In this paper, a three layer composite chiral metamaterial (CCMM) is proposed to achieve diode-like asymmetric transmission and high-efficiency cross-polarization conversion by 90° polarization rotation with ultrabroadband range simultaneously in microwave region, which was verified by simulation and experiment. This CCMM is composed of a disk-split-ring (DSR) structure sandwiched between two twisted sub-wavelength metal grating structures. The simulation agrees well with experiment in principle. The simulation results indicate that the incident y(x)-polarized wave propagation along the -z (+z) direction through the CCMM slab is still linearly polarized wave with high purity, but the polarization direction is rotated by ± 90°, and the polarization conversion ratio (PCR) is greater than 90% in the frequency range of 4.36-14.91 GHz. In addition, in the above frequency range, the asymmetric transmission coefficient (Δlin) and the total transmittance (Tx) for x-polarized wave propagation along the -z axis direction are both over 0.8. Finally, the above experiment and simulation results were further verified by the electric field distribution characteristics of the CCMM unit-cell structure. Our design will provide an important reference for the practical applications of the CCMM for polarization manipulation.
The study and design of a wideband aperture coupled microstrip patch array is presented. The proposed design considers the 2.4 to 3 GHz frequency range but may be adapted to other frequencies. A 16 element planar array of the size of about 400 mm by 400 mm by 12.5 mm provides measured gain between 15.4 to 16.8 dBi and Side-Lobe Level (SLL) between 15.3 to 20.7 dB without a reflector within the 2.4 to 3 GHz frequency range. With a reflector significant increase in F/B is obtained but at the expense of higher SLL.
An analysis on the calculation of the inverse discrete Fourier transform (IDFT) of passband frequency response measurements in terms of lowpass equivalent responses is shown, in order to specify the differences in the results given from different common algorithms; differences with respect to the calculation of the IDFT for true lowpass responses are remarked. It is shown how the basic sequence has to be represented in time domain by invoking the causality, which is supported by results. Results are corroborated by an application on measured data in a reverberation chamber. The present analysis helps readers understand different IDFT algorithms used by Manufacturers and make their own codes whenever desirable.
In this paper, a circularly polarized antenna for Synthetic Aperture Radar (SAR) application is presented. The antenna is proposed to be implemented for the airborne SAR and the spaceborne SAR. To enhance the bandwidth of the antenna, the Circular-Ring-Slot (CRS) technique is implemented on the ground plane and in a square slot in the centre of the patch. In this antennas design, the model of the slot on the radiator is also investigated. The antenna is printed on NPC-H220A substrates with the dielectric constant of 2.17 and thickness of 1.6 mm. The resonant frequency of the antenna design sets at 9.4 GHz with the minimum requirement of the bandwidth of 800 MHz. The antenna design is produced under the -10 dB bandwidth of reflection coefficient, S11 of approximately 27% (8.2 GHz-10.76 GHz) and left-handed circular polarization (LHCP). The gain of the antenna is 6.5 dBic and 12.7% (8.8 GHz-9.84 GHz) for the axial ratio bandwidth (ARBW). This paper includes the description and presentation of the completed discussion.
Metasurfaces, due to its designable surface electric and magnetic impedances, have largely enhanced electromagnetic wave manipulation techniques. The conventional approach to realize the surface magnetic impedance requires non-planar structures, such as metallic loops, which is not easy to fabricate, especially at optical frequencies. In this work, we theoretically and rigorously prove that eective surface magnetic and electric impedances can be obtained using parallel electric metasurfaces. A synthesis method is presented which allows independent designs of surface electric and magnetic impedances. Finally, a polarization converter with high energy efficiency is designed using the proposed impedance synthesis method for verification. The proposed synthesis method is favorable for reducing fabrication complexities.
For the purpose of two-dimensional (2-D) imaging in the Terahertz (THz) near field through 2-D synthetic aperture radar technology, Fourier transform (FT) is one of the most popular imaging ways. However, FT-based algorithms would encounter performance loss either when spatial sampling is under Nyquist frequency or there are off-grid scatterers in the scene of interest. Therefore, by exploiting the theory of matrix enhancement and continuous parameter estimation, we propose to use matrix enhancement and matrix pencil (MEMP) method and matched filter to deal with arbitrarily located scatterers when spatial under-sampling is adopted. Through constructing a specifically expanded matrix, the information of the scatterers involved in the small data set can be enhanced. Then, highresolution grid-independence 2-D imaging can be achieved by the combination of MP and matched filter. Simulation results verify the effectiveness of the proposed algorithm.
We propose a novel approach for the broadband generation of orbital angular momentum (OAM) carrying beams based on the Archimedean spiral. The mechanism behind the antenna is theoretically analyzed and further validated by numerical simulation and physical measurement. The results show that the spiral-based antenna is able to reliably generate the OAM carrying beams in an ultra-wide frequency band. Of particular interest is the fact that the mode number of radiated beams is reconfigurable with a change in operating frequency. Prototypes of a single-arm spiral antenna (SASA), a multi-arm spiral antenna (MASA), and a compact multi-arm spiral antenna (CMASA) are investigated and demonstrated to support our arguments. The proposed approach provides an effective and competitive way to generate OAM carrying beams in radio and microwave bands, which may have potential in wireless communication applications due to its characteristics of simplicity, broadband capacity and reconfiguration opportunities.
In this work, reflectarray antennas are proposed for their use as probes in compact antenna test ranges. For that purpose, the quiet zone generated by a single oset reflectarray is enhanced, overcoming the limitation imposed by the amplitude taper of the feed antenna. First, the near field is characterized by a radiation model which computes the near eld of the reflectarray as far field contributions of each element, which are modeled as small rectangular apertures and thus taking into account the active element pattern. Then, a phase only synthesis is performed with the Levenberg-Marquardt algorithm in order to improve the size of the generated quiet zone. Due to the nature of the application, this near eld synthesis takes into account both the amplitude and phase, making it a more challenging task than an amplitude-only synthesis. The optimization is focused on flattening the amplitude while trying to preserve the phase front generated by the reflectarray.
This paper describes a highly robust and efficient parallel computing method for the transient simulation of low-frequency electromagnetics with nonlinear materials and/or permanent magnets. In this method, time subdivisions are introduced to control the memory usage and nonlinear convergence. A direct block triangular matrix solver is applied to solve the formulated block matrix for each subdivision. This method has been implemented using the Message Passing Interface (MPI) for distributed memory parallel processing. Depending on the number of available MPI processes and physical memory, the entire nonlinear transient simulation can be divided into several subdivisions along the time-axis such that each MPI process handles only the computation for one time-step. Application examples are presented to demonstrate that this method can achieve excellent scalability of speedup.