This paper presents a fast technique for the automated design of pseudo-elliptic lters in in-line topology implemented in substrate integrated waveguide (SIW) technology. The proposed method is based on an optimization routine with cost function involving zeros and poles of scattering parameters. To realize transmission zeros in in-line topology, frequency-dependent couplings were used. Such dispersive couplings were implemented as shorted stubs. The design process starts with the generation of a suitable starting point. To this end, an approximation of SIW as a rectangular waveguide is used and a fast electromagnetic solver based on mode-matching technique is utilized (μWave Wizard). The next step is the optimization process of a lter in a full-wave 3D EM simulator Ansoft HFSS. To increase the speed of convergence, a built-in derivative calculation feature was used and zeros and poles and their derivatives with respect to design parameters were extracted using the vector fitting algorithm. Experimental validation of the method is demonstrated by a third-order filter with asymmetric response and a fifth-order filter with two transmission zeros in addition to an asymmetric response. The experimental results show good agreement between the simulated and measured data.
The analytical formulas for the average intensity and power in the bucket of the relay propagation of partially coherent cosh-Gaussian (ChG) beams in non-Kolmogorov turbulence have been derived based on the extended Huygens-Fresnel principle. The influences of the beam parameters, relay system parameters and the non-Kolmogorov turbulence parameters on relay propagation are investigated by numerical examples. Numerical results reveal that the relay propagation of the beam is different from that in the case of Kolmogorov turbulence. It is shown that the relay propagation has advantages over direct propagation, and the relay propagation of partially coherent ChG beams depends greatly on the beam parameters, relay system and the generalized exponent α . The focusability of the beam at the target in non-Kolmogorov turbulence increases with larger inner scale, larger relay system radius, smaller outer scale, and smaller generalized structure constant. The results are useful for the practical applications of relay propagation, i.e., free-space communication.
This paper presents results of signal propagation studies for wireless sensor network planning in aquaculture environment for water quality and changes in water characteristics monitoring. Some water pollutants can cause widespread damage to marine life within a very short time period and thus wireless sensor network reliability is more critical than in crop farming. This paper shows that network coverage models and assumptions over land do not readily apply in tropical aquaculture environment where high temperatures are experienced during the day. More specifically, due to high humidity caused by evaporation, network coverage at 15 cm antenna height is better than at 5 m antenna heights due to the presence of a super-refraction (ducting) layer. For a 69 m link, the difference between the signal strength measured over several days is more than 7 dBm except under anomaly conditions. In this environment, the two-ray model has been found to provide high accuracy for signal propagation over water where there are no objects in close proximity to the propagation path. However, with vegetation in close proximity, accurate signal variation predication must consider contributions from scattered and diffused components, taking into account frequency selective fading characteristics to represent the temporal and spatial signal variations.
This paper presents a wideband model, from Direct Current (DC) to W band, for a single Anode Schottky Diode based on a commercial VDI chip. Different measurements have been performed to obtain a complete large-signal equivalent circuit model suitable for the device under consideration up to 110 GHz, and for its integration in planar circuits. The modeling has been done using a combination of DC, capacitance measurements, and RF scattering measurements. The test structure for on-wafer S-parameter characterization has been developed to obtain an equivalent circuit for Coplanar to Microstrip (CPW-Microstrip) transitions, then verified with 3D Electromagnetic (EM) tools and finally used to de-embed device measurements from empirical data results in W band. 3D EM simulation of the diodes was used to initialize the parasitic parameters. Those significant extrinsic elements were combined with the intrinsic elements. The results show that the proposed method is suitable to determine parameters of the diode model with an excellent fit with measurements. Using this model, the simulated performance for a number of diode structures has given accurate predictions up to 110 GHz. Some anomalous phenomena such as parasitic resistance dependence on frequency have been found.
An antenna consisting of a full-wavelength dipole on a GaAs membrane covered by a frequency-selective surface is proposed for improved output power from photomixers used as terahertz (THz) sources. The antenna structure reduces the vertical dimension of a typical photomixer antenna using a substrate lens while still exhibiting high total efficiency and high directivity. The resulting antenna after optimization produced an input resistance of 3870 Ω and a radiation efficiency of 60%, corresponding to a total efficiency of approximately 48.3% and a maximum directivity of 20.2 dBi at the resonance frequency of 1.03 THz. The proposed antenna is expected to be a promising alternative THz photomixer design.
