The influences of confined phonons on the nonlinear absorption coefficient (NAC) by a strong electromagnetic wave for the case of electron-optical phonon scattering in doped superlattices (DSLs) are theoretically studied by using the quantum transport equation for electrons. The dependence of NAC on the energy (hΩ), the amplitude (E0) of external strong electromagnetic wave, the temperature (T) of the system, is obtained. Two cases for the absorption: Close to the absorption threshold ∣khΩ - hω0∣<< ε and far away from the absorption threshold ∣khΩ - hω0∣>> ε (k = 0, 1, 2..., hω0 and ε are the frequency of optical phonon and the average energy of electrons, respectively) are considered. The formula of the NAC contains a quantum number m characterizing confined phonons. The analytic expressions are numerically evaluated, plotted and discussed for a specific of the n-GaAs/p-GaAs DSLs. The computations show that the spectrums of the NAC in case of confined phonon are much different from they are in case of un-confined phonon and strongly depend on a quantum number m characterizing confinement phonon.
In this paper, right handed circular polarization (RHCP), left handed circular polarization (LHCP), and linear polarization (LP) reconfigurable antenna is proposed by reconfigured fabrication. The proposed antenna comprising of two square patches, a T-stripline, and a finite ground plane is designed for HiperLAN2 5 GHz operation. The patches are symmetrically placed along the vertical portion of T-strip and coupling fed by the strip. The planar structure is in LP sense while CP sense is achieved as the structure bent. For the bent structure, the vertical and horizontal portions of T-strip not only respectively feed the coplanar patch but also provide a 90° phase difference between the feeds. Two orthogonal E-fields with quadrature are excited to achieve CP sense. Moreover, the switching between RHCP and LHCP is easily achieved by folding the structure along opposite vertical edge of T-strip. Instead of electrically controlling switches, the polarization reconfiguration can be manually constructed.
Frequency-dependent energy tunneling that results in full transmission of electromagnetic energy through wire-loaded sharp waveguide bends is demonstrated by full-wave simulations. The frequencies at which the tunneling takes place is predicted by a numerical method that involves a variational impedance formula based on Green function of a probe-excited parallel plate waveguide. Analogous tunneling effects have also been previously observed in waveguide bends filled with epsilon-near-zero media. However, since the frequency response in the wire-loaded waveguides can be tailored by simply modifying the lengths of the wires, the phenomenon is scalable over a broad range of frequencies and can be potentially exploited in various filtering and multiplexing applications.
A compact single-feed dual-band circularly polarized (CP) microstrip antenna is evaluated numerically and experimentally. The dual-band performances with small frequency ratio (about 1:1.1) are achieved by a circular patch and a narrow annular-ring, which have small difference in radius. The CP characteristics are achieved by an unequal cross-slot embedded in the circular patch and two orthogonal linear stubs spurred from the annular-ring. The antenna is easy to fabricate. Good agreement is obtained between measured and simulated results.
A simplified extended composite right/left-handed (SE-CRLH) transmission line (TL) is proposed for dual-band applications. The dual-band bandpass behavior is realized with a simplified non-dual circuit with only two broadband balanced conditions. The dispersion relation and frequency response of SE-CRLH TL are analyzed by circuit analysis, Bloch-Floquet theorem, and full wave simulation. A demonstration of SE-CRLH structure is designed. The measurements are in agreement with simulations and theory.
A LOD-like method that characterizes the analytical solution is proposed to study the one-dimensional (1-D) chiral media. Through theoretical analysis and numerical simulation, it is found that the proposed scheme is unconditionally stable. This scheme employs the new mesh-dividing method for bi-isotropic media, in which the two sections on the right side of the rearranged curl equations are regarded as two directions and the LOD-like algorithm is used to deal with the equivalent two-dimensional (2-D) problem. In the first substep, the conventional LOD method is used in computation, while for the second substep, the analytical solution is employed instead. By simulating the polarization rotation of a mono-frequency linear polarized wave both in a 1-D homogeneous chiral media and through a chiral slab, the scheme is testified to be unconditionally stable.
