MULTIBAND MULTIMODE ARCHED BOW-SHAPED FRACTAL HELIX ANTENNA

Abstract

A novel circular arc fractus named Arched Bow-shaped Fractal Curve (ABFC) is originally proposed. Four ABFCs are connected end-to-end, forming so called Arched Bow-shaped Fractal Loop (ABFL). The loop antenna peculiarly presents multiband multimode characteristics with resonance compression. The normal mode, which is pertinent to the loop area and circumference, is found improved with the iterative procedure. Thus, an eight-turned wire helix of small pitch angle (α = 3◦) with a circular disc ground called Arched Bow-shaped Fractal Helix (ABFH) antenna is shaped from K2 ABFLs. It can unprecedentedly operate in multiband of axial and off-axial modes with dual-sensed circular polarizations and high gain. Four matched bands (|S11| ≤ −10 dB) are obtained within 2 GHz– 8GHz, of which f1 = 2.34GHz (400MHz, 17.09%; G = 10.63 dBi; RHCP), f2 = 4.24GHz (770 MHz, 18.16%; G = 12.43 dBi; LHCP), f3 = 5.48 GHz (300 MHz, 5.47%; G = 8.13 dBi; RHCP), and f4 = 6.98GHz (960 MHz, 13.75%; G = 15.89 dBi; RHCP). The unique multiband multimode property has been theoretically analyzed with illustrations and can be attributed to existence of the fractal boundary, which particularly encloses multiple equivalent loops with considerable areas. These peculiarities make K2 ABFH antenna a very attractive candidate for multiband circularly polarized antennas, especially for space applications, such as spacecrafts communication, remote sensing, and telemetry, where reduction of quantity, height and weight of antennas are urgently wanted. It can also be configured into large array for higher gain service like radars and radio astronomy. Received 9 May 2013, Accepted 22 June 2013, Scheduled 9 July 2013 * Corresponding author: Daotie Li (maplebirchpaeony@yahoo.com.cn).