Desired Frequency Band Research Articles

Compact triple-band implantable antenna for multitasking medical devices

Abstract This paper presents a compact implantable antenna’s design, fabrication, and measurement for biotelemetry applications. The proposed design with the size of 255 mm3 provides a triple-band operation that covers all the Medical Implant Communication Service (MICS: 402 MHz), Medical Device Radiocommunications Service (MedRadio: 405 MHz), and Industrial, Scientific, and Medical (ISM: 433, 915 and 2450 MHz) bands simultaneously. The compact structure with triple- band performance is essentially achieved by using a spiral-like radiator loaded with meandered and internal gear-shaped elements excited by a vertical coaxial probe feed. Also, the slots-loaded partial ground plane is utilized to improve impedance matching at the desired frequency bands. The design and analysis of the antenna were carried out using the Ansoft HFSS software in a homogenous skin model and the CST Microwave Studio in a realistic human model. The proposed antenna was fabricated to validate the simulated results, and characteristics of its return loss and radiation patterns were measured in minced pork meat. Moreover, realized gains and specific absorption rate (SAR) values of the antenna were numerically computed using the simulators. Based on the simulated and measured results, the proposed antenna performance was found to be comparable to the limited number of multiband implantable antenna designs reported in the recent literature.

A novel laser-based duffing oscillator system to identify weak ultrasonic guided wave signals related to rail defects

Laser-generated Rayleigh wave is a promising candidate for noncontact and remote inspection of railway as it can inspect in line-to-line fashion. Attribute to the recent advancement of optical design, wavelength of the laser generated-Rayleigh wave can be controlled at desired frequency band. By adjusting the wavelength of the Rayleigh wave, detection of defect occurred at different depths in rail become possible. Internal and subsurface defects that occur beneath the surface of railhead usually only reflect very small portion of wave energy hence accurate determination of their presences becomes challenging. Besides, such reflected-defect signal is usually contaminated with strong random noise which further hinder identification of weak reflected-defect signal. This study presents a novel method for detection of surface, subsurface and internal defects in railhead using laser-generated Rayleigh wave and chaotic oscillator. The use of laser-generated Rayleigh wave provides a fast mean to assess the health condition of railhead without the need to physically mounting sensor on the specimen. The use of chaotic oscillator can accurately reveal wave signal that is related to defect occurred in railhead. The effectiveness of the proposed method has been verified using numerical simulation model. Three rail specimens were machined with internal, subsurface and surface-breaking defects, respectively. Experimental results revealed that the proposed method can accurately and reliably reveal the presence of reflected-defect signal under strong random noise conditions. The present study also shows that the proposed system is promising in revealing hazardous defects occurred on rai

Derivation and Validation of Bandgap Equation Using Serpentine Resonator

Bandgap refers to a frequency band where free waves do not propagate. One of the characteristics of a bandgap is its ability to block the propagation of bending waves in a specific frequency band with a periodic structure. Additionally, it has been reported in previous studies that the vibration-reduction performance of a bandgap is superior to that of other reduction methods. A bandgap can be generated in various frequency bands through a simple parameter change in the unit structure. However, the bandgap for a desired frequency band can be determined accurately only with intensive simulations. To overcome this limitation, we have mathematically derived the bandgap using a serpentine spring as a unit structure. The bandgap equation is derived from the general mass–spring system and the final bandgap is derived by substituting the system into the serpentine resonator. The error map for the major design parameter is confirmed by comparing the derived bandgap with the simulation result. In addition, the theoretical bandgap is compared to the experiment value and the vibration-reduction performance of the serpentine resonator is also confirmed. Based on the theoretical and experimental result, the proposed serpentine resonator verifies that the bandgap can be derived mathematically without numerical analysis. Therefore, serpentine resonator is expected to have various applications since it dramatically reduces the time and cost for forming the bandgap of the desired frequency band.

Size reduction of a conical horn antenna loaded by multi‐layer metamaterial lens

In this paper, a conical horn antenna in the presence of a metamaterial lens in the X-band is introduced and fabricated. The annular metamaterial lens is located at the aperture of a shortened horn antenna, whose length is half the length of the corresponding optimum horn. The phase velocity in the metamaterial lens is more than the phase velocity along the axis of the antenna for the same propagation distance, so the phase distribution at the aperture of the antenna is uniform and the gain of the shortened horn antenna increases. Metamaterial cells are designed in the form of a printed circuit board that have easy to build and suitable cost. The design process is based on how the waves incident on the proposed metamaterial cell, and finally, by using the particle swarm optimisation (PSO) algorithm proper radiation characteristics in the desired frequency range can be achieved. The radiation characteristics of an antenna with a metamaterial lens are similar to that of an antenna with optimum length in the desired frequency band. The difference is that the weight and volume of these antennas are reduced, so they have better performance in satellite and radar systems.

