**2. History of UWB antennas**

In 1898, Oliver Lodge [1] firstly introduced the concept of UWB antenna design, such as spherical dipoles, square plate dipoles, triangular or "bow-tie" dipoles, and biconical dipoles. Fig.1 depicts Lodge's biconical antennas which are unmistakenly used in transmitreceive links. After that, a number of types of UWB antennas were developed in the following several years [2-7]. *i.e.*, one of interest rediscoveries of the biconical antenna and conical monopole is done by P. S. Carter in 1939 [2] (See Fig.2). Carter improved upon Lodge's original design by incorporating a tapered feed, one of the key steps towards the design of broadband antennas.

Ultra-Wideband Antenna and Design 129

**Figure 3.** Schelkunoff's spherical dipole (1940)

**Figure 4.** Lindenblad's coaxial horn (1941).

**Figure 5.** Volcano smoke antennas (1940).

**Figure 6.** Brillouin's coaxial horn (1940).

**Figure 1.** Lodge's biconical antennas (1898).

**Figure 2.** Carter's improved match biconical (1939).

In 1940, S. A. Schelkunoff [3] proposed elaborate conical waveguides and feed structures in conjunction with a spherical dipole (see Fig.3). Unfortunately, his design of the spherical dipole antenna was not very useful. Almost at that time, the most well-known UWB antenna was the coaxial horn proposed by N. E. Lindenblad [4]. In order to make the antenna more broadband, Lindenblad took the design of a sleeve dipole and introduced a continued impedance change, as shown in Fig.4.

**Figure 3.** Schelkunoff's spherical dipole (1940)

128 Ultra Wideband – Current Status and Future Trends

**2. History of UWB antennas** 

design of broadband antennas.

**Figure 1.** Lodge's biconical antennas (1898).

**Figure 2.** Carter's improved match biconical (1939).

impedance change, as shown in Fig.4.

*fl* – the lower frequency of the operation band. *fh* – the higher frequency of the operation band. *fc* – the center frequency of the operation band.

In 1898, Oliver Lodge [1] firstly introduced the concept of UWB antenna design, such as spherical dipoles, square plate dipoles, triangular or "bow-tie" dipoles, and biconical dipoles. Fig.1 depicts Lodge's biconical antennas which are unmistakenly used in transmitreceive links. After that, a number of types of UWB antennas were developed in the following several years [2-7]. *i.e.*, one of interest rediscoveries of the biconical antenna and conical monopole is done by P. S. Carter in 1939 [2] (See Fig.2). Carter improved upon Lodge's original design by incorporating a tapered feed, one of the key steps towards the

In 1940, S. A. Schelkunoff [3] proposed elaborate conical waveguides and feed structures in conjunction with a spherical dipole (see Fig.3). Unfortunately, his design of the spherical dipole antenna was not very useful. Almost at that time, the most well-known UWB antenna was the coaxial horn proposed by N. E. Lindenblad [4]. In order to make the antenna more broadband, Lindenblad took the design of a sleeve dipole and introduced a continued

**Figure 4.** Lindenblad's coaxial horn (1941).

**Figure 5.** Volcano smoke antennas (1940).

**Figure 6.** Brillouin's coaxial horn (1940).

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 slot antenna, in 1979.

Ultra-Wideband Antenna and Design 131

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

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

**3.1. UWB planar monopoles** 

volumes.

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

The planar monopole antenna was firstly reported in 1976 by G. Dubost and S. Zisler [10]. It can be realized by replacing a conventional wire monopole with a planar monopole, where the planar monopole is located above a ground plane and commonly fed using a coaxial probe. Up to now, many planar monopole antennas have been introduced due to their wideband performance. Several representative structures are shown in Fig.9, and these antennas achieve the impedance bandwidth ratio from 2:1 to more than 10:1. *i.e.*, Agrawall *et al.* [11] carried out a bandwidth comparison of several planar monopoles with various geometries, such as circular, elliptical, rectangular, and trapezoidal monopoles. The results show that the circular and elliptical monopoles exhibit much wider bandwidth performance than those of others, and both can obtain the impedance bandwidth ratio

**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..
