**3. Omni-directional UWB antenna and design**

130 Ultra Wideband – Current Status and Future Trends

slot antenna, in 1979.

**Figure 7.** Master's diamond dipole (1947).

 **Figure 8.** Stohr's ellipsoidal monople and dipole (1968).

The conventional UWB antennas have been wide used in the broadcast communication applications, but they are not suitable for some high frequency applications in modern and further due to their solid structure and un-integration. In the following sections, some new

types of UWB antennas will be introduced for high frequency applications..

In 1940, J. C. Kraus [5] also developed an antenna similar to the Lindenblad's coaxial horn and named it volcano smoke antenna (See Fig.5), which played a significant role as the cornerstone of television development. Investigations carried out on this antenna showed that this bulbous monopole-like structure yields an impedance bandwidth ratio of 5:1. During that period, coaxial transitions became one of the design techniques for other antenna researchers and designers. In 1948, L. N. Brillouin [6] developed omni-directional and directional coaxial horns, as shown in Fig.6. But these two antennas are difficult to manufacture and use because of their widely structure. Thus, some aspects such as manufacturing cost and complexity of procedures become the important considerations in the design of broadband antennas. The well-known "bow-tie" antenna reveals those benefits, which was originally proposed by Lodge and later rediscovered by G. H. Brown and O. M. Woodward. In 1947, R. W. Masters [7] proposed a similar type of antenna, the inverted triangular dipole, which was later referred to as the "diamond antenna". More recent, other UWB antennas were also developed. W. Stohr [8] introduceed the ellipsoidal monopole and dipole antennas in1968, as shown in Fig. 8. P. J. Gibson proposed the Vivaldi antenna [9] as an amalgamation of slot and Beverage antenna, collectively called tapered

Along with the wireless system miniaturization and operation frequency increasing, some novel types of onmi-directional UWB antennas have been developed in the last decade. Mainly consisting of two types, the UWB planar monopole antenna and the UWB printed monopole antenna, both types are basically developed from the principles of conventional UWB antennas, such as the biconical antenna, the cone-disc antenna, the cage antenna, and etc. Based on several techniques in terms of bandwidth enhancement, omni-directional radiation improvement and size reduction, they can provide almost the same bandwidth and radiation performances as the conventional UWB antennas but with much smaller volumes.

**Figure 9.** Various geometries of planar monopole antennas [11-14].
