Design of Non-Uniformly Excited Linear Slot Arrays Fed by Coplanar Waveguide

Abstract

Slot dipole antennas fed by coplanar waveguide (CPW) have a number of appealing characteristics that include relatively low feed line dispersion and losses at millimeter-wave frequencies, ease of integration with circuit components due to the uniplanar configuration, and considerably wider impedance bandwidth than microstrip patch antennas on comparable substrates, e.g., (Miao et al., 2000). In the sub-millimeter and millimeter-wave ranges, CPW-fed slots have been used to feed dielectric lens antennas (Focardi et al., 2002); arrays of CPW-fed slots are also expected to be used for space applications (Neto et al., 2003). While a variety of CPW-fed slot arrays have been reported (see section 3), rigorous design procedures for CPW-fed slot arrays that incorporate the effects of element interactions in the form of mutual coupling have only rarely been presented (Huang et al., 1999; Jacobs & Joubert, 2009b). An iterative design typically involves the a priori generation of selfadmittance data for representative slot dimensions, and requires the calculation of mutual coupling between all possible slot pairs in the array; this is especially pertinent if a nonuniform aperture distribution aimed at achieving reduced sidelobe levels is to be realized. In this chapter an overview of the current state-of-the-art in the design of non-uniform linear CPW-fed antennas, as well as its subsidiary calculations, is presented. In section 2, the field distribution in an isolated CPW-fed is shown; this is important information for the calculation of mutual coupling. Section 3 focuses on the calculation of mutual coupling using a reciprocity-based paradigm. This is done in the context of two important practical cases. The first involves mutual coupling between slots on electrically thin substrates, where a simplified yet accurate method can be used that obviates use of the substrate Green’s function. Arrays of slots on such substrates exhibit bi-directional radiation. The second involves an extended reciprocity approach for calculating the mutual admittance between slots on a conductor-backed two-layer substrate, a configuration that would be useful when unidirectional radiation is required. Section 4 gives details of two types of CPW-fed linear array design. First, the iterative design using an approximate procedure of a uniform array on a conductor-backed two-layer substrate is summarized; measured results are presented. The procedure doesn’t require the explicit calculation of the mutual admittance between 25