44 IEEE Antennas and Propagation Magazine, Vol. 54, No. 6, December 2012 Compact Wideband Direction-Finding Antenna M. C. Bailey 1 , T. G. Campbell 1 , C. J. Reddy 1 , R. L. Kellogg 2 , and Phuc Nguyen 3 1 Applied EM 144 Research Drive, Hampton, VA 23666 USA E-mail: m.c.bailey@appliedem.com; tom_campbell@appliedem.com; cjreddy@appliedem.com 2 Argon ST 12701 Fair Lakes Circle, Fairfax, VA 22033 USA E-mail: Robert.L.Kellogg@Boeing.com 3 Imaging and EW Sensors Program Office (PMS435) 614 Sicard Street, SE, Washington Navy Yard, DC 20376-7027 USA E-mail: phuc.n.nguyen@navy.mil Abstract In this paper, we describe a compact, wideband (70-3000 MHz), and high-gain antenna technology that can replace multiple types of antennas currently in use to cover the wide frequency band. The design eliminates the frequency-band breaks associated with the use of multiple arrays. The wideband direction-finding array (with a height of 5.5 in and a diameter of 15.5 in) is the result of end-to-end integration of the antenna array with the receivers presently used, or to be used, on platforms of interest. Development of the wide-bandwidth direction-finding antenna array is described, and computer simulations of its performance are presented. The wideband direction-finding antenna system has been verified on the receiver manufacturer’s outdoor test range. Keywords: Antennas; spiral antennas; broadband antennas; direction finding; correlation; antenna arrays 1. Introduction T he basic task of a radio direction fnder is to estimate the line-of-bearing (LoB) or angle-of-arrival (AoA) for a signal by measuring and evaluating the received signal. There are a number of methods for accomplishing this. They range from simple mechanical rotation of an antenna with a highly directional beam to sophisticated signal processing of signals received from multiple antennas. Obtaining an estimate of the line-of-bearing or angle-of-arrival over a wide frequency band is limited by (1) the method of analyzing the received signal from multiple antennas, and (2) the bandwidth of the individ- ual antennas. The primary purpose of this paper is to report on the development of a wide-bandwidth antenna array and its performance when used in a direction-fnding system. Only a brief discussion and description of direction-fnding systems will therefore be presented. 2. Direction-Finding Techniques Although the purpose of this paper is to describe an antenna array developed for wideband direction fnding, we begin with a cursory description of two basic methods of direction fnding, in order to demonstrate that the signal proc- essing plays an integral role in wideband direction fnding. The frst method is referred to as phase interferometry. The Watson-Watt and the Butler matrix approaches are common commercial systems based upon this frst method. The second method is referred to as correlative vector direction fnding (CVDF), which includes the family of algorithms from Bartlett correlation to MUSIC. These techniques involve a comparison of the measured signals with those of a known antenna system at a given incidence angle. We demonstrate a basic comparison of the two techniques as applied to wide-bandwidth direction fnding. We restrict our discussion to uniformly spaced circular ISSN 1045-9243/2012/$26 ©2012 IEEE