Compact and Digitally Controlled D-Band Vector Modulator for Next-Gen Radar Applications in 130 nm SiGe BiCMOS

Radar systems got very popular in sensing applications in the last two decades besides the traditional military sector. Nowadays, many applications favor multiple-input multiple-output (MIMO) radar over phased-array radar. Here, time-division multiplexing (TDM) and code-division multiplexing (CDM), like a phase-modulated continuous wave (PMCW), are well-known techniques. However, every method needs special components on the MMIC. In this article, a <inline-formula><tex-math notation="LaTeX">$\text{125}\,\text{GHz}$</tex-math></inline-formula> vector modulator (VM) circuit is presented, which can operate as a switchable amplifier in TDM systems, as a binary-phase modulator in CDM systems, and as a phase-shifter in phased-array systems. Based on simulations and <inline-formula><tex-math notation="LaTeX">$S$</tex-math></inline-formula>-parameter measurements, the VM itself and the three different operating modes are analyzed. We also present a technique to separate coupler imperfections from the <inline-formula><tex-math notation="LaTeX">$S$</tex-math></inline-formula>-parameter measurements to analyze the VM separately. We designed the VM with the B11HFC silicon-germanium technology (<inline-formula><tex-math notation="LaTeX">$f_{t} / f_{max} = 250/370\, \text{GHz}$</tex-math></inline-formula>), using both HBTs (heterojunction bipolar transistors) and CMOS transistors. Inside the VM, two cross-connected power amplifiers (PAs) are fed by an in-phase (I), and two cross-connected PAs are fed by a quadrature-phase (Q) signal. The four PAs are controlled by a 4-bit interface to switch them on or off, thus generating output signals in the range of <inline-formula><tex-math notation="LaTeX">$0^\circ$</tex-math></inline-formula> to <inline-formula><tex-math notation="LaTeX">$360^\circ$</tex-math></inline-formula>.