voltage-controlled frequency tuning of an antenna
The standard way to tune things is with a varactor.

Although a typical varactor can achieve more than a 4:1 variation in capacitance, once that's embedded in a circuit, including bias, parasitics and a corresponding inductor, you rarely see the hoped-for octave tuning range. Replace the inductor with antenna elements and you'll see even less than one octave.

You can get varactors in capacitance ranges and packages appropriate for frequencies in the order of MHz to GHz. However, I've often had a hankering to test very high-K ceramic capacitors like Y5U to see what the 'varactor' performance would be like at very low frequencies indeed.

You would need to restrict a transmit antenna to very low power levels to use voltage controlled tuning, as the RF voltage would modulate the tuning, not a problem with a receive antenna.

You may need to use several varactors, to tune both the antenna and the matching network to the feed. It will not be a trivial or 'cookbook' task.

Digital tuning may be easier to use, where you would use hard switching to change the physical lengths of antenna elements. Historically, PIN diodes have been used for this purpose. At low enough frequencies (&lt;100MHz), you could even experiment with the humble 1N4148 (not a PIN) to get a feel for what can be done. Silicon on sapphire CMOS switches are a modern alternative RF switch, easier to bias than diodes, and capable of handling some quite impressive powers, look for 'CMOS RF switch'.