I’ve been looking for some new wire antennas to try. The Half Square (HS) looks interesting. It is two 1/4 wave vertical elements, with a 1/2 wave horizontal element connecting them. The ARRL Antenna Book has a writeup that looks interesting. I really need something cut for 20 meters and this might be worth trying.
The HS is usually fed at one of the top corners with coax. One benefit is that it is forgiving to symmetrical distortion of the design (like bending the legs due to mounting restrictions). The downsides are that it is high-Q (thus narrowbanded – bandwidth is less than a dipole) and it appears to be a primarily vertical polarity antenna. L.B. Cebick provides a model of the HS for EZNEC (along with anything else you could ever want to know about antennas).
What really makes this antenna interesting is the fact that it can be built as a 2-element array (or wire beam). This is attractive to me due to my operating QTH, where only the water is to my East. In any US-based operating, I want to push more of my power to the West. I may also mount it close to the ground, to improve NVIS performance for QSO parties.