UWB and SWB Planar Antenna Technology

Various wideband antennas have been interesting subjects in antenna designs and have found important applications in military and civilian systems. For examples, the super-wideband (SWB) antenna is a key component of electronic counterwork equipment in the information warfare; while the ultra-wideband (UWB) antenna is widely used in impulse radar and communication systems. With the development of high-speed integrated circuits, and the requirement of the miniaturization and integration, the research and application of UWB/SWB planar antennas have been growing rapidly. On February 14, 2002, the Federal Communications Commission (FCC) in the United States allocated the 3.1-10.6GHz spectrum for commercial application of UWB technology, which has sparked renewed attention in the research of ultra-wideband planar antennas. Fig.1 shows its some applications. It is worth noting that the actual frequency range of an indoor UWB communication antenna in the provision of UWB technology is from 3.1 to 10.6GHz with a ratio bandwidth of 3.4:1,while the antenna with a ratio bandwidth not less than 10:1 is generally called the super-wideband (SWB) antenna in antenna engineering. Both types are reviewed and for simplification, usually they are called the UWB antenna in this chapter. In the UWB system, the former operates just like a kind of pulse figuration filter, which requires the antenna to radiate pulses without distortion. To that end, the UWB antenna should not only possess an ultra-wide impendence bandwidth, but also have good phase linearity and a stable radiation pattern. Hence, for this sort of UWB antenna some particular considerations are entailed [1]. The earliest antenna with wideband properties is the biconical antenna executed by Oliver Lodge in 1898, as shown in Fig.2a. It can be regarded as a uniformly tapered transmission line excited by TEM mode so as to possess the ultra-wideband input impedance properties. Its bandwidth is mainly influenced by the ending reflection due to its limited dimension. Following improvements consist of Carter’s improved match biconical antenna(Fig.2b) and conical monopole antenna (1939), Schelkunoff’s spheroidal antenna (1941), Kandoian’s discone antenna (1945), Brillouin’s omni-directional and directional coaxial horn antenna (1948), etc[2]. All these antennas are based on three-dimensional structures with bulky volume. In the late 1950s and early 1960s, a family of antennas with more than 10:1 4