A broadband circularly polarized (CP) slot antenna array fed by an asymmetric coplanar waveguide (CPW) with stepped and inverted T-shaped strips is proposed. Using four square slot antenna elements with sequential rotation oblique feed and a modified sequential-phase (SP) feeding network, broadband CP can be achieved. The measured -10 dB reflection coefficient bandwidth and 3 dB axial ratio (AR) bandwidth are 55.4% (1.63-2.88 GHz) and 58% (1.65-3 GHz), respectively. Good radiation characteristics with gain more than 6 dBic over the operating band are obtained by the proposed antenna array with a compact size of 155×155×0.8 mm3. Details of the proposed antenna array design and experimental results are presented and discussed.
A triple-band bow-tie-shaped CPW-fed slot antenna design for wireless communication applications is proposed. The antenna consists of a signal strip, two conducting strips and bow-tie-shaped slots. With simple tuning geometrical parameters, the proposed antenna is suitable for WLAN 2.4/5.2/5.8 GHz bands. This antenna is designed on a single-layer PCB FR4 substrate with permittivity εr = 4.4, loss tangent tanδ = 0.0245 and thickness h = 1.6 mm. The antenna size of the radiating area and ground plane is 60×45 mm2. The measured results show a positive agreement with the simulated results.
An accurate complexity-reduced simplified Volterra (ACR-SV) series is introduced for RF power amplifiers (PAs). Based on the conventional simplified Volterra (SV) series, it takes memoryless nonlinearity and memory effect into consideration separately, while connected with a nonlinear memory effect (NME) in order to increase accuracy of the model. The proposed ACR-SV model is assessed using a GaN Class-F PA driven by two modulated signals (a WCDMA 1001 signal and a single carrier 16QAM signal with 40 MHz band width). The experimental results in forward modeling and DPD application demonstrate that the proposed ACR-SV model outperforms the memory polynomial (MP) model, the augmented complexity-reduced generalized memory polynomial (ACR-GMP), and the SV model. Compared with the MP model, the ACR-SV model shows a normalized mean square error (NMSE) improvement of 2.61 dB in forward modeling, average adjacent channel power ratio (ACPR) improvement of 3.7/4.2 dB in the DPD application with less 13% number of model coefficients. In comparison with the ACR-GMP model, the ACR-SV model shows NMSE improvement of 1.39 dB, ACPR improvement of 0.7/0.6 dB with comparable number of model coefficients. In contrast with the SV model, the ACR-SV model achieves similar model accuracy, but reduces approximately 53% of coefficients.
In this paper, a novel dual notch bands Ultra Wide-Band (UWB) antenna for WLAN and WiMAX applications is presented. The antenna contains a taper rectangular monopole antenna with new feed line which is designed and modified for 2-12 GHz. To achieve notch band at WLAN frequencies, different methods are compared, such as L-shape slots for one notch or dual rings in notch designing. On the other hand, the novel F-shape feed line is designed to achieve dual notch band characteristic. The effects of stubs parameters at notch frequencies are presented. The benefit of this novel feed line is designing multi-band and reconfigurable antenna by changing stub line parameters. The simulated results of prototype antenna are obtained with HFSS and CST. Total size of the antenna is 60 mm×60 mm×1.6 mm. It is fabricated on FR-4 low cost substrate and fed by 50 Ω microstrip line.
In this paper, we present a new design of multi-resonance monopole antenna for use in microwave imaging systems is presented. The antenna configuration consists of an ordinary square radiating patch, a feed-line, and a modified ground plane with pairs of L-shaped slits and parasitic structures which provides a wide usable fractional bandwidth of more than 130% (2.95-14.27 GHz). In the presented design, by cutting a pair of L-shaped slits and also by embedding a pair of inverted L-shaped parasitic structures in the ground plane additional resonances at 9.5 GHz and 13.7 GHz can be achieved. By using these structures, the usable upper frequency of the antenna is extended from 10.3 GHz to 14.27 GHz. The proposed antenna has a symmetrical structure with ordinary square radiating patch, therefore displays a good omni-directional radiation patterns even at higher frequencies. The antenna has sufficient and acceptable gain level and also its radiation efficiency is greater than 86% across the entire radiating band. The designed antenna has a small dimension.
A compact triband asymmetric coplanar strip (ACS)-fed monopole antenna for WLAN/WiMAX applications is proposed and investigated in this paper. The proposed antenna is composed of an ACS-fed folded monopole and two inverted-L branches, which occupies a very compact size of 26.5×12 mm2 including the ground plane. By carefully adjusting the lengths and positions of these branches, three desired resonant frequencies can be achieved and adjusted independently. The antenna exhibits three resonances covering the 2.4/5.8 GHz WLAN bands and 3.5 GHz WiMAX band. Details of the antenna design, simulation, and experimental results are presented and discussed. The proposed antenna shows nearly omnidirectional radiation characteristics and moderate gains in the operating bands. The compactness, simple feeding technique and uniplanar design make it easy to be integrated within the portable device for wireless communication.