The existence of drains in the field of the point source both for the spherical cavity with perfectly conducting boundary, filled with a homogeneous medium, and for unbounded Maxwell's fish eye (MFE) are rigorously proved. The existence of all class of generalized Green functions for unbounded MFE medium is established. The Green function describing the perfect focusing is found in this class. The same result for the MFE lens is obtained.
A new and exact series solution for the scattering and coupling problems by dielectric-loaded multiple slits in a perfectly conducting screen is presented. The case of normal incidence and TM polarization is considered. The scattered and transmitted elds are represented in terms of an innite series of radial modes. By applying the appropriate boundary conditions, the coecients of scattered and transmitted elds are obtained and some numerical results are given.
In order to solve the defects that the end-effect of magnetic field is ignored in two dimension (2-D) analytical method or 2-D finite element method (FEM); meanwhile, mass computer resource and time for parametric design or optimization are wasted in three dimension (3-D) FEM, a concise and efficient 3-D analytical approach is put forward for the calculation of the air-gap magnetic field and torque of coaxial magnetic gears. Based on the cylindrical coordinates where a coaxial magnetic gear is in, the equivalent current model and vector magnetic potential equation of permanent magnets in high speed permanent magnetic ring are constituted. By superposed magnetic flux density of every tile permanent magnets on high speed permanent magnetic ring in cylindrical coordinates, a air-gap magnetic field 3-D analytical formula is set up without ferromagnetic pole-pieces; in the interest of modulated air-gap magnetic field 3-D analytical formula with ferromagnetic pole-pieces, three types boundary conditions using state equations of contact surfaces between ferromagnetic pole-pieces and air-gap are established by a thorough analysis of the modulate mechanism of ferromagnetic pole-pieces. Finally, magnets of the low speed permanent magnetic ring are reduced to a distribution of equivalent current, which experience the Lorentz force in modulated magnetic field of high speed permanent magnetic ring for torque calculation. The integrals in all aforementioned calculation are axial, so the end-effect is embodied in above analytical model and more precise than 2-D analytical method or 2-D FEM. As the calculation results, the formula is accurate but faster than the 3-D FEM. The analytical model is suited for programmable calculation and that will make the structural and parametric design or optimization of coaxial magnetic gears simple and timesaving.
The phase-shifting characteristic of a novel composite right/left handed transmission line (CRLH TL) for two frequency points is analyzed in this paper. Samples of (90˚, 0˚) and (180˚, 0˚) phase-shifting TLs for two frequency points (f1, f2) are deigned and the total length of the CRLH TLs has decreased by more than 77% compared to the conventional microstrip lines. Then a four way power divider made by three Wilkinson power dividers and interconnected with the (90˚, 0˚) and (180˚, 0˚) phase-shifting TLs is designed to feed an antenna with two different operating modes at two different frequency bands. Four radiating patches arranging symmetrically in a loop are printed in an upper substrate and connected with the four outputs of the feed network by four copper pins. When the four rectangular patches are excited by four sources with equal amplitude and phase at f1, metamaterial antenna with conical beam and linear polarization (LP) is achieved; while four sources with equal amplitude but 90˚ phase difference for each adjacent output at f2 leads to wideband antenna with broadside beam and circular polarization (CP). One antenna prototype with dual-band dual-mode dual-polarization property is fabricated and good agreements between simulation and measurement results are obtained. This single-feed patch antenna is valuable in wireless communications for its radiation pattern selectivity and polarization diversity.
Maxwell's equations specify that electromagnetic fields are generated by accelerating charges. However, the electromagnetic fields of an accelerating charge are seldom used to derive the electromagnetic fields of radiating systems. In this paper, the equations pertinent to the electromagnetic fields generated by accelerating charges are utilized to evaluate the electromagnetic fields of a current path of length l for the case when a pulse of current propagates with constant velocity. According to these equations, radiation is generated only at the end points of the channel where charges are being accelerated or decelerated. The electromagnetic fields of a short dipole are extracted from these equations when r>>l, where r is the distance to the point of observation. The speed of propagation of the pulse enters into the electromagnetic fields only in the terms that are second order in l and they can be neglected in the dipole approximation. The results illustrate how the radiation fields emanating from the two ends of the dipole give rise to field terms varying as 1/r and 1/r2, while the time-variant stationary charges at the ends of the dipole contribute to field terms varying as 1/r2 and 1/r3.
