Abstract
Log-periodic antenna is a special antenna type utilized with great success in many broadband applications due to its ability to achieve nearly constant gain over a wide frequency range. Such antennas are extensively used in electromagnetic compatibility measurements, spectrum monitoring and TV reception. In this study, a log-periodic dipole array is measured, simulated, and then optimized in the 470–860 MHz frequency band. Two simulations of the antenna are initially performed in time and frequency domain respectively. The comparison between these simulations is presented to ensure accurate modelling of the antenna. The practically measured realized gain is in good agreement with the simulated realized gain. The antenna is then optimized to concurrently improve voltage standing wave ratio, realized gain and front-to-back ratio. The optimization process has been implemented by using various algorithms included in CST Microwave Studio, such as Trusted Region Framework, Nelder Mead Simplex algorithm, Classic Powell and Covariance Matrix Adaptation Evolutionary Strategy. The Trusted Region Framework algorithm seems to have the best performance in adequately optimizing all predefined goals specified for the antenna.
Highlights
Log-periodic antennas are widely used because of their broadband characteristics in TV reception, electromagnetic compatibility measurements and wideband precision measurements
The Log-periodic dipole arrays (LPDAs) has much larger bandwidth compared to YagiUda antenna
Each dipole of LPDA is connected to the feeding source, whereas in Yagi-Uda antenna only one dipole is connected to the feeding source and all other dipoles are passive [4]
Summary
Log-periodic antennas are widely used because of their broadband characteristics in TV reception, electromagnetic compatibility measurements and wideband precision measurements. Log-periodic dipole arrays (LPDAs) present an almost flat gain over a wide. The LPDA is designed by using several dipoles of different lengths. In this way, each dipole operates in resonance condition at a certain frequency and this happens when the dipole length L is equal to half wavelength (λ/2). By employing dipoles of varying lengths, the LPDA is capable of operating effectively at a wide frequency range [4]. The values of τ and σ are properly chosen by the user to design the antenna with predefined average directivity over the operating bandwidth, and this is done by using the well-known Carrel’s graph [5, 9, 10]
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