Analog predistortion is an efficient method for improving the linearity of power amplifiers. This paper presents a simple and tunable analog predistortion linearizer with low insertion loss, capable of reducing the non-linearity effects of microwave power amplifiers. The linearizer employs Schottky diodes as a distortion generator and does not require any additional matching circuit. By controlling the DC bias of the diodes, various combinations of characteristics can be obtained; therefore, this structure can be used to match different device behaviors. Experimental validation using a εr = 3.38, 20-mil thick Rogers substrate at the center frequency of 2 GHz shows that the fabricated linearizer can provide up to 7.5 dB gain expansion. The fractional bandwidth and insertion loss of the linearizer are 10% and 1.7 dB, respectively. The simulated and measured results are in good agreement with each other. To illustrate an approach for compensating the limited phase characteristics of the presented structure, the design and simulation of a dual-branch linearizer utilizing the reflective Schottky diode predistortion linearizer as a nonlinear unit are also presented.
The design of a compact Pi-shape microstrip antenna for dual-polarized wideband response is proposed. The Pi-shape geometry is realized by modifying a compact C-shape patch. The two stubs placed on the Pi-shape patch edge, optimize the spacing in between the higher order TM20 and TM30 modes with respect to the fundamental TM10 mode which yield a bandwidth of more than 430 MHz (>35%). On an air suspended substrate, antenna exhibits broadside gain of more than 5 dBi over the impedance bandwidth. The orthogonal surface current variations across the TM10, TM20 and TM30 modes realize polarization agility satisfying the requirements of GSM900/navigation satellite applications/ISM900. With respect to the band start frequency, the proposed configuration offers 11% reduction as compared with the equivalent rectangular microstrip antenna. Further, by defining the resonant length at each of the Pi-shape patch modes, the formulation for their resonant frequency is proposed. The Pi-shape antennas redesigned using them at the given fundamental mode frequency yield similar dual polarized wideband responses offering bandwidth of > 35%.
In this paper, a novel mechanical-variable-flux flux-intensifying interior permanent magnet (MVF-FI-IPM) motor is proposed, which employs a mechanical flux-adjusting device and owns the characteristic of Ld>Lq. The magnetic poles can be rotated by the mechanical device to vary the leakage flux and adjust the angle of magnetization direction relative to the d-axis. The characteristic of Ld>Lq is achieved through the adoption of surface flux barriers. The topology structure and operation principle of the machine are introduced. Then, the operation of the mechanical flux-adjusting device is analyzed by virtual prototype technology. Based on the two-dimensional finite element method (FEM), the electromagnetic characteristics of the proposed motor and FI-IPM motor are compared. Finally, the results show the proposed motor with a better flux-weakening capability and a lower risk of irreversible demagnetization than that of the FI-IPM motor.
The concept of ultra-wideband (UWB) reconfigurable mmWave/THz microstrip antenna with a newfangled gold radiating patch with two PIN diodes installed on a benzocyclobutene (BCB) polymer is presented. The reconfigurable types of the proposed antenna are frequencies, bandwidths (BWs), and beams reconfigurations. This reconfigurable antenna was designed and simulated with the time-domain based on a FIT solver at the CST MWS solver, while the comparison was with the frequency-domain based onthe FEM solver at the CST MWS solver. The simulation results obtained from both solvers were in fair agreement, supporting the proposed antenna design. These antennas may be used in cellular communication at mmWave/THz band for beyond 5G.
Double-stator switched reluctance motors (DSSRMs) acquire attention because of their high torque/power generating capability compared to conventional and segmented rotor switched reluctance motors. One of the main limiting performance indices of such motors for industrial applications is its high torque ripple. This paper proposes a 12/10/12 pole DSSRM with an angular shift of half of the stroke angle between inner and outer stators. The respective phase windings of the inner and outer stators are parallelly excited with the same phase angle shift to reduce the torque ripple. Each rotor segment is constructed with a pair of half rotor segments that are isolated from each other through the insertion of a non-magnetic isolator between them. Firstly, the design hypothesis for a low torque ripple DSSRM has been presented; thereafter, some geometric modifications have been suggested and investigated to obtain a nearby response in the proposed DSSRM. The calculation of the width of the non-magnetic isolator, modification in the pole height of outer stator and modification in the arc angles of rotor segments/stator poles are discussed in detail. The effectiveness of the proposed motor is investigated through a 2D finite-element modelling and simulation in ANSYS/MAXWELL software. Simulation results show that the torque ripple is significantly reduced by 74.9% in the proposed DSSRM compared to the baseline DSSRM.