This paper presents the design, analysis, and prototyping of a novel axial-flux permanent-magnet (AFPM) motor capable of auto-starting. The preliminary design is a slot-less double-sided solid-rotor line-start AFPM motor with 4 poles for high torque density and stable rotation. One spaced raised ring was added to the inner radii of the rotor disc for smooth line-start motor. The design allows the motor to operate at both starting and synchronous speeds. The basic equations for the solid ring of the rotor of the proposed axial-flux permanent-magnet motor are presented. Non-symmetry of the designed motor led to its 3D time-stepping finite element analysis (FEA) via ANSYS 13.0, which evaluated the design parameters and predicted the transient performance. The designed motor was fabricated and tested, the experimental results showing good agreement with FEA simulation results. The prototype motor showed high starting torque and good synchronization.
Recent years, a new SAR concept based on Multi-Input Multi-Output (MIMO) configuration has demonstrated the potential advantages to simultaneously improve the performance of Synthetic Aperture Radar (SAR) imaging and ground moving target detection by utilizing multiple antennas both at transmission and reception. However, the precise signal model, as well as the effect of ground moving target in image domain and the approaches for moving target indication based on MIMO SAR system are rarely investigated. Our paper has three main contributions. Firstly, we present a detailed signal model for stationary scene and moving target based on a colocated MIMO SAR system, and analyze the motion effect of the moving target. Secondly, we provide an algorithm of phase compensation to combine the multiple virtual channel data in order to enhance the image quality. Thirdly, an adaptive optimal approach is applied for clutter suppression, then the velocity of the moving target is estimated via Delay-and-Sum (DAS) beamforming approach. Finally, several numerical experiments are provided to illustrate the derivation and analysis in this paper.
This paper presents a six-port network over an ultra-wideband (UWB) of 2-8 GHz. Its key component is the six-port junction, which consists of a Wilkinson power divider and three 3-dB quadrature couplers, This six-port junction is accomplished in a low dielectric constant substrate (Rogers RT/duroid 5880). Multi-section impedance transformation is applied in the power divider, and the quadrature coupler is realized by using two 8.34 dB couplers in tandem. An ultra-wideband operation of the six-port junction is verified by full electromagnetic simulations and measurements. The results show that the designed devices exhibit good performance across 2-8 GHz band: the return losses at input ports are higher than 15 dB, the insertion losses from input ports to the remaining ports are 7.2 dB ± 1.7 dB, the isolation between two input ports is greater than 20.5 dB, and the maximum phase difference compared with the theoretical behavior between two test ports is 10°. For the manufactured six-port junction, a six-port phase measurement system and a calibration technique based on support vector regression (SVR) are introduced. Results show that the SVR model can achieve a mean phase error of 1.5274°.
This paper presents a novel range-spread target detection algorithm for frequency stepped chirp radar (FSCR) which transmits a chirp-pulse train with frequency stepped carriers. FSCR achieves high range resolution by synthetic wide-band technique, and its process includes intra-pulse matched filtering and pulse-to-pulse inverse discrete Fourier transform (IDFT) or wavelet transform. For FSCR, the high resolution range profile (HRRP) of a target is obtained by target extraction from overlapping HRRPs which is caused by oversampling. During the target extraction (sometimes called de-correlation), some strong scattering points of target echo are discarded, as the result, the signal-to-clutter ratio (SCR) might be reduced and the target detection capability is degraded. To solve this problem for FSCR, a novel detection algorithm without target extraction is addressed. The new algorithm based on the power spectrum of radar echo uses not only the amplitude information, but also the phase information of overlapping HRRPs of a target to improve the SCR, therefore, has significant performance. Moreover, the test statistic and the false alarm probability of the detector are derived, and the implementation procedure and the flow chart of the detection algorithm are designed. Finally, the detection performance is assessed by Monte-Carlo simulation, and the results indicate that the proposed algorithm has about 3 dB detection improvement in SCR compared with the spatial scattering density generalized likelihood ratio test (SSD-GRLT) detector, and at the same condition, is superior to the integrator detector. In addition, the proposed algorithm is robust and easy to implement.
