<Table> <Tr> <Td> Part of a series on </Td> </Tr> <Tr> <Th> Antennas </Th> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> Common types (show) <Ul> <Li> Dipole </Li> <Li> Fractal </Li> <Li> Loop </Li> <Li> Monopole </Li> <Li> Satellite dish </Li> <Li> Television </Li> <Li> Whip </Li> </Ul> </Td> </Tr> <Tr> <Td> Components (show) <Ul> <Li> Balun </Li> <Li> Block upconverter </Li> <Li> Coaxial cable </Li> <Li> Counterpoise (ground system) </Li> <Li> Feed </Li> <Li> Feed line </Li> <Li> Low - noise block downconverter </Li> <Li> Passive radiator </Li> <Li> Receiver </Li> <Li> Rotator </Li> <Li> Stub </Li> <Li> Transmitter </Li> <Li> Tuner </Li> <Li> Twin - lead </Li> </Ul> </Td> </Tr> <Tr> <Td> Systems (hide) <Ul> <Li> Antenna farm </Li> <Li> Amateur radio </Li> <Li> Cellular network </Li> <Li> Hotspot </Li> <Li> Municipal wireless network </Li> <Li> Radio </Li> <Li> Radio masts and towers </Li> <Li> Wi - Fi </Li> <Li> Wireless </Li> </Ul> </Td> </Tr> <Tr> <Td> Safety and regulation (show) <Ul> <Li> Mobile phone radiation and health </Li> <Li> Wireless electronic devices and health </Li> <Li> International Telecommunication Union (Radio Regulations) </Li> <Li> World Radiocommunication Conference </Li> </Ul> </Td> </Tr> <Tr> <Td> Radiation sources / regions (show) <Ul> <Li> Boresight </Li> <Li> Focal cloud </Li> <Li> Ground plane </Li> <Li> Main lobe </Li> <Li> Near and far field </Li> <Li> Side lobe </Li> <Li> Vertical plane </Li> </Ul> </Td> </Tr> <Tr> <Td> Characteristics (show) <Ul> <Li> Array gain </Li> <Li> Directivity </Li> <Li> Efficiency </Li> <Li> Electrical length </Li> <Li> Equivalent radius </Li> <Li> Factor </Li> <Li> Friis transmission equation </Li> <Li> Gain </Li> <Li> Height </Li> <Li> Radiation pattern </Li> <Li> Radiation resistance </Li> <Li> Radio propagation </Li> <Li> Radio spectrum </Li> <Li> Signal - to - noise ratio </Li> <Li> Spurious emission </Li> </Ul> </Td> </Tr> <Tr> <Td> Techniques (show) <Ul> <Li> Beam steering </Li> <Li> Beam tilt </Li> <Li> Beamforming </Li> </Ul> <Ul> <Li> Bell Laboratories Layered Space - Time (BLAST) </Li> <Li> Multiple - input multiple - output (MIMO) </Li> </Ul> <Ul> <Li> Reconfiguration </Li> <Li> Spread spectrum </Li> </Ul> <Ul> <Li> Wideband Space Division Multiple Access (WSDMA) </Li> </Ul> </Td> </Tr> <Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> </Table> <Tr> <Td> Part of a series on </Td> </Tr> <Tr> <Th> Antennas </Th> </Tr>

What is the principle role of a tower within a cellular system