VK2ABQ beam of the 1970s. Think of it like a 2 element yagi but with the ends bent in. That makes a horizontal Moxon narrower - useful if you've only got a small yard and need a small turning radius. Or, if you're using it vertically you'd only need a shorter pole to support it. Yet the gain can be nearly as good, thanks to 'critical coupling' as explained in Les Moxon's book HF Antennas for All Locations.
Moxons can be built either from metal tubing or wire. The latter needs some sort of support frame such as bamboo or fishing poles. Their main shorcoming is that some dimensions are critical, in particular the separation between the elements. That means that you need supports to be the right spacing or the correct amount of tension applied. They're mostly a single band antenna, though if you are willing to spend the time adding and optimising each wire element they can be made multiband as well.
Here's some Moxon links to peruse:
* DU1RZ multiband wire Moxon beam
* KD6WD Moxon antenna project
* Multibanding the Moxon Rectangle by W4RNL
* Handheld 2m/70cm satellite antenna using a Moxon on 2m
* VP9KF Moxon antenna calculator
* Portable QRP with a Moxon (video)
PS: Want to read more about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.