A $Ka$ -Band Broadband Power Amplifier With Transformer-Based Lossy Magnetically Coupled Resonator Network: Analysis and Design

This article presents the design and theoretical analysis of a broadband power amplifier (PA) using the transformer-based lossy magnetically coupled resonator (MCR) network. The frequency-independent transformer loss coefficient
${\alpha}$
and its detailed extraction procedure are obtained by analyzing the double-
${\pi}$
model of the inductor. Theoretical derivation shows that for lossy transformers, broadband matching without gain ripple can only be achieved by using asymmetrical MCRs. Based on this, four new mismatch parameters
${m}$
,
${n}$
,
${\omega_0}$
, and
${Q_0}$
of asymmetrical MCRs are introduced to facilitate the analysis. A straightforward design flow based on the asymmetrical lossy MCRs to realize broadband matching including output matching and input/interstage matching is provided, which can effectively guide the implementation of broadband PAs. To demonstrate the proposed design methodology, a
$Ka$
-band broadband PA is implemented in a 65-nm CMOS process. The measurement results show that the proposed PA achieves 30.9% peak power added efficiency (
$\text{PAE}_\text{max}$
), 17.9-dBm saturated output power (
$P_\text{sat}$
), and 16.4-dBm output 1-dB compression point (
$\text{OP}_\text{1\,dB}$
). The measured 3-dB gain bandwidth ranges from 20 to 42 GHz, corresponding to a fractional bandwidth (FBW) of 71%, covering the entire
$Ka$
-band. The PA demonstrates a flat gain with an in-band gain ripple of only 0.25 dB. To the best of the authors’ knowledge, this is the first article that thoroughly analyzes the lossy MCR matching theory.