Coupled-line-based millimeter-wave CMOS spiral power dividers with tapered TLs

We propose a power divider comprising of two parallel λ/4 coupled lines with a shared input signal line. An isolation resistor R is included to enhance the output-port reflection coefficients (S22 and S33) and the isolation between the output ports (S32 and S23). In theory, the power divider can achieve perfect input-port reflection coefficient (S11) and equal power coupling from the input to the outputs (i.e. S21 = S31). To achieve compact chip area, three prototyped power dividers with single-spiral- structure are designed and implemented. Tapered width from 8 to 3 μm is used at the output port transmission lines (TLs) (the first power divider) or the input port TL (the second and the third power dividers) to compensate for the single spiral structure for its non-ideality. This leads to enhancement of the reflection coefficients, and amplitude imbalance (AI) and phase difference (PD) of S21 and S31 of the power dividers. Prominent results are obtained. For instance, the second power divider (divider-2) occupies a chip area of 0.02 mm2 (i.e. 2.4 × 10–4λ02), one of the smallest normalized chip areas ever reported for millimeter-wave power dividers. At 33 GHz, divider-2 achieves decent S11 of −13.4 dB, S22 of −17.6 dB, S33 of −22.1 dB, S32 of −17.1 dB, S21 of − 4.68 dB, S31 of − 4.37 dB, AI of −0.31 dB, and PD of − 1.1°. The remarkable results of the power divider indicate that it is suitable for Ka-band communication systems.