All-Metal Wideband Frequency-Selective Surface Bandpass Filter for TE and TM Polarizations

A novel technique to design a low-cost frequency-selective surface (FSS) bandpass filter is presented in this article. Wideband polarization-independent FSS bandpass filters are predominantly made of multiple microwave dielectric substrates or noncommercially available composite materials with or without active components, contributing to a very high manufacturing cost. The presented FSS filter has neither microwave substrates, nor any active devices, while it has a large controllable operational frequency band, which can support all polarizations, due to its symmetrical configuration. To the best of our knowledge, such a polarization-independent wideband bandpass response has never been achieved by any low-cost fully metallic FSS filter. The proposed FSS filter is made of three thin metal sheets composed of an engineered metallic substrate (EMS) and a metallic orthogonal dipole resonator (ODR). The EMS is responsible for ensuring the mechanical integrity of the filter without imposing electromagnetic (EM) restrictions throughout the desired frequency band. The integration of EMS and ODRs realizes a fully controllable wideband bandpass verified thorough circuital and modal analyses. According to the predicted and measured results, the FSS filter has a large bandwidth of around 31%, extending from 8.76 to 11.96 GHz with sharp roll-offs for the normal incidence. Simulated and measured results show a low sensitivity of the FSS filter response to oblique angles of incidence for both TM and TE polarizations.

A Low-Cost Metamaterial Sensor Based on DS-CSRR for Material Characterization Applications.

This paper presents a metamaterial sensor using a double slit complementary square ring resonator (DS-CSRR) that has been utilized for the measurement of dielectric materials, especially coal powder. The design is optimized for best performance of deep notch depth in transmission coefficient (Magnitude of S). Sensitivity analysis of transmission coefficient with respect to structure dimensions has been carried out. Metamaterial properties of double negative permitivity and permeability were extracted from the S–parameters of this sensor. The optimized structure is fabricated using low cost FR-4 PCB board. Measured result shows resonance frequency of 4.75 GHz with a deep notch up to −41 dB. Simulated and measured results show good agreement in desired frequency band. For material characterization, first, two known materials are characterized using this metamaterial sensor. Their respective resonances and dielectric constants are known, so the transcendental equation of the sensor is formulated. Afterwards, the proposed sensor is used for dielectric measurement of two types of coal powder, i.e., Anthracite and Bituminous. The measured value of dielectric constant of Anthracite coal is 3.5 and of Bituminous coal is 2.52. This is a simple and effective nondestructive measurement technique for material testing applications.

Low-SAR Four-Antenna MIMO Array for 5G Mobile Phones Based on the Theory of Characteristic Modes of Composite PEC-Lossy Dielectric Structures

A low-specific absorption rate (SAR) four-antenna multiple-input–multiple-output (MIMO) antenna array is designed for fifth-generation (5G) mobile phones based on the theory of characteristic modes (TCM) of the composite perfect electric conductor (PEC) and lossy dielectric structures. First, the TCM of composite PEC-lossy dielectric structures is reviewed briefly. Then, the application of the theory for low-SAR antenna design is demonstrated through a four-antenna MIMO antenna array. Finally, the proposed MIMO array is fabricated, and its performance is measured. Its −10 dB impedance bandwidth can cover the desired frequency band from 3.4 to 3.6 GHz. The isolations between different antenna elements are higher than 15.4 dB. Their total efficiencies range from 81.3% to 89.9%. The envelope correlation coefficient (ECC) is lower than 0.07. The 10 g spatial-average body SAR corresponding to the situation that four antennas simultaneously radiate is 0.47 W/kg. Compared with the state-of-the-art 5G MIMO antenna arrays, the proposed MIMO antenna array has the lowest peak SAR value, satisfactory efficiency, isolation, and ECC. This article provides a general methodology for the design of low-SAR mobile phone antennas.

