This chapter mainly focused on the recent trends in the antenna design techniques for next-generation wireless communication systems. Ultra-wideband antenna and multi-input-multi-output antennas are very useful to achieve higher data rates. An antenna is a transducer that changes guided electromagnetic energy in a transmission line to radiated electromagnetic energy in free space. Antennas may also be observed as an impedance transformer, coupling among an input or line impedance, and the impedance of free space. The looming widespread commercial deployment of ultra-wideband (UWB) systems has flashed new interest in the subject of ultra-wideband antennas. The power levels approved by the FCC mean that every dB counts in a UWB system as much as or possibly even more so than in a standard narrowband system. Thus, in effect, UWB antenna is a precarious part of an overall UWB system design. Basic principles for ultra-wide-band (UWB) antenna design and radiation are presented and discussed in this chapter.
TopUwb Antenna’S Desirable Properties
The ultra-wide frequency bandwidth is the key parameter in differentiating the UWB antenna with various other antennas. In accordance with the FCC's specific description (Fields & R. E, 1997) an appropriate UWB antenna should have the ability to deliver an overall bandwidth of in no way lower than 600 MHz frequency or simply a fractional-bandwidth concerning at minimum 0.20 dB. In addition, UWB antenna should be remain working or operational. Also it must show steady impedance matching covering the whole frequency spectrum of 3.1-10.6 GHz in the circumstance of Impulsive-UWB in accordance with the outlined spectral mask defined in the FCC guidelines. In some cases, it might be needed (such as in European countries) in which UWB antennas need to be furnished the band-rejected feature with various other narrowband systems and applications accounting for the exact same operational band.
Depending on the nature of the application being processed, the directional or simply Omni-directional antenna characteristics are often desired in accordance to the functional software programs (Cordeiro et al., 2005) Omni-directional patterns are more often than not preferred in cellular and hand-held devices. Directional radiation patterns are generally preferred for radar units and additional directional unit in which high-gain is often required.
Substantial radiation efficiency is generally needed for antennas as far as it is essential and critical for an UWB antenna considering that the power spectral density being transmitted is overly low (Porcino et al., 2003). As a result, any kind of substantial loss received by the antenna may sometimes compromise the operation of the device.
An acceptable antenna requires to be compact as well low in weight for its suitability to various applications (Dietrich, Dietze, Nealy, & Stutzman, 2001) . When we design UWB antenna for some specific requirements such as mobile and other portable (Mazhar et al., 2013) systems, it is generally advisable to design the UWB antenna into low profile feature and therefore it should also meet the compatibility condition for integration on printed base.
An effective structure involved with UWB antenna needs to remain optimum to get relatively high performance of the entire system. In order to avoid the likely in-band/out-band disturbance between the UWB devices and accessible other digital devices/instruments, the antenna must be designed in such a way that the entire system (antenna being used and the RF front-end system) is in accordance with the necessary power emission mask mentioned in by FCC and also various other regulatory organizations guidelines. The emission boundaries shall be driven by together with the selection of source pulse as well as the design of the UWB models/systems antennas.