Search

Two-dimensional (2D) materials have been demonstrated to be promising candidates to design high performance photodetectors owing to their strong light-matter interaction. However, the performance of 2D material photodetectors is still unsatisfactory, such as slow response speed due to defects and vulnerable contact interface, which impede their rapid development in the field of optoelectronics. In this paper, we obtained the ideal and large photosensitive van der Waals Schottky interface by the laminating-flipping method. Hence, a fast response speed ( 1012 Jones) are observed on the van der Waals Schottky junction photodiode. More importantly, benefiting from the flat Schottky interface (the roughness ∼0.6 nm), a sub-bandgap light response modulated by the Schottky barrier height (cut-off edge at 1050 nm) has been detected based on the large Au/MoSe2 sensitive Schottky interface internal photoemission. As a result, a universal strategy for the sub-bandgap near-infrared van der Waals Schottky junction detector of 2D materials was obtained.

When the power conversion efficiency (PCE) of perovskite solar cells (PSCs) rapidly approaches that of commercial solar cells, the stability becomes the most important obstacle for the commercialization of PSCs. Aside from the widely studied slow PCE degradation, the PSCs also show a unique rapid PCE degradation. Although the degradation due to oxygen and humidity can be avoided by encapsulation, that due to bias voltage, light and heat could not be effective suppressed and will lead to considerable degradation. Usually, the rapid PCE degradation is believed to be from ion migration. However, a systematic investigation is yet to be carried out. This work quantitatively and systematically investigated the relationships between external fields (bias voltage, light or heat), ion migration and device performance. By comparing the performance of reference PSCs after 90 min degradation under these fields, we conclude that (1) the electric field affects the spatial distribution of mobile ions; (2) the light field changes the mobile ion densities and drives the ion migration; (3) the heat field results in perovskite decomposition as well as changing the mobile ion densities. In addition to the analysis of the reference device, we experimentally proved that the improved device stability upon introducing phenethylammonium iodide (PEAI) or poly-methyl methacrylate (PMMA) layers originates from the inhibition of mobile ion density and migration.

A back-to- back microstrip patch antenna with a switchable pattern is proposed for WLAN applications. The patch elements, printed on FR-4 substrates with a common ground plane, are switched with a single-pole double-throw PIN diode circuit. Switching the feed selects either of two identical radiation patterns in the opposing hemispheres for spatial diversity that would benefit a distributed network.

A dual-stub co-planar Vivaldi antenna with a parasitic element is presented. The dual stub is coupled between the parasitic element and two tapered slots. The parasitic element shape and size is optimised. The use of slits on the outer edge of the ground plane is shown to provide control of beamwidth and maximum gain. A bandpass filter is used for performance control and sub-harmonic suppression.

A compact ultrawideband (UWB) circularly polarized (CP) slot antenna is proposed with a methodology for automated reoptimization for packaging with proprietary devices. The slot structure employs a dual-feed with an integrated compact UWB phase shifter. The design process involves an advanced optimization algorithm and demonstrates the use of spline curves for generation of CP signals. These allow easy optimization, while preserving phase coherency across a wideband. The prototyped antenna has a CP bandwidth of 54% (from 3.2 to 6.1 GHz).

A printed triangular monopole antenna with wideband circular polarization is presented. The wideband circular polarization is achieved by asymmetrical excitation of a triangular ground plane and planar triangular monopole. The combined radiation provides a wide axial-ratio bandwidth spanning from 1.42 to 2.7 GHz (62%). A parametric study of key geometric parameters is given for clear understanding of the radiation mechanism.

An omnidirectional microstrip patch antenna, capable of reconfiguring both polarisation and radiation pattern is proposed. It operates with two orthogonal ±45° slanted linear polarisations and can produce two dipole-like radiation patterns, providing 360° coverage in either the horizontal or elevation plane. With appropriate steering, this enables a single antenna to provide full spherical coverage for any polarisation. The reconfiguration is realised by phase shifting, thus does not require switching elements, such as microelectromechanical system or pin diodes embedded into antenna. The basic principles of operation are discussed and validated by numerical and measured data.

