Design of a miniaturized CPW fed Z-shaped monopole antenna using theory of characteristics modes for bandwidth enhancement

This article presents a theory of characteristic mode (TCM)-based method of easy three steps for designing a very wide impedance band antenna. Initially, the characteristic mode (CM) analysis is done to comprehend the different modes of antenna geometry in absence of a feeding structure. Then modal currents and their corresponding modal fields (radiation patterns) are determined for recognizing modes to be selectively excited to generate the required radiation pattern. These will help in choosing a proper feeding configuration that stimulates the desired modes and acts as an excellent impedance matching. Here, initially CM analysis has been carried out for a Z-shaped monopole antenna to identify the higher order modes to be utilized to achieve linear polarization over a wideband frequency. TCM analysis gave direction for choosing CPW-fed as the feed of choice for exciting six desired modes. Modification of the CPW-fed ground by etching two semicircular notches helped in further increase of the impedance bandwidth (IBW). Measured findings relate satisfactorily with simulations done using Ansys Electronics Desktop 2020R1. The proposed design exhibits simulated IBW of 21.2 GHz (i.e. 4.2–25.4 GHz, 143%) having its center frequency (fc) at 14.8 GHz, and the measured IBW below 10-dB is from 3.8 GHz to up to 14 GHz (as beyond 14 GHz, IBW could not be measured using the available vector network analyzer). Simulation results are further validated in CST microwave studio. Proposed antenna is fabricated on FR-4 epoxy substrate of 0.8 mm thickness and exhibits a very small footprint of just 400 mm2 (20 × 20 mm2, 0.46λgL × 0.46λgL × 0.018λgL, where λgL is the simulated guided wavelength at lower resonating frequency frL=4.2 GHz) with 53% reduction in size. This antenna may be utilized for contemporary and upcoming wireless communication systems.