What is a Half Square Antenna?

Half square antenna consists of two vertical quarter wave elements and a horizontal half wave element which acts as the phasing line between the two vertical elements. The antenna is fed at the top corner with inner conductor of the coax connecting to one vertical element and the outer shield connecting to the horizontal phasing line. This leads to the vertical elements being fed in phase. Radiation is along the broad side of the antenna and is supposed to be good for working DX, especially on lower bands like 80m and 160m, with moderate gain over a simple dipole antenna. It can be fed directly with a 50 ohms coaxial cable. Half square antenna has nulls along the ends of the horizontal element. Coax should be kept perpendicular to the vertical elements to prevent interaction.

WB3GCK has made a modified version for portable operations with speaker wire. As it was for portable operations, the feed point was shifted to the bottom of the vertical element, which is a high impedance region. Hence a 9:1 unun was used along with an antenna tuner and radials. Hence it could be even used as a multi-band antenna. Details of on field performance during portable operations and details of construction and mounting are available on the web page in case you wish to try it out. He has mentioned that as the impedance on 80m was low, he does not recommend the 9:1 unun on that band. The antenna elements were cut for 40m and the internal tuner of his radio could tune from 80m to 6m and there were plenty of spots on Reverse Beacon Network on 40m with signal to noise ratio of 20 dB or more. It has been mentioned that the 49:1 transformer of end fed half wave antenna might also work with this configuration which is also end fed.

Many more versions of half square antenna are available at the web page of MD0MDI. He has also mentioned that W8HXR had referred to it as a Bobtail and had suggested using a quarter wave ladder-line to change it from broad side fired to end fired version, using an SPDT switch. Another version mentioned is a phased Lazy U. I found all these quite complex and may be I will get back to them at a later date when I have acquired more knowledge about the principles of these antennas. Any one who is interested could refer to the page by MD0MDI as it documents in detail his experiments with these designs and EZNEC antenna modeling graphs.