A Yagi-Uda Antenna, is a directional antenna system consisting of an array of a dipole and additional closely coupled parasitic elements (usually a reflector and one or more directors). The dipole in the array is driven, and another element, typically 5% longer, effectively operates as a reflector. Other elements shorter than the dipole may be added in front of the dipole and are referred to as directors. This arrangement increases antenna directionality and gain in the preferred direction over a single dipole. Directional antennas such as the Yagi-Uda are commonly referred to as beam antennas orhigh-gain antennas (particularly for transmitting). Yagi antennas are commonly used for reception of television broadcasts. Yagi-Uda antennas are also widely used by amateur radio operators for communication on frequencies from short wave, through VHF/UHF, and into microwave bands. Amateur radio operators (HAMs) often use type of antenna for various communication purposes.
Amidst the plethora of available antennas , the ground-station will be using a set of four crossed Yagi antennas set to resonate on the two operating frequencies of 145MHz. and 437MHz. The nomenclature of these antennas comes straight from their structure consisting of two planes of Yagi antennas fixed at 90 degrees angle with respect to each other on the same metallic boom.
