UWB Planar Bulbous Dipole Antennas Hans Gregory Schantz *1 (h.schantz@ieee.org); William Beeler (bill.beeler@timedomain.com); David Dickson 2 (david.dickson@alereon.com) Time Domain Corporation; 7057 Old Madison Pike; Huntsville, AL 35806 1 Current Address: Next-RF, Inc.; 515 Sparkman Drive; Huntsville, AL 35816 2 Current Address: Alereon, Inc.;7600 North Capital of Texas Highway, Bldg. C, Ste. 200; Austin, TX 78731 ABSTRACT This paper presents experimental results for a variety of planar bulbous UWB antennas including elliptical and ovoid shapes. This paper further considers the shapes and assesses which shapes yield the best combination of size and performance. 1. INTRODUCTION Ever since the 1890’s when Oliver Lodge demonstrated that biconical antennas and bow tie antennas worked comparably well in RF systems, antenna designers have known that planar cross- sections of solid antennas are a viable antenna design option [1]. That planar antennas can make good ultra-wideband (UWB) antenna elements not obvious, however. “Fatter is better,” is a key principle of UWB antenna design. This principle has been understood empirically since the pioneering antenna designs of Nils Lindenblad in the late 1930’s and was made explicit by John C. Slater in the 1940’s [2, 3]. These “bulbous” antennas are characterized by smoothly varying generally spheroidal, ellipsoidal, or ovoidal type shapes. One of us has addressed the history of the development of these antennas at length elsewhere [4-6]. That planar cross-sections of bulbous antennas might yield good UWB antenna elements has only become evident in recent years. In the early 1990’s, Mike Thomas and Ronald I. Wolfson introduced planar UWB dipoles with circular elements [7]. But circular elements hardly exhaust the possibilities for planar bulbous UWB antennas. The present paper considers a variety of planar bulbous UWB antennas including elliptical and ovoidal elements. This paper also present experimental gain results and evaluates the performance of these antennas versus size to determine which yields the best performance in the most compact form factor. 2. PLANAR BULBOUS UWB ANTENNAS This paper presents results for four specific kinds of planar ovoidal antennas: “Fat” elliptical dipoles: antennas with elliptical elements whose semi-minor axes are co-linear. Figure 1(a) shows a matched pair of fat elliptical dipoles. “Skinny” elliptical dipoles: antennas with elliptical elements whose semi-major axes are co- linear. Figure 1(b) shows a matched pair of skinny elliptical dipoles. “Lilliputian” ovoidal dipoles: antennas with ovoidal elements fed from the skinny end. These antennas are named after the little people described in Jonathan Swift’s tale, Gulliver’s Travels, who ate their eggs from the small end. Figure 1(c) shows a matched pair of Lilliputian ovoidal dipoles. “Blefuscudian” ovoidal dipoles: antennas with ovoidal elements fed from the fat end. These antennas are named after the hereditary rivals of the Lilliputians who ate their eggs from the fat end. Figure 1(d) shows a matched pair of Blefuscudian ovoidal dipoles. Figure 1 includes two further planar bulbous UWB antennas: Asymmetric Circle Dipoles: antennas with circular elements of unequal sizes. The element asymmetry allows the frequency range to be extended somewhat beyond that of comparable antennas with symmetric elements. Figure 1(e) shows asymmetric circle dipoles. Truncated Elliptical Dipoles: elliptical element antennas truncated at their foci. This design achieves a more compact size than the standard skinny planar elliptical dipoles of Figure 1(b) at the cost of increased return loss, worse matching, and narrower bandwidth Figure 1(f) shows truncated elliptical dipoles. 0-7803-8883-6/05/$20.00 ©2005 IEEE