Decoupling and Matching Network for Dual-Band MIMO Antennas

This article presents a novel method to design the decoupling and matching network (DMN) for dual-band multi-input–multioutput (MIMO) antennas. The DMN consists of a grid of metallic microstrip stubs, some of which are connected while others are not. The connecting condition in the DMN is the only unknown variable for realizing high antenna isolation. It is determined by rigorous design formulas upon scattering matrix and optimized by the binary optimization algorithm, e.g., genetic algorithm (GA). Thus, high isolation among antennas can be achieved without requiring the optimization process in the electromagnetic simulation tool. Three decoupling examples of two two-element symmetric and asymmetric arrays and a four-element array are presented to elaborate the design procedure and verify the advance of the proposed decoupling method. Results show that the adoption of DMN offers enhancement in impedance matching, isolation, and efficiency, as well as the reduction of envelop correlation coefficient within two desired frequency bands for all cases, validating the proposed decoupling method.

Travelling Wave Antenna Based MIMO for 5GHz WLAN Band Application With Pattern Diversity

ABSTRACT A single-layer, four-element multiple-input-multiple-output (MIMO) antenna for 5 GHz (5150–5850 MHz) band WLAN application is proposed. Each unit element consists of three sections and this behaves as a travelling wave antenna, which enables frequency scanning feature. The combination of orthogonal feeds and placement of elements introduce dual-polarisation, and pattern diversity respectively. Thus, the proposed MIMO antenna offers a higher degree of freedom (pattern diversity, frequency scanning and dual polarisation), which makes it exceptional. The proposed MIMO antenna has a maximum impedance bandwidth of 17% (4.93–5.87 GHz) corresponding to port 4 and isolation of 17.5 dB, which is achieved without additional decoupling/isolation enhancement circuits. The envelope correlation coefficient of 0.25, capacity loss less than 0.4 bits/sec/Hz, and the mean effective gain (MEG) ratio of 0 dB in the desired frequency band quantifies the diversity performance for WLAN applications. The proposed MIMO has gain from 2 to 5.5 dB and occupies a compact volume of 1.3 λ × 1.3 λ × 0.02 λ mm3, which may be one of the most miniaturised electrical configurations.

Design of a Highly Efficient Wideband Multi-Frequency Ambient RF Energy Harvester.

For low input radio frequency (RF) power from −35 to 5 dBm, a novel quad-band RF energy harvester (RFEH) with an improved impedance matching network (IMN) is proposed to overcome the poor conversion efficiency and limited RF power range of the ambient environment. In this research, an RF spectral survey was performed in the semi-urban region of Malaysia, and using these results, a multi-frequency highly sensitive RF energy harvester was designed to harvest energy from available frequency bands within the 0.8 GHz to 2.6 GHz frequency range. Firstly, a new IMN is implemented to improve the rectifying circuit’s efficiency in ambient conditions. Secondly, a self-complementary log-periodic higher bandwidth antenna is proposed. Finally, the design and manufacture of the proposed RF harvester’s prototype are carried out and tested to realize its output in the desired frequency bands. For an accumulative −15 dBm input RF power that is uniformly universal across the four radio frequency bands, the harvester’s calculated dc rectification efficiency is about 35 percent and reaches 52 percent at −20 dBm. Measurement in an ambient RF setting shows that the proposed harvester is able to harvest dc energy at −20 dBm up to 0.678 V.

Differential-Fed, Dual-Aperture Based, Quasi-End-Fire 5G mmWave Antenna-in-Package Design

A low-profile, wideband antenna-in-package (AiP) design is proposed for 5G mmWave mobile applications. The aperture-coupled feeding incorporated with the microstrip feed line through the slots in the ground is used to excite the patch antenna. Firstly, a thin quarter-wave shorted patch antenna (QW-SPA) with the dominant <i>TM</i>^<i>z</i>_1/2,0,0 mode is realized. To broaden the operating band, the QW-SPA is extended along its resonant length so that the <i>TM</i>^<i>z</i>_1,0,0 mode can also be excited. The offset introduced into the two slots together with the additional shorting via wall are applied to enhance the beam tilt toward the end-fire direction. The proposed single-patch design shows a wide fractional bandwidth, covering the 5G mmWave band n257 (26.5&#x2013;29.5 GHz). Furthermore, to increase more beam tilt, the differential-fed, two-patch sub-array formed by two QW-SPAs spaced a half-wavelength at 28 GHz apart is also presented. Compared with the single-patch design, the beam-tilt enhancement of around 10&#x2013;27 degrees is obtained over the desired frequency band with the peak gain of around 8.2 dBi for the sub-array AiP design.

