A 7 8 Butler Matrix-Fed Multibeam Antenna Based on Substrate Integrated Waveguide Technology

In this letter, a novel 7 x 8 Butler matrix (BM) operating in the millimeter-wave band is presented. It is composed of a 3x4 BM, two 3x4-like BM, two phase shifters and two couplers, achieving equal amplitude output distribution and seven output phase differences (0 degrees, +/- 45 degrees, +/- 90 degrees, +/- 135 degrees). The proposed 7 x 8 BM can be realized by dual-layer substrate integrated waveguide structure easily, which is difficult formerging the two central ports of the traditional 8x8 BM. To verify the concept, a multibeam antenna fed by the proposedBMis designed and fabricated, achieving seven beams in the frequency range of 26.5-29.5 GHz. Compared with counterparts, the proposed antenna features compact size, broadside radiation, and relatively wide bandwidth.