An antenna is a device to transmit and/or receive electromagnetic waves. An antenna must be tuned (matched) to the same frequency band as the radio system to which it is connected, otherwise reception and/or transmission will be impaired. Most cell phone antennas are as long as ¼ the wavelength of the wave they are transmitting or receiving. Your cell phone (usually) operates at a range of frequencies around 1900 MHz. What is the length (in cm) of the antenna in your phone?