Portable ultrawideband (UWB) applications promise impressive transfer of large amounts of data using broad wireless bandwidths. Of course, one of the keys to implementing this technology is the availability of antennas capable of handling continuous frequencies from 3.1 through 11.0 GHz and higher. Fortunately, Researchers from the Department of Electrical and Electronic Engineering at the University of Hong Kong have explored the capabilities of multiple-input, multiple-output (MIMO) antennas with notched bands to avoid interference of existing more-narrowband wireless applications by those UWB signals.
The experimenters developed their UWB MIMO antenna on a flexible substrate film with compact dimensions of 22 × 36 mm2. A strip on the ground plane was used to create the notch band to avoid interference of wireless-local-area-network (WLAN) band frequencies. The researchers simulated the performance of the antenna with and without the T-shaped ground slot and found how the slot helps achieve enhanced isolation between the two input ports, especially at frequencies below 5 GHz.
The MIMO antenna was prototyped and evaluated with a commercial microwave vector network analyzer (VNA) from Rohde & Schwarz, a model ZVA 24. The antenna yielded simulated and measured impedance bandwidths in excess of 2.6 to 11.0 GHz, suitable for MIMO operation in the UWB frequency range approved by the U.S. Federal Communications Commission. To suppress interference in the WLAN band, the antenna includes a notched band from 5.15 to 5.85 GHz. The measured antenna efficiency across the UWB frequency range was better than 70%, dropping to less than 4% in the WLAN-notched band. The compact antenna design shows outstanding performance for use in UWB applications which can also effectively coexist near WLAN systems.
See: “Compact MIMO Antenna for Portable UWB Applications With Band-Notched Characteristic,” IEEE Transactions on Antennas and Propagation, May 2015, p. 1,917.