A novel design of planar dual and triple narrow-band bandstop filter is presented by adopting the proposed meandered slot defected microstrip structure (MS-DMS) and the simplified spiral microstrip resonator (SSMR). Through this design, the stopbands of the dual- and triple-band bandstop filters can be individually controlled and the improved spurious responses are achieved. First, the fundamental and the first spurious resonances of the MS-DMS and SSMR are analyzed to provide the design rules. Then, by utilizing the prominent stopband of the MS-DMS and the stopband produced by the SSMR coupled to main microstrip line, a dual narrow-band bandstop filter is constructed before its design procedure is outlined. Based on above investigations, a triple narrow-band bandstop filter is implemented by inserting extra SSMRs to another side of the main microstrip line of the dual-band filter to generate a new stopband. To verify the aforementioned design concepts, a dual and triple narrow-band bandstop filter are designed, simulated and tested. Both the simulation and measurement indicate that the fabricated filters exhibit good stopband/passband performance and improved first spurious resonance. Moreover, these filters are simple to design and quite compatible with planar fabrication technique, making them very attractive for practical applications.
The problem of localizing small scatterers (in terms of wavelength) by Time Reversal-MUSIC (TR-MUSIC) algorithm is addressed. In particular, we focus on uniqueness problems that might arise for certain far zone configurations when noise corrupts data. These lead to reconstructions affected by ghost targets from which it is difficult to discern actual targets. In order to remedy such a drawback, data obtained at multiple frequencies are employed. In detail, a new multi-frequency version of TR-MUSIC is introduced. It consists in mixing reconstructions obtained at different frequencies. Numerical analysis shows that this method outperforms classical TR-MUSIC as well as its multi-frequency implementation already present in literature.
This paper presents a method for focusing a moving target in single channel SAR data utilizing a novel technique for range migration correction. The First Order Keystone transform is first applied to remove the range-walk of the moving target signature. A search procedure based on maximizing a contrast cost function is then employed to determine the phase correction which compensates for the remaining range curvature. Finally an adaptive notch filter is used to construct an estimate of the azimuth compression filter necessary to focus the moving target. An experimental result is provided for airborne SAR data to demonstrate the performance of the approach.
A new compact and wide-band waveguide dual circular polarizer at Ka-band is presented and tested in this paper. This compact structure is composed of a three-port polarizing diplexer and a circular polarizer realized by a simple pair of large grooves. The polarizing diplexer includes two rectangular waveguides with a perpendicular H-plane junction, one circular waveguide coupled in E-plane. A cylindrical step and two pins are used to match this structure. For a LHCP or RHCP wave in the circular port, only one specific rectangular port outputs power and the other one is isolated. The accurate analysis and design of the circular polarizer are conducted by using full-wave electromagnetic simulation tools. The optimized dual circular polarizer has the advantage of compact size with a volume smaller than 1.5λ³, broad bandwidth, uncomplicated structure, and is especially suitable for use at high frequencies such as Ka-band and above. The prototype of the polarizer has been manufactured and test, the experimental results are basically consistent with the theories.
This study presents a novel miniaturized dual-band coupled-line impedance transformer. This dual-band matching technique uses the characteristics of coupled-line and dual-band stubs to realize matching arbitrary complex impedance to arbitrary complex impedance at two arbitrary uncorrelated frequencies. Especially, it satisfies the demand of dual-band matching at two relatively closed operating frequencies (n= f2 / f1 ≤ 1.2), and occupy a very small circuit area with inherent DC-Block function. The proposed synthesis approach is validated by the design and fabrication of a 30 W gallium nitride (GaN)-based class-AB power amplifier (PA) for GSM and WCDMA at 1800 MHz and 2140 MHz. The PA's output matching network based on the proposed structure can accurately match 50 Ω to the ideal load impedances of the transistor at two designed frequency simultaneously and has 20% and 15% bandwidth for which the reflection coefficient magnitudes are less than 0.1, respectively.
Volumetric left-handed metamaterials made up of an array of split-ring resonators (SRRs) and wires exhibit negative index of refraction in a very narrow bandwidth due to the resonant nature of SRRs. We investigate the possible bandwidth enhancement by adding resonances to the system using fractals. The operating bandwidth of the system is increased when the additional resonances are placed close enough to each other. The Sierpiński-carpet fractal pattern is chosen as the distribution for the SRRs. The principle is demonstrated through simulations, and prototypes are fabricated and tested to verify consistency with simulations.
