Design of a compact wideband slot antenna using parasitic reactive tuning

Multi-band antennas are increasingly deployed in wireless systems (e.g., cellular base stations) utilizing multiple dissimilar radiators with separate feed networks for each band. A major difficulty in such design is to control the isolation between bands, and often the elements are widely separated in space, for example, by allocating the antennas for each frequency band to a separate dielectric layer. Two major challenges to overcome then are the increased array size and weight, and the complexity in feed design. This paper presents the design of a compact, dual-port, printed slot antenna that employs parasitic reactive coupling from an inter-digitated capacitor (IDC) embedded in the microstrip feed line to provide broadband impedance matching. An overlay film above the IDC (such as low-loss graphene thin films) can be incorporated in the design for additional tunability of the wide frequency band. Antenna losses are minimized by isolating the IDC and the film from the radiator. The effects of the IDC and the overlay film´s surface impedance variation are parametrically examined through simulations, and the wide impedance bandwidth (greater than 100%) is experimentally corroborated with and without a graphene overlay film.