24.3 A 200-to-350GHz SiGe BiCMOS Frequency Doubler with Slotline-Based Mode-Decoupling Harmonic-Tuning Technique Achieving 1.1-to-4.7dBm Output Power

Silicon-based ultra-broadband terahertz (THz) generation has attracted growing interest in recent years, as it provides a low-cost and high-integration solution for high-resolution radar, hyperspectral imaging, and rotational spectroscopy systems [1]. However, direct THz-signal generation with an extensive bandwidth and high output power
$(\mathsf{P}_{\mathsf{out}})$
remains challenging due to the degraded tuning range of varactors and the limited
$\mathsf{f}_{\mathsf{T}}/\mathsf{f}_{\mathsf{max}}$
of transistors. A practical alternative is frequency multiplication, which depends on the nonlinearity of devices and extracts the output high-order harmonics, thereby extending the bandwidth of the input signal. Prior broadband THz-frequency multipliers, whether employing distributed architecture or not, were merely based on the broadband input fundamental and output harmonic matching [1–5]. Part of them have considered the input high-order harmonics, but simply added harmonic reflectors to improve
$\mathsf{P}_{\mathsf{out}}$
and efficiency at the cost of bandwidth reduction [2]. However, any neglect or underuse of the high-order harmonics leaked or generated at the input of the nonlinear device limits the THz-frequency multiplication performance, especially the
$\mathsf{P}_{\mathsf{out}}$
bandwidth.