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 • to 360 • .

We study the reversibility of skew Hurwitz series at zero as a generalization of an αrigid ring, introducing the concept of skew Hurwitz reversibility. A ring R is called skew Hurwitz reversible (SH-reversible, for short), if the skew Hurwitz series ring (HR, α) is reversible i.e. whenever skew Hurwitz series f, g ∈ (HR, α) satisfy f g = 0, then gf = 0. We examine some characterizations and extensions of SH-reversible rings in relation with several ring theoretic properties which have roles in ring theory.