the RFID tag at four different angles: 0°/360°, 90°, 180°, and 270°according to the algorithm programmed in the microcontroller. It is found that the Ground Reflection (Two-Ray) propagation model is very crucial in determining the projection and height of reconfigurable antenna to efficiently cover the scattered measurement points of 1 up to 10 at four angles with different ranges of distance. The proposed antenna has a great potential in realizing the new smart antenna system replacing the conventional adaptive array antenna and Wimax application.

Rain drop size distributions (DSD) are measured with disdrometers at five different climatic locations in the Indian tropical region. The distribution of drop size is assumed to be lognormal to model the rain attenuation in the frequency range of 10-100 GHz. The rain attenuation is estimated assuming single scattering of spherical rain drops. Different attenuation characteristics are observed for different regions due to the dependency of DSD on climatic conditions. A comparison shows that significant differences between ITU-R model and DSD derived values occur at high frequency and at high rain rates for different regions. At frequencies below 30 GHz, the ITU-R model matches well with the DSD generated values up to 30 mm/h rain rate but differ above that. The results will be helpful in understanding the pattern of rain attenuation variation and designing the systems at EHF bands in the tropical region.

This paper shows the design of a fractal patch antenna, which uses a unique fractal geometry known as Pythagoras tree with co-planer waveguide (CPW) feeding. The antenna has been designed for dual band operation at the WLAN/WiMAX (2.4 GHz) and WiMAX (3.5 GHz) for Ultra-Wideband applications. The antenna was simulated using CST Microwave Studio. The fabricated antenna's measurement results were found to be in good agreement with the simulated ones.

Generalized synthesis of the rat race ring coupler is developed with its four arms being allowed to have different characteristic impedances. The transmission line theory incorporated with the even-odd analysis is used to formulate the conditions for solving the circuit parameters. The solution shows that a rat race ring with a normalized area of 41.82% or 0.97λ-circumference can be achieved. Based on the solutions, simulated bandwidths of the new ring hybrids are reported. Two experimental circuits are measured for validation check. One uses stepped-impedance sections to realize the four arms for further size reduction. This circuit occupies only 13.12% of that of a conventional hybrid ring at 1 GHz. It is believed that this implementation has the best size reduction for a microstrip ring hybrid in open literature. Measured scattering parameters show good agreement with the simulated results.

In this paper, we present the design, simulation, and measurement of a dual-band metamaterial absorber in the microwave region. Simulated and experimental results show that the absorber has two perfect absorption points near 11.15GHz and 16.01GHz. Absorptions under different polarizations of incident EM waves are measured with magnitude of over 97% at low-frequency peak and 99% at high-frequency peak respectively. Current distribution at the dual absorptive peaks is also given to study the physical mechanism of power loss. Moreover, it is verified by experiment that the absorptions of this kind of metamaterial absorber remain over 90% at the low-frequency peak and 92% at the high-frequency peak with wide incident angles ranging from 0° to 60° for both transverse electric wave and transverse magnetic wave.

A novel fractal structure using Koch and Sierpinski fractal-shapes is proposed. By inserting the Sierpinski carpets into the single patch and etching the inner and outer patch edges according to Koch curves, the resonant frequency of the patch antenna can be lowered significantly. And the higher of the iteration order of the fractal shapes, the lower the resonant frequency becomes. In this paper, a novel small-size single patch microstrip antenna based on the proposed fractal-shapes is designed, fabricated and measured. It is experimentally found that the size reduction can reach 80.3%. Compared to the conventional square single patch antenna, the proposed antenna maintains comparable radiation patterns. Therefore, the small-size single patch microstrip antenna considered here can be applied to portable wireless communication systems requiring small devices.