What is boom correction in Yagi antennas?

When the elements are not electrically isolated from a conducting boom in a Yagi antenna, length of the elements have to increased slightly to resonate on the design frequency. That is because a thick metal boom shifts the resonant frequency of the elements upwards. This is known as boom correction in simple terms. Elements passing through the boom and electrically bonded to the boom needs more boom correction for length. If elements are electrically isolated even if passing through the boom, correction needed is lesser. This can be done by using sleeves of insulators where the elements pass through the boom. In the first case, the correction needed may be 25-45% of the boom diameter while in the latter case, the correction need be only 15-25% of the boom diameter. Correction needed can be higher on higher frequencies. Actual correction needed will also depend on the type of antenna design and style of mounting of elements. It can be determined by antenna simulation in antenna designing software.

Reference

Yagi Antenna Elements Boom Correction by YU1AW.