A new wideband vertical planar printed unidirectional antenna is presented. The proposed antenna is composed of a bowtie electric dipole, a loop antenna and a microstrip-to-coplanar stripline balun. All of them are printed in the same plane perpendicular to the ground. The antenna has a wide impedance bandwidth of 87.2% for SWR≤2 from 3.3 to 8.4 GHz and a stable gain of 7.3±1.5 dBi over the operating frequencies. Moreover, stable unidirectional radiation pattern with low back-lobe radiation, low cross polarization and nearly identical E- and H-plane patterns is also demonstrated over the frequency of interest. A prototype is fabricated and measured. The measured results indicate that the antenna is suitable for wideband wireless communication system.

As a very powerful optimization algorithm, invasive weed optimization has been widely applied to continuous optimization problems in electromagnetic (EM) field. However, the optimization of a thinned array can be formulated as a discrete-variable optimization problem with solutions encoded as binary strings. Therefore, in this paper, an improved binary invasive weed optimization (IBIWO) is proposed to design a thinned array with minimum sidelobe levels. To evaluate the performance of the proposed algorithm, two examples have been presented and solved. Simulation results of the proposed thinned arrays obtained by IBIWO are compared with published results to verify the effectiveness of the proposed method.

Automatic detection of human motion is important for security and surveillance applications. Compared to other sensors, radar sensors present advantages for human motion detection and identification because of their all-weather and day-and-night capabilities, as well as the fact that they detect targets at a long range. This is particularly advantageous in the case of remote and highly cluttered radar scenes. The objective of this paper is to investigate human motion in highly cluttered forest medium to observe the characteristics of the received Doppler signature from the scene. For this purpose we attempt to develop an accurate model accounting for the key contributions to the Doppler signature for the human motion in a forest environment. Analytical techniques are combined with full wave numerical methods such as Method of Moments (MoM) enhanced with Fast Multipole Method (FMM) to achieve a realistic representation of the signature from the scene. Mutual interactions between the forest and the human as well as the attenuation due to the vegetation are accounted for. Due to the large problem size, parallel programming techniques that utilize a Graphics Processing Unit (GPU) based cluster are used.

Here we realize a broadband absorber by using a hyperbolic metamaterial composed of alternating aluminum-alumina thin films based on superposition of multiple slow-wave modes. Our super absorber ensures broadband and polarization-insensitive light absorption over almost the entire solar spectrum, near-infrared and short-wavelength infrared regime (500-2500 nm) with a simulated absorption of over 90%. The designed structure is fabricated and the measured results are given. This absorber yields an average measured absorption of 85% in the spectrum ranging from 500 nm to 2300 nm. The proposed absorbers open an avenue towards realizing thermal emission and energy-harvesting materials.

We present a multi-color STED fluorescence microscope providing far-field optical resolution down to 20 nm for biomedical research. The optical design comprises fiber lasers, beam scanners, and a set of active and passive polarizing elements that cooperatively yield an optically robust system for routinely imaging samples at subdiffraction length scales.

A single-feed dual-band dual-sense circularly polarized (CP) microstrip antenna is proposed. The antenna consists of a circular radiating patch with a ring slot, two substrates with an air layer sandwiched between them and a capacitive coupling feed. The two resonant frequencies are controlled by the size of the circular radiating patch and the ring slot. By introducing the perturbation, the fundamental resonant mode splits into two orthogonal degenerate modes, and the CP radiation pattern is obtained. Capacitive disk coupling feed is also used in the design to enhance the band-width. The key parameters of the design are investigated to show how to obtain dual-band and dual-sense CP. The proposed antenna prototype is fabricated and measured. Experimental results show that good CP radiation performances are obtained at both resonant frequencies.

Environment monitoring and automatic control of a building is a vital application of wireless sensor network, however, to maximize the network lifetime is a key challenge. The investigation of designing an efficient sensor network that minimizes energy dissipation in a battery of the sensor node, with limited battery power, is a vital consideration for the sensor network lifetime. Battery lifetime greatly affects the overall network communication performance, hence, the careful management of communication distance is very important. In this paper we propose a model to estimate the mean square distance from the sensor to the cluster head in sensor fields, such as the ones used for monitoring humidity, temperature, light intensity and air quality (CO and CO₂ level), considering three dimensional building structures. We use experimental datasets of the link quality distribution in an indoor building environment (single storey as well as multi-storey buildings) to investigate the possible building length of the different clusters and the data success rates. We then statistically analysed the data success rate of the experimental datasets using the Wilcoxon Rank Sum test and found that there was no statistically significant difference (p > 0.05). Our results show that the clustering is important for the single storey and multi-storey building sensor networks, however, after a certain size of the building it is unimportant. Our results also demonstrate that we can save sensor battery energy, significantly, by optimizing the distance from the sensor to the cluster head, while obtaining a high data success rate. The results over different clusters of sensor networks suggest its applicability for different building sizes. Based on this paper the designers can optimize energy e±ciency subject to the required specifications.

