Considerations for Harmonics Distribution in Aperture-Tuned Inverted-F Antenna for Cellular Handheld Devices

An analysis of the harmonics distribution in the aperture-tuned inverted-F antenna (IFA) using the first-order transmission line model is presented. The analysis allows identifying local minimums for the second and third harmonics for a given use case, providing the mechanism for optimization of the nonlinear performance of an antenna system. The theoretical findings are verified on a hardware demonstrator, comprising a mechanically reconfigurable IFA and a single-pole single-throw (SPST)-based aperture tuning network. The aperture tuning network comprises a radio frequency (RF) high-voltage switch, including a voltage detector with low-harmonic feedback and a parallel inductor. The integrated circuit (IC) was fabricated in Infineon 130-nm dedicated RF switch technology. The hardware demonstrator enables the measurements of the impedance at the feed, harmonics, RF voltage along the radiating element, and impedance at aperture tuning port. The latter provides a mechanism for optimization of load impedance at integer multiplies of transmitted frequencies, which allows minimization of harmonic content generated by the tuning IC.