Application of Theory of Characteristics Modes for Bandwidth Enhancement of a Miniaturized Minkowski Fractal Antenna

This article presents a miniaturized modified Minkowski fractal antenna with enhanced linearly polarized impedance bandwidth (IBW) in the lower frequency region. Applying theory of characteristic modes (TCM) analysis on a second iterated modified Minkowski radiator without feeding structure, modal currents and their corresponding modal fields (radiation patterns) were determined to recognize symmetric dominant modes to be specifically excited to generate the required radiation pattern. It gave direction for choosing quarter-wave microwave line feeding as the feed of choice to excite the four desired modes at 2.7, 5.7, 5.9, and 8.7 GHz and providing excellent impedance matching to generate the very wide IBW. Measured results matched well with simulations done using Ansys HFSS 2020R1. Measured IBW is 9.7 GHz (160%), from 1.2 to 10.9 GHz, with center resonance frequency (f(rc)) at 6.05 GHz, whereas simulated IBW is 9.4 GHz (162%), from 1.1 to 10.5 GHz with f(rc) at 5.8 GHz. The antenna size is 36 x 34 x 1.6 mm(3) (0.216 lambda(gL) x 0.204 lambda(gL) where at lower resonating frequency f(rL) = 1.1 GHz, lambda(gL) is the guided wavelength) with 82.24% reduction in size. This antenna may be utilized for "L", "S" band and UWB wireless communication.