@article{chauhan_collaert_wambacq_2022, title={A 120–140-GHz LNA in 250-nm InP HBT}, url={https://doi.org/10.1109/LMWC.2022.3189607}, DOI={10.1109/LMWC.2022.3189607}, abstractNote={This letter presents a $D$ -band low-noise amplifier (LNA) in 250-nm InP HBT technology for the next-generation wireless applications. The LNA has a measured peak gain of 13 dB, a 3-dB bandwidth greater than 20 GHz (120–140 GHz), and a measured noise figure (NF) of less than 6 dB in the band. A reduction in the 3-dB bandwidth from simulation was observed during the measurements which was attributed to the substrate waves using full chip electromagnetic (EM) simulation. EM simulations show that a partial or complete removal of the back side metallization of the InP substrate, holes in metal-1 ground plane, or a strategic placement of through-substrate vias suppress these substrate waves. To the authors’ knowledge, this is the first 120–140-GHz LNA in the InP 250-nm HBT technology.}, journal={IEEE Microwave and Wireless Components Letters}, author={Chauhan, Vikas and Collaert, Nadine and Wambacq, Piet}, year={2022}, month={Nov} }
 @article{chauhan_hong_schoenherr_floyd_2021, title={An X-Band Code-Modulated Interferometric Imager}, volume={69}, ISSN={["1557-9670"]}, url={http://dx.doi.org/10.1109/tmtt.2021.3101243}, DOI={10.1109/tmtt.2021.3101243}, abstractNote={Code-modulated interferometry (CMI) enables a lens-less approach to imaging in which incoming signals are code modulated, combined, and processed through a shared hardware path; visibility functions are demodulated from an aggregate power-detected response; and an image is obtained using an inverse Fourier transform of the visibility samples. CMI allows the imager to be constructed using low-cost conventional beamforming hardware. This article presents the theory of operation of a code-modulated interferometer array intended for active imaging. This includes the selection of codes, the use of phase shifters for modulation, the demodulation of visibility functions, the necessary calibration, and the image processing. The architecture and design of an active imaging prototype is then presented, where it is created using a commercially available 16-element 8–16 GHz beamforming receiver along with a sparse antenna array that generates 169 distinct visibility samples. The imaging capabilities are demonstrated through the detection of multiple point sources at 10 GHz. Finally, the feasibility of creating a larger 64-element imager with 961 visibility samples is demonstrated through construction and measurements of a single row within that array.}, number={11}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Chauhan, Vikas and Hong, Zhangjie and Schoenherr, Simon and Floyd, Brian A.}, year={2021}, month={Nov}, pages={4856–4868} }
 @article{board-level code-modulated embedded test and calibration of an x-band phased-array transceiver_2021, year={2021}, month={Jul} }
 @article{hong_chauhan_schoenherr_floyd_2021, title={Code-Modulated Embedded Test and Calibration of Phased-Array Transceivers}, volume={69}, ISSN={["1557-9670"]}, url={https://doi.org/10.1109/TMTT.2020.3041022}, DOI={10.1109/TMTT.2020.3041022}, abstractNote={We present improved methods for built-in test and calibration of phased arrays in free-space using a code-modulated embedded test (CoMET). Our approach employs the Cartesian modulation of test signals within each element using existing phase shifters, the combination of these signals into a code-multiplexed response, creation of code-modulated element-to-element “interference products” using a built-in power detector, demodulation of correlations from the digitized interference response, and parallel in situ extraction of amplitude and phase per element using an equation solver. In this article, we review CoMET’s methodology and then analyze the impact of noise within the system. To improve CoMET accuracy, a reference-element methodology is introduced, where all measurements are referred to as one element in the array whose phase is held constant. This is compared with another method in which the modulation axes are rotated to allow accurate extraction of phase near the original 0°/90°/180°/270° axes. Our techniques are demonstrated for both receive and transmit modes using an eight-element 8–16-GHz phased-array packaged and assembled together with patch antennas. Compared with network analyzer measurements, CoMET-extracted gain and phase using the reference-element method are accurate to within 0.4 dB and 2°–3° for free-space measurements, respectively. CoMET is then used within a calibration loop to equalize elemental gain and achieve a 7-bit phase resolution. In free space, the maximum gain and phase offsets between active antenna elements are reduced from 3.5 dB and 20°–90° to 1.1 dB and 0°, respectively. Calibrated beam patterns show significant improvement with peak-to-null ratios of >30 dB.}, number={3}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Hong, Zhangjie and Chauhan, Vikas and Schoenherr, Simon and Floyd, Brian A.}, year={2021}, month={Mar}, pages={1846–1859} }