The paper presents an analytical investigation of three-layer twisted clad liquid crystal fiber in respect of its power propagation characteristics. The fiber under consideration has dielectric non-magnetic materials in its core and inner clad sections, whereas the outermost clad is made of radially anisotropic liquid crystal material. Twist in the fiber is introduced in the form of superfine helical turns at the interface of the core and the inner clad regions with specified values of pitch angle. Results demonstrate large confinement of optical power in the outermost liquid crystal section. Further, the angle of twist is seen to have its pronounced effect on controlling the flow of power as it exhibits the ability of governing the propagation characteristics of the medium. The observed propagation feature is attributed to the radial anisotropy of the liquid crystal outer region as well as the amount of twist introduced, and attracts useful applications of such complex fiber structures in evanescent field optical sensing and other coupling devices primarily used in integrated optics.
In this work, complex photonic band structure (CPBS) in a semiconductor-dielectric photonic crystal (SDPC) operating at terahertz frequencies are theoretically investigated. The SDPC is air/(S/D)N/air where the dielectric layer D is SiO2, the semiconductor layer S is an intrinsic semiconductor InSb, and N is the number of periods. Using the experimental data for the strongly temperature-dependent plasma frequency and damping frequency for InSb, we calculate the CPBS for the infinite SDPC at distinct operating temperatures. The CPBS is then compared with the calculated transmittance, reflectance, and absorptance as well in the finite SDPC. Based on the calculated CPBS, the role played by the loss factor (damping frequency), in InSb is revealed. Additionally, from the calculated transmittance spectra, we further investigate the cutoff frequency for the SDPC. The dependences of cutoff frequency on the number of periods and the filling factor of semiconductor layer are numerically illustrated.
This paper brings forward a simple local approximation finite-difference time-domain (FDTD) method for the analysis of short apertures with a finite thickness. By applying the equivalence principle together with a simple local approximation, the varying field distribution is accurately derived. The updating equations for the slot field can be derived by casting the field distributions into the contour paths containing the aperture. The method has been applied to two problems and the results are compared with the high-resolution standard FDTD simulation and the measurement results. The accuracy of the proposed method is verified from the comparison of both the field distribution and the time-domain and frequency-domain slot coupling results. It is demonstrated that the local approximation is highly efficient and timesaving, and the present method is stable, numerically and computationally efficient.
In this paper, an antenna-mode-switch technique is proposed to reduce the array size for the DOA (direction-of-arrival) estimation. Conventional DOA estimation requires many elements of antenna array to achieve high resolution, and then suffers from large array size. To improve such disadvantages, this paper proposes an antenna-mode-switch technique to reduce the required number of array elements. Numerical simulation shows that the required number of array elements will be greatly reduced by using the proposed technique. Furthermore, the bow-tie antenna design for implementing the proposed antenna-mode-switch technique is also given. The result proves that high-resolution and accurate properties of such a practical antenna design is very close to those of the ideal antenna mode.
Magnetic Induction Tomography (MIT) is a new and emerging type of tomography technique that is able to map the distribution of all three passive electromagnetic properties, however most of the current interests are focusing on the conductivity and permeability imaging. In an MIT system, coils are used as separate transmitters or sensors, which can generate the background magnetic field and detect the perturbed magnetic field respectively. Through switching technique the same coil can work as transceiver which can generate field at a time and detect the field at another time. Because magnetic field can easily penetrate through the non-conductive barrier, the sensors do not need direct contact with the imaging object. These non-invasive and contactless features make it an attractive technique for many applications compared to the traditional contact electrode based electrical impedance tomography. Recently, MIT has become a promising monitoring technique in industrial process tomography, for example MIT has been used to determine the distribution of liquidised metal and gas (high conductivity two phase flow monitoring) for metal casting applications. In this paper, a low conductivity two phase flow MIT imaging is proposed so the reconstruction of the low contrast samples (< 6 S/m) can be realised, e.g. gas/ionised liquid. An MIT system is developed to test the feasibility. The system utilises 16 coils (8 transmitters and 8 receivers) and an operating frequency of 13 MHz. Three dierent experiments were conducted to evaluate all possible situations of two phase flow imaging: 1) conducting objects inside a non-conducting background, 2) conducting objects inside a conducting ackground (low contrast) and 3) non-conducting objects inside a conducting background. Images are reconstructed using the linearised inverse method with regularisation. An experiment was designed to image the non-conductive samples inside a conducting background, which is used to represent the size varying bubbles in ionised solution. The temporal reconstruction algorithm is used in this dynamic experiment to improve the image accuracy and noise performance.