It is well known that in the pulse compression radar theory, the sidelobe reduction using nonlinear frequency modulation (NLFM) signal processing represents a major and present research direction. Accordingly, the main objective of this paper is to propose an interesting approach related to the design of efficient NLFM waveforms namely, a temporal predistortioning method of LFM signals by suitable nonlinear frequency laws. Some aspects concerning the optimization of the specific parameters involved into analyzed NLFM processing procedure are also included. The achieved experimental results confirm the significant sidelobe suppression related to other NLFM processing techniques.
In this paper, a different method for designing a novel and compact microstrip-fed slot antenna with band-notched characteristic for UWB application is proposed. In the proposed antenna, a pair of cross-shaped strips protruded inside an extra rectangular slot in the ground plane are used to crate an additional resonance in higher frequencies. By obtaining this resonance, the usable upper frequency of the antenna is extended from 9 to 14.8 GHz which provides a wide usable fractional bandwidth of more than 135%. Additionally, by using a square-ring radiating stub with a pair of protruded T-shaped strips inside the ring, a desired frequency band-stop performance has been obtained. Simulated and experimental results obtained for this antenna show that it exhibits good radiation behavior within the UWB frequency range. The proposed antenna can operate from 3.04 to 14.8 GHz for VSWR < 2 with a rejection band around 5.1 to 6 GHz to suppress any interference from wireless local area network (WLAN) systems. Simulated and experimental results obtained for this antenna show that it exhibits good radiation behavior within the UWB frequency range.
In this paper, a behavioral model with multi-status is represented to describe electrothermal memory of power amplifiers. In the model, a multi-point linearity approximation method is introduced to estimated the model coefficients at random status. The parameters of the new model can be identified by traditional identification algorithms such as recursive least square (RLS) with the input and feedback data at predetermined status points captured by the digital predistortion (DPD) system. Compared with traditional models, the coefficients estimation speed for the new model at new status is very fast. The final experiment result proves that the multi-status model can efficiently ameliorate the performance deterioration caused by electrothermal memory in the the DPD system, and at the same time it still keeps very high DPD performance.
We present the design, characterization, and experimental verification of a dual-band metamaterial absorber (MA) in the microwave frequencies. The proposed MA consists of a metallic gammadion-shaped structure and a complete metal layer, separated by a dielectric spacer. The results show that the proposed MA has two absorption peaks at nearly 5.6 GHz and 6 GHz with absorption rates of 97% and 99%, respectively. The interference theory is used to investigate the physical mechanism of the proposed MA. The experimental results are in good agreement with the theoretical predictions.Furthermore, it is verified by simulations that the absorption of the proposed MAis almost insensitive to the incident wave polarization and oblique incident angle for the both TM and TEmodes. This MA has broad prospect of potential applications.
In this paper, we present the measurement methodology and results for a low voltage Power line Communications (PLC) network under different configurations. Based on the measurements, a correlation of the channel transfer characteristics to the network topology is established and a deterministic model based on two-wire transmission line theory for transverse electromagnetic (TEM) wave propagation is proposed. The channel frequency response in frequency range of 1-30 MHz is determined, where the model results agree well with the measurements.
Most wireless channel models assume fixed scatterers with specific geometrical distributions in the propagation environment. In reality most scatterers move with random movements on the azimuth plane. In this paper, the effects of such scatterers' random movements on the cross correlation function (CCF) of wideband (WB) and ultra-wideband (UWB) non-isotropic multiple-input multiple-output (MIMO) channels are characterized. The CCF of WB/UWB MIMO channels is calculated not by assuming a specific geometry for scatterers in space but based on specific mathematical relationships between physical parameters of the wireless channel along with appropriate assumptions on their probability density functions (pdfs). The CCF is used to determine the inuence of moving scatterers, in a stationary scenario, on the power spectral density (PSD) and the coherence time of WB and UWB multiple-input single-output (MISO) channels, as a particular case of MIMO channels. Unlike the fixed scatterers case, the PSD is not a band-limited process, it decays with frequency.
In this article, the approach involving Dynamic Threshold Optimization (DTO) algorithm is considered to optimize a new compact reconfigurable antenna to be applied to triple band Radio Frequency Identification (RFID) and to ultra wideband (UWB) antenna with multiple bands notched. The antenna is implemented by using the existing techniques, such as loading an L-type band-stop filter, inserting a split ring resonator (SRR) as well as connecting L branches to the radiation disk proposed by us. In case of RFID applications, triple-band RFID 915/2450/5800 MHz are achieved separately. The results prove that this kind of antenna can be applied in RFID reader to avoid interference with other wireless systems. RF MEMS switches are used to reconfigure the antenna to be suitable for the application in the notched UWB communication systems. The DTO algorithm program is implemented using MATLAB-software and linked to the CST Microwave studio software to simulate the antenna. In addition, the optimized antenna is assessed using the Finite Difference Time Domain (FDTD) program written with MATLAB to validate the results. The experimental results for the RFID and UWB antennas show good agreement with simulated ones. The radiation patterns are satisfactorily omnidirectional across the antenna's operation bands.
