I'm fairly new to RF technology, but a direction-finding application has come up where a highly directional antenna can offer a convenient solution, so I started searching for such antennas.
Most, like Yagi antennas, that can be purchased seem to have gain patterns that are not very focused, with half-power beamwidths of no less than 30 degrees, often much greater.
Is it possible to design PCB antennas (or alternatively, purchase pre-made antennas) with a very narrow/focused radiation pattern -- Ideally, I'm looking for a small (size < 10 cm) antenna with a half-power beamwidth under 10 degrees? Assume any transmission frequency between, e.g., 433 Mhz up to 10 GHz is acceptable (because the application has some leeway in this).
What keywords should I research for this, or are such antennas impossible due to scientific limitations?
For example, Wikipedia contains this image within a radiation-pattern article, but I haven't yet been able to find an antenna with such favorable pattern: