Abstract
This talk will cover several research projects on advanced RF structures designed and built for various applications in accelerators and vacuum electronic devices, including: 

1. an X-band metamaterial structure for beam-driven wakefield acceleration tested at AWA; 
2. an S-band metamaterial-based backward wave oscillator built and tested at MIT;
3. an S-band accelerator cavity designed and built for rapid proton beam energy modulation in cancer therapy at SLAC; 
4. an X-band klystrino design for a compact, cost-effective and high-efficiency microwave source at SLAC. 

Emphasis will be placed on how the advanced RF designs helped to improve device performances in different applications.