A low-cost directional log periodic log spiral antenna

Abstract

The Square Kilometer Array (SKA) derives its name from its total aperture area, predominately achieved by thousands of parabolic dishes, each with an antenna feed situated at its focal point. The type of antenna feed selected for SKA operation in the 1 GHz to 10 GHz frequency range, referred to as a Wide Band Single Pixel Feed (WB+SPF) [1], has drawn increasing attention. This paper introduces a new WB+SPF to meet SKA scientific demands while also providing a cost-effective solution. The wide bandwidth of this new antenna is achieved by employing frequency independent (FI) design principles for the development of a log periodic (LP) antenna [2]. A basic adherence to FI principles can be seen in several of the antennas currently proposed as WB+SPF solutions for the SKA, including the Allen Telescope Array (ATA) feed [3], the Quasi-Self-Complementary (QSC) feed [4], and the Eleven feed [5]. These antennas efficiently illuminate the radio dish with a single main lobe, ruling out entirely planar FI antennas, which generate two radiation lobes orthogonal to the plane of the antenna. High sensitivity requirements prohibit the 3 dB power loss that would result from attenuating one of the lobes with an absorption cavity, as is often done for directional FI antennas. Scaling the LP elements into three-dimensional space, potentially over a ground plane [6], is the present method used for directional LP antennas. We instead propose confining these often complex LP elements into a single plane, while the ground “plane” takes on a three dimensional form. Planar LP patterns permit low-cost implementations, including PCB and water jet cutting technology, without requiring the introduction of a complicated scaffolding to support the LP elements in 3-D. Additionally, various technologies such as metal spinning, can cost-effectively shape the ground “plane” into a 3-D structure. This low-cost WB+SPF solution would scale well in the implementation of the thousands of antenna feeds that the SKA demands. We also introduce a previously unreported LP design: the log periodic log spiral (LPLS) antenna.