Compared to low Earth orbit (LEO) synthetic aperture radar (SAR), geosynchronous (GEO) SAR has a larger coverage and shorter revisit period. However, due to its longer integration timeit will be affected byionospheric time-variant total electron content (TEC), which introduces a phase error into the SAR azimuth signal.Using U.S. total electron content (USTEC) data, TEC variation with timeon GEO SAR trackis analyzed. It is shown thatquadratic phase error caused by time-variant TEC is main effect on image focusing compared to higher order errors. Therefore, contrast optimization autofocus (COA) algorithm can beusedfor compensation. The key steps of COA are given. Simulations based on scenes derived from PALSAR2 data demonstrate the effectiveness of COA.
A novel miniaturized multilayer substrate integrated waveguide (SIW) filter is designed. The filter is constructed with four compact SIW resonator cavities, and each cavity supports TE101 mode, which can be controlled by the slot located between layers. The area of the compact SIW resonator is just 1/16 of that of original substrate integrate waveguide (SIW) resonator. Meanwhile, the area of the four-order filter is 13.2 mm×26.4 mm. The insertion loss and return loss of the fabricated filter are -1.8 dB and -14.6 dB, respectively. Meanwhile, the tunable filter realizes center frequency linearity, which works at 1.6 GHz with an adjustable range of 51.8%. The insertion loss is -1.2 dB, and the return loss is less than -15 dB. The coplanar cavity coupling structure achieves a switchable bandwidth.
In this paper, design of a triple band ultrathin compact polarization insensitive metamaterial absorber for S-, C- and X-band applications is proposed. The proposed absorber consists of periodic arrangement of a modified triple circular slot ring resonator as unit cell printed on the top of a continuous metal backed FR-4 dielectric substrate. The proposed absorber is ultrathin having thickness of λ0/135.66 at the lowest absorption center frequency. The measured wide stable absorption bands of 0.40 GHz, 0.45 GHz and 0.47 GHz with absorption peaks of 97%, 96.45% and 98.20% at absorption center frequencies of 2.90 GHz, 4.18 GHz and 9.25 GHz respectively are observed. The temperature profile of absorber is measured by using lock in infrared thermography, and a temperature increase of 1°C at absorbing frequency as compared to non-absorbing frequency is observed. The absorber is demonstrated to be polarization insensitive to TE and TM polarized angles of incidence of electromagnetic wave with wide angular stability up to 45°. The absorber is fabricated and tested in an anechoic chamber. Experimental results agree well with measured ones.
This paper studies distribution characteristics of paraxial magnetic field of solenoid with inner relaxation polarization medium and driven by ac signal. Firstly, the paraxial electromagnetic field model of hollow solenoid was constructed by Maxwell equations, and the influence of the driving signal frequency was analyzed. Then, based on the established paraxial electromagnetic field model of hollow solenoid, the magnetic field model of solenoid with inner relaxation polarization medium was established by ampere loop law. Finally, the effects of relaxation polarization medium and driving signal frequency on magnetic field amplitude and phase shift were analyzed in detail. The conclusions were drawn as follows: driving signal frequency affects magnetic field amplitude; the relaxation polarization medium will cause the phase shift of magnetic field; and the phase shift will increase as the driving signal frequency increases.
Jamming and anti-jamming techniques for global position systems (GPS) play important roles in electronic countermeasure. Least mean square (LMS)-based anti-jamming algorithm is widely used in GPS receivers, since it can avoid matrix inversion and has low complexity. For convenience, we call them LMS-GPS receivers. To improve the anti-jamming performance of the LMS-GPS receivers, it is very meaningful to study the jamming technique. Considering that existing jamming signals are easily suppressed by LMS-GPS receivers, a new jamming method named as optimal power difference jamming is proposed in this paper to improve the jamming effect further. Specifically, the analytical relationship between jamming-to-signal ratio (JSR) and the power difference of two interference signals is firstly given. Then, the conclusion that there is always an optimal power difference where the JSR can take the extreme value is drawn. Finally, the optimal power difference is derived as about 22 dB for single-tone interference and 29 dB for band-limited Gaussian noise interference. Simulation results show that the proposed method with optimal power difference is able to improve the JSR remarkably.
