A Printed Log Periodic Dipole Antenna with Broadband Application from 0.5 to 15 GHz

Abstract

As a kind of ultra wideband antenna, the log periodic dipole antenna (LPDA) can operate on infinite large bandwidth in theory. But in fact, the higher frequencies of LPDAs are limited by the manufacturing accuracy of the short dipoles which closed to the feed, and the lower frequencies are limited by the size of the long dipoles. So the real bandwidth of the LPDA can reach about 20 : 1 at most. This may limit the applications of LPDA.In this paper, a printed LPDA with a 30:1 bandwidth which operating from 0.5 to 15 GHz is present. The dipoles and feed lines of the LPDA are printed on a PFTE board with a size of 392 mm × 250 mm × 1.5 mm and a e r of 2.55. Due to the limitation of manufacturing accuracy, the width of the dipoles which operate on high frequencies could not be too small. In order to overcome this limitation, the width of the shortest dipole is increased to 1 mm. This may lead to mismatching of impedance on high frequencies, and the distances of these dipoles are optimized to eliminate the mismatching. For low frequencies, a parasitic dipole is added close to the third longest dipole, which can be used to improve the VSWR on low frequencies. At last, the LPDA is fabricated, and the measured results indicate a VSWR less than 2.0 and a gain better than 4 dBi through the whole band. The radiation patterns of the antenna show stability directional beams for the most frequencies of the operating band.