Coherent power combination in multi-element sub-THz RTD oscillators coupled with MIM stub structure

We observed coherent power combination in 3- and 6-element oscillator array using resonant tunneling diodes coupled through planar circuits in sub-THz range. InGaAs/AlAs resonant tunneling diode oscillators with slot antennas are arranged collinearly on the same InP wafer, and coupled with each other through a metal-insulator-metal stub structure. In 3-element array, a single peak at 293 GHz with the output power of 13 muW was observed due to the mutual injection locking. Because the individual output power of each element is around 2-3 muW at most due to relatively low current density for THz and sub-THz oscillators, the output power of the array is much higher than the sum of the powers of each element, indicating coherent power combining. Experimental results are explained with the theoretical analysis of the effect of multi-element oscillator arrays.