In this paper, the design of a multiband antenna for WLAN and WiMAX applications is proposed. The proposed antenna comprises a circular radiating patch with a pair of rectangular slits and an inverted U-shaped slot. A hexagon-shaped slot is cut on the ground plane. By adjusting the inverted U-shaped slot, a pair of rectangular slits, and a hexagon-shaped slot, three distinct resonance frequencies centered at 2.4 GHz, 3.52 GHz, and 5.68 GHz can be generated. The measurements show that the proposed antenna can cover three frequency bands with sufficient bandwidth. The proposed antenna exhibits an omnidirectional radiation pattern and acceptable gain.The overall dimension of the proposed antenna is 25 × 39 × 1.59 mm³.

Forward-looking imaging has extensive potential applications, such as self-navigation and self-landing. By choosing proper geometry, bistatic synthetic aperture radar (BiSAR) can break through the limitations of monostatic SAR on forward-looking imaging and provide possibility of the forward-looking imaging. In this special bistatic configuration, two problems involving large range cell migration (RCM) and large range-azimuth coupling are introduced by the forward-looking beam, which make it difficult to use traditional data focusing algorithms. To address these problems, a novel Omega-K algorithm based on two-dimensional non-uniform FFT (2-D NUFFT) for translational variant (TV) bistatic forward-looking SAR (BFSAR) imaging is proposed in this paper. In this study, we derive an accurate spectrum expression based on two-dimensional principle of stationary phase (2-D POSP). 2-D NUFFT is utilized to eliminate the range-variant term, which can make full use of the data and improve the computational efficiency as well. The experimental results, presented herein, demonstrate the effectiveness and advantages of the proposed algorithm.

A compact band-notched ultra-wideband (UWB) spatial diversity antenna is presented in this paper. The antenna is fabricated on an FR4 substrate and consists of two tapered microstrip feeding lines and two radiating elements. The wireless local area network (WLAN) for IEEE 802.11a operating in 5.15-5.825 GHz and-notched function is achieved by introducing two slits in the radiators as λ/4 resonators. The simulated and measured results show that the presented antenna has a broadband impedance bandwidth which covers UWB band and also has a band-notched characteristic. Additionally, the antenna has a good transmission coefficient better than -15 dB across the UWB. The radiation patterns, peak gain, and envelope correlation coefficient are measured and discussed.

A novel dual-band circularly polarized (CP) antenna with wide axial ratio (AR) and impedance bandwidths is proposed. Based on a rectangular ground, the antenna consists of a trapezoid patch, an L-shaped strip, a cavity, and T-shaped and L-shaped perturbations. By embedding a feeding line with a trapezoid patch and an L-shaped strip, dual-band input impedance performance and a CP performance at upper band are obtained. In order to achieve a CP performance at the lower band, a T-shaped perturbation is embedded inside the slot. Moreover, the CP performance is enhanced by inserting an L-shaped perturbation at the right bottom corner of the slot. Furthermore, using a cavity underneath the antenna, unidirectional radiation patterns with greatly gain enhancement are obtained. The measured results show that the impedance bandwidths for S₁₁<-10 dB are 22.7% (2.34-2.94 GHz) and 79.8% (4.64-10.8 GHz) while the axial ratio bandwidths (AR<3 dB) are 26.4% (2.3-3 GHz) and 12.6% (5.2-5.9 GHz) at the lower and upper bands, respectively. Additionally, the measured gain is more than 7.4 dB and 2.4 dB in the two operating bands, respectively. Thus, the antenna can be well applied for both 2.4/5.8 GHz WLAN bands and 2.5/5.5 GHz WiMAX bands.

In this paper two novel antennas, suitable for access and backhaul links, are designed, fabricated and tested for a Relay Station in a WiMAX wireless network. A single modified E-shaped patch antenna is described, presenting 10 dB gain over 12.4% bandwidth. This antenna element is used for the design of a 4×4 planar array which provides experimental gain of 21.2 dB. The antenna system on the Relay Station operates at 3.4 GHz and includes one single antenna element for access link realization and an antenna array for the backhaul link realization. These antennas are installed in two configuration arrangements and tested in terms of their radiation performances and coupling effects. The simulated and measured results are quite satisfactory and in good agreement at which the maximum coupling between the access and backhaul antennas is found below -25 dB for all tested cases.

A planar monopole loaded with composite right/left-handed transmission line (CRLH-TL) for broadband LTE mobile phone is presented. The CRLH-TL with a propagation constant of zero is added to widen the input impedance bandwidth of the antenna. The proposed antenna covers the LTE700/2500/GSM850/900/1800/1900/UMTS2100 and WLAN2400 bands. Impedance bandwidths of VSWR<2.5 (S₁₁<-7 dB) ranging from 675 to 1010 MHz and 1690 to 2550 MHz are obtained. The size of the monopole is 60×16×1mm³ which is smaller than most of the LTE antennas. Detailed design considerations of the monopole are described. A prototype is fabricated and tested. Both simulated and experimental results are discussed.

