In this article, a novel band-notched ultra-wideband (UWB) bandpass filter based on hybrid microstrip/slotline structure is proposed. A quad-mode stubs-loaded slotline resonator is fed by two orthogonal microstrip lines and ultra-wideband bandpass characteristic is excited. A stub-loaded dual-mode microstrip resonator is externally loaded to the quad-mode slotline resonator, and a notched band with sharp roll-off characteristic is achieved. The circuit model for the dual-mode microstrip resonator loaded slotline is given and analyzed. The proposed filter is designed and fabricated. Simulated and measured return losses are -12 dB/-18 dB and -18 dB/-10 dB in lower and higher passband. The return loss in the notched band is greater than 15 dB.

A broadband CPW-fed circularly polarized square slot antenna for ultra-high-frequency (UHF) radio frequency identification (RFID) applications is proposed. It consists of a square slot embedded with a spur line along diagonal and an F-shaped feeding structure. The proposed antenna achieves an imped-ance bandwidth about 307 MHz (34.6% @886 MHz) and a 3 dB axial ratio (AR) bandwidth about 232MHz (24.3% @954 MHz). The 3 dB AR beam-width is about 96 degrees over the UHF band of 840-960 MHz. The proposed reader antenna based on CPW structure is easy to integrate. With the symmetry and bidirectional radiation pattern, there are less readers needed in some applications, such as access con-trol, than the reader with unidirectional pattern, which will definitely decrease the implemented cost. Therefore, this universal design with desired performance across the entire UHF RFID band (from 840 MHz to 960 MHz) can be applied to all the UHF RFID applications worldwide. Detailed considera-tions of the design and main parameters will be studied in this paper.

A compact UWB (Ultrawideband) MIMO (Multiple-input multiple-output) antenna with asymmetric coplanar strip (ACS)-fed structure is proposed in this paper. The antenna consists of two modified ACS feeding staircase-shaped radiation elements which are orthogonally placed, and the wideband isolation is achieved through a fence-like stub between them. The effectiveness of the fence-like stub is analyzed. Measured results show that the presented antenna can achieve a broad impedance bandwidth (|S₁₁|≤-10 dB) of 3.1-11 GHz with good performance in terms of isolation >15 dB. Radiation patterns and correlation coefficient (ECC) denote the consistent diversity performance across the entire UWB bandwidth. By introducing the ACS-fed structure, the antenna size can be considerably reduced to 43.5 mm×43.5 mm×1.6 mm compared to the recently published UWB MIMO antennas, which makes the antenna suitable for portable UWB MIMO applications.

In this letter, a new design of dual-band circularly polarized (CP) slot antenna is proposed. By embedding a vertical stub, a T-shaped strip and a slit to the ground plane, the CPW-fed slot antenna can radiate right-handed circularly polarized (RHCP) wave in two bands 3.0 GHz and 5.0 GHz. The designed antenna with a size of 33 × 27 × 1 mm³ is fed by a 50-Ohm SMA connector and fabricated on a low-cost FR-4 substrate. Experimental results show that the measured 10-dB return loss impedance bandwidths are 20.4% for the lower band and 23% for the upper band, and the measured 3-dB axial-ratio (AR) bandwidths are 14.1% and 15.8%, with respect to 3 GHz and 5 GHz, respectively.

A dual grating waveguide accelerator structure is investigated and compared with the dielectric wakefield accelerator at THz frequencies. In a dielectric wakefield accelerator, thinner liners for a given current and liners having lower dielectric constant are not preferable due to the fact that they generate much lower axial wakefields. This limits the operation of the device at THz. On the other hand, it is shown that a grating waveguide is tuned at THz with shallower slot heights with competitive wakefield gradients than a dielectric wakefield accelerator.

