Normal-mode, Logarithmic, Ultra-wideband Tape Helix

Abstract

The ultra-wideband (UWB) technology is of current interest in both academics and industry. UWB provides a potential solution to the frequency shortage issue and offers a significant increase in data-throughput. In addition, the UWB technology can be used for realizing ubiquitous network environments [1, 2]. For antennas to support UWB communications, various planar, monopole-like UWB antennas have been proposed as shown in Fig. 1. The antennas include monopoles of rectangular shape (Fig 1a) [3-4], an inverted triangular form similar to the bow-tie dipole (Fig. 1b) [5], a triangular form (Fig. 1c) [6], a round disk (Fig. 1d) [7], elliptical disk (Fig. 1e) [8], a half-disk (Fig. 1f) [9], and inverted cone with holes (Fig.1g) [10]. The antennas are shown in monopole form, but they can also be configured as balanced antennas or used with small ground planes parallel to the antenna. Typically, the ratio of height-to-width of these antennas is in the range of 2 to 1. However, the footprint for some portable UWB applications, such as notebook computers, cell phones, and MP3 players, requires a higher ratio, making the width a more critical specification than height. To meet this need, several sample structures were constructed in a rolled form to create UWB antennas with a higher ratio. The bi-arm rolled monopole (Fig. 1h) is created by wrapping the rectangular monopole to achieve about a 5.3:1 height-to-width ratio [11] and showing a good impulse response with a fast decayed ringing. The monopole with a twist (Fig. 1i) is created by wrapping the half of a triangular monopole to obtain about a 2:1 ratio [12]. However, the metal patterns of both antennas are not located on the surface of the cylinder with fixed radius, which poses a challenge when printed on flexible printed circuit boards or on thin film for mass production. In this paper, we investigate a logarithmic tape helix with equiangular width of Fig. 2. The metal pattern is located on the surface of the cylinder with fixed radius. Some experimental and simulation results in both time and frequency domains are provided to characterized the test antenna. The return loss and link impulse response are compared with a fat monopole of the same size.