Employing characteristic mode theory (CMT), a shape-first feed-next design methodology for compact planar antennas is proposed, which facilitates rapid and systematic design of self-matched, multi-port antennas with optimal bandwidth and high isolation. First, the optimal antenna shape with multiple self-resonant modes is synthesized using a binary genetic algorithm. Then, the optimal feed positions that provide good input matching and high isolation between the excitation ports are specified using a virtual probe modeling technique. A two-port microstrip antenna with an electrical size of 0.45λd×0.297λd is designed, fabricated and measured. The measured operating frequency is within 2% of the full wave simulation, and the overall S parameter characteristics and far field patterns agree well with the simulation result, validating our design methodology. Mutual coupling S21 < -30 dB at the center frequency is achieved in this design.
To enhance the accuracy of estimated rotor position for sensorless controlled permanent magnet synchronous motor, the strategy based on sliding mode observer (SMO) with dual second order generalized integrator (DSOGI) is proposed. The SMO is utilized to estimate the back electromotive force (EMF). Considering the estimated back-EMF harmonics resulting from both flux spatial harmonics and inverter nonlinearities, the DSOGI is applied to eliminate multiple orders harmonics and extract the fundamental wave of the estimated back-EMF for calculating the rotor position. Therefore, the DSOGI can effectively reduce the influence of the estimated back-EMF harmonics and improve the accuracy of rotor position estimation. In addition, the software quadrature phase-locked loop with back-EMF normalization is utilized to calculate the rotor position in order to eliminate the influence of the changed back-EMF magnitude at different speed. Finally, to illustrate the effectiveness of the proposed strategy, the experimental platform of an open-winding permanent magnet brushless motor is built. The comparison results verified that the drive system performance of both steady state and dynamic state is improved.
In this paper, a novel circularly polarized rectenna using a dual-feed array antenna with inclined patches is proposed to provide a dual-axis wide-angle reception capability. A new conical and pencil dualbeam circularly polarized array antenna integrating planar magic-Ts is designed and fabricated to overcome the polarization and main-beam misalignment between the transmitting and receiving antennas. To improve the rectenna's output power, open stub matching networks are used to achieve the impedance matching between the antenna and rectifying diodes. Two types of circularly polarized dual-axis rectennas which respectively allow the parallel and series connections of two diodes are experimentally evaluated and compared to confirm the wide-angle reception capabilities in the x-z and y-z planes.
A high selectivity compact size coupled open-loop resonator (OLR-) band pass filter (BPF) in 0.18 μm TSMC Complementary Metal Oxide Semiconductor (CMOS) with low insertion (IL) is presented in this manuscript. First, shape optimization and folding are used to guarantee compact size. Then, high performance of the proposed BPF is obtained by virtually increasing the height of the oxide between the OLR's traces and their ground plane. This virtual increase in the oxide height is realized by etching large slot areas below each of the OLRs. Consequently, the traces are characterized by wider width which in return exhibit lower attenuation constant and hence lower IL. The simulated and measured responses have a very good agreement. The fabricated BPF shows an IL of 3.5 dB at 59 GHz with a return loss of 15 dB and a fractional bandwidth of 16.5%. The fabricated chip has an area of 378 × 430 μm2 including the measurements pads.
In order to improve the resolution of microwave biomedical imaging, a new method has been proposed in this pa-per, using a water-immersed wide band horn antenna at S-band. Considering the microwave penetration depth and the reflection at the interface between tissues and environment in deionized water, 2.45 GHz is selected as the central frequency of this antenna. Due to the high dielectric constant of water, the design of the impedance matching structure between the coaxial line and rectangular waveguide is most challenging. Therefore, the idea that using water as the medium of the coaxial impedance matching structure is proposed to deal with the problem of processing in our work. Simulated and experimental results show that this antenna has good impedance characteristics (S11 < -10 dB from 2.1 GHz to 3.8 GHz), good reasonable losses (5.1 dB total for two antennas and coaxial line at 3 GHz), and high maximum gain (8.52 dBi at 2.45 GHz).