In this paper, a 3-port compact MIMO antenna is designed using Characteristics Mode Analysis (CMA). It consists of three antenna elements. Ant-1 is 45˚ tilted, and Ant-2 and Ant-3 has L-bend transitions. Ant-2 is 1/4th, and Ant-3 is 1/2 in size w.r.t. Ant-1. To improve 10-dB impedance bandwidth and isolation > 17 dB, fractal slot is etched at bottom, and deformity in antenna structures has three distinct modes. Ant-1 operates in UWB mode from (4.8-10.6) GHz with 75.32% IBW, and Ant-2 and Ant-3 operate in wide-band mode from (8.1-10.8) GHz with 28.57% IBW and from (7.2-9.8) GHz with 30.58% IBW. CMA is utilized to investigate the anonymous behaviour of antenna, predicts modal significance (MS), characteristics angle (CA) and eigen values (EV). From these parameters bandwidth potential, radiation energy source and Q-factor are estimated. For investigations first six modes are swept in modal navigator, where dominant modes are traced as ideal antenna resonant modes, and unwanted modes are neglected. The antenna gain is (3-7) dBi with ECC < 0.08. The proposed antenna is fabricated and measured for validation. From the outcomes, it is found suitable for UWB, air traffic and defense tracking, meteorological, amateur satellite, maritime vessel traffic controlling, and X-band satellite applications.
In this paper, a Q-band GaAs low noise amplifier (LNA) for satellite communications is presented. The LNA is designed using common-source (CS) topology, self-biased configuration and current-reused technology. Simultaneous noise and input matching are achieved by employing source series inductance. The current-reused LNA is fabricated in a 90 nm GaAs pseudomorphic high electron mobility transistor (pHEMT) process. On-wafer measurement results show that the LNA features a small-signal gain of 23.8~24.5 dB, noise figure (NF) of 2~2.1 dB, and output 1-dB compression point (OP1 dB) of 6.6~8 dBm over 36~42 GHz, while consuming 10.9 mA with a supply voltage of 5 V. The chip size is 1.6×0.8 mm2 including all RF and dc pads.
The use of invasive weeds optimization in the synthesis of antenna arrays has become popular in the last few years. This optimization method is robust, simple and can be easily improved. Like other stochastic algorithms, IWO suffers from premature convergence and other drawbacks. To overcome these problems, a dynamic IWO is proposed and used for synthesizing two antenna array topologies (linear and circular array). This proposed method tries to achieve an optimal array pattern by acting on the amplitude excitation of elements in the non-uniform circular array and their positions on the array to obtain an array pattern with deep nulls in some directions of interferences and low side lobe level. For the linear array, the nulls control can be achieved by acting on the relative amplitude excitation of each element in the array for an optimal inter-element spacing. This proposed method improves the performance greatly and allows to achieve a maximum reduction in side lobe level in band Nulls with an acceptable dynamic range ratio (DRR). To show the performance of the proposed method, for each topology, our results are compared to other results of the literature.
In this paper, new fractal curves are designed, simulated, and implemented for passive UHF RFID application. 5-, 6-, 7-, and 8-sides polygon fractal loops are proposed and implemented in this work based on the 2nd iteration. It is shown that increasing the number of sides can improve the performance and minimize the size of the fractal antenna. The designed fractal loop antennas have been compared with other fractal loop antennas published previously, and the recent antennas show a better performance. The designed antennas are fabricated using PCB technology, and the antenna parameters are measured experimentally and compared to CST simulations. There is an acceptable agreement between the simulated and measured results. The effect of different materials on antenna performance is also studied.
In this paper, the performance analysis of a dual-hop reconfigurable intelligent surface (RIS)-aided power line communication (PLC) system is presented under different relay transmission protocols. The relay is assumed to be decode-and-forward (DF) or amplify-and-forward (AF) relaying protocol. It is also assumed that the RIS link is subjected to Rayleigh fading while the PLC link undergoes Log-normal fading with the influence of additive background and impulsive noise. To evaluate the system performance, the end-to-end cumulative distribution function for both relaying protocols are derived. Based on these, the analysis expressions for the system outage probability and average bit error rate (ABER) are derived under DF and AF relaying protocols. To gain further insight about the system performance, the asymptotic analysis for the derived expressions is obtained at high signal-to-noise ratio regime. The findings illustrate the significant impact of the number of RIS elements and impulsive noise on the overall system performance. In addition, the accuracy of the analytical results is justified through Monte-Carlo simulations.
