Coherent emission from a linear array of RTDs

We report coherent emission from a linear array of resonant tunneling diodes (RTDs), each embedded in a slot antenna. The line array consists of 11 RTD elements. The RTD array shows single-frequency oscillation, which is an indication of coherent coupling of the RTDs. The emission frequency features two regimes: a low-frequency regime, where the odd mode will oscillate (the phase of neighboring RTDs are opposite); a highfrequency regime, where the even mode will oscillate (the phase of neighboring RTDs are the same). Which of the two regimes dominates is found to depend on the oscillation frequency of the RTDs.