Two different kinds of artifical magnetic conductors (AMCs) are used to reduce the out-of-band radar cross section (RCS) of microstrip patch antenna. The principle of this method is based on the high impedance characteristic of the AMC structures. The simulated results show that out-of-band RCS of the proposed patch antenna is much lower than that of the reference antenna over the frequency range of 5-12 GHz. The in-band scattering characteristic of the microstrip patch antenna is analyzed, and two slots are cut on the patch antenna to reduce in-band RCS. Prototypes of the reference and designed antennas are manufactured and tested, and the measured and simulated results of the two antennas are in good agreement.

This paper presents a dual-band tunable bandpass filter with independently controllable dual passbands based on a novel asymmetric λ/4 resonator pair with shared via-hole ground. Because two separated passbands can be independently generated by the two λ/4 resonators with different electric lengths, the asymmetric λ/4 resonator pair can realize flexible passband allocation when it is utilized to design dual-band filters. Two varactors are placed at the two open circuit ends of the asymmetric λ/4 resonator pair to control the two dominant resonant frequencies, respectively. A prototype tunable dual-band filter with Chebyshev response is designed and fabricated. The measured results are in good agreement with the full-wave simulated ones. The results show that the first passband varies in a frequency range from 0.88 GHz to 1.12 GHz with the 3-dB fractional bandwidth of 5.1%-6.4%, while the second passband can be tuned from 1.5 GHz to 1.81 GHz with the 3-dB fractional bandwidth of 5.4%-6.4%.

This work demonstrates an all-optical slow light Time Division Multiplexing (TDM) structure based on photonic crystals (PCs). The structure shows good ability of divide time domain signal into repetition time slots signal by four tunable group velocity waveguides from 0.006*c to 0.248*c where c is the velocity of light in the vacuum at the center wavelength of 1550 nm and over a bandwidth 4.52 THz with group velocity dispersion below 10 ² ps²/km. New high efficiency Y-type directional coupling output can get larger than ~1.4 times intensity and ~93% loss improvement which are comparable to conventional output device. The proposed PCs waveguide structure is leading the way to achieve the TDM application and has good capability to extend the application of the optical communication and optical fiber sensors systems.

In Chinese Compass Navigation Satellite System (CNSS for short), dual-band antennas are more attractive, because they can provide both navigation and communication services. In this paper, we present a dual-band dual-circular-polarized planar spiral-slot CNSS antenna. This antenna works at L Band (1616±5 MHz, left-handed circular polarization, LHCP) and S Band (2492±5 MHz, right-handed circular polarization, RHCP). Numerical results show that the impedance bandwidth (S₁₁<-10 dB), 3 dB axial ratio bandwidth and antenna gain at L Band are about 242 MHz, 79 MHz and 4.92 dB, respectively, while the simulated impedance bandwidth (S₁₁<-10 dB), 3dB axial ratio bandwidth and antenna gain at S Band are about 180 MHz, 58 MHz and 5.25 dB, respectively. An experiment was carried out to verify our design. Measured results show that impedance bandwidth (S₁₁<-10 dB) and 3 dB axial ratio bandwidth L Band are about 300 MHz and 14 MHz, respectively, while the measured impedance bandwidth (S₁₁<-10 dB) and 3 dB axial ratio bandwidth at S Band are about 210 MHz, 10 MHz, respectively. The measured results basically agree with the simulated ones and meet the requirement of CNSS terminal antennas.

A compact wideband planar microstrip-fed quasi-Yagi antenna is presented. In order to achieve a high gain, the traditional rectangular director in one row is replaced by two rows of directors with an angle, and the overall size of the antenna is unchanged. By adjusting the angle between the two rows of directors, a better performance is achieved. The measurement results show that a broadband impedance about 85.5% (1.84-4.59 GHz) for S₁₁ less than -10 dB and a gain about 4.5-9.3 dBi are obtained. Simulation and measurement results are provided and discussed. The agreements between the simulation and measurement results indicate that the antenna is suitable for wireless communication applications and phased arrays.

