This article presents a new broadband three-way series Doherty power amplifier (DPA) topology, which enables a broadband output power back-off (OBO) efficiency enhancement of up to 10 dB or higher. The proposed DPA topology achieves Doherty load modulation and three-way power combining through a transformer, which requires only a low coupling factor, thus facilitating its implementation in double-sided PCBs or monolithic microwave integrated circuit (MMIC) processes. The design equations for the proposed DPA topology are proposed and analyzed in detail. A proof-of-concept PA at the 2.1–2.8 GHz band using commercial GaN transistors was designed and fabricated to validate the proposed concept. Within the operating frequency band, it achieves a saturated output power ($P_{\mathrm{sat}}$) of 44.5–46.5 dBm with a peak drain efficiency (DE) of 60–72%, and 43–52% DE at 10 dB OBO. Moreover, under a 20 MHz long-term evolution (LTE)-modulated signal, the PA demonstrates a 36.8–37.5 dBm average output power ($P_{avg}$) and 47–53% average drain efficiency (${DE}_{avg}$). Notably, the adjacent channel leakage ratio (ACLR) is as low as −35–−28.2 dBc without any digital predistortion (DPD).

This letter presents a reconfigurable series Doherty power amplifier (PA) that supports dual-mode operation with 6- and 12-dB power back-off (PBO) by adjusting the dc bias voltages of the sub-PAs. As a proof of concept, a prototype PA operating in the E-band was fabricated using 40-nm CMOS technology. The PA exhibits a measured $P_{\text {sat}}$ of 15.2–16.5 dBm and a peak power-added efficiency (PAE) of 13.5%–16.4% across 72–82 GHz. In Mode-1, it demonstrates a 6-dB back-off PAE of 8.7%–11.7%. In Mode-2, it achieves a 12-dB back-off PAE of 5.2%–7.5%, providing a maximum efficiency enhancement of up to $1.84\times $ over an ideal Class-B PA. For a 6-Gb/s 64-QAM signal, the PA delivers $P_{\text {avg}}$ of 8.9/8.8 dBm and $\text {PAE}_{\text {avg}}$ of 9.0%/9.8% with an error vector magnitude ( $\text {EVM}_{\text {rms}}$ ) of −25.4/−24.8 dB in Mode-1/Mode-2, respectively.

Benzocyclobutene (BCB) resins have aroused much interest because of their excellent physical and chemical properties. Unfortunately the temperature required to induce cross-linking in typical BCBs is higher than 250°C, which restricts their applications. In this study, a novel cyano-containing BCB-terminated imide monomer was synthesized through the reaction of 1-cyano-5-amino-benzocyclobutene with 4,4′-oxydiphthalic anhydride. This monomer allows a 50–100°C lower curing temperature in comparison with typical BCBs, and it is highly soluble in various solvents and can easily convert to cured film at 150–200°C. Because of the presence of rigid imide group and strong polar cyano group, the cured film exhibits excellent mechanical strength with tensile strength up to 87.8 MPa, high glass transition temperature up to 350°C, low coefficient of thermal expansion (36.9 ppm K⁻¹), and outstanding planarity with the average surface roughness as low as 0.26 nm.

This article presents an ultracompact, wideband, bidirectional, switchless power amplifier–low noise amplifier (PA-LNA) for W-band wireless applications. The proposed design employs a single-signal-path architecture incorporating highly efficient 8-shaped transformers and tri-coil baluns, which effectively reduce electromagnetic (EM) cross-coupling and insertion loss while enhancing linearity within a compact footprint. The tri-coil baluns provide high isolation (ISO) and ultralow coupling between the PA and LNA interstage matching networks, thereby enabling independent design and optimization for each amplifier. The prototype PA-LNA is fabricated in a 40-nm bulk CMOS LP process, achieving a core area of only 0.1 mm². In the PA mode, the circuit exhibits a measured 3-dB bandwidth of 79–92 GHz, a saturated output power ( ${P} _{\text {sat}}$ ) of 13.7 dBm, an output 1-dB compression point (OP ${}_{1{\,}\text {dB}}$ ) of 8.7 dBm, and a maximum power-added efficiency (PAE) of 9.5%. In the LNA mode, it achieves a noise figure (NF) below 9 dB across the 3-dB bandwidth of 86–98 GHz, with a minimum NF of 8.2 dB.