Wideband Three Loop Element Antenna Array for Future 5G mmwave Devices

In this work, a compact, light-weight, low-cost, and easy install and incorporate mmwave printed square loop antenna with a perturbed ground plane is proposed. The antenna is fabricated on an ultra-thin 0.254 mm Rogers RT/Duroid 5880 substrate. The antenna resonates between 26 GHz and 40 GHz providing the broad bandwidth of 13 GHz ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 47$ </tex-math></inline-formula> %). First, a single element consisting of three rectangular square loops and a transmission line with total dimensions of 9 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times11$ </tex-math></inline-formula> mm ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.84\,\,\lambda _{0} \times 1\,\,\lambda _{0}$ </tex-math></inline-formula> ) is designed. The loop elements are arranged on top of each other and with the further insertion of square slot in ground plane, wideband resonance response has been achieved. The antenna demonstrates gain of more than 3.3 dBi, and radiation and a total efficiency of 98% at 28 GHz. The proposed design enables spatial diversity and minimize the effects of interference between adjacent channels by providing dual-beam within desired frequency band. In addition, a linear array ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$18.5\times22.5$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of four elements with a traditional feeding network is also designed, simulated, and measured. The gain of the array is 10.1 dBi, while the radiation and the total efficiency is more than 92 % at 28 GHz. A brief literature review and comparison of this work with other published works is also presented. To validate the proposed design and concept, a prototype is fabricated for both, a single element, and an array. It is found that the measured results and the computed results are in good agreement. Therefore, we believe that this system will find its applications within modern mmwave communication cellular devices.

A GaN Microwave Power Amplifier Design Based on the Source/Load Pull Impedance Modeling via Virtual Gain Optimization

Generation of proper source/ load pull impedances for a selected GaN device is essential to design a microwave power amplifier for optimum gain and power-added efficiency. As they are obtained, these impedances may not be realizable network functions over the desired frequency band. Therefore, in this paper, first, we introduce a new method to test if the given source and load impedances are realizable. Then, a novel numerical procedure is introduced to model the source and load pull impedances as realizable network functions, which in turn results in the optimum power intake and power delivering capacity for the GaN transistor used in the design. In the numerical modelling process, a robust tool called “Virtual Gain Optimization” is presented. Numerically generated realizable source and load impedances are modelled analytically. Eventually, these impedances are synthesized using our automatic Darlington Synthesis Robot software to yield the optimum input and output matching network topologies with component values. Examples are presented to test the realizability of the given source/load pull impedance data. Then, the power intake and delivery capacity of the active device are assessed for a 10W-GaN power transistor, namely “Wolfspeed CGH40010F” over 0.8-3.0 GHz bandwidth. Eventually, the power amplifier is designed and manufactured. It is shown that the computed and the measured performance of the amplifier is very close with 10 Watts output power, 11.4±0.6 dB gain and 49% to 76 % power added efficiency.

Millimeter-Wave Antenna With Gain Improvement Utilizing Reflection FSS for 5G Networks

A millimeter-wave (mm-wave) antenna with enhanced gain for new 5G networks is introduced in this work. A rectangular slot antenna operating at the fundamental mode of the desired frequency band is utilized in this study. The antenna gain is improved by employing a Frequency Selective Surface (FSS). The FSS-based reflectors are designed at the same fundamental mode of the antenna and added under the antenna at a specific distance to achieve the required gain enhancement with a suitable dimension of 25 &#x00D7; 25 &#x00D7; 5 mm³. The antenna gain is increased by around 5.3 dBi when the FSS-based reflectors are added under the antenna. The antenna and the FSS are fabricated and tested. The antenna has tested outcomes without FSS with S₁₁ &#x2264; -10 dB from 26 GHz up to 29.8 GHz and realized gain of around 4.5 dBi within the entire frequency band and radiation efficiency of around 93 %. While the antenna with FSS has achieved bandwidth with S₁₁ &#x2264; -10 dB from 25.5 GHz up to 30.8 GHz and realized gain around 10.3 dBi at 28 GHz and radiation efficiency around 90 %. The simulated and tested outcomes have the same trend which validates the suggested antenna to be operated in the new 5G applications. All simulation results are completed using the CST Microwave Studio.