Using the Green's dyad technique based on cuboidal meshing, we compute the electromagnetic field scattered by metal nanorods with high aspect ratio. We investigate the effect of the meshing shape on the numerical simulations. We observe that discretizing the object with cells with aspect ratios similar to the object's aspect ratio improves the computations, without degrading the convergency. We also compare our numerical simulations to finite element method and discuss further possible improvements.

Based on the Collins integral, an analytical expression of a general Lorentz-Gauss vortex beam propagating in free space is derived, which allows one to calculate the linear momentum density of a general Lorentz-Gauss vortex beam in free space. The linear momentum density distribution of a general Lorentz-Gauss vortex beam propagating in free space is graphically demonstrated. The x- and y-components of the linear momentum density are composed of two lobes with the equivalent area and the opposite sign. Therefore, the overall x- and y-components of the linear momentum in an arbitrary reference plane are equal to zero. The longitudinal component of the linear momentum density is proportional to the intensity distribution. The influences of the Gaussian waist, the width parameters of the Lorentzian part, the axial propagation distance, and the topological charge on the linear momentum density distribution of a general Lorentz-Gauss vortex beam in free space are examined in detail.

In this paper, a circular microstrip patchcentrally etched with a cross slot is studied. The slot dimensions are varied for controlling the reflection lossand thephase range of a reflectarray. It is found that the dominant TM mode of the slotted circular patch can be easily excited, and the slot length can be varied to function as a phase-changing parameter. Cross slots with equal and unequal arms are investigated. Study shows that the slope of the S curve can be made slow-changing by increasing the slot width. A maximum reflection phase range of 328.68º is achievable in the S curve. Rectangular waveguide method has been deployedfor simulating and verifying the design idea. Reasonable agreement is found between the measurement and simulation.

The design of a differential K-band UWB(Ultra Wideband) Short Range Radar (SRR) transmitter in 90nm bulk CMOS is presented. Implementation of SRRs in deep submicron CMOS technology is attractive, in terms of cost and monolithic integration of RF font-end with signal base-band processor. The transmitted pulse bandwidth limits the range resolution of the radar system. Due to the wide bandwidth and high frequency of CMOS implementation, UWB transmitters in the K-band are challenging to make and critical for the system performance. The design presented is based on frequency up conversion using a double balanced mixer. The differential output is combined and matched with the antenna using an on-chip balun. To mitigate local oscillator (LO) leakage of UWB differential transmitters we propose a new Pulse Generator (PG) design. A switching technique is used to minimize the LO leakage enabling continuous wave operation with very wideband pulses. Measurements of the proposed transmitter achieves a -10 dB bandwidth (BW) of 5 GHz. Using a Pulse Repetition Frequency (PRF) of 100 MHz the peak average power is -40 dBm. Compared to measured transmitter performance of a single balanced mixer design, the LO leakage of this dual balanced mixer is decreased with more than 20 dB, and is lower than the peak average power of the pulse. It consumes 11 mW from a 1.2 v supply where 6 mW is from the LO.

A PLDRO (Phase Locked Dielectric Resonator Oscillator) with the output frequency of a fractional multiple of reference is proposed and implemented. The key element in the proposed PLDRO is an image rejection mixer placed between a VCDRO (Voltage Controlled Dielectric Resonator Oscillator) and SPD (Sampling Phase Detector). The image rejection mixer shifts the coupled signal from the VCDRO before the signal feeds the SPD. Therefore, the output frequency of the PLDRO can be realized such that it is not harmonically related with its reference frequency. The frequency divider and multiplier generate the IF frequency for the mixer from the reference frequency. The general PLL (Phase Locked Loop) design parameters such as the damping coefficient and the natural frequency are derived for the proposed topology of the PLDRO. A 7.25 GHz PLDRO with a 100MHz reference, intended for use as a local oscillator for a ka band Block-up Converter (BUC), is designed and measured. A BJT (Bipolar Junction Transistor) is used as an active component of the VCDRO and a modified two micro-strip line coupled DR model is presented and used for frequency tuning range estimation. The measured phase noise at 10 kHz/100 kHz offset is 101 dBc/Hz and 115 dBc/Hz, respectively. The fabricated PLDRO size is 100 mm by 105 mm by 23 mm including a 100 MHz reference crystal oscillator.

