Compact UWB-to-C band reconfigurable filtenna based on elliptical monopole antenna integrated with bandpass filter for cognitive radio systems

Abstract

In this study, a compact configuration of frequency reconfigurable filtenna, designed by integrating a bandpass filter and with a monopole radiator, is demonstrated for achieving high-frequency selectivity along with compact size. The proposed filtenna can be efficiently tuned between ultra-wideband (UWB) and C-band states of operation. A bandpass filter, based on rectangular stepped impedance stub loaded multiple-mode resonator (MMR), is embedded to an elliptical monopole radiator to construct the filtenna circuit. The filtenna design approach leaves out the necessity of cascading an additional 50 Ω microstrip feed line in between the antenna and filter elements which makes the system more compact. The designed filtenna occupies 3.6-10.6 GHz band in its UWB state of operation and 3.63-4.70 GHz band in its C-band state of operation, respectively. The UWB operating state is intended for spectrum sensing application whereas the C-band operating state can be implemented for communication in a cognitive radio environment. The shifting between two operating states is controlled by appropriately switching the PIN diodes. An average peak gain of 2 dBi is observed within the passband. The overall size of the filtenna is optimised to 1.35λ0 × 0.96λ0 × 0.04λ0 (λ0 is calculated at 6.85 GHz). For validation purpose, the filtenna prototype is fabricated and characterised. A very close agreement is achieved with the suggested configuration.