Increasing the Bandwidth of Wideband Antennas Using the Frequency Pulling Technique

Frequency pulling technique (FPT) is a recently developed method for increasing the bandwidth (BW) of microstrip antennas. It is based on the insertion loss methodology used for the design of bandpass filters. Namely, to apply this technique, the resonators in a bandpass filter are replaced with antennas that have identical equivalent resonant circuits. Also, all the equivalent resonant circuits can represent symmetrical feeding points of a single antenna. Therefore, when these circuits are properly connected in accordance with the FPT rules, they create a matching network that increases the BW of a single antenna. However, prior studies on this method are limited to (1) narrowband antenna designs, (2) antennas with feeding points located at the same plane, and (3) feeding networks implemented as single feeding lines (e.g., microstrip lines) which have introduced several limitations and design complexities. In this work, we address these challenges by (1) extending FPT to wideband designs, (2) using feeding points located at different planes, and (3) designing feeding networks as unequal power dividers. Such networks not only simplify the design complexities associated with the traditional approach but also offer the capability to apply FPT to non-planar designs (e.g., 3D antenna configurations). To demonstrate the latter, we properly engineer a triangular tapered slot antenna, feeding it with a coupled microstrip line. As a result, the bandwidth of our modeled antenna increases from 34.51% to 78.25%, demonstrating excellent agreement between simulated and measured results.