The single-scattering properties of hexagonal columns and plates were studied using Discrete Dipole Approximation at 94GHz, including scattering efficiency, absorption efficiency, asymmetry factor, backscattering cross section and phase function. Random and horizontal orientations of particles were compared, and 35 sizes of maximum dimension D ranging from 1 um to 10 mm were selected. The results indicate that scattering and absorption efficiencies of horizontally oriented hexagonal columns are larger than those of the randomly oriented ones, whereas this phenomenon does not appear to hexagonal plates. The asymmetry factor of horizontally oriented hexagonal plates has a negative value, which means that the backscattered energy is more than forward energy when the particle is large enough. The backscattering cross sections of horizontally oriented hexagonal columns and plates are larger than those of random orientation, which can be explained by that different cross sections of particles will be exposed to incident plane wave. When the particle size is smaller than incident wavelength, little scattering energy difference between random and horizontal orientation exists, while if the particle is larger than incident wavelength, a turning point will happen at θ=110˚, which can be explained by the theory of energy conservation.

We construct an analytical model for the description of emission of undulator radiation (UR) harmonics with account for several sources of line broadening, including the effect of a constant magnetic constituent. We compare it with that of the beam energy spread, emittance and focusing components. The analytical expressions obtained for the UR intensity and spectrum allow for profound analysis of homogeneous and inhomogeneous losses in their explicit form. We analyse the contributions to the fundamental frequency as well as to higher harmonics in long undulators. We study a possibility to compensate for the off-axis effects in undulators by a properly imposed constant magnetic field and obtain an expression for the intensity of such compensating effect. The results obtained are discussed in the context of their possible applications to free electron lasers (FEL). Recommendations for improvement of an UR harmonic line quality, profitable for FEL, are also proposed.

In this paper, a new wire inverted-F antenna (IFA) is proposed, which is structured by grids of thin wires. This novel wire grid IFA is ~0.3λ long and ~0.14λ high and renders 41% fractional bandwidth which is nearly 5 times higher than the bandwidth of a classic IFA. In addition to the novel structure and high bandwidth, the distinguishing feature of the design process employed is its computational efficiency. While the constituent wires of the wire grid (WG) model are one-dimensional (1D) thin wires, they can indirectly form very thick arms leading to bandwidth enhancement. The thin-wire structure of the WG-IFA provides the opportunity to carry out the analysis and design accurately and fast in a 1D MoM-based software like NEC.

This paper describes the concept, design, and measurement of a multi-band circularly polarized printed slot antenna with a single microstrip feed line. The antenna design for circular polarization (CP) at 1.5 GHz for GPS, 2.4 GHz for Bluetooth, and 3.75 GHz for WiMAX application is given. The proposed antenna also provides a fourth linear polarized band over 5.2 to 6 GHz covering the WLAN band. The design is such that all three CP bands can be tuned for any other desired frequencies. Three configurations of the proposed antenna with different design parameters for different circularly polarized bands are reported in the paper. A prototype of the proposed antenna is fabricated, and measured results are compared with those of the simulations.

In this paper, we develop and present a complete analytical method to analyze the spectral response of a non-uniform multimode fiber Bragg grating assisted devices supporting a few modes. We present the analytical solution while taking into account the two forward and two backward propagating even or odd normal modes of the grating using the matrix method of multimode coupled grating assisted coupler, for sensing application. Earlier, these types of numerical technique based analysis were presented by other researchers, but no one seems to present a complete analytical solution for the given case. The present analytical analysis can simulate a single mode to multimode coupled sensing waveguide devices based on non-uniform grating assisted operation in a coupled structure. The potential applications of our findings will be mostly in sensing devices.