An Accurate Filtenna Synthesis Approach Based on Load-Resistance Flattening and Impedance-Transforming Tapped-Feed Techniques

In this paper, an accurate filtenna synthesis approach is investigated and verified for achieving the expected filtering response. The load-resistance flattening technique is carried out by attaching the shunt inductive/capacitive elements to cancel the unwanted parasitic element in the antenna model. The synthesis procedure was presented for a filtenna using a planar inverted-F antenna based on parallel-coupled lines. Furthermore, to economize the circuit area, hairpin resonators are adopted to replace the straight resonators in the PCL filtenna, and a tapped-feed structure is utilized for feeding. Thorough investigation reveals that conventional tapped-line feeds based on a singly loaded resonator adopted in a generic coupled-resonator filter requires careful modification to retrieve zero-reactance at the operation frequency. For verification, two bandpass filters were designed with hairpin uniform-impedance and stepped-impedance resonators, thereby validating the practicality of the proposed impedance-transforming tapped feeds. Eventually, the load-resistance flattening and impedance-transforming tapped-feed techniques are combined for developing an accurate filtenna synthesis approach. Two filtennas taking advantage of inverted-L and slotline antennas were designed and fabricated, thus, validating the feasibility of the proposed approach.