Two double-rotor flux-modulated permanent-magnet (DR-FMPM) machines are proposed for direct-drive applications, including the DR coaxial magnetic-geared (CMG) type and the DR PM vernier (PMV) type. The key of the DR-CMG type is to utilize two modulation rings for obtaining the desired magneticgearing effect, whereas the key of the DR-PMV type is to utilize the flux-modulation poles and fractional-slot concentrated-winding arrangement for achieving the magnetic-gearing effect. Thus, both proposed machines are able to directly connect their rotors with two different rotating loads. Their rotating speeds can also be independently controlled by two sets of armature windings. The proposed machines are designed and then analyzed by using the time-stepping finite element method. The corresponding results confirm the validity of the proposed machine design.
This paper presents the analysis of a six-phase permanent magnet synchronous machine dedicated for electrical power steering system applications. The motor design is briefly described, as well as the construction of the studied motor. The study is validated by finite element method and via experimental results. Some simulated results prove the machine's capability to work in faulty conditions. The machines performances are validated experimentally though scalar control.
In this paper, evaluations of diversity gains and capacities of multi-element antenna based on limited channel samples in a reverberation chamber (RC) are studied. It is shown that, for a large antenna array, the classical sample estimation based on finite channel samples tends to underestimate its diversity gain and capacity. An improved (yet slightly more complicated) eigenvalue estimation method is applied in both diversity gain and capacity calculations, which effectively alleviates the estimation bias. The findings of the present paper are applicable for measurements where the maximum independent channel samples per antenna element are limited. Apart from simulations, we also evaluate the performances of the classical and improved eigenvalue estimators based on measurements in a RC. Based on the results of this paper, the performance of the RC measurement (with limited samples) for multi-element antennas can be readily enhanced.
Biomass used for energy, whether it is extracted from forest residues or agricultural waste, contributes in many areas, such as power production, the construction industry, and also as a major source of different organic and inorganic compounds in the petrochemical industry. In recent years, research has identified a very remarkable use of agricultural waste, especially rice husks, as a microwave absorber in a pyramidal shape. However, absorbers built in this shape are fragile and require a very high degree of care, especially near the access panels, doors, and high traffic areas of the anechoic facility. This paper presents the results of a detailed experimental investigation of a more-robust, new design that is based on the concept of impedance or dielectric grading of rice-husk material. The absorber was fabricated using multiple layers of rice-husk material with increasing dielectric loss along the incident wave propagation axis. This type of fabrication technique provides more robust design of the microwave, rice-husk absorber with less thickness, as compared to the geometricallytapered, pyramid, or wedge absorbers. Free-space transmission and radar cross section (RCS) methods have been used, to study the electromagnetic compatibility (EMC) performance over the frequency range of 4-8 GHz. After the receiving equipment was calibrated by the thrureflect-line (TRL) calibration technique, the experiments were performed inside the anechoic chamber. The performance of the absorber was evaluated by incorporating the effects of circular-hole perforation, cross-polarized seams, and different metallic back plates. The proposed absorber demonstrated good performance (< -10 dB) for normal and 60° off the normal incident angles over the frequency range of 4-8 GHz. Reflectivity performance also was found to be comparable to one of the commercially-available absorbers.
This paper describes the radio frequency identification(RFID)-based steel coil identification system for supply chain management in the steel and iron industry. During crane operation, coil information is automatically updated by reading an RFID tag which is attached to the coil. One of the technical challenges associated with the RFID-based coil identification is the fall of the identification performance due to neighboring metallic objects. In order to cope with this problem, a system was developed in two directions. First, an effective tag attachment method considering the work process and the environmental conditions was proposed. Second, an antenna case was developed to improve the reading performance by minimizing the influence from the attached surface and focusing the RF signal to the target tag. The simulation and experimental results at the POSCO steel company verify that the proposed system can sense the target RFID tag successfully.