A High-Precision Ultra-Broadband Quadrature Generation at Millimeter-Wave Frequencies

In this paper, a high-precision ultra-broadband quadrature signal generator for millimeter-wave frequency band is proposed. The structure of cascade directional couplers is adopted, and the transmission line and equivalent lumped model are used to connect couplers. The proposed structure and the transmission line and lumped model are analyzed using the S-parameter matrix, and the corresponding theoretical formulas are provided. The simulation prototype is constructed using the 28 nm CMOS technology, so it can be integrated into a small area chip. In the frequency range of 50-150 GHz, the measured S11 and S22 of the proposed design are both less than -10 dB, while the gain mismatch is less than 1 dB, and the phase mismatch is fewer than five degrees. Compared to the traditional quarter wavelength directional coupler, the proposed generator can guarantee a high-precision quadrature output signal when the output load changes while reducing the gain and phase mismatches. In the same frequency range, the image rejection ratio is over 20 dB. The whole size of the proposed high-precision ultra-broadband quadrature coupler (HPUBC) is 260 um $\times 450$ um. The proposed designs are verified by 3D electromagnetic simulation.