The formation process of antenna mode scattering is analyzed, and a new prediction method to calculate the antenna mode scattering is proposed. Since the antenna mode scattering is essentially the reradiation of reflected energy, this reflected energy comes from the incident wave received by the antenna and reflects on the mismatched point of the feed network. Thus the calculation of the antenna mode scattering can be divided into three steps: 1. calculation of the antenna received energy; 2. calculation of the reflected energy from the feed network; 3. reradiation of this reflected energy. The numerical results of antenna mode scattering from a patch antenna and a dipole array are proposed to verify this approach.
A novel CPW-fed triple-band monopole antenna designed by embedding an S-shaped meander strip into a C-shaped strip is proposed for WLAN and WiMAX applications. The antenna with a very simple and compact structure is easy to be fabricated, and the prototype of the proposed antenna has been constructed and measured. The triple operating bands with 10-dB return-loss bandwidths of about 110 MHz centered at 2.45 GHz, 310 MHz centered at 3.55 GHz, and 39% ranging from 4.1 to 6.2 GHz, covering the required bandwidths of 2.4/5.2/5.8 GHz WLAN and 3.5/5.5 GHz WiMAX standards, are obtained. In addition, good radiation performance and antenna gain across the three frequency ranges have been obtained.
In this paper, a novel band-notched wide slot antenna for UWB applications has been proposed. The antenna consists of a circularly slotted square ground, two wide-slots separated by a conductive ring, and an equiangular spiral feed line, which excites the antenna through traveling-wave. Experimental prototypes are fabricated and tested. The obtained results indicate that the proposed antenna has a small size and offers a broad bandwidth from 3.1 to 12 GHz, with a band notch from 3.4 to 3.9 GHz. The radiation patterns display nearly omnidirectional performance and the measured group delays are within ±1 nanosecond except for the notch band.
Design of a compact planar phase shifter is described that possesses ultra-wideband (UWB) performance. The proposed device is composed of 50Ω input/output microstrip-lines which are connected to a low-impedance rectangular microstrip patch, and located at close proximity to each other. The common ground-plane incorporates a slot-line terminated with two rectangular slots, which are located under the rectangular patches in order to provide effective electromagnetic coupling between the microstrip-line and slot-line. Thus a phase shifter is realized with ultra-wideband characteristics on a single substrate. The length of the slot-line and width of patch determines the desired phase shift required between the input and output ports. It is demonstrated that the design can provide phase shift anywhere between 4°- 27° across the entire UWB frequency band from 3.1 to 10.6 GHz. The simulated results show fixed phase shift 5.625°± 0.865°, 11.25°± 1.93°and 22.5°± 2.5°with insertion-loss less than 0.5 dB and return loss better than 12 dB across the ultra-wideband frequency span. The phase shifter is relatively compact in size with a dimension of 15×25 mm2. The phase shifter was fabricated and its performance measured to validate the simulation results.
An omnidirectional horizontally polarized antenna with improved gain is realized by using EBG cavity. The EBG cavity is composed of ring metallic strips etched on thin FR4 substrate and two metallic reflectors installed on up/down sides, which is designed to have a low effective index of refraction (n<1). The metallic strips are arranged in concave shape. Compared with the antenna without EBG cavity, the EBG cavity makes the vertical beam become narrow and effectively improves the omnidirectional antenna gain. An experimental prototype is fabricated to validate the proposed analysis. Measured data show the gain of the antenna with the EBG cavity improved by about 2.72 dBi at 5.7 GHz, and the measured data have a good agreement with numerical results.
A new composite power plane using spiral electromagnetic bandgap (EBG) and external magnetic material is proposed for simultaneous switching noise (SSN) suppression in mixed-signal systems. The proposed power plane has an external magnetic material partially placed on the top of perforated spiral-bridged EBG plane. The EBG bandgap is shifted to lower frequencies by the real part of the permeability (μr') and the power plane Q-factor is decreased by the imaginary part of the permeability (μr") associated with the magnetic loss. 30 dB suppression of the SSN propagation has been measured from 190 MHz to 1 GHz by virtue of the complex permeability. The proposed EBG power plane is expected to reduce the circuit size and to improve the power integrity of the mixed-signal systems.
