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1. A Compact Single-Ended Common-Base Doherty PA in 90-nm BiCMOS With 37.3% Peak PAE for 5G Beamforming Arrays

   https://doi.org/10.1109/TMTT.2024.3432602  

   Ali_Mokri, Mohammad; Afshar, Emad; Aminul_Hoque, Md; Miraslani, Soodeh; Mirabbasi, Shahriar; Heo, Deukhyoun (January 2025, IEEE Transactions on Microwave Theory and Techniques)

   This article presents a back-off efficient power amplifier (PA) for mm-wave 5G and upcoming 6G beamforming phased array transceivers (PATs), incorporating advanced circuit designs and novel implementations in both passive and active components. Conventional back-off efficient PAs in the mm-wave frequency range occupy a large chip area, making it hard to fit them into PATs. To overcome this issue, we propose a compact back-off efficient Doherty PA (DPA) with a common base (CB) structure as the core of the PA and small low-loss passive elements. In addition, the proposed architecture moves the role of the input hybrid coupler to the interstage matching network while maintaining DPA functionality. The interstage matching provides the required phases for the main and auxiliary PAs, power division, and impedance matching. The PA prototype is fabricated in the GlobalFoundries 90-nm BiCMOS (9 HP) process. It achieves a peak gain of 20.4 dB at 28.45 GHz with a 1-dB bandwidth of 4.45 GHz. Under large-signal conditions, it archives >19.5-dBm Psat with >36% PAEsat. Its P1dB at 26, 28, and 30 GHz are 19.4, 19.3, and 19.3 dBm with 38.5%, 37.3%, and 36.8% PAE1 dB, respectively. In the 6-dB power back-off region, it reaches efficiencies of 29.1%, 31.1%, and 29.3% at 26, 28, and 30 GHz, respectively. When tested with the NR-FR2 test model at these frequencies, the PA achieves Pavg of 8.25, 8.45, and 8 dBm, and PAEavg of 13.9%, 14.5%, and 13.7% for a 400 M 1-CC 64-QAM signal, maintaining an rms error vector magnitude (EVMrms) of −25.8, −25.8, and −25.7 dB. In addition, in adjacent channel power ratio (ACPR) tests, the PA achieves −27, −26.2, and −30.8 dBc on the lower side and −28.4, −28.5, and −27.6 dBc on the higher side channels at 26, 28, and 30 GHz, respectivelyNot Available 

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2. Cosmology Large Angular Scale Surveyor (CLASS): pointing stability and beam measurements at 90, 150, and 220 GHz

   https://doi.org/10.1117/12.2630649  

   Datta, Rahul; Brewer, Michael K.; Denes Couto, Jullianna D.; Eimer, Joseph R.; Li, Yunyang; Xu, Zhilei; Appel, John W.; Bustos, Ricardo; Chuss, David; Cleary, Joseph; et al (August 2022, Proc. SPIE 12190, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XI)

   Zmuidzinas, Jonas; Gao, Jian-Rong (Ed.)

   The Cosmology Large Angular Scale Surveyor (CLASS) telescope array surveys 75% of the sky from the Atacama desert in Chile at frequency bands centered near 40, 90, 150, and 220 GHz. CLASS measures the largest-angular scale (θ ≳ 1 ° ) CMB polarization with the aim of constraining the tensor-to-scalar ratio, r, measuring the optical depth to reionization, τ , to near the cosmic variance limit, and more. The CLASS Q-band (40 GHz), W-band (90 GHz), and dichroic high frequency (150/220 GHz) telescopes have been observing since June 2016, May 2018, and September 2019, respectively. On-sky optical characterization of the 40 GHz instrument has been published. Here, we present preliminary on-sky measurements of the beams at 90, 150, and 220 GHz, and pointing stability of the 90 and 150/220 GHz telescopes. The average 90, 150, and 220 GHz beams measured from dedicated observations of Jupiter have full width at half maximum (FWHM) of 0.615±0.019° , 0.378±0.005° , and 0.266 ± 0.008° , respectively. Telescope pointing variations are within a few % of the beam FWHM. 

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3. Development of an MKID Frequency-to-Pixel LED Mapper for SPT-3G+

   https://doi.org/10.1109/tasc.2024.3519087  

   Martsen, E S; Barry, P S; Benson, B A; Dibert, K R; Fichman, K N; Natoli, T; Rouble, M; Yu, C (August 2025, IEEE Transactions on Applied Superconductivity)

   SPT-3G+ is the next-generation camera for the South Pole Telescope (SPT). SPT is designed to measure the cosmic microwave background (CMB) and the mm/sub-mm sky. The planned focal plane consists of 34,000 microwave kinetic inductance detectors (MKIDs), divided among three observing bands centered at 220, 285, and 345 GHz. Each readout line is designed to measure 800 MKIDs over a 500 MHz bandwidth, which places stringent constraints on the accuracy of the frequency placement required to limit resonator collisions that reduce the overall detector yield. To meet this constraint, we are developing a two-step process that first optically maps the resonance to a physical pixel location, and then next trims the interdigitated capacitor (IDC) to adjust the resonator frequency. We present a cryogenic LED apparatus operable at 300 mK for the optical illumination of SPT-3G+ detector arrays. We demonstrate integration of the LED controls with the GHz readout electronics (RF-ICE) to take data on an array of prototype SPT-3G+ detectors. We show that this technique is useful for characterizing defects in the resonator frequency across the detector array and will allow for improvements in the detector yield. 

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4. Thermoreflectance-based thermometry of silicon thin films with resonantly enhanced temperature sensitivity

   https://doi.org/10.1364/OE.511938  

   Shi, Changxing; Wang, Xinchao; Zheng, Qifan; Maroske, Jan; Thompson, Dakotah (January 2024, Optics Express)

   We demonstrate a thermoreflectance-based thermometry technique with an ultimate temperature resolution of 60 µK in a 2.6 mHz bandwidth. This temperature resolution was achieved using a 532 nm-wavelength probe laser and a ∼1 µm-thick silicon transducer film with a thermoreflectance coefficient of −4.7 × 10⁻³K⁻¹at room temperature. The thermoreflectance sensitivity reported here is over an order-of-magnitude greater than that of metal transducers, and is comparable to the sensitivity of traditional resistance thermometers. Supporting calculations reveal that the enhancement in sensitivity is due to optical interference in the thin film. 

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5. High-resolution mapping of the radial electric field in RF plasma sheath using a single optically trapped particle

   https://doi.org/10.1088/1361-6595/ae13be  

   Ekanayaka, Pubuduni; Wang, Chuji; Chakraborty_Thakur, Saikat; Thomas, Edward (October 2025, Plasma Sources Science and Technology)

   Abstract Mapping individual components of the electric field,E, with high spatial resolution around the plasma sheath remains challenging, as mostin situplasma probes are generally too intrusive for reliable plasma potential measurements. An optically trapped micron-sized particle in a plasma environment represents the smallest, nonintrusive, or minimally intrusive diagnostic tool because it causes minimal disturbance to the plasma environment in which it is suspended. These microparticles can be used to map the electric fieldin situwith high spatial resolution in a radio frequency (RF) plasma sheath region. In this study, we optically trapped micron-sized single particles and precisely transported a single trapped particle within the cylindrically symmetric capacitively coupled plasma (CCP), over a radial distance of ∼ 0–15 mm, a 2400-fold displacement relative to the particle size, corresponding to a spatial resolution of tens of micrometers. We measured |E| and its spatial distributions in the examined range by analyzing the particle’s trajectory in the plasma after the optical forces were turned off. The radial component of the electric field, |E_r|, was measured at multiple locations parallel to the electrode at 6.7 Pa. The |E_r| was strongest near the circular electrode edges, reaching 0.478 ± 0.005 V mm⁻¹, and decreased to 0.458 ± 0.001 V mm⁻¹toward the center of the electrode. We reconstructed the radial plasma potential, yielding a center-to-edge potential decrease of 4.6 V over one centimeter. This ΔVis consistent with reported CCP trends of small mid-plane radial potential gradients and serves as the confining potential for dust crystal and dust cluster studies. These results highlight the use of optical trapping of a single particle as anin situ, nonintrusive microprobe for quantitative mapping ofE_r(r) andV(r) in RF plasmas. 

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