Phase noise and frequency stability of Ka-band harmonic dielectric resonator oscillators

Harmonic dielectric resonator oscillators (HDROs) designed for 25 and 27 GHz were fabricated using a two-stage GaAs MESFET amplifier and a passive two-port resonant structure (RS). The RS consists of a metal cavity, an X-band ceramic dielectric resonator, 50 Ω microstrip transmission lines, and a support for elevating the dielectric resonator inside the cavity. The electromagnetic behavior of the RS was analyzed using Hewlett-Packard´s High Frequency Structure Simulator (HFSS). The simulator was used to calculate the electromagnetic fields and S-parameters of the passive RS. Solutions were obtained for the dominant mode. The predicted computer results were then compared to measured data. The material properties of dielectric resonators were obtained from two different vendors and evaluated for low-noise microwave oscillator applications. The important material properties for oscillator applications are the unloaded Q, the temperature coefficient, and the dielectric constant. Measured data for resonators from both vendors are presented. The measured phase noise levels at 27 GHz are a 15-20 dBc/Hz improvement over previously published results for DROs. The oscillator also demonstrated a superior frequency vs. temperature characteristic, over the temperature range ±55°C, of less than 40 ppm