A non-invasive thermometry approach for monitoring core (internal) tissue temperature using microwave radiometry is presented. We detail the design and analyses of a microwave antenna capable of detecting core temperature at depth. Performance of the radiometer with a printed dipole antenna is evaluated at frequency of 1.4 GHz in a multilayer 3D computational structure consisting of skin, fat, and muscle. To study this approach, a human tissue model was constructed with skin, fat, and deep muscle tissues having electrical properties at working frequency of 1.4 GHz. One of the main challenges is the Radio Frequency (RF) interface; hence, frequency selection will be important. Moreover, the antenna must be designed for characteristics in close proximity of biological medium in the selected frequency band. The Specific Absorption Rate (SAR) and volume loss density have been used to determine the amount of absorbed power in each tissue layer and thus emitted power from each tissue layer. This approach has been designed to detect thermal emissions radiated from tissue up to 23 mm deep. We present the numerical analysis of 3D tissue-layer power emission and temperature sensing by a microwave radiometric antenna from a single frequency band of 1.4 GHz. Computed results show that this method senses the internal temperature in each tissue layer.
A novel circularly polarized (CP) square slot antenna for covering the universal ultrahigh-frequency (UHF) radio frequency identification (RFID) band is proposed. The antenna uses low-cost FR4 material as the dielectric substrate and coplanar waveguide (CPW) to feed. Circularly polarized radiation can be realized by embedding two symmetrical rectangular grounded planes with L-shaped slits in opposite corners of the square slot. The widened vertical tuning stub at the end of the signal line fed by CPW can improve the CP and impedance matching operation, and finally realizes broadband characteristic. The measured 10 dB impedance bandwidth and 3 dB axial ratio (AR) bandwidth are 1250 MHz (710-1960 MHz) and 180 MHz (840-1020 MHz), respectively. The measured peak gain is about 3.4 dBi in the whole UHF RFID frequency band (0.84-0.96 GHz). The dimension of the CP square slot antenna is 116×116 ×1.6 mm3. The proposed antenna has the advantage of simple structure, is easy to be processed, can exhibit dual CP radiation characteristic, and covers the broadband frequency range, which can be applied to the UHF RFID handheld reader environment.
In this article, a novel idea of designing a graphene based planar plasmonic patch antenna for terahertz wireless applications with detailed analysis is proposed. Based on the Surface Plasmon Polariton Waves (SPP) behaviour in graphene, a novel wideband planar graphene-based patch antenna is investigated here. As graphene with its wondered properties supports SPP in much lower infrared frequencies unlike the noble metals such as gold and Nickle which support SPP at much higher frequencies, the proposed planar antenna works on THz gap (0.1-10 THz) by covering a range of frequencies from 0.1 THz and goes beyond 10 THz, thus covering the whole THz gap. The proposed antenna is a simple planar structure with overall size of 31.8 x 6.4 μm2 having a Silicon with a relative permittivity (εr) of 11.9 used as a substrate material, and simple plane wave is used for excitation. Furthermore, radiating material comprises single layer graphene and copper with a partial ground of copper material, and for comparison purpose, only graphene layer as a radiating material is also analysed. Single layer graphene conductivity having chemical potential of 0.4 ev, relaxation time of 0.6 ρs, and a temperature of 298 K is discussed. Parametric analysis for getting optimum results is also studied. The unity peak absorption of above 98% is observed throughout the resonating frequency range. The proposed design is numerically simulated in CST MWS v2020, and other parameters results, such as unity peak absorption and surface current, are also discussed.
A conformal circularly polarized UHF antenna integrated on the body of a CubeSat is presented. The antenna operates at 485 MHz and provides at least 10 MHz impedance bandwidth. Traditional UHF antennas for CubeSat have been wire or tape measures that require mechanical deployment, whereas the antenna reported in this paper does not need such treatment and therefore has a potential application in CubeSat mission by promising a more reliable communication link and reduced cost. The measurements showed good agreements with the design data, validating frequency response, bandwidth, and circular polarization level of the proposed antenna.
This article presents the design and development of a low profile substrate integrated waveguide semi-circular cavity-backed antenna loaded with dielectric cylinders of glass-reinforced epoxy and Teflon. The substrate integrated waveguide semi-circular cavity-backed antenna without dielectric loading radiates at 5.8 GHz with 3.13 dB gain. The antenna is modified by putting dielectric cylinders of different materials and different sizes at the edge of a semi-circular cavity to enhance the gain of the antenna. The new antenna thus created has improved gain of 8.13 dB. All simulations are done using high frequency structure simulation software. The proposed design is fabricated on a glass-reinforced epoxy substrate with a semi-circular cavity having a size of 60 mm x 50 mm. The measured results are in good agreement with simulated ones.
The Ricean probability density function (pdf) is widely used to estimate the electromagnetic field distribution in indoor environments. The goal of using the Ricean or other pdfs is to evade the computational cost of deterministic field calculation. The parameters of the pdfs are usually obtained using the maximum-likelihood estimation which is here shown to fail in local areas close to the antenna where the direct field varies significantly. This paper presents the new localized maximum likelihood method which is valid in close regions as well. Moreover, the maximum-likelihood method requires a large number of field values within the local area to yield the parameters of the pdf. This paper presents the ray-tracing maximum-likelihood (RTML) method where a much lower number of field values are required. These values are determined using ray-tracing and without the need to account for the computationally expensive higher-order reflections. The RTML fails in local areas close to the antenna, and thus the new localized RTML is presented to restore accuracy.
