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Generalized Friis Transmission Equation for Orbital Angular Momentum (OAM) Radios
摘要： Generalization of a Friis transmission equation for orbital angular momentum (OAM) radios is rigorously formulated using the Lorentz reciprocity theorem and a near-and-far-field convolution integral (NFCI). Based on the discretization of NFCIs, we computed the generalized Friis transmission equation to obtain the power-receiving behaviors of practical helicoidal parabolic reflector antennas (HPRAs) with continuously deformed surfaces. A simplified Friis equation is also used for computing the link budget and approximate Rayleigh length of discrete uniform circular arrays (UCAs) composed of 2×2 dipole antennas. The transmission coefficients for the given OAM modes, represented by our equations for the HPRA and UCA, agree very well with commercial numerical simulators. In addition, an mth-order NFCI, which is an orthogonal convolution integral for the mth OAM mode, is proposed to define a figure of merit for the OAM mode purity of transmitting and receiving antennas.
关键词： antenna arrays,transmitting antennas,receiving antennas,Electromagnetic propagation,reflector antennas,reciprocity principle
更新于2025-09-23 15:22:29
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Optimisation of phase factor in phase retrieval for reflector antennas with active surface
摘要： The deformation of reflector surface can be obtained by Misell algorithm using two far-field amplitude patterns: one with the antenna in focus and the other with the antenna defocused. For reflector antennas with active surface, the defocused pattern can be measured by adjusting the panels to get a more effective phase factor instead of offsetting the sub-reflector. The shape and size of phase factor have a great influence on the accuracy of convergent solution. To improve the performance of Misell algorithm, this study proposed an optimisation method for phase factors under different surface deformations. This method utilises Levenberg–Marquardt algorithm to get an estimation of the aperture distribution and then applies the particle swarm optimisation to optimise the phase factor parameterised by Zernike polynomials. Numerical simulations show that the proposed method is an efficient tool to achieve applicable phase factors under different surface deformations. Using the optimised phase factor, Misell algorithm can get a better convergent performance than traditional Misell algorithm.
关键词： Misell algorithm,particle swarm optimisation,Levenberg–Marquardt algorithm,active surface,phase retrieval,reflector antennas,Zernike polynomials
更新于2025-09-09 09:28:46