Owing to the hardware cost and power consumption limitation, hybrid precoding has been recently considered as an alternative to the fully digital precoding in millimeter wave (mmWave) largescale multiple-input multiple-output (MIMO) systems. Although the number of radio frequency (RF) chains is reduced to a certain extent in the hybrid precoding structure, a great number of phase shifters are still needed. In this paper, we present a new hybrid precoding architecture based on switch network to decrease the power consumption of hybrid precoder by reducing the number of phase shifters greatly. The new hybrid precoding architecture consists of three parts, a digital precoder, an analog precoder, and a switch network, in which the switch network is used to offer a dynamic connection from phase shifters to antennas. Afterwards, a two-stage algorithm is proposed to determine each part of the hybrid precoding implementation. Specically, the product of the analog precoding matrix and digital precoding matrix is viewed as a whole matrix rstly, thereby the original problem is simplified into a two-variable problem which is relatively easy to be solved. Then, the decomposition of the analog precoding matrix and digital precoding matrix is considered in the second stage. Simulation results show that the presented implementation can not only provide a better trade-off between hardware complexity and system performance, but also achieve higher energy eciency with far fewer phase shifters than previous works.
A novel triple-band ultrathin metamaterial absorber (MA) with polarization independence is designed, characterized and realized in this study. The designed absorber consists of three layers. The top metallic patch is patterned in an ultrathin dielectric substrate that is backed with a ground metallic plate. The numerical simulation results show that the presented metamaterial absorber exhibits three distinct absorption peaks of 99.95%, 99.28% and 96.36% under normal incidence at frequencies of 8.115, 11.4 and 15.12 GHz, respectively. Due to its fourfold symmetry, the absorbing properties are independent of the polarization of the incident radiation angle. Moreover, in the cases of TE and TM polarization modes, the proposed absorber displays an outstanding absorption response over a wide range of incident angles. The physical mechanism of the absorption performance is explained by investigating the surface current and field distributions at three distinct absorption peaks. Furthermore, the presented absorber is practically validated by the excellent agreement observed between the experimental and simulated results. The designed absorber has an ultrathin thickness of 1 mm, which is 0.027λ0 with respect to the lowest peak absorption frequency, and can be useful for several potential applications, such as electromagnetic compatibility, stealth technology and super lenses.
Recent reports on metasurfaces have focused on beam-deflector, a canonical optical element that can be used to compose other functionalities. Most reported designs, however, are limited to small deflection angles; large-angle (≥50 degrees deflection) transmission-mode beam steering designs show poor efficiency. Furthermore, rapid efficiency degradation is also observed for small deviations in the angle of incidence. This paper presents a numerical study of beam-deflectors based on extended unitcell metagratings (unit-cells containing multiple differently sized nanoantenna members). In comparison to previous reports, the designs achieve significant efficiency improvements, wider acceptance angles and better polarization filtering. The versatility of the design technique is demonstrated by designing polarizing beam deflectors polarization insensitive beam deflectors and prismatic beam deflectors.
Global Navigation Satellite System (GNSS) reflectometry is a promising technology used to estimate soil moisture, sea surface height, ice properties, etc. Interference signal technique is an important method to estimate these geophysical parameters. The effect of this method is closely related to the terrain and the receiving antenna placement. This study aims to investigate the effects of terrain and antenna placement on height measurement through simulation and field experiments. In this paper, we first simulated the interference signal in different types of terrain by parabolic equation method and analyzed the influence of terrain on the height measurement. Then we conducted three typical field experiments and processed experimental data. The simulated and experimental results indicate that the interference signal is affected by the terrain and the receiving antenna placement. Height measurement result is correct by both horizontal-looking and zenith-looking antenna when the ground is flat. However when the ground is not flat, the soil block near the receiving antenna leads to estimation errors. A more accurate estimation is obtained by using zenith-looking antenna to suppress the influence from the near terrain than horizontal-looking antenna. When a slope is near the receiving antenna, the signal with a high elevation may achieve an obvious interference effect if high elevation minus slope is equivalent to a low elevation. In this situation, the measurement height is the distance between the antenna and slope surface.
This paper presents an analytical method for designing a high-efficiency frequency selective surface FSS-sandwiched dual-band circularly polarized reflectarray antenna. Results are obtained using the Computer Simulation Technology Microwave Studio (CST MWS). The antenna is designed to operate within the receiving (19.6-21.2 GHz) and transmitting (29.4-31 GHz) bands while sharing the same unit and aperture. A double-layer FSS is loaded between the upper and lower antennas to suppress mutual coupling. An analytic approximation method using conformal mapping to determine the effective permittivity (εr, eff) is observed. The transmission and reflection coefficients of the proposed FSS are synthesized using the transmission line approach. The comprehensive analyzed results obtained are compared with results obtained from the simulations performed in the CST MWS. To validate the performance of the proposed FSS-backed element configuration, a 20/30-GHz dual-band circularly polarized reflectarray with a 90-mm aperture is designed. The simulated gains are 23.3 dBi at 20 GHz and 27.7 dBi at 30 GHz with aperture efficiencies exceeding 45.25% and 57.85% in the receiving and transmitting bands, respectively.
