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 125 GHz 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 S-parameter measurements, the VM itself and the three different operating modes are analyzed. We also present a technique to separate coupler imperfections from the S-parameter measurements to analyze the VM separately. We designed the VM with the B11HFC silicon-germanium technology (f(t) / f(max) = 250/370 GHz), 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 0 degrees to 360 degrees.

Automated summary

Radar systems, especially multiple-input multiple-output (MIMO) radar, have become increasingly popular in sensing applications. This article presents a 125 GHz vector modulator (VM) circuit that can serve different functions in different systems. The VM's performance and a technique to separate coupler imperfections from S-parameter measurements are analyzed through simulations and measurements.