Two-Dimensional Scanning Antenna Array Driven by Integrated Waveguide Phase Shifter

A Butler matrix-fed two-dimensional (2-D) scan linearly polarized 2 × 2 microstrip ring antenna array (MRAA) is proposed and validated in low-cost substrate integrated waveguide (SIW) technology for Ka-band applications. The highly efficient, compact, and passive beam forming network (BFN) consists of SIW cruciform couplers as coupling unit, and its special topology is well adapted for feeding planar arrays. The wideband and high radiation efficiency antenna elements are aperture-coupled through slots etched on the top of a high permittivity SIW feed substrate. Such four antenna elements are used to construct 2 × 2 MRAA and to form four fixed beams, one in each quadrant at an elevation angle of 20 ° from the broad side array axis. A triangular grid arrangement is chosen to avoid grating lobes in the visible space. A 50- Ω grounded coplanar waveguide (GCPW) to SIW transition is used to avoid spurious input feed radiation loss. The array is measured to exhibit 3-dB beam width of 30 ° in both of the orthogonal planes, radiation efficiency of 70% for each port, and stable radiation pattern bandwidth of 7.6% at 26.5 GHz. The physical size of the demonstrated 2 × 2 array is 2.86λ_o×2.86λ_o×0.22λ_o.