For a quick example, a dipole antenna for the 20 m band ... with each end soldered to one half of a dual variable capacitor which allows this antenna to tune from the 30 m bands to the 10 m ...

Energy-storage devices called capacitors deliver power rapidly ... The authors disrupted the antiparallel dipole arrangement of lead zirconate by introducing regions of non-polar dielectrics ...

Of course, you could source your own, but finding variable capacitors that can handle ... Or you could have a look at a very short dipole-like antenna called the Poynting vector antenna.