In this work, we report a novel phase change material: Hf-doped VO2(M1) with negligible thermal hysteresis width for low-power silicon photonic reconfigurable device applications. As dopant concentration rises from 0% to 3%, the material maintains the metal-insulator transition (MIT) property of VO2(M1) thin films, and the thermal hysteresis width significantly narrows from 7 ºC to <1 ºC, leading to a good control of material electrical and optical constants as a function of temperature. A ring resonator with Hf-doped VO2(M1) material partly deposited on the ring has been fabricated. Temperature dependent transmission spectrum of the device has been tested, which shows resonant peak shift due to the phase transition of Hf doped VO2(M1). Doping Hf makes this material become a promising candidate for a variety of silicon integrated reconfigurable photonic devices.
A new microstrip ultra-wideband (UWB) bandpass filter (BPF) with quad notched bands using quad-mode stepped impedance resonator (QMSIR) is investigated in this paper. The resonance properties of the QMSIR are studied. Then, quad notched bands inside the UWB passband are implemented by coupling the proposed QMSIR to the main transmission line of a basic microstrip UWB BPF. The quad notched bands can be easily generated and set at any desired frequencies by varying the design parameters of QMSIR. For verification, a new microstrip UWB BPF with quad notched bands respectively centered at frequencies of 5.2 GHz, 5.8 GHz, 6.8 GHz and 8.0 GHz is designed and fabricated. Both simulated and experimental results are provided with good agreement.
General design guidelines for unidirectional electrically small parasitic array has been proposed by several researchers; however, the input resistance of these antennas is normally very low. In order to practically ``transfer'' this high directivity into realized gain, an appropriate matching mechanism is necessary. This paper gives a simple matching method by adding an inductive stub close to the antenna feed, which can effectively increase the antenna input impedance to 50 Ω and keep the gain almost invariant. Besides, it could make the resonant frequency very close to the frequency where maximum gain occurs, thus a high realized gain can be achieved. Computed and measured examples are given to validate this method.
In this paper, a novel broadband circular polarized (CP) antenna for mobile communication is proposed. The antenna is constructed as a square ring with a gap and coplanar waveguide (CPW) feed. To achieve a broadband CP wave, a cross patch is embedded at the center of the slotted square ring to excite two orthogonal resonant modes with equal amplitude and 90° phase difference for CP radiation. Furthermore, on one side of ground a stub is embedded to match impedance bandwidth that can cover the whole CP bandwidth completely. Loading the AMC (Artificial magnetic conductor) structure on the back of the antenna achieves unidirectional radiation of circular polarized waves. An antenna was fabricated based on simulation and optimization. The simulated and measured results show that the bandwidth with S11<-10 dB is 66.9% from 1.82 GHz to 3.65 GHz, and the 3 dB axial ratio bandwidth is 52.8% from 1.95 GHz~3.35 GHz.
This paper proposes a novel clip-shaped meander-line resonator (CSMLR) to realize miniaturized ultra-narrowband (UNB) bandpass filter design. The main advantage is that it can achieve very weak coupling between adjacent resonators with keeping them very close and introduce transmission zeros (TZs). To further demonstrate the feasibility of using this configuration, a six-pole UNB filter with a fractional bandwidth (FWB) of 0.20% at the center frequency of 1915 MHz was designed on double-sided YBCO high temperature superconducting (HTS) thin films with a thickness of 0.5 mm and dielectric constant of 9.8 by using CSMLR. The measured responses agree rather well with the simulated ones. The measured results show a maximum insertion loss of 0.31 dB and return loss of 15.5 dB in the passband. Two transmission zeroes (TZs) are generated to improve the passband selectivity, which causes the band-edge steepness better than 50 dB/MHz in both transition bands.
In this paper design of a stacked circular patch antenna is presented for high gain and wideband applications. The main radiator of this design is a circular patch antenna, which is fed by using a coupling mechanism. Wide impedance bandwidth of 40% and linear polarization of gain 9.5 dBi at the center frequency of 2.4 GHz is measured. The antenna gain is further increased by using regular period of N circular patch directors on top of the main radiator. The first director is placed in a distance of about one half of the wavelength and the next directors are placed with regular distances of about a quarter of the wavelength. The antenna gain is tuned and increased with the number of the directors in the range of 9.5-16.5 dBi with N up to seventeen. The antenna impedance change due to the added directors is adjusted by using two parasitic circular patches between the main radiator and the first director. A prototype antenna is designed, manufactured and measured. The antenna operation can be further extended using dual feed geometry in which we can obtain two orthogonal radiation patterns or circular polarizations.