An omnidirectional circularly polarized antenna with a rotatable dipole-shaped radiation pattern is proposed. The antenna is realized using a back-to-back coupled microstrip patch arrangement. The pattern is rotated by means of a phase shift, enabling reception (or transmission) of signals from all angles around a sphere. The method enables continuous pattern steering without the need for semiconductor or MEMS components integrated into the antenna. It also allows the use of more than one radiation pattern simultaneously, potentially providing coverage for any spherical angle. The theory is supported by simulation and measurement of four typical antenna configurations. The maximum gains are between 1.9 and 4 dBic and average axial-ratio varies between 2.5 and 3.65 dB at 2.47 GHz. The impedance bandwidth is from 2.4 to 2.51 GHz and the reconfigurable circular polarization is achieved from 2.464 to 2.484 GHz.

This communication proposes a new patch antenna with dual circularly polarized capability at 2.575 GHz. The design exploits the even and odd modes in a coplanar waveguide transmission line and enables simultaneous right- and left-handed circular polarization, with two individual excitation ports. A patch antenna is fed by multimode transmission line and the advantages and disadvantages are discussed. A prototyped antenna realized up to 20 dB isolation between ports with S21

A differentially-fed omnidirectional circularly-polarized antenna is investigated for application in RF energy harvesting. The antenna is composed of a two-layer substrate and back-to-back printed square patches which have two diagonal stubs and one truncation. The patches share a common ground plane. Both patches generate circular polarization (CP) and omnidirectional CP is provided. The antenna provides an axial-ratio bandwidth of 20 MHz from 2.43 GHz to 2.45 GHz. In order to measure the proposed differentially-fed antenna, a feed network connected between the SMA port and differential port is designed. Furthermore, the combined configurations with the proposed antenna, bandpass filter and rectifier can be built and convert the electromagnetic field to DC. The measured output voltage is 255mV at 2.40GHz.

A new design approach of a dual-stub coplanar Vivaldi antenna with integrated filter is presented. The dual-stub excites coupling between a parasitic elliptical element and tapered slots. The dimensions of the parasitic element are studied and optimized for wide beamwidth. The band pass filter is used for sub harmonic suppression and pattern shaping.

A new design of a dual-frequency dual circularly-polarized slot antenna is presented. The dual-frequency is achieved using a single-layer microstrip-fed configuration coupled to a modified annular-slot antenna. The dual sense circular-polarization is obtained by four unequal linear slots which augment the annular slot. Experimental results show the proposed antenna has good circular polarization characteristics for both right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP). The 10 dB return loss impedance bandwidths for the lower (RHCP) and higher (LHCP) bands are 26.7% and 11.3%, respectively. The 3 dB axial-ratio bandwidths are 6.1% and 6.0% with respect to 1.5 GHz (RHCP) and 2.6 GHz (LHCP), respectively.

A novel probe-fed single-layer annular-ring patch antenna for dual-frequency circular polarization is evaluated numerically and experimentally verified. The proposed antenna consists of a small circular patch surrounded by two concentric annular-rings, which is loaded by an unequal lateral cross-slot ground plane. The circularly-polarized frequency ratio of the two resonant modes is tunable to a small value, suitable for wireless communications systems. The patch size of the proposed antenna is reduced by about 53% compared to the conventional circular patch at a given frequency. The radiation characteristics of the novel antenna are also presented.

A novel low-cost low-profile dual-frequency circularly polarized patch antenna for GPS applications is presented. By stacking two square patches with truncated corners on a two-layer fractal electromagnetic bandgap structure substrate, the coverage of the entire GPS bandwidth is achieved. Two bandgaps exist for the proposed fractal EBG structure, from 1.16 to 1.32 GHz and from 1.45 to 2.10 GHz, which include the lower and upper frequency GPS band. The antenna is low-profile and has improved gain and axial ratio bandwidth, as well as broader impedance bandwidths compared to the same antenna without EBG. Good circularly polarized radiation patterns are realized. Measurements on prototypes are in good agreement with simulation. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2630–2634, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22815

A back-to-back linearly polarized patch antenna with a single microstrip line feed is proposed for WLAN applications. The antenna consists of two identical rectangular patch elements on the front and rear sides of a common ground plane. One patch antenna can be switched on at a time using a single-pole double-throw PIN diode switching circuit, offering a switched pattern angle of 180° in the Z-axis.

