This article discusses the design of a compact antenna system for spectrum interweaved cognitive radio (CR). The system consists of a sensing filtenna and three communicating antennas. The sensing ultra‐wideband (UWB) antenna is a coplanar‐waveguide (CPW)‐fed monopole (2.2–11 GHz). The narrowband communicating patch antennas are reconfigurable through a switching mechanism, operating in six different frequency bands (5.54, 6.12, 7.60, 8.25, 9.64, and 10.29 GHz). To block the Wi‐MAX and WLAN bands, the proposed design uses a meandering slot and a stepped U‐slot in the monopole. Analysis of communicating antennas using the theory of characteristic mode analysis indicates good radiation in the desired frequencies. Isolation among these antennas is better than −18 dB. A constant group delay and linear phase response indicate a good time‐domain performance of the proposed UWB antenna. Simulated results match closely with those from measurements on the prototype. The proposed antenna system can find applications in various sectors adopting CR like internet of things.
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