A design of a half-mode substrate integrated waveguide (HMSIW) cavity-backed self-diplexing antenna is proposed with a two-layer structure. The top layer comprises two HMSIW based cavities, and radiating patches are etched on the top-cladding of each cavity. The radiating patches are excited by two distinct printed microstrip lines on the backside of the bottom layer by using shorting-pins. The shorting-pin excites the corresponding cavity in its dominant mode, which resonates at two different frequencies in X-band. The simulated results demonstrate that the proposed design resonates at 8.20 GHz and 10.55 GHz with an isolation of higher than -25 dB between two excitations, which helps to introduce the self-diplexing phenomenon. Also, both resonant frequencies can be tuned independently by varying the dimensions of the corresponding cavity. Moreover, HMSIW cavity-backed structure and proposed feeding technique reduce the overall size of the antenna significantly, while it maintains high gain and unidirectional radiation characteristics for both operating frequencies.
A small size dielectric image line (DIL)-based leaky wave antenna (LWA) is proposed in this paper. Three H-shaped patches as radiation elements are periodically printed on top surface of DIL, which generates infinite higher order space harmonics, and the proposed antenna works at the first order mode. The H-shaped unit cell has high attenuation constant, which leads to power leaking quickly. So high radiation efficiency can be realized with only 3 unit cells. Simultaneously, the open stopband (OSB) is suppressed using H-shaped unit cells to get high efficiency at broadside. The working principle of the proposed antenna is analyzed, and the numerical results validate the theory analysis. Over the operating band (11.5~14.6 GHz), the proposed antenna covers 71° from -41° to 30° (including the broadside) with stable gain (8.7 dBi~10.6 dBi) varying less than 2 dBi. A prototype is fabricated and measured, which have good agreement with simulation results.
In this paper, a very compact 6.1GHz band notched printed multiple-input multiple output (MIMO) antenna with the size of only 25×25 mm2 is presented for Ultra-wideband (UWB) applications. Two symmetrical antenna elements are placed in vertical direction which make it easy to realize good diversity performance. The antenna elements are made up of a microstrip feed line and rounded patch. One slit is in the diagonal position, and one slot line is designed to improve the isolation between two orthogonal antenna elements. The 6.1 GHz band notch weakens the probable interference between C band satellite uplink communications and UWB system. Simulated and measured results show that it covers from 3.1 to 12 GHz with S11<-10 dB except rejected band, and the isolation is better than 15 dB in full UWB spectrum.
This paper presents a Ku-band filter based on groove gap waveguide (GGW) technology which is composed of a filter with two transitions GGW and WR-62. The filter is operated from 13.8 GHz to 14.2 GHz. Actually, a fractional bandwidth of about 2.85% is obtained for maximum return loss of 20 dB and the maximum insertion loss of 0.05 dB over the bandwidth. The validity of the design results is confirmed both numerically and experimentally. Measurement results show that the performance of filter agrees well with simulation. This filter could be used as part of a gap waveguide based structure.
A novel flexible frequency and pattern reconfigurable antenna for wireless system is proposed. The antenna is composed of two completely symmetrical radiating elements, a feedline and ground. By controlling the on and off of 8 PIN diodes loaded on the symmetric hexagonal split ring and monopole branches to select the radiation element, the antenna achieves frequency reconfiguration in 1.9G band and 2.4G band, and is capable of steering the beam in two directions in each band. Meanwhile, the antenna works at four states with omnidirectional radiation patterns. Finally, the bending characteristics of the antenna at different bending degrees are analyzed. Measured results are in good agreement with simulations, which denotes that it is suitable for wireless systems.
This article presents a new method for studying the near-field electromagnetic interaction between a dielectric filled open ended circular waveguide (OECW) and a layered dielectric structure. The proposed model is based on plane wave spectrum theory using a novel and computationally efficient two step integration method. The first integral, involving multiple singularities in the integration path, is efficiently solved using a deformed elliptical integration path which encircles the singularities of the integral. The infinite domain tail integral involving the slowly converging integrand is further solved using an efficient trigonometric transformation. The proposed OECW based method is capable of determining the unknown material properties of any layered dielectric medium, and hence finds application in nondestructive evaluation of materials.
A novel microstrip balun bandpass filter (BPF) is designed by using open loop resonators having interdigital capacitors. The interdigital capacitors are employed to control the center frequency easily. Opposite phase difference between the balanced outputs can be provided according to the suitable coupling topologies based on parallel and anti-parallel coupled lines. By this way, minimized magnitude imbalances between the balanced ports can also be obtained. In order to obtain two poles inside the passband, two identical resonators are coupled to each other. The designed balun BPF was fabricated and measured to validate the proposed methodology. Phase and magnitude imbalances inside the passband were measured within 180±5˚ and 0.5 dB, respectively. The simulated and measured results are in good agreement.
