In this paper, a waveguide filter using miniaturized-element frequency selective surface (FSS) is presented. The proposed FSS is composed of periodic array of metallic patches separated by small gaps and metallic lines. The array of patches constitutes a capacitive surface and the lines a coupled inductive surface, which together act as a resonant structure. At about 5.0 GHz, a narrow bandpass response is designed. Dimensions of the FSS element are much smaller than the operating wavelength, which is less than 1/13λ. For this miniaturized element, grating lobes are restrained and do not appear event to 25 GHz. Moreover, the FSS has stable performances for various incident angles. Design procedure and measurement results of the FSS are presented and discussed.

The iterative Fourier technique (IFT) is a high efficiency method that was proposed in recent past for the synthesis of large planar thinned arrays with isotropic radiating elements. However, the selection mechanism of IFT cannot always include the most useful elements in the "turned ON" families, which make the method trap in some local minima. Therefore, in this paper, inspired by invasive weed optimization (IWO) algorithm, a developed version of the iterative Fourier technique (IFT), IWO-IFT, is proposed for thinning large planar arrays. In this new method, the initial weeds are produced by IFT, and are further perturbed by IWO through repeatedly reproduction, dispersion, and exclusion over search space to find better weeds. Numerical results for synthesizing different circular thinned arrays demonstrated the superiority of IWO-IFT over the IFT method.

In this paper, a compact three-order mixed-cross coupled bandpass filter (BPF) with enhanced frequency selectivity is proposed. Multiple transmission zeros (TZs) can be obtained near the passband for high frequency selectivity by introducing mixed-cross coupling between the nonadjacent resonators. The frequency-dependent mixed-cross coupling matrix of the proposed filter is presented to explain the occurrence of the TZs caused by mixed-cross coupling. A new BPF centered at 2.7 GHz with 11.5% fractional bandwidth has been designed and fabricated to verify the validity of the proposed method. The measurement result shows four finite TZs in the stopband, located at 1.74 GHz with 52.16 dB rejection, 2.53 GHz with 24.67 dB rejection, 3.83 GHz with 47.52 dB rejection, and 7.75 GHz with 54.83 dB rejection, respectively. The circuit only occupies 6.2×7.6 mm².

A compact microstripbandpass filter using miniaturized hairpin resonators is presented in this letter. Two modified stepped impedance hairpin resonators connected by parallel coupling are designed for the bandpass filter. The proposed miniaturized hairpin resonator is composed of amicrostrip line and rectangular ring structures between parallel high impedance lines. A big capacitance in the hairpin resonator is provided by the gaps ofrectangular ring structures in the parallel high impedance lines. Therefore, the proposed bandpass filter using the hairpin resonators has a low insertion loss, low return loss and compact size. The proposed bandpass filter with acenter frequency of4.96GHz is designed with EM full wave simulator IE3D andverified with experiment.

This paper presents a Monte-Carlo multidomainpseudospectral time-domain (MPSTD) algorithmdeveloped for the analysis of scattering from a three dimensional (3D)objectburied below arandom rough surface separating two half spaces. In the development, special attention is paid to the 3Dcomputation domain decomposition and subdomain mapping involving the random rough surfaceas well as the subdomain patching along the rough surface. The Mote-Carlo MPSTD algorithm is then employed to determine the scattering of 3D objects of various shapes and electromagnetic properties; embedded in the lower half space with different permittivity and the roughness of the random rough surface may vary.Sample numerical results are presented, validated, and analyzed.Through the analysis, it is observed that the roughness of the random rough surface and the electromagnetic properties of the lower half space can significantly affect the scattered signature of the buried object.

This paper presents a compact band stop filter (BSF) based on the dual metal plane configuration with multiple rejection zeros (RZs). Quasi-lumped technique with novel patch-via-spiral dual mode resonator is applied to the design of the proposed filter. Multiple rejection zeros are introduced by open-end stubs for high selectivity. Design equations are obtained by using a lossless transmission line model. The calculated results show that the lower and upper rejection zeros can be easily tuned by the coupling capacitor and the open-end stubs respectively. By using the Microstrip-Coplanar-Waveguide (CPW) structure, the size of the proposed filter can be reduced to 12.8 mm x 9 mm(i.e., 0.24λ_g x 0.17λ_g), where λ_g denotes the guided wavelength at center frequency.

A novel method for tapered rectangular dielectric rod antenna design is presented. This method can be used to design from millimetre to terahertz antennas. The work modes of antenna have been analyzed. The input modes are fundamental mode and second mode, and the end-fire mode is only fundamental mode. The calculation formulas for bottom diameter and top diameter are given according to the work modes. In order to avoid standing wave in the antenna, the wave will not reflect on the boundary surface of antenna. The calculation formula of antenna length is given based on the radial theory. Different shaped 300 GHz antennas have been designed based on the method. The results indicate that this method is suitable for different shapes of rectangular rod antennas. We also give the other two 1 THz and 32 GHz antenna design to demonstrate this method. The antenna gain will increase with the length expanding based on our design. The bottom and top diameters can be tuned slightly because the work mode formulas of rectangular dielectric waveguide are derived approximately. As an example different tuning designs of 100 GHz indicate that the tuning region is based on the calculation results. The design results have ultra wide bandwidth which is almost 50% of center frequency and high gain.

