Antennas are designed for radiating and receiving the electromagnetic signal. A transmitting antenna, in general, must be able to handle much more electrical energy than a receiving antenna. The frequency range of FM broadcasting is from 88 to 108 megahertz (MHz). At these frequencies a typical wavelength is about 3 meters (10 feet) long, and the antenna must be adjusted more precisely to the electromagnetic wave, both in transmitting and in receiving. An antenna also may be designed to transmit at specific frequencies at 2.4 GHz for Wi-Fi and 3.5GHz for Wi-Max frequencies. The size of the antenna is also reduced for the above applications because it uses the radio frequency spectrum. Antennas may consist of single lengths of wire or rods in various shapes (dipole, loop, and helical antennas), or of more elaborate arrangements of elements (linear, planar, or electronically steerable arrays). Reflectors and lens antennas use a parabolic dish to collect and focus the energy of radio waves, in much the same way that a parabolic mirror in a reflecting telescope collects light rays. Directional antennas are designed to be aimed directly at the signal source and are used in direction-finding.
Recent technology developments have made advanced antenna systems (AAS) a viable option for large scale deployments in existing 4G and future 5G mobile networks. AAS enables state-of-the-art beam forming and MIMO techniques that are powerful tools for improving end-user experience, capacity and coverage. As a result, AAS significantly enhances network performance in both uplink and downlink. Finding the most suitable AAS variants to achieve performance gains and cost efficiency in a specific network deployment requires an understanding of the characteristics of both AAS and of multi-antenna features. The latest developments of antennas are microstrip antenna. These antennas are very attractive because their dimensions are in millimeters. This microstrip antennas are developed for various wireless applications such as cognitive radio,MIMO systems ,medical wearable systems and Body area networks. The recent developments of antennas are Meta material, unit cell concepts, millimeter and Terahertz antennas.