A novel tri-band monopole antenna applied to WLAN / WiMAX applications is proposed in this paper. The antenna comprises of two semicircles: one is fed by a microstrip line, and the other is shorted to the ground. By incorporating L-shaped strips, good filter as tri-band performance is achieved. The proposed antenna shows a good multi-band property to satisfy the requirement of WLAN in the 2.4/5.2/5.8 GHz bands and WiMAX in the 2.5/3.5/5.5 GHz bands. In addition, a near omni-directional radiation characteristic is also obtained. Experimental data show that the antenna can provide three separate impedance bandwidths of 400 MHz (centered at 2.6 GHz), 400 MHz (centered at 3.4 GHz) and 1100 MHz (centered at 5.3 GHz) with two fine notched bands at the undesired bandwidths.
Study of a novel design of dual-band folded antenna with an L-shaped slot on the ground plane has been proposed for wireless local area network (WLAN) applications. The proposed antenna occupies a low profile above the ground plane. This characteristic makes it suitable for laptop PC applications. The proposed antenna can provide two impedance bands at 2.4 and 5.2/5.8 GHz, which satisfies WLAN applications. Details of the proposed antenna design and measured results are presented and discussed.
Solidification of pure aluminum without and with a magnetic field has been investigated by differential thermal analysis (DTA). DTA curves showed that the nucleation temperature of pure aluminum was decreased as a magnetic field strength increased although its melting process was almost not influenced. The nucleation suppression could be attributed to the increase of the solid-liquid interfacial energy which might originate from more orderly arrangement of atoms on the solid-liquid interface upon applying a magnetic field.
A wideband elliptical bowtie impulse antenna is proposed and investigated in this paper. Simulated results reveal that it can achieve an impedance bandwidth of 141% for S11≤-10 dB, a broadside gain of 2.4-5.3 dB, and stable radiation pattern over the whole operating band. The measured reflection coefficient is less than -10 dB over the frequency from 1.30 to 6.65 GHz, and it agrees well with the simulated results. The characteristics of frequency-domain such as radiation pattern, phase center and time-domain behaviors are discussed. The antenna electrical dimension is 0.31λ0, where λ0 is the free-space wavelength at lower edge of the operating frequency band. Parameters are studied to optimize the antenna performance.
In this paper, a directional slot antenna with parasitic patch and windowed superstrate is presented. Through this composition, high-gain property can easily be obtained by this proposed antenna. The proposed antenna has a measured impedance bandwidth of 2.41-2.49 GHz for S11<-10 dB, which can cover the 2.4-2.484 GHz frequency band of WLAN application. Simulated and measured results show that high-gain features up to 11.50 dBi across the corresponding impedance band are achieved. Details of the proposed slot antenna configurations and design procedures are given; the experimental results are also given and discussed.
A novel rectangular slot antenna with embedded self-similar strips is proposed for wireless local area network (WLAN) applications. The proposed antenna comprises a T-shaped monopole and inverted self-similar strips embedded in the rectangular slot etched on the ground plane. The measured results of the fabricated antenna show that the impedance bandwidths (VSWR<2) are 180 MHz from 2.36 to 2.54 GHz and 920 MHz from 5.05 to 5.97 GHz, which cover all the 2.4/5.2/5.8 GHz WLAN operating bands. And the radiation patterns are almost omni-directional in the azimuthal plane within the lower operating bands.
The feasibility of using a capacitive sensor to sense the proximity of an external load, especially a finger, to a mobile terminal antenna was experimentally studied using a PIFA-type antenna as one of the sensor's electrodes. It was found that with the proposed arrangement it is possible to detect objects with permittivity close to that of body tissue or the conductivity level of aluminium and the size of a human finger at distances up to 15 mm.
This work presents an accurate and realistic positioning approach for indoor environments based on fingerprinting and ray-tracing techniques. Fading caused by multipath seriously degrades the performance of communication systems operating inside buildings. For this reason, the proposed localization method considers multipath effects due to reflections and diffraction from walls, roof and floor. However, fading in indoor environments can also be caused by the movement of people or the presence of furniture. Because people are the primary absorption agents in indoor channels, their influence on the radio propagation channel must be considered. The proposed localization method takes into account the effects of human body shadowing to provide a realistic estimation of the mobile station position. Numerical calculations in real indoor scenarios show reasonable results.
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