We have found that a single finite-boundary bowtie aperture (FBBA) antenna with gap separation of 10 nm between its tips is capable of confining the electric field to a 18 nm X 18 nm region (λ/39.4) and enhancing its near-field intensity by 365-fold at 5 nm beneath the gold film enhancing its near-field intensity by 1, 800-fold inside the gap. The FBBA antenna is thus able to provide enhanced trapping potential by virtue of such extraordinarily high (but exponentially decaying) optical near-fields. We have been able to show that 12 nm gold nanoparticles can, in principle, be trapped by the FBBA antenna with 20 nm gap separation; stable trapping is assured where the trapping potential is found to be several times higher than Brownian-motion potential in water. In addition to trapping nanoparticles, this simple but efficient FBBA antenna may find ready application in near-field optical data storage.

Propagation of Radio Frequency (RF) waves in indoor corridors is very complex and diverse as the propagation effects in the indoor scenarios are those that change over fractions of wavelength. Therefore, understanding of RF propagation characteristics is vital for the design of air interface and estimation of propagation losses is very much needed especially for wireless networks such as randomly deplorable Wireless Sensor Communications. In this research work, short-range, near floor/ground RF propagation path loss measurements at low antenna heights of 2 cm and 50 cm from the floor were made in typical narrow and wide straight indoor corridors at 915/2400 MHz in a modern multi-storied building utilizing RF equipment. Comparisons between measured and simulated path loss values were made utilizing Matlab simulations of Ray-tracing technique, free space and ITU-R models. Mean path loss exponent values were deduced from the measured data. The research work reported in this paper is predominately geared towards characterizing radio link for Wireless Sensor Communications/Networks in typical indoor corridor environments.

A novel coax-fed wideband loop antenna loaded with rectangular patches and U-shaped elements is presented and studied. By inserting a pair of rectangular patches inside the strip loops and employing a pair of U-shaped elements as the parasitic resonators, two additional resonances are excited and a good performance of bandwidth enhancement can be obtained. The measured results indicate that the impedance bandwidth (VSWR≤2) is about 87.1% from 1.58 to 4.02 GHz, which covers the required operating bands of DCS1800 (1710-1880 MHz), PCS1900 (1850-1990 MHz), UMTS2100 (1920-2170 MHz), WLAN2400 (2400-2484 MHz), LTE2300/2500 (2300-2690 MHz) and WiMAX3500 (3300-3690 MHz). In addition, good radiation characteristics such as symmetrical radiation pattern, moderate peak gain, low back radiation, and low cross-polarization are observed over the entire operating band.

Two 2-D natural fractal monopoles generated by electro-deposition are characterized in term of measured return loss. Depending on their different shapes, previously reported multi-band behaviour and new ultra-wideband (UWB) characteristics are obtained. Finally, sufficient efficiencies are measured for both antennas proving their possible use as radiating element.

A novel type of dual circular polarizer for simultaneously receiving and transmitting right-hand and left-hand circularly polarized waves is developed and tested. It consists of a H-plane T junction of rectangular waveguide, one circular waveguide as an E-plane arm located on top of the junction, and two metallic pins used for matching. The theoretical analysis and design of the three-physical-port and four-mode polarizer were researched by solving Scattering-Matrix of the network and using a full-wave electromagnetic simulation tool. The optimized polarizer has the advantages of a very compact size with a volume smaller than 0.8λ³, low complexity and manufacturing cost. A couple of the polarizer has been manufactured and tested, and the experimental results are basically consistent with the theories.

In this paper, a directional coupler incorporating the bandpass frequency response characteristic is proposed and characterized. This structure is modified from a conventional branch-line coupler. Two wide open-ended coupled lines are used instead of microstrip branch lines. As such, good restraint performance outside the passband can be achieved. The even-odd mode technique is employed to analyze and synthesize such a coupler. After that, frequency tuning is achieved by modifying the electrical length of the open-ended coupled lines with varactors. Measured results validate the correctness of our theory and design.

The microwave power transmission is an approach for wireless power transmission. As an important component of a microwave wireless power transmission systems, microwave rectennais widely studied. A rectenna based on a microstrip dipole antennas and a microwave rectifier with high conversion efficiencywere designed at 2.45 GHz.The dipole antenna achieved a gain of 5.2 dBi, a return loss greater than 10 dB, and a bandwidth of 20%. The microwave to DC (MW-DC) conversion efficiency of the rectifier was measured as 83% with 20 dBm input power and 600 Ω load. There are 72 rectennasto form an array with an area of 50 cm by 50 cm. The measured results show that the arrangement of the rectenna connection is an effective way to improvethe total conversion efficiency,when the microwave power distributionis not uniform on rectenna array. The experimental results show that the highest microwave power transmission efficiency reaches 67.6%.

