The generation of high-quality wideband frequency sweeps presents a significant challenge, particularly in modern telecommunication, radar, and measurement systems where miniaturization is paramount. While phase-locked loops (PLLs) have become the dominant technique for signal generation, their application in broadband sweeps necessitates fractional-N operation. This, in turn, degrades phase noise and introduces unwanted spurs. This paper proposes a novel approach for broadband signal generation. By cascading two PLLs and utilizing a coaxial resonator, we achieve a high-performance oscillator that operates without the excessive fractional spurs, maintaining their level below -80 dBc across the entire frequency band. The prototype demonstrates non-degraded phase noise performance, reaching -102 dBc/Hz at 100 kHz offset and -121 dBc/Hz at 1 MHz offset for signal at 10 GHz. Despite significant frequency jumps, our design achieves lock times below 41 µs. These results, supported by theoretical analysis, validate the proposed method's effectiveness in generating low-noise broadband frequency sweeps, ideal for local oscillator applications.

With a recent advance in photonic integrated circuits (PIC), a new field of frequency agile coherent radar systems is being thoroughly researched. In contrast to the traditional all-electronics radiofrequency (RF) radar techniques, a fully photonics-based system does not suffer from bandwidth limitation and noise degradation when switching from S to X or K-band and can achieve excellent phase noise even at frequencies exceeding 20 GHz. However, recent state-of-the-art PICs still exhibit high processing losses in the optical domain, which must be addressed in the electrical part of the RF domain. This study presents a comprehensive analysis of the challenges in designing RF front-end amplifier chains for microwave photonic radars, particularly in maintaining stability, minimizing noise, and reducing intermodulation distortion. Furthermore, a comprehensive demonstration of the RF front-end, encompassing both the optical generation of RF signals and experimental measurements of a rotor blade's Doppler fingerprint to validate the system's performance is presented.