Orbital angular momentum (OAM) as vortex wave has potential application for dense communication. A multislot antenna is proposed based on Archimedean spirals to generate/detect the OAM waves. The antenna equips three radiation slots in a disk-manner to realize three different OAM modes simultaneously. A serial-fed microstrip array is designed for circularly polarized (CP) radiation. The lengths of the slots and microstrip lines are chosen to radiate at 3.5 GHz with 20% fractional bandwidth. So, it can identify the receiving modes of vortex wave with this mechanism. A prominent spiral phase plane is observed for the generated OAM wave. In addition, the far-field pattern presents a doughnut-shape beam. The whole antenna is fabricated on a 13 cm printed circuit disk board. Both the experimental and simulation results show that the proposed antenna has valuable features to produce different vortex modes.
A novel method for designing a compact low‐pass filter (LPF) with a sharp cut‐off and wide stop‐band is presented. In this technique, a simple open‐stub microstrip line is printed on top of a substrate and the desired performance is obtained by optimising the shape of the defected ground structure using the genetic algorithm. Details of the design procedure are presented and evaluated through designing two different LPFs. The first LPF is optimised for a 3.5 GHz cut‐off frequency and a stop‐band up to 10 GHz, whereas the second one is optimised for a 5 GHz cut‐off frequency and the stop‐band is extended to 16 GHz. Both filters are fabricated and good agreement between simulation and measurement result is obtained. The designed filters have a sharp transition along with a compact size of 25 × 20 × 0.787 mm3.
Source current reconstruction method (SRM) is a field transformation technique in which the equivalent currents at the antenna aperture are reconstructed from the known radiated fields. To stabilise SRM equations and reduce the effect of measurement errors and noise, the Tikhonov SRM has been frequently used. However, finding the regularisation parameter and solving the Tikhonov SRM equation have a high computational cost especially for large‐scale problems or in the presence of both electric and magnetic currents. Here, a hybrid regularised least‐square minimum residual (LSMR) technique is proposed to implement the Tikhonov SRM equation. In this method, the Tikhonov SRM is applied on the Krylov subspace that is created by the LSMR iterative solver. The regularisation parameter of the hybrid Tikhonov equation is determined at each iteration of the projected problem with the generalised cross‐validation method. Results of current reconstruction and near‐field/far‐field transformation with the proposed hybrid Tikhonov SRM are reported in this study and compared with the standard Tikhonov SRM. It is shown in both simulation and measurement examples that a significant improvement in the computational cost is realised with the proposed hybrid method while all of the benefits of the traditional method are preserved.
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