A simple polarization reconfigurable printed monopole antenna is proposed for wireless applications. Conducting strips are used to connect to the ground plane providing the necessary additional modes for circular polarization. Linear polarization, right-hand or left-hand circular polarization can be realized using only two PIN diodes, which connect to the ground plane, minimizing their effect on radiation characteristics. The mechanism is described, and key antenna parameters are studied and optimized. The antenna is prototyped and tested for all polarization configurations.

A compact high-performance circularly-polarized microstrip antenna for the global positioning system application is proposed. It comprises a fractal hi-impedance surface electromagnetic bandgap (EBG) structure printed on a high permittivity substrate. Measurements and simulation of return loss and axial ratio are in good agreement. It is shown that the proposed Global Positioning System antenna has good axial ratio performance in the upper half-plane, an improvement in gain and a significantly wider axial ratio bandwidth when compared to the same antenna without EBG

Several novel compact circularly-polarized probe-fed annular-ring microstrip patch antennas are examined experimentally and numerically. In order to reduce the antenna size and provide a suitable input impedance match, two techniques are employed; the insertion of strips into the annular ring and placing a cross-slot into the ground plane. The proposed annular-ring patch with a cross-slotted ground plane yields a much smaller size for a given frequency. This novel patch antenna can effectively be reduced by about 55 percent in size compared to conventional annular-ring patch antennas. The antenna displays wide bandwidth and good circular polarization characteristics. The results of a parametric study for three novel strip-loaded annular-ring patch antennas and for the compact circular patch antenna augmented by a narrow annular ring with a cross-slotted ground plane are discussed in this paper.

A triple-band circularly polarised microstrip patch antenna operating in the 2.4, 3.5 and 5.7 GHz bands is presented. The antenna consists of two substrate layers with an electromagnetically coupled low-band patch in the middle layer and a probe-fed dual-band patch on the top layer. The impedance bandwidths (voltage standing wave ratio (VSWR) < 2.5) for the three frequency bands are 112, 118 and 427 MHz with 3 dB axial-ratio bandwidths of 15, 44 and 36 MHz, respectively. The peak gains across the operating bands are 4.2, 5.5 and 4 dBic, respectively.

An optimized design for the rectangular printed monopole antenna with a slitted groundplane is presented. A parametric study of antenna parameters, including the length and width of the ground plane, the length and width of the rectangular plate, and the gap between the patch and ground plane is presented. A slit in the ground plane is shown to reduce the lower-edge frequency and improve the bandwidth. A parametric study of the slit is given.© 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1585–1587, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22524

A printed circularly polarized monopole antenna operating at 2.45 GHz is presented. It consists of a half-cross shape radiating component fed by a microstrip line and matched to a 50 Ω microstrip feed. It is fabricated on a FR-4 substrate with dielectric constant of 4.6. Simulated and measured results are reported and effect of key parameters is described.

A novel omni-directional circularly-polarised GPS antenna suitable for differential feed is presented. The antenna covers the GPS L1 frequency band. The antenna provides an input impedance of 300 Ω and an axial-ratio bandwidth of 10 MHz from 1.570 GHz to 1.580 GHz. The cross polarization is better than 20 dB.

We propose an omnidirectional circularly polarised planar microstrip patch antenna, in which both impedance bandwidth and circular polarization properties can be adjusted after antenna manufacture. This is done by appropriately tuning four adjustable capacitors, incorporated into the patches. To demonstrate the properties, the proposed antenna is tuned to the GPS L1 band and then re-tuned for Beidou/Galileo E2 band by only changing capacitors values. Design guidelines for such retuning are provided.

