Optimization-Based Behavioral Modeling of Mixers for Frequency Comb OFDM Radar Processing

Abstract

This paper presents an optimization-based behavioral model for mixers driven by multi-tone local oscillator (LO) signals, considered specifically for frequency comb orthogonal frequency-division multiplexing radar applications. Unlike traditional models, the proposed approach is designed and tested for multi-tone LO excitations. The model uses polynomial nonlinearities for both intermediate frequency and LO ports, supported by spectrum-domain fitting that selectively emphasizes strong intermodulation products. In addition, a polynomial block is introduced to capture input power-dependent phase nonlinearity. The approach is validated using circuit-level simulations and supported by measurements. Radar processing results show the model replicates distortive effects in simulations. The proposed model enables rapid system-level performance estimations and waveform optimization, replacing computationally expensive circuit-level simulations.

Figures (6)

• Figure 1: Mixer schematic including bias circuitry. The resistors $R_{1-6}$ function as termination resistors, creating differential virtual-ground nodes at the connections of $R_{1}$ and $R_2$, $R_{3}$ and $R_4$, and at $V_\mathrm{cc}$.
• Figure 2: Mixer micrograph, total size (including pads): $\qty{900}{\micro\meter}\times\qty{900}{\micro\meter}$, core area $\qty{100}{\micro\meter}\times\qty{180}{\micro\meter}$ highlighted in red.
• Figure 3: System model of the considered single-mixer multi-LO architecture.
• Figure 4: ADS () and measurement () comparison for fundamental mix ($\mathrm{f_{IF,1}+f_{LO}}$) in (a) for IM3 ($\mathrm{2f_{IF,1}-f_{IF,2}+f_{LO}}$) (), () in (b). $\mathrm{P}_{\qty{1}{dB}}$ for each (), () is indicated in (a) respectively.
• Figure 5: AM-AM curve of fundamental mix (${f_\mathrm{IF1}+f_\mathrm{LO1}}$) for ADS () and multibox model () with ($\mathrm{P}_{\qty{1}{dB}}$) for ADS () and multibox () indicated. IM3 (${2f_\mathrm{IF1}-f_\mathrm{IF2}+f_\mathrm{LO1}}$) AM-AM results for ADS () and multibox () are shown in (b). The spectrums for ADS () and multibox model () for 4--14 are shown in (c).