5GHz coax dipole, omnidirectional antenna. Normally these antennas are made entirely from coax. My method though replaces the outer braided copper wire with metal tubes cut to the correct wavelength. This method is much easier to construct and get the wavelength correct in each section of the antenna.
The 2.4GHz version of this antenna gives around 6db gain. Testing the 5GHz version seems to give around the same 6db.
Use a coax with a solid copper centre element. Metal tubes salvaged from cheap telescopic antennas.
5.8GHz ¼ wavelength 12.93mm
5.5GHz ¼ wavelength 13.61mm
5.2GHz ¼ wavelength 14.42mm