Widely applied in confined areas communication, leaky coaxial cable (LCX) is used as an antenna to provide communication services for mobile devices. In order to improve the quality of mobile communication in narrow and long spaces such as subway or tunnel, the method of designing LCX with circular polarization radiation property is proposed, which consists of aperture's design, circular polarization simulation verification and coupling loss test. Firstly, the regular circumferential asymmetry apertures are designed and slotted in the outer conductor of the LCX to achieve radiating φ component of the electric field, and the optimized size of the aperture for achieving circular polarization is obtained by the simulation results from Ansoft HFSS. Then, the circular polarization characteristics in the maximum radiation direction are obtained. Further, the relation between it and the gain of the optimized aperture is analyzed. Finally, the coupling loss is calculated for evaluating the performance of the LCX. The simulation results show that the two designed LCXs have the circumferential circular polarization range of 30~70 deg in the maximum radiation direction at 900MHz, and the range is twice of the conventional LCX. The coupling loss indicator also meets the requirements.
Graphene, a one-atom thick layer of carbon atoms arranged to form a honeycomb lattice exhibits intriguing mechanical, thermal and electrical properties, which make it attractive for bio- and chemical sensors as well as flexible electronics applications. In this paper, graphene films with different amounts of graphene loading (weight fraction 12.5% and 25%) deposited by screen printing technique are characterized in the microwave frequency range. By fitting the measured scattering parameters of graphene-loaded microstrip lines with Advanced Design System (ADS) circuit simulations, a simple equivalent lumped circuit model of the film is obtained. The proposed equivalent lumped circuit model presented in this paper proves suitable as an initial step towards the full-wave electromagnetic modeling and analysis of graphene loaded microwave structures intended for sensing and tuning applications.
The design of a terahertz short-slot coupler with curved waveguide is proposed. A traditional short-slot coupler uses a step-like structure in order to suppress higher order modes and improve bandwidth. It becomes difficult to control the fabrication of tiny steps with the incensement of frequency especially in terahertz band. The designed coupler is composed of two curved waveguides overlapping in the middle to realize a specific coupling coefficient. Then the step-like structure can be replaced with a curved structure which is much easier to fabricate. The coupling coefficient of the coupler is 3 dB, and the variation is less than 1dB around the center frequency. The phase difference between two output ports is 90°. The isolation is greater than 10 dB in the whole working band. Measured results show high agreement with simulation predictions. The designed coupler can be widely used as feed networks of horn antenna array.
We performed an experiment to verify quadrupole model of the electric field of a rotating magnet. It is found that the rotating magnet insulated from the earth and enclosed in a conductive insulated screen induces the potential difference across an air capacitor arranged on the outside the screen. The field of an electric quadrupole cannot penetrate through the screen; therefore the electric field detected outside the screen has the source of another nature. The field observed in the experiment can be explained by arising of a fictitious electric charge upon rotating of the magnet in accordance with the transformations of the electromagnetic field in the theory of relativity.
Unlike conventional systems in which two identical resonant loops are employed, a pair of novel planar loops is developed for wireless power transfer. The proposed transmitting and receiving coils have different distances between turns while the wire length is the same. The effect of mutual inductance on transfer efficiency is analyzed. The mutual inductance of the proposed loops is more uniform than the conventional one, which is helpful for suppressing frequency splitting at closer transfer distance. Moreover, the power transfer performance is enhanced at longer distance. Additionally, an experimental prototype is fabricated to verify the distance insensitive characteristic of the proposed system.
The work presents an inventive, simple and implementable design approach to enhance the bandwidth of conventional Salisbury Screen Microwave Absorber (SSMA). Theoretically, the maximum fractional bandwidth of SSMA for FR4 substrate with an optimum sheet resistivity of 308 Ω/sq for -10 dB reflection is nearly 42.1%. In comparison, the bandwidth for square patch based SSMA is 59.7% with the same thickness. The design comprises square patches of SSMA placed periodically on a metal sheet. The square patches consist of an FR4 substrate and a 200 Ω/sq resistive sheet. A single reflection null is observed in the SSMA due to λ/4 resonance whereas in the proposed absorber an additional resonant mode is introduced due to coupling between the nearby patches. The simultaneous overlapping of the λ/4 mode and the additional coupling mode results in bandwidth extension. The close agreement between the simulation and measurement data is observed.
A compact microstrip Rotman lens is proposed in this paper. The microstrip Rotman lens consists of a lens body and Chebyshev impedance transformers. The Chebyshev impedance transformers are used as beam ports, array ports and dummy ports. Compared to the traditional linear tapered transition, the Chebyshev impedance transformer is shorter, which leads to the size reduction and insertion loss improvement for the Rotman lens. An X-band 4×7 Rotman lens using Chebyshev impedance transformers is designed and fabricated. Compared to a traditional Rotman lens, the proposed Rotman lens shows a size reduction of about 56% and an insertion loss improvement at 10 GHz. The measured results demonstrate that better than 15 dB return loss throughout the bandwidth from 8 to 12 GHz is obtained.