In this paper, a wideband log periodic dipole antenna (LPDA) with small size is proposed. The arms of the dipole are in the shape of a second order fractal, which makes each dipole element to resonate in more than one frequency. This results in a LPDA antenna whose size can be greatly reduced. The proposed antenna has a substrate size of 90 × 60 mm 2 and operates over 2-8 GHz bandwidth with VSWR< 2. The antenna has stable pattern over the frequency range.

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.

Abstract-This paper describes the concept and design of a novel compact self-supported cup feed antenna for parabolic reflectors. The feed antenna consists of an open waveguide cup which is excited by a disk loaded dipole. This structure is fed by a coaxial waveguide through a split-coaxial balun and has a rear radiation pattern toward the reflector antenna. Two different types of this configuration are designed in this paper: a linearly-polarized grid reflector antenna fed by a single dipole excitation, and a circularly-polarized solid reflector antenna fed by a cross dipole excitation. The measurement is done for the former, and simulation results of the latter via two different software packages CST and HFSS are compared in this paper. Analyzing the results shows that both types of cup feed antenna have an excellent aperture efficiency and low side lobe level.

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