Exceptional Points of Degeneracy in a Linear Array Oscillator with Gain and Loss Balance

We demonstrate a new paradigm for dispersion engineering in coupled transmission lines (CTLs) based on the occurrence of an exceptional point of degeneracy (EPD), which represent coalescence of eigenmodes. We experimentally verify the existence of the EPD through dispersion measurements in microstrip-based CTLs at microwave frequencies. We propose the "gain and loss balance" regime as a route for recovering the EPD in the presence of radiation losses hence enabling a new class of coherent EPD-based single-frequency radiating oscillators. This versatile EPD concept is promising in applications requiring high power efficiency oscillators and high radiation efficiency.