A dual-band omnidirectional circularly polarized antenna is proposed. The antenna comprises back-to-back microstrip patches fed by a coplanar waveguide. A very low frequency ratio of 1.182 has been achieved, which can be easily tuned by adjusting four lumped capacitors incorporated into the antenna. An analysis of the omnidirectional circular polarization mechanism as well the dual band operation is provided and confirmed by numerical and experimental data. Key parameters to tune the resonant frequencies and the axial ratio have been identified. The prototype antenna provides omnidirectional circular polarization in one plane with cross polar isolation better than 12 dB for both frequency bands.

Several types of omni-directional Circularly Polarized (CP) antennas are presented, which are employed by three different types of feedlines: Coplanar Waveguide (CPW) fed, Microstrip fed, and Differential-fed, to achieve omni-directional CP performances. The Dual-frequency Omni-directional CP antenna is proposed by using slot and inductor embedded into radiated patches. These omnidirectional CP antennas have potential application on GPS, WLAN and RFID systems.

A two antenna array is proposed for generating circular polarization for an ultra-wideband system. It consists of two orthogonal antipodal vivaldi antennas and a feed network which provides the appropriate phase and amplitude over the band of interest. The proposed structure is low cost and easy to manufacture, offering an axial-ratio bandwidth of 74%.

A wideband unidirectional circularly polarized antenna is proposed for Global Positioning System (GPS) and Galileo Systems. The antenna consists of a printed dipole-like element, spaced from a planar reflector. The fed element comprises a printed asymmetrical dipole with an open-ended slot between the feed lines. The operating frequency range covers the GPS system (L1, L2), GLONASS and Galileo system (E5, E6, E1-E2-L1). A parametric study of key parameters including reflector size and spacing are discussed. The impedance bandwidth, axial-ratio and gain are analyzed.

The paper reports recent improvements in the performance of printed circularly-polarized terminal antennas. These advances include the miniaturization of printed circularly-polarized geometries, simplification of geometries which provide dual circular-polarization, widening of the axial-ratio bandwidth, as well as increasing the axial-ratio beamwidth.

A slot antenna which realizes dual frequency dual-sense circular polarization is proposed. A printed spiral slot is fed using a T-shaped microstrip feedline. The results show that axial-ratio bandwidths of 4.5% and 3.5 % are obtained for right-hand circular polarization and left-hand circular polarization, respectively. A detailed parametric study and description of circular polarization mechanism are presented.

A dual-band antenna with right-hand circular polarization for the first frequency and the counter polarization at the second frequency is realized with compact printed spiral slots. The coupled spiral slots are fed by a 50 Ω microstrip line. Dual-sense circularly-polarized performance is achieved by realizing oppositely-directed current rotation for the two frequency bands. A parametric study shows that the additional slot significantly improves the bandwidth for both frequency bands. Measured results show that the fractional impedance bandwidth is greater than 18% for both bands. The 3 dB axial-ratio bandwidths are 4.5% and 3.5% for the RHCP and LHCP bands, respectively.

A wideband dual-frequency dual-polarized printed antenna is proposed for LTE, WLAN, and UWB systems. The dual-band antenna provides wide impedance bandwidths of 74% with respect to the center frequency of 2.725 GHz, and 39% with respect to the center frequency of 7.15 GHz. An open slot in the ground plane between the feed arms provides an orthogonal path to realize an embedded circularly polarized band at 2.35 GHz with an axial-ratio bandwidth of 16%. Dual-band characteristics are achieved by an asymmetrical dipole-like element and the coupling configuration between the T-shaped feed line and the wide ground-plane slot.

A circularly polarised printed dipole-like antenna employing asymmetrical arms and an orthogonal slit in the ground plane is presented. It is fed by a stepped microstrip line which connects to the shorter arm. By utilising surface currents on the asymmetrical arms and the orthogonal feedline structure, circular polarisation is realised. Experimental and numerical data are in agreement and the measured results show a fractional impedance bandwidth of 41.3% (1.77-2.69 GHz) and a wide axial-ratio bandwidth of 38.4% (1.81-2.67 GHz).