A novel (2×2) high gain circularly polarized rectangular dielectric resonator antenna array integrated with helical-like exciter is proposed. The array offers a maximum gain of 12.9 dBi at the operating frequency. The circular polarization is obtained by incorporating helical-like exciter in the array structure. A prototype of the proposed configuration integrated with helical-like exciter has been fabricated and tested, and the idea has been verified. A good agreement has been obtained between the measured and simulated results.

Radio refractivity values obtained for different heights (Ground surface, 50 m, 100 m and 150 m) over a tropical station, Akure, South-Western Nigeria using in-situ data over a period of five years has been investigated for chaos. Several chaos quantifiers such as entropy, Lyapunov exponent, recurrence plot were used. Determinism was detected in the time series studied at all the levels. Results obtained from the computation of radio refractivity show that the value of radio refractivity decreases with increasing altitude while chaotic quantifiers obtained at ground level and height 100m are found to be more chaotic than the other two levels (50 m and 150 m).

A novel approach to design microstrip ultra-wideband (UWB) bandpass filter (BPF) using modified genetic algorithm (MGA) is proposed in this paper. To achieve high efficiency and accuracy, conventional GA is modified. By improving the fitness evaluation, selection, crossover, and mutation, the two possible drawbacks of conventional GA, i.e., slow rate of convergence and local-best solution, are overcome. The modified genetic algorithm is then applied to simultaneously search for the appropriate circuit topology and the corresponding electrical parameters with UWB characteristic. To demonstrate the effectiveness of the novel approach, a new microstrip UWB BPF is designed and fabricated. Measurement results agree well with the design index and full-wave EM simulated results.

A miniature platform tolerant antenna is presented which is suitable for low frequency applications. A Split Ring Resonator (SRR) antenna loaded with lumped capacitances is proposed. The antenna is compact, low profile and easy to fabricate. It has a maximum dimension of λ/9 and -10 dB bandwidth of 1%. Miniaturized artificial magnetic conductor surfaces (AMCs) are designed using capacitance loaded metal patches with individual elements measuring just λ/70. Placing the SRR above the AMC improves the bandwidth to between 1.5 and 3.5% dependent on the overall size of the AMC and produces a platform tolerant antenna measuring 0.11λ×0.17λ×0.019λ. The performance of the antenna over an AMC with and without vias is studied and discussed. The AMC mounted antenna's performance in free space and over a ground plane is also compared.

In this paper, a miniaturized dual-band bandpass filter with high selectivity and band-to-band isolation is presented. The filter consists of two quarter-wavelength stepped impedance resonators (SIRs) which share a common grounded via-hole and two symmetrical half-wavelength SIRs which are embedded into the inner space to reduce the size of the filter. Two independent mixed coupling paths which are created by the coupling between these SIRs introduce two different passbands. Five transmission zeros (TZs) are generated near the two passbands to achieve high frequency selectivity and band-to-band isolation. To validate the design theory, a dual-band filter operating at 2.45 and 5.2 GHz was designed and fabricated. The size of the proposed filter only occupies 0.095λ_g × 0.109λ_g and the measured 3 dB fractional bandwidth (FBW) of the first and second passbands is 11.5% and 7.4% respectively. The measured results are in good agreement with the simulated results.

In this article, in a simple way, simple relations are derived between the electric field components of an electrically uniaxial medium and those of an isotropic medium. The permittivity of the isotropic medium is the same as the permittivity of the uniaxial medium that is common to the axes transverse to the optic axis. Using the spectral representation, the vector wave equation for the electric field intensity vector of the uniaxial medium is solved for the x directed, y directed and z directed point sources. For the x directed and y directed point sources, the electric field components transverse to the optic axis are written in terms of the corresponding components of the isotropic medium plus some other terms. Part of these terms are closed forms expressions, and the rest are Sommerfeld type integrals. Elements of each group are related to each other by coordinate transformations. The electric field components parallel to the optic axis are shown to be obtained from the isotropic medium components using coordinate transformations. The relations between the uniaxial medium and isotropic medium field components are verified by comparing the results of a previous study in the literature to the results obtained using the relations in this study. Good agreement is achieved between these results.

In this paper, a microstrip double-layered reflectarray element is studied. The unit element consists of a circular patch sandwiched between two substrates and a cross-slotted circular patch placed on the top-most surface. The radii of the two circular patches as well as the cross-slot lengths are varied simultaneously for controlling the phase range and the gradient of the reflection phase angle. Study shows that the sensitivity of the reflection phase angle can be made slower by utilizing substrates with lower dielectric constants. The component performance is studied using a rectangular waveguide and good agreement is found between thesimulation and experiment. A wide reflection phase range of 681.82° with loss magnitude of less than -1 dB is achievable in the reflection phase angle. A complete parametric analysis has been conducted to study the reflection characteristics of the proposed reflectarray unit element.