In this paper, an application of artificial neural network based on multilayer perceptron (MLP) model is presented for predicting the slot size on the radiating patch for improvement of the performance of patch antenna. Several performance affecting parameters like resonance frequencies, gain, directivity, antenna efficiency, and radiation efficiency for dual band frequency are observed with the variation of slot size. For validation of this work, a prototype X-shaped patch antenna is fabricated using glass epoxy substrate and its performance parameters are measured experimentally and have been found in good agreement with ANN and simulated values.
A right-handed circularly polarized (CP) substrate integrated waveguide (SIW)-based square ring-slot antenna array is proposed in this study. The array is composed of four elements and is based on a sequential rotation feeding technique to achieve wideband circularly polarization performance and high polarization purity. The feeding network for the array adopts SIW power divider having phase delay characteristic. In order to validate our design method, the antenna array is fabricated and measured. The measured impedance and axial ratio (AR) bandwidths are 8.5% (VSWR<2) and 6.1% (AR<3 dB), respectively, whereas the impedance and AR bandwidths for the element are 6.5% and 1.5%. It can be observed that this technique has significantly enhanced the AR bandwidth. Moreover, the antenna has a stable CP peak gain more than 12 dBi from 9.15 GHz to 9.5 GHz.
Splitting a cylinder dielectric resonator into four uniform quarters generates a new dielectric resonator antenna(DRA) shape, which is named a quarter volume of cylinder dielectric resonator antenna (QVCDRA) in the paper. On the basis, a novel compactthree-port dielectric resonator antenna with reconfigurable radiation pattern is presented for WLAN systems at 5.2 GHz. A -10 dB impedance bandwidth of 16.20%,covering the frequency range from 4.75 GHz to 5.54 GHz, is obtained with an isolation of lower than -19 dB. The structure consists of three QVCDRAs that arrange evenly around Z axis, and as a result possesses the advantage of compact structure, wide impendence bandand reconfigurable radiation patterns. The volume of the proposed three-port DRA without ground plane is only 0.0216 (is the dielectric wave length at the central operation frequency). The proposed antenna is analyzed in detail. Antenna prototype is fabricated and tested. The simulation and test results are in good agreement.
A compact planar monopole UWB antenna with quadruple band-notched characteristics is analyzed and presented. By introducing a C-shaped slot, nested C-shaped slot in the radiating patch and U-shaped slot in the feed line, quadruple band-notched characteristics are achieved at frequencies of 2.5, 3.7, 5.8 and 8.2 GHz. The proposed antenna has been fabricated and tested. Measured impedance bandwidth of the antenna is 2.35-12 GHz, which covers Bluetooth and UWB band, for VSWR < 2 and also has four stop bands of 2.44-2.77, 3.42-3.97, 5.45-5.98 and 8-8.68 GHz, for VSWR > 2, for rejecting 2.5/3.5 GHz WiMAX, WLAN and ITU 8 GHz band signals, respectively. The average gain of this antenna is 4.30 dBi with a variation of ±1.8 dBi over the whole impedance bandwidth. Significant gain reduction over the rejected band is also observed. The antenna shows good omnidirectional radiation patterns in the passband with a compact size of 40 mm × 34 mm.
In this paper, a 42 GHz frequency synthesizer fabricated with 0.13 μm SiGe BiCMOS technology is presented, which consists of an integer-N fourth-order type-II phase locked loop (PLL) with a LC tank VCO and a frequency doubler. The core PLL has three-stage current mode logic(CML) and five stage true single phase clock (TSPC) logic in the frequency divider. Meanwhile, a novel balanced common-base structure is used in the frequency doubler design to widen the bandwidth and improve the fundamental rejection. The doubler shows a 41% fractional 3 dB bandwidths with a fundamental rejection better than 25.7 dB. The synthesizer has a maximum output power of 0 dBm with a DC power consumption of 60 mW. The worst phase noise at 100 kHz, 1 MHz and 10 MHz offset frequencies from the carrier is -71 dBc/Hz, -83 dBc/Hz and -102.4 dBc/Hz, respectively.
The far-field pattern symmetry of the cavity backed planar spiral antenna is analyzed. We discover that the back radiation of the planar spiral and the cavity effects degrade the pattern symmetry. To improve the pattern symmetry, an improved method to reduce the back radiation is proposed. Then a novel antenna configuration is designed. The center section of the planar spiral is replaced with a conical spiral. So the back radiation at higher frequency band can be restrained. The broadside gain, axial ratio and pattern symmetry are compared. The results show that this novel configuration can achieve better far-field symmetry at a wider band.
This paper presents a technical which improves energy efficiency of AC rotating machines by using Grain Oriented (GO) steel at stator core instead of Non Oriented (NO) steel. The losses of GO steel are less important only if the magnetic flux circulates along the rolling direction; consequently it is rarely used in AC machines where the magnetic flux rotates. By stacking many shifted GO laminations of AC machine stator, the flux pass from one lamination to another, and the core losses are reduced. A lot of experimentations have been done with unidirectional field, rotating field and with real induction machines. They show important improvements with GO shifted steel. The efficiency difference between a classical 10kW induction machine and a modified machine with GO stator is more than 2 points. Moreover, the no-load current and so the reactive power are smaller. This technical creates environmental and financial gains.