Design of a new omnidirectional, circularly polarized antenna for FM broadcast

• Main Authors: Mappatao, Gerino P., Caluyo, Felicito S.
• Format: text
• Published: Animo Repository 2009
• Subjects: Antenna radiation patterns; FM broadcasting; Signal Processing; Systems and Communications
• Online Access: https://animorepository.dlsu.edu.ph/faculty_research/9281
• Institution: De La Salle University

FM broadcasters are having problems on the high cost of operating expenses of broadcast stations. The greatest part of these expenses is the power consumption of the broadcast transmitter. Most, if not all FM stations operating in the country use antenna systems that transmit signals almost in all directions on the horizontal plane, even in directions where signals are not needed. With these antenna systems, higher transmitter power is needed to cover the station's service area. To save much on energy, the antenna system must radiate signal only where it is needed, i.e. the radiation pattern is dependent on the location of the population within the service area of the station. In this way, much lower transmitter power is needed to serve the entire population. To realize an antenna system with customized radiation pattern, a basic antenna (called bay) having an omnidirectional pattern is needed. Most FM antenna systems available in the market today use bays that do not have omnidirectional radiation pattern because of the presence of metallic materials around the radiator. Antenna manufacturers use non-radiating poles or towers during antenna measurements. However, in actual applications, metallic poles or towers are used and definitely affect the circularity of the bay radiation pattern. The design of a new antenna that can be used as a bay in an antenna system for FM broadcast having an omnidirectional pattern and circular polarization even in the presence of a metallic pole or tower is described. The antenna is basically composed of dipoles whose physical parameters like element length, skew angle, bending radius and distance of the elements from the tower are varied to obtain the desired and optimized circularity of the radiation pattern and other antenna parameters required for FM broadcast antennas.