Four ultra-wideband (UWB) antennas are proposed: one referenced antenna without notch and three novel antennas with one, two and three notched-bands, respectively. The UWB referenced antenna consists of a beveled rectangular metal patch, a 50 Ω microstrip line and a defective ground plane. Then, by utilizing one, two and three electromagnetic bandgap (EBG) structures on the UWB antenna, respectively, the antennas present one, two and three notched-band responses. The frequency domain characteristics including VSWR, transfer coefficient S₂₁, radiation patterns and Group delay are investigated. It is found that the EBG design approach is a good candidate for frequency rejection at the desired frequencies, owing to high performance of notch design and the notched-band bandwidth controlling abilities. Meanwhile, these abilities also enable less useful frequencies false rejected. The design examples exhibit good band-rejected characteristics in the WiMAX/WLAN interference bands (3.4, 5.2 and 5.8-GHz bands). Moreover, good time-domain characteristics of the antennas are checked based on group delay, waveform response, correlation factor and pulse width stretch ratio (SR). Therefore, the antennas are good candidates for portable UWB devices.

The design and ultra-wideband performance of a cavity-backed bowtie antenna with the parasitic dipole and parasitic circular ring is presented. Besides the elliptical bowtie dipole and the taper feeding microstrip for obtaining ultra-wideband impedance characteristics, the parasitic dipole and parasitic circular ring to effectively improve the radiation pattern can be used for obtaining the stable broadside unidirectional radiation patterns. An ultra-wideband impedance characteristic of about 118.2% for VSWR ≤ 2 ranging from 2.75-10.7 GHz is achieved. A unidirectional radiation pattern, a stable peak gain of around 7.4-10.8 dBi and low cross polarization over the whole operating band are also produced. A prototype has been fabricated and tested, and the experimental results validate the design procedure.

A novel structure of dual-composite right/left-handed transmission line (D-CRLH-TL) is proposed in this paper, and its electromagnetic characteristics are investigated in theory and simulation. The dispersion curve of the proposed structure has been derived by using Bloch-Floquet theory. The structure is composed with an "H"-shaped defected ground structure (DGS) and two stubs with rectangular patches, compared with the structure of D-CRLH-TL proposed in paper [5] and [6], this structure is simpler and more easily adjusted. Then, an ultra wide-stopband (UWSB) bandstop filter based on the proposed D-CRLH-TL is designed, fabricated, and measured. The simulated and measured results show that the centre frequency of the filter is 5.1 GHz, the bandwidth of stopband is 90.2%, and the filter has sharp transmissions at the two edges of the stop-band. Besides, the designed filter in this paper has a smaller size than traditional ones, and can be easily fabricated.

This article presents the coplanar capacitive coupled probe fed microstrip antennas for dual frequency band operation. The proposed antenna is excited by a single probe feed connected to a capacitive strip. Of the two dual band antennas presented here, the first one uses small air gap and the other is designed without air gap. In the first case an effort has been made to reduce the height of suspended antenna. A vertical slot is placed to obtain antenna resonance at low frequency side, and also for proper impedance matching. After presenting the basic geometry the second configuration (which uses no air gap) which also offers dual band operation at the expense of reduced bandwidth is presented. Measured values fairly agree with the simulated results.

A switchable microstrip patch antenna for multi-frequency operation is presented. The antenna is fed by a coplanar waveguide via capacitive coupling slot. The antenna allows easy reconfigurability of the frequency band of operation by incorporating switches in the coupling slot. The resonant frequency of the antenna can be adjusted by setting the switches on or off. Two prototypes are presented. The first incorporates two PIN diodes and capable of switching between four frequency bands, over a frequency range of 1.23:1. The second prototype incorporates four PIN diodes and is capable of switching between sixteen frequency bands, over a frequency range of 1.5:1. The structure has a compact and simple biasing circuit. Simulation and measurement indicate that the proposed antennas demonstrate very good impedance matching, stable radiation patterns and good gain at all frequency bands.

In this work, a special indefinite medium is used to produce a plane wave beam due to its linear type equifrequency contour resulted by the zero parameter in the permeability tenser. Only one transmitting mode exists in such a medium, composing the plane wave beam propagating along the zero parameter direction. Parameters along the field vectors of the wave are 1, enabling the wave propagation in the medium like in the air, which is totally different from the zero-index medium. A split ring resonator (SRR)-arrays based metamaterial is used to realize such a medium and produce an approximate plane wave beam experimentally. This idea proposes a feasible way to generate a near field plane wave beam with certain beamwidth, which can also be applied in cylindrical coordination or 3D cases.