Reconfigurable and Highly-Miniaturized Low-Noise Amplifiers Based on Tunable Filtering Loads

This article reports on new types of reconfigurable and multifunctional low-noise amplifier filters (LNAF) for sub-6 GHz New Radio (NR) S-band applications. The proposed LNAF concepts are based on complex-terminated bandpass filter (BPF)-type output matching networks that facilitate quasi-elliptic transfer functions that can be tuned in terms of bandwidth (BW), center frequency ( $f_{cen}$ ), and can be intrinsically switched-off. To validate the proposed approaches, four proof-of-concept LNAF prototypes were realized by means of static and varactor-loaded microstrip resonators. Further size reduction is introduced in one of the prototypes through a co-designed filtering-based LNAF using tapped line resonators. For practical validation purposes, four alternative prototypes, namely LNAF I-IV, were manufactured and tested. They exhibit the following features: i) LNAF I: passband mode with $f_{cen}$ tuning: 2.64-3.25 GHz, fractional bandwidth (FBW) tuning: 11.9-31.6% (2.65:1), gain: 16.5 dB, noise figure (NF) <0.86 dB, third order output intercept point (OIP3): 10.87 dBm, and an intrinsically switched-off mode with isolation >39 dB; ii) LNAF II: passband mode with $f_{cen}$ tuning: 3.61-3.82 GHz, FBW: 6.3%, gain: 10.2-12.6 dB, NF <0.95 dB, OIP $3\gt 11.15$ dB, and an intrinsically switched-off mode with isolation >37.07 dB; iii) LNAF III: passband mode with $f_{cen}$ : 3.99 GHz, FBW: 6.48%, gain: 14.3 dB, NF <1.1 dB, OIP $3\gt 13.2$ dB, and footprint reduction of 49% with respect to LNAF II. A 2-stage LNAF prototype, named LNAF IV, is implemented to achieve higher gain of 22.6 dB and NF <1.1 dB at 3.98 GHz with 15% less area than LNAF II.