In the gyrotron traveling wave amplifier (gyro-TWA), high loss dielectric materials loaded in a cylindrical waveguide are adopted to suppress the unwanted parasitic oscillations. It is of great importance to accurately understand the relative permittivity εr and tanδ for studying the microwave and millimeter wave dispersion, and loss properties of a specific mode. The high lossy dielectric loaded circuit of the gyro-TWAs made of the BeO-SiC ceramic with certain relative permittivity and loss tangent are theoretical calculated, simulated and measured. The field distribution, dispersion and loss properties of three different dielectric loaded circular HEd12, HEd22 and TEd02 modes (corresponding to the TE11, TE21 and TE01 modes in the smooth hollow cylindrical waveguide respectively) in different frequency bands are respectively investigated. The theoretical analysis, simulation, and measurement results have a good agreement. This work has clear guiding significance for the stable work of gyro-TWAs.
Recently, optical nano-antennas (NAs) have been introduced as an alternative approach for photovoltaics devices in solar power harvesting application. In this work, we introduce a new modification to the conventional Archimedean spiral NA to improve its radiation/harvesting efficiency and directivity. The proposed design is a rectangular spiral NA of two tip-to-tip opposing arms which are separated by an air gap. The reported design performance is investigated in terms of the radiation efficiency, directivity, polarization, radiation pattern and total harvesting efficiency. The numerical study is carried out using the finite integration technique (FIT) within the wavelength range 300-1600 nm. The presented design offers a maximum radiation efficiency of 88% in free space and 97.9% on top of silicon dioxide (SiO2) substrate at a wavelength of 500 nm where the maximum radiation of the sun occurs. In addition, the proposed design has a maximum directivity of 10.8 in free space which is increased to 19.1 on top of a substrate at 500 nm. It is found that the suggested rectangular design shows an enhancement in the radiation efficiency and directivity over the counterpart Archimedean nano-spiral antenna by 10% and 208%, respectively. The proposed rectangular design introduces total harvesting efficiencies of 96.2%, 98.1% in free space and on the substrate, respectively. Moreover, the effect of round edges that may appear in the fabrication process is also considered.
Using multiple-Input Multiple-Output (MIMO) configuration is not new in the field of wireless communication to increase the capacity of the system. This configuration is still valid to use nowadays with the modern wireless configuration such as the Fifth generation (5G). Massive MIMO is the key resource of the 5G systems due to its huge ability to increase the capacity of the network and on the other hand its ability to enhance both spectral and transmit-energy efficiency. The need for using Massive MIMO comes from the increase in using smartphones, tablets, and the rise of the Internet of Things. This increasing demand for the use of wireless applications requires networking and Internet infrastructures to meet the needs of current and future multimedia applications which massive MIMO satisfies. The key limitation of using massive MIMO is the cost of installation of these antennas and how to multiplex between them. In addition to this, the Radio Frequency (RF) links are also increased where this increase leads to high system complexity and hardware energy consumption. Because of this, reducing the required number of RF chains is essential to use by performing antenna selection which this paper aims to evaluate without significant performance loss which can be performed by employing low-resolution Analog-to-Digital Converter (ADC) to select an antenna with the best tradeoff between the additional channel gain and increase in quantization error. In this paper, Quantization-Aware Greedy Antenna Selection (QAGAS) algorithm has been proposed and compared with other antenna selection algorithms especially simple algorithms like random selection and Fast Antenna Selection (FAS) algorithm. The achieved capacity is compared with that of a very simple scheme that selects the antennas with the highest received power. The system capacity obtained from QAGAS is evaluated related to the transmit power of the Base Station (BS) and the quantization bits used in the low-resolution ADC. The simulation is also performed for different numbers of users served by the BS and with the number of antennas at the BS. The simulation results show that the proposed algorithm indicates a potential for significant reductions of massive MIMO implementation complexity, by reducing the number of RF links and performing antenna selection using simple algorithms.
This paper presents the analytic analysis, and proof-of-principle prototyping of a new type of magnetic spring with preload and a linear stroke length. An analytic based magnetic charge modeling approach is utilized to investigate the magnetic spring's energy density, stiffness characteristics and linearity. It is shown that whilst the proposed magnetic spring has a lower mass and energy density than a mechanical spring, the magnetic spring offers several unique characteristics, such as contact-free operation, inherent preload as well as over-force failure protection. In addition, the operating principle of the presented magnetic spring can be extended to realize both positive and negative variable stiffness adjustment characteristics.