Design and Analysis of Ka-Band Power Amplifier With Sandwiched-Coupler-Balun and Folded-T-Line Power Combiner

This article presents a two-way current-combining
Ka
-band power amplifier (PA) in a 130-nm SiGe BiCMOS process. A two-way power-combining network composed of sandwiched-coupler-balun (SCB) and folded-T-line (also known as meander line) is utilized to realize low-loss broadband large-signal impedance matching under a high impedance transformation ratio. Parallel peaking inductance is also employed in the cascode amplifiers to improve the power gain and efficiency, and the quality factor (
Q
factor) of the peaking inductance is considered during the design process. The symmetrical interstage matching network (ISMN) between the driver and two output stages (OAs) is utilized to improve large-signal performance under broadband operation. The measurement result shows that the proposed PA has a peak small-signal gain of 30.5 dB at 34.8 GHz and a 3-dB bandwidth of 10 GHz (31–41 GHz). At 35 GHz, the PA achieves a 23.5-dBm
P
sat with 33.9% peak power added efficiency (PAE) and 22.2-dBm OP1dB. Across 31–39 GHz, the
P
sat and peak PAE of the PA remain 22.7–23.8 dBm and 24.5%–33.9%, respectively. For modulated signal tests, this PA demonstrates
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25.4-dB rms error vector magnitude (EVM) and
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25.3-dBc adjacent-channel power leakage ratio (ACLR) at 35/37/39 GHz with a 250-MSym/s 64-quadratic-amplitude modulation (QAM) signal, and it also demonstrates
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25.3-dB rms EVM and
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27.1-dBc ACLR at 35/37/39 GHz with a 400-MSym/s 64-QAM signal.