Fixed physical length spoof surface plasmon polariton delay lines for a 2-bit phase shifter

A novel and promising candidate for the main building block of the 2-bit, 360 degrees phase shifters, namely, the fixed physical length, spoof surface plasmon polariton (sSPP) delay lines, is presented. An analytical approach is used for the calculation of the electrical lengths of the sSPP delay lines for what we believe is the first time. The delay lines use the idea of changing the corrugation depths of the sSPP waveguides (WCs), which allows us to obtain different electrical lengths without changing the physical length of the WG. The special design of the coplanar WG to sSPP WG transitions maintains the mode conversion under different phase states and minimizes the insertion and return losses for all phase states. The measurement results of the fabricated delay lines for four different phase states show good agreement with the simulations, having average and maximum phase errors of 1.7% and 3.6% with respect to the ideal phase states, 0.5% and 1.2% with respect to the simulations, and average and maximum insertion losses of -0.26 and -0.43 dB at 7.15 GHz, respectively. The proposed designs, to the best of our knowledge, are the first instances of the sSPP delay lines for low-loss, high-accuracy, compact phase shifters with real-life design constraints. (C) 2020 Optical Society of America