I ran across this article for an interesting design. The antenna uses capacitance and inductance for tuning.
The build in the article is for shortwave, but I wonder if it could be adjusted for use on 700 MHz.
Shortwave antennas need to be extremely wideband. The range of frequencies varies by about a factor of 10 (1000%) from the lowest (2.3MHz) to highest (26MHz). Variable tuning is required, but such designs are far less efficient than a typical 1/4-wave antenna.
700MHz band has a less than 5% difference between min and max frequencies. A simple 1/4-wave whip can handle that bandwidth with reasonably low SWR, and there is no need to use variable tuning elements in the antenna design.