A bidirectional circularly polarised (CP) antenna for 1.575 GHz GPS L1 band is presented. The antenna consists of two back-to-back coupled patches and is fed directly by 50Ω Coplanar Waveguide (CPW). It is compact and relatively easy to manufacture compared to other antennas with similar properties. The bidirectional CP pattern is achieved by proper adjustment of patch dimensions as well as feed parameters. A study of the key parameter is provided.

A wideband circularly-polarized printed antenna is proposed, which employs an asymmetrical dipole and a slit in the ground plane which are fed by an L-shaped microstrip feedline using a via. The proposed antenna geometry is arranged so that the orthogonal surface currents, which are generated in the dipole, feedline and ground plane, have the appropriate phase to provide circular polarization. A parametric study of the key parameters is made and the mechanism for circular polarization is described. The measured results show that the impedance bandwidth is approximately 1.34 GHz (2.45 GHz to 3.79 GHz) and the 3 dB axial ratio bandwidth is approximately 770 MHz (2.88 GHz to 3.65 GHz) which represent fractional bandwidths of approximately 41% and 23%, respectively, with respect to a centre frequency of 3.3 GHz.

A tunable compact printed monopole antenna for digital video broadcast handheld terminals systems is presented. The antenna comprises a two segment inductor-loaded monopole strip connected to a plate on the opposite side of the substrate. By appropriate adjustment of inductor values the working frequency is shifted from 915 MHz to 470 MHz. The dimensions of the proposed monopole antenna can be significantly reduced by over 56% in comparison with the conventional monopole antenna and its dimension is 24 mm × 120 mm. The radiation patterns are omnidirectional. The peak gains of the proposed monopole antenna at 470 MHz, 600 MHz and 860MHz are −1.5dBi, 0.74dBi, 2.0 dBi respectively.

A compact dual-band high-impedance-surface EBG struc- ture is employed as a re∞ector for a dual-band annular-slot antenna. The re∞ector comprises an array of miniaturized EBG cells which uti- lizes square patches augmented by four S-shaped corrugated arms to reduce the resonant frequency of the proposed EBG structure. In or- der to broaden the bandwidth and adjust the frequency ratio for the dual-band EBG structure, a log-periodic spacing between the S-shaped strips is introduced. The combination of microstrip-fed annular slot and EBG re∞ector provides directional properties for both frequency bands with reduced size and low-proflle.

The design of a miniaturised low-profile efficient hyperthermia applicator is presented. The efficiency is attributed to small size, resilience to detuning and wide bandwidth. The antenna provides a high value of SAR and is well matched to tissue, even at close distances.

A novel printed monopole antenna employing a slotted-plate, which is electromagnetically coupled to the microstrip-fed planar element, is proposed to provide notch-frequency function. This technique enables stopband characteristics with improved control, compared to placing the slot in the microstrip-fed element. A detailed investigation of the rejectband properties has been made for the UWB antenna. Measured data for the optimized case show the 10 dB return loss bandwidth to be 9.8 GHz (from 2.80 GHz to 12.60 GHz) with a notchband frequency from 5.15 GHz to 5.825 GHz. Propagation measurements indicate that the electromagnetically coupled slot provides a greater reduction in stopband gain for the three principal planes, compared to placing the slot in the fed element. This is desirable to mitigate interference from WLAN systems. A full parametric study of the antenna is presented.

