How do antennas over 1/2 wavelength work?

I've been told countless times that an antenna should be 1/4, or 1/2 wavelength. That increasing this size to a higher multiple of 1/4 will work, but it will distort the radiation pattern to include several high gain lobes shooting energy off in useless directions (like straight upwards).

But I also see stuff like this for sale https://www.dxengineering.com/parts/dmn-x300a. How does this antenna work when it's around 1.5x the wavelength for 2m, and about 4.25x the wavelength for 70cm? Is it just some tech I'm not familiar with, or are these just giant useless poles?

• I think you're on to something in that, yes, it's right that this radiates! But: "one of the red areas and will cancel out against the blue, leaving one red area radating" isn't how electromagnetic waves and antennas work! And consequently, the radiation pattern of a $1.5\lambda$ antenna is not the same as that of a $0.5\lambda$ antenna. So, I don't think we can let this stand as it is, as it is sadly incorrect :( Things will radiate even if equal amounts of currents flow in opposite directions, as you're ignoring the spatial aspects here, which define an antenna! Commented Jul 31, 2022 at 11:21
• but, for the $1.5\lambda$ dipole (and only for the $1.5\lambda$ dipole) you're right in result, if not in explanation: The effective area of a $1.5\lambda$ dipole is the same as that of the $0.5\lambda$ dipole. But again, that's not because of regions of current density cancelling each other out simply by existing in the same antenna, that's because they're exactly a wavelength apart, and thus, as you very astutely observed, the generated fields a bit away from the antenna cancel out. Commented Jul 31, 2022 at 11:25