I want to use some flexible substrate for my antenna design as well as for circuit design at 900 MHz or higher range of frequency, can anybody help me please , that what substrate i can purchase. which are commercially available.
The below papers on IEEE discuss flexible systems that might be of interest to you.
[1] S. Lemey, S. Agnessens, P. V. Torre, K. Baes, J. Vanfletern and H. Rogier, "Wearable Flexible Lightweight Modular RFID Tag With Integrated Energy Harvester," IEEE Transactions on Microwave Theory and Techniques, vol. 64, no. 7, pp. 2304-2314, 2016
[2] S. Lemey, F. Declercq, and H. Rogier, “Dual-band substrate integrated waveguide textile antenna with integrated solar harvester,” IEEE Antennas Wireless Propag. Lett., vol. 13, pp. 269–272, Jan. 2014.