The development of the high data rate wireless communication systems, has placed significant demands on antenna designers, in particular, the requirement for smaller elements with broader bandwidths. In this paper, a novel UWB antenna with notch-band frequency is studied. Effects of the various parameters for antenna performances are also discussed. An optimized compact UWB antenna with notch-frequency function is fabricated and experimentally examined. The measured results show the proposed UWB antenna can achieve a return loss greater than 10 db over an ultrawide bandwidth, of 9.8 GHz, from 2.97 GHz to 12.77 GHz with a tunable notch-frequency band of 5.15 GHz to 5.825 GHz

A small microstrip patch/slot antenna, which achieves a very large bandwidth on a relatively thin substrate (about 0.01lambda0), is presented. The performance is achieved by employing a combination of annular-ring loading on the patch radiator and the use of a crossed-slot for miniaturisation. An additional ring-slot in the ground plane is used to produce the wideband characteristics of the antenna. Simulated and measured results indicate that a 53% fractional impedance bandwidth is achieved with respect to the centre frequency of 1.409 GHz and the size of the antenna is reduced by 50% compared to the conventional circular patch antenna with respect to a given frequency

The proliferation of wireless communication systems has promoted the development of miniaturized antenna designs. Annular ring patch antennas are reported to reduce antenna size. In this paper, several novel compact probe-fed annular-ring microstrip patch antennas are presented. In order to reduce the antenna size and provide a suitable input impedance match, two techniques are employed; the insertion of strips into the annular ring and placing a cross-slot into the ground plane. The proposed annular-ring patch antennas with a cross-slotted ground plane yield a much smaller size for a given frequency and are easily matched to 50 Ohms. These novel patch antennas can effectively be reduced by about 55 percent in size compared to conventional annular-ring patch antennas. The antenna can be designed for single band circular-polarization, dual-band circular polarization, triple band, or wideband operation, depending on parameter selection. Some significant advantages are evident for these structures, such as the centre-frequency exhibiting weak dependence on the position of the feedpoint as well as compact size. Good circularly polarized properties and wide CP bandwidths are obtained for these compact antennas. The multiband versions can provide small frequency ratios. The optimized dimensions for four different type antennas are displayed.

Several novel compact multiple-band high-impedance surface EBGstructures arepresented. Byutilizing four S-shape corrugated armsorspiral armsconnected to theedgeofa smallsquare patch toincrease the inductance, theresonant frequency oftheEBG structure canbesignificantly reduced. Inorder to broaden thewidth ofthestopband andadjust theratio ofthecentre frequencies formulti-band EBG,alog periodic distance between theS-shape strips is implemented. Theeffects oftheparameters ofthe EBGstructure onthewidth ofstopbands arediscussed indetail. Theresults showthat theproposed novel EBGstructure canprovide moremultiple bandgap and reduce theEBG sizefora fixed periodicity. This proposed EBG canbeusefully applied tomultiple frequency antennas andlowfrequency antennas.

th iteration). For the 1 st and 2 rd iteration, each side is replaced with new scaled generator (A1=A/3; B1=0.5*A1, A2=A1/3, B2=0.5*A2), where A1, A2 and B1, B2 are segment and indentation lengths, respectively (Fig.1). The period of the proposed EBG structure is 32.5mm, and A=27mm. A fractal patch connected to the continuous ground plane through a shorting pin constitutes a unit of the lattice. The radius of the shorting pin is 0.5mm. The dispersion characteristics of the fractal Hi-Impedance Surface EBG structure is calculated using the Finite Element Method (FEM). The results illustrated in Fig.2 show a wide bandgap from 1.27GHz to 2.05GHz. A square patch antenna with truncated opposite corners is designed as Fig.3, which excites both the TM01 and TM10 orthogonal modes, can produce circularly polarized fields. The square patch antenna size is 56.0×56.0m

An annular-ring loaded circular patch antenna with slot-ring array of EBG cells on the ground plane is presented. A comparison is made between the annular ring loaded patch on a conventional PEC groundplane and the same patch on a groundplane with a 2times2, a 4times4 and a 6times6 slot-ring EBG array. It was found that the annular-ring patch antenna with a 4 times 4 slot-ring array in the ground plane is superior in the overall performance (gain, impedance and axial-ratio bandwidth). The array of EBG was found to improve gain by 3.5dB and increase the bandwidth of input impedance by about 60% (from 56 MHz to 85 MHz) and the bandwidth of axial ratio increased by about 70% (from 14 MHz to 24 MHz).