A Sub-6 GHz MIMO Antenna Array for 5G Wireless Terminals

This paper presents a novel antenna with its array and MIMO configuration for the 5G sub-6 GHz applications. The proposed antenna element operates at the central frequency of 5.57 GHz dedicated for Sub-6 GHz 5G communication applications. The antenna element holds a circular-shaped radiating portion with an inner-circular slot, plus a rectangular slot at its right edge to make the proposed design resonate at the desired frequency band. The RT5880 substrate is used with a thickness of 0.787 mm, and the low-loss tangent of 0.0009. To achieve a desired gain of 12 dB, a four-element array configuration is adopted, which improved a bore side gain to 12.4 dB from 6.66 dB. Then, the two-port configuration is adopted such that the isolation achieved between them is more than −30 dB. The total efficiency of the proposed antenna array is observed to be more than 80% within the operating bandwidth. Moreover, the Specific Absorption Rate (SAR) analysis is also presented for the proposed MIMO configuration, obeying the standard value (i.e., &lt;2 W/kg for any 10 g of tissue). The measured results are in good agreement with the simulated results. All the simulations of the proposed design are performed in the CST MWS software.

Stable and Lifelong Head Phantoms Using Polymer Composition Mimicking Materials to Test Electromagnetic Medical Imaging Systems

Phantoms are critical items for testing and evaluating new prototypes of electromagnetic medical imaging systems. Realistic tissues distribution, size, shape, and dielectric properties of tissue-mimicking materials across the desired frequency band; in addition, long-term stability is required. In this study, a polymer composition that use to develop head tissues-mimicking materials that satisfy the aforementioned requirements. Polyepoxides (Epoxy), and assorted types of micro scale additive, including graphite, aluminium oxide, carbon black, and brass powders, are used to fabricate the phantom. Different mixing ratios are used to mimic four healthy head tissues; white matter, grey matter, skull, and skin. Blood-mimicking material is also included in the unhealthy phantom to represent stroke (hemorrhagic) at different locations and sizes. Also, water-based mimicking material is used to emulate cerebrospinal fluid (CSF) tissue. The measurements confirm close agreement to properties of actual head tissues across the frequency band 0.5–5 GHz, which has been used in the ongoing research activities of electromagnetic head imaging systems. Stability over time is investigated and compared with the widely used gelatin-in water-based mimicking materials. The results show the superiority of the developed phantom compared to currently using gelatin-based phantoms.

Development of multi-band tuned rail damper for rail vibration control

The intense interaction force between the wheel-rail causes the vibration of wheel and rail, and generates rolling noise. Increasing the rail damper is an effective way to suppress rail vibration. In this paper, a shear-type multi-band tuned rail damper (MTRD) consist of internal mass bars and external resilient layer to reduce rail vibration is proposed. Mass bars are wrapped inside resilient layer and placed along the length of rail. Resilient layer between two adjacent mass bars can enforce them perform shearing motion corresponding to the layer along the main vibration direction of rail. Different oscillation frequencies corresponding to different mass bars can be tuned by adjusting the structure of MTRD. It achieves an increase in the operating frequency band and a widening of the operating frequency range of MTRD. The influence of parameters of MTRD on its performance is investigated by the finite element method (FEM). One of three designed MTRD models is selected for prototype production after comparative analysis. Laboratory measurements are conducted on a rail specimen and 12 m track platform. Results show the main operating frequency band of designed MTRD is in the range of 200 Hz–800 Hz, achieves the goal of the desired frequency band. Frequency response function tests of rail on 12 m platform show the MTRD could suppress rail vibration in the range of 100–2000 Hz. To estimate the practical reduction effects of MTRD on vibration, a small radius curve of metro line is selected for field measurements. The measured track decay rate (DR) shows MTRD could increase DR at frequencies above 80 Hz with a max increment of 5 dB/m and 9.3 dB/m in vertical and lateral direction respectively. Reduction of rail vibration and rolling noise when trains pass is also measured. The overall vibration level of rail achieves a max reduction of 10.9 dB and 6.3 dB in vertical and lateral directions respectively. The overall sound pressure level is reduced by 5.9 dB(A) at the speed of 60 km/h.

