Micro-coaxial lines for active hybrid-monolithic circuits

This paper discusses fundamental properties of rectangular micro-coaxial lines fabricated in the PolyStrata™ process for broadband applications from 2–20 GHz. The possible impedance ranges for coaxial lines implemented with both five and eleven Cu layers are discussed and compared with measured results for the lowest impedance (8Ω) line. Power handling and thermal properties of these miniature lines are analyzed and measured. A 50Ω line with outer conductor cross-section of 600µm by 400µm is experimentally shown to handle 53W at 2:5GHz with a 10% duty cycle. Integration with active components is investigated and a 1–10GHz measurement of a GaN 50 MMIC amplifier shows minimal performance degradation relative to on-wafer measurements.