PET-Based Instant Inkjet-Printed 4 x 4 Butler Matrix Beamforming Network

In this paper, a novel planar Butler matrix (BM) utilizing only 3 dB hybrid couplers and a crossover are implemented using a low-cost silver-nano inkjet printing technique. Unlike in the conventional design of BM where a phase shifter is required, this novel design does not need a phase shifter to be implemented. However, the use of delicate substrates like polyethylene terephthalate (PET) in the design makes it unique. This is not possible with the conventional thermal curing process, as PET substrate cannot be subjected to an excessively feverish temperature. The results obtained show good return loss and transmission coefficients better than 26.10 and 23.54 dB, respectively, at the center frequency. Similarly, an amplitude imbalance of less than 2.4 dB with phase mismatch within +/- 0.25 degrees is achieved at the center frequency. The BM has a -10 dB bandwidth of 24.79% with a beam pattern produced at +13 degrees , -40 degrees, +40 degrees, and -13 degrees when ports 1-4 of the BM are energized.