Foldable Dual-Band Monopole Antenna Using Nitinol Memory Alloy and Flexible Substrate for Satellite Mobile Terminals and Walkie-Talkies

Hundred-megahertz bands are widely used in long/short-range communications, such as satellite service and walkie-talkies. Due to the wavelength exceeding 1 meter, most hundred-megahertz mobile antennas are long-external whips, which not only affect portability but also degrade mechanical strength. This work proposes the first foldable hundred-megahertz mobile antennas. Mobile terminals are mostly in standby mode, so eliminating external antennas in standby mode is beneficial for portability and strength. A segment of nitinol memory alloy is adhered to a flexible copper-clad laminate, constituting the foldable antenna branch. In standby mode, the antenna is completely hidden on side surface of the terminal under external force. In operational mode, release of the force allows the antenna to spring out quickly and exhibit high performance. The mechanical property of the nitinol alloy is analyzed. The proposed antenna operates at two frequencies, with the printed copper strip for 280 MHz and nitinol for 433.92 MHz. Classical doughnut-shaped patterns with the measured maximum gains of 1.1/1.8 dBi and out-of-roundnesses of 1.9/1.3 dB are obtained. The reflection coefficient is stable after folding 50~500 times, demonstrating robust mechanical performance and practical value. The proposed strategy offers a higher level of portability and operational convenience compared with traditional retractable solutions.