A 33 MHz Fast-Locking PLL with Programmable VCO and Automatic Band Selection for Clock Generator Application

This paper presents a prototype of an auto-ranging phase-locked loop (PLL) with low jitter noise over a wide operating frequency range using the multiband programmable voltage-controlled oscillator (VCO) gain stage with automatic band selection. We successfully reduce the VCO gain (Kvco) and retain the desired frequency band. The proposed PLL comprises a prescaler, phase frequency detector (PFD), charge pump (CP), programmable VCO and automatic band selection circuit. The PLL prototype with all subblocks was implemented using the TSMC 0.18 μm 1P6M process. Contrary to conventional PLL architectures, the proposed architecture incorporates a real-time check and automatic band selection circuit in the secondary loop. A high-performance dual-loop PLL wide tuning range was realized using an ASIC digital control circuit. A suitable way to maintain the Kvco low is to use multiple discrete frequency bands to accommodate the required frequency range. To maintain a low Kvco and fast locking, the automatic frequency band selection circuit also has two indigenous, most probable voltage levels. The proposed architecture provides the flexibility of not only band hopping but also band twisting to obtain an optimized Kvco for the desired output range, with the minimum jitter and spurs. The proposed programmable VCO was designed using a voltage-to-current-converter circuit and current DAC followed by a four-stage differential ring oscillator with a cross-coupled pair. The VCO frequency output range is 150–400 MHz, while the input frequency is 25 MHz. A sequential phase detection loop with a negligible dead zone was designed to adjust fine phase errors between the reference and feedback clocks. All circuit blocks of the proposed PLL were simulated using the EDA tool HSPICE and layout generation by Laker. The simulation and measured results of the proposed PLL show high linearity, with a dead zone of less than 10 pV. The differential VCO was used to improve the linearity and phase noise of the PLL. The chip measured results show rms jitter of 19.10 ps. The PLL prototype also has an additional safety feature of a power down mode. The automatic band selection PLL has good immunity for possible frequency drifting due to temperature, process and supply voltage variations. The proposed PLL is designed for −40 to +85 °C, a wide temperature range.

The development of the 499.8 MHz superconducting cavity system for BEPCII

In order to accommodate the luminosity improvement strategy, two superconducting 499.8 MHz radio frequency (rf) cavities have been adopted for the Upgrade project of Beijing Electron Positron Collider (BEPCII), a double-ring electron–positron collider as well as a synchrotron radiation (SR) light source. The in-house development of the 499.8 MHz superconducting cavity system was initiated at IHEP since 2008. One prototype niobium cavity with all the parts except for the flanges and the pickup port formed by spinning was fabricated and then vertical-tested successfully in July 2011. Four prototype input couplers were manufactured and high-power tested with one reaching a maximum rf power of continuous wave (cw) 420 kW. One prototype HOM damper with a satisfactory absorbing efficiency at the desired frequency band was also constructed and high power tested up to cw 4.4 kW. In the meanwhile, a frequency tuner consisting of a stepping motor and a piezoelectric oscillator was developed. Finally, the bare cavity was dressed with one input coupler, two HOM dampers and one frequency tuner, mounted in a domestic-developed cryostat and then high-power tested successfully in Oct. 2011. The achieved accelerating voltage is 2.2 MV with corresponding Q0 measured to be 5.8 × 108, beyond the designed goal. This is the first in-house developed 499.8 MHz HOM-damped superconducting cavity system in China. The design, fabrication, post processing and tests of the niobium bare cavity and its auxiliaries, as well as the horizontal high-power test of the cavity system are presented.

Design of a MIMO Antenna with High Gain and Enhanced Isolation for WLAN Applications

A multi-input multi-output (MIMO) antenna for wireless local area network (WLAN) applications operating in 2.4 GHz and 5.8 GHz frequency bands is proposed in this paper. The proposed dual-band MIMO antenna is composed of two symmetrical radiation elements, and the isolation performance is improved by adopting parasitic elements and a defective ground plane. The measured reflection coefficients are less than −10 dB in the bandwidth range of 2.12–2.8 GHz and 4.95–6.65 GHz, respectively. The measurements show excellent isolation of −21 dB and −15 dB in both desired frequency bands, respectively. The total peak gain is greater than 4.8 dBi. The calculated envelope correlation coefficients (ECC), based on the measured S-parameters, are smaller than 0.01 and 0.024 in the lower and higher frequency bands, respectively. The dimension of the presented antenna occupies 50 × 40 × 1.59 mm3. It is suitable for IEEE 802.11 a/b/g/n (2.4–2.4835 GHz, 5.15–5.35 GHz and 5.725–5.85 GHz) WLAN applications.