When we talk about "small antenna", I think about the homebrew antenna I have made for WiFi devices on 2.4GHz.
Now, you can make Yagis for any frequency right? Right, so have a look at this; Antenna directs light at the nanoscale.
"Niek van Hulst and colleagues at the Institute for Photonic Sciences in Barcelona ... fabricated a number of nanoscale Yagi Uda antennas containing the tiny parasitic elements made from gold using lithography to etch the devices onto a glass substrate. The total length of individual antennas was 830 nm where individual feeds were just 145 nm, each separated by 175 nm."