An outdoor TV antenna generally consists of multiple conductive elements that are arranged in such a way that it is a directional antenna. The length of the elements is about one half of the signal wavelength. Therefore the length of each element corresponds to a certain frequency.
The arrangement of an outdoor VHF/UHF antenna is usually the longer elements (for picking up VHF frequencies) are at the rear of the antenna, relative to the antenna’s directionality. The shorter UHF elements are anterior and the antenna works best when aligned to the source of the signal to be received.
The smallest elements in this design, located in the front are UHF (ultra high frequency) and use Yagi antenna principles. The longest elements, located in the back of the antenna use VHF (very high frequency) Log-periodic design principles. Combining these two types of antenna creates the combination VHF/UHF antenna commonly used providing reasonable performance and price.
An antenna can have a smaller or larger number of directors and depending on physical constraints can have more or less directors it has (requiring a longer/shorter boom). More Directors create a more accurate beamwidth and consequential higher gain. For the commonly used Yagi antenna this is not a linear relationship as the antenna gain is the ratio of the signal received from the preferred direction to the signal from an ideal omnidirectional antenna.
Gain is inversely proportional to the antenna’s acceptance angle. Two or more directional rooftop antennas can be set up and connected to one receiver. Antennas designed for rooftop use are sometimes located in attics or ceiling cavities to protect them from weather elements.
Sometimes television transmitters are organized in such a way that all receivers in a given location need receive transmissions in only a relatively narrow band of the full UHF television spectrum and from the same direction so that a single antenna provides reception from all stations. Again providing reasonable manufacture and retail cost.