5.1.1 General

With the remarkable progress in mobile communications systems, antenna systems have also advanced in the recent decade. The typical mobile systems are mobile phone systems, evolved from analog systems, called the first generation (1G) systems, to digital systems, called the second generation (2G) systems, and further to the third generation (3G) systems, which are capable of multimedia transmission. Now the 3G systems are advancing to the fourth generation (4G) systems through 3.5G systems, which are designed to stand between 3G and 4G systems in order to advance smoothly from 3G systems to 4G systems. In addition to the mobile phone systems, various wireless mobile systems (WMS) have been deployed and offer services in various areas. The services of WMS range from very short distances to intermediate distances, whereas mobile phone systems provide nationwide service. The operating frequencies used by WMS ranges from the kilohertz regions to as high as the gigahertz regions, depending on the system performance, complexity, transmitting media, and data. The WMS provide not only communication services, but also perform control, data transmission, identification, and sensing, either through their network or with their own structure. Typical short range systems are Bluetooth, near field communication (NFC) systems (including RFID), and UWB. Middle to long range systems include wireless local area network (WLAN), wireless metropolitan area network (WMAN), and mobile worldwide interoperability for microwave access (WiMAX) as the middle to long range systems.