A Novel Interference-Based Approach for Harmonic Suppression in Microwave Frequency Doublers

This paper presents a novel doubler module designed for frequency doubler applications. The module is designed in Keysight ADS software and fabricated on FR4 substrate (with dielectric constant, $\varepsilon_{\mathrm{r}}=4.6$) to achieve the harmonic suppression of f
0
& $3 \mathrm{f}_{0}$ at 2.29 GHz and 6.87 GHz, respectively, while effectively extracting $2 \mathrm{f}_{0}$ at 4.58 GHz by a special means of constructive and destructive interference of the signal. The mathematical analysis demonstrates an impressive (more than 60 dB) suppression of the fundamental and third harmonics. The proposed structure is subjected to simulation, fabrication, and measurement along with a typical harmonic generator to validate its concept. BFP840ESD transistor is used to design the non-linear module(harmonic generator), and the doubler module is integrated along with the non-linear harmonic generator to assess its performance.