A classification algorithm is applied to UHF radio frequency identification (RFID) system to estimate the indoor position of a passive tag utilizing a received signal strength indicator (RSSI). Passive tag signals are collected by conventional UHF RFID reader antenna located at two different positions. K-NN and curve fitting are used for distance estimation and examined at different frequencies within the range 902-928 MHz to find suitable frequencies which can minimize the average error. In the proposed method, the measured RSSI values are compared with the fingerprint database in different frequencies to find the nearest neighbor. The best accuracy achieved at frequency range 926-928 MHz is 18.3 cm. The monitoring system is composed of a reader and tags under test, which makes the proposed system robust, easy to set up, and with low cost. The limitation of the proposed method is also discussed.
To obtain the volume fraction of a gas-liquid two-phase flow, a contactless electromagnetic coupling resonance based volume fraction detection (CECR-VFD) technique is proposed. By mathematical calculation and numerical simulation, it is found that the CECR-VFD method is a better alternative than the conventional electromagnetic induction based method. The distance between the excitation coil and receiving coil is firstly determined. Then the effect of the pipe length is investigated. Additionally, the relationship between the output voltage across the receiving coil and the volume fraction is studied for stratified flow and annular flow. Experiments have been carried out for validation, and the results indicate that the output voltage can be used to predict the volume fraction of a two-phase flow.
Decreasing eddy current is very important for the realization of stability control of HoMB system. In order to improve the dynamic performance precision of HoMB in the design stage, the dynamics and stiffness analysis of a homopolar magnetic bearing (HoMB) has been studied in this paper. Because the polarities of the magnetic poles were not changed during the rotation of rotor, the effect of eddy-currents was often ignored in the previous researches. However, when the frequencies of vibration caused by external disturbance and control currents are very high, eddy-current effects have significant influence on the performance of HoMB. In order to predict the HoMB performance, guide the HoMB design and control of the HoMB system in high frequency, a dynamics model was built on the equivalent circuit method. Parameters of dynamic Modeling are frequency-dependent. The effect of eddy-currents on the current stiffness was studied. The analysis results show that the eddy current effect on HoMB can be reduced by increasing the air gap, decreasing the laminations thickness and decreasing the laminations conductivity.
A novel single probe-fed, single-layer, and single-patch triple-band microstrip antenna is presented. By incorporating two identical U-slots in the patch whose length is λd instead of 1/2λd in a conventional patch, three operating bands are achieved. Dual-beam radiation pattern is obtained at the upper band, and a single broadside beam radiation pattern is obtained at each of the lower and middle bands. The antenna's structure is simple. Only by using a single probe-fed point, the impedance matches well at all the three resonant frequencies. The measured and simulated results are in good agreement. The measured lower, middle, and upper bands are centered at 2.442 GHz, 3.505 GHz, and 5.787 GHz, respectively. The measured gains are 6.2 dBi at 2.442 GHz and 5.5 dBi at 3.505 GHz, respectively. At 5.787 GHz, the measured gains for the dual radiation beams are 8.4 dBi directed at 26° and 8.2 dBi directed at -38°, respectively. The proposed antenna can be a candidate for WLAN 2.4 GHz, WLAN 5.8 GHz, and 3.5 GHz of 5G (the fifth-generation mobile communication) operation.
A time reversal method is proposed for imaging and hyperthermia of tumors in breast tissues. Time reversal is based on the reciprocal nature of the electromagnetic scalar wave equation. Time reversed scattered electric fields recorded by the receiver antenna array are back-propagated in an FDTD assisted numerical model to focus back at tumor locations. The potential of this approach for thermal therapy applications is demonstrated by calculating specific absorption rates associated with the time-reversed electromagnetic fields. Simulation results elucidate the feasibility and robustness of the approach. A pulsed time domain measurement system is developed for conducting experiments to detect and measure heat absorbed by single and multiple tumors inside a simple breast phantom.