 @phdthesis{phd thesis on code modulated interferometric imaging system using phased arrays_2021, year={2021}, month={Jul} }
 @inproceedings{chauhan_seo_greene_kam_floyd_2020, title={A 60 GHz code-modulated interferometric imaging system using a phased array}, volume={11411}, url={http://dx.doi.org/10.1117/12.2565589}, DOI={10.1117/12.2565589}, abstractNote={This paper presents a millimeter-wave code-modulated interferometric imaging system, which is a lens-less approach to realizing imagers using repurposed phased arrays. To use a phased array as an interferometer, incoming signals are code modulated using phase shifters, multiplexed using a power combiner, and processed through a shared receiver chain. An interference pattern is then obtained by a squaring operation, from which complex visibilities can be demodulated. Here, a four-element 60-GHz phased array chip is packaged with slot antennas, and a single 60-GHz output is measured using a power detector. This scalar measurement is then demodulated to obtain the interferometric visibilities. The four-element phased array is thinned to obtain a 13-pixel image and the system is demonstrated through a point-source detected at different locations.}, booktitle={Passive and Active Millimeter-Wave Imaging XXIII}, publisher={SPIE}, author={Chauhan, Vikas and Seo, Haekyo and Greene, Kevin B. and Kam, Dong G. and Floyd, Brian}, editor={Robertson, Duncan A. and Wikner, David A.Editors}, year={2020}, month={Apr} }
 @inproceedings{from 5g to 6g: will compound semiconductors make the difference?_2020, url={https://publons.com/publon/43689215/}, DOI={10.1109/ICSICT49897.2020.9278253}, abstractNote={In this work, we will address the opportunities of a hybrid III-V/CMOS technology for next generation wireless communication, beyond 5G, moving to operating frequencies above 100GHz. Challenges related to III-V upscaling and CMOS co-integration using 3D technologies will be discussed.}, booktitle={IEEE International Conference on Solid-State and Integrated Circuit Technology (ICSICT)}, year={2020} }
 @article{the revival of compound semiconductors and how they will change the world in a 5g/6g era_2020, url={https://publons.com/publon/43689205/}, DOI={10.1149/09805.0015ECST}, abstractNote={The world is more than ever relying on connectivity in our daily life as well as our professional life. With 5G being rolled out, the industry is looking already at the next generation of mobile communication to bring even higher speeds and more connections than previous generations. But with 5G we are at an inflection point where it is not only about higher data rates and more connections, but about connecting different kind of devices and the new ways humans and machines interact with each other. The higher frequencies, low latency and reliability requirements will put a lot of strain on the technologies to enable this. While CMOS is the preferred vehicle, to fulfill these demands compound semiconductors like GaN and InP might be the better options for particular functions of the radio architecture. This paper will address the progress toward upscaling these materials to a Si platform and to make them CMOS and 3D compatible to enable the final heterogeneous systems that will be needed for 5G and beyond.}, journal={ECS Transactions}, year={2020} }
 @inproceedings{chauhan_schonherr_hong_floyd_2019, title={A 10-GHz Code-Modulated Interferometric Imager Using Commercial-Off-The-Shelf Phased Arrays}, volume={2019-June}, url={http://dx.doi.org/10.1109/mwsym.2019.8700850}, DOI={10.1109/mwsym.2019.8700850}, abstractNote={Code-modulated interferometric imaging is a lens-less approach to imaging in which existing analog phased-arrays are repurposed as an interferometer using code modulation. A 33-pixel, eight-element prototype is created using two commercially-available ADAR1000 phased-array receivers from Analog Devices Inc. The chips are connected at board level to a patch antenna array. The serial interface is used to apply codes whereas the on-chip power detector and data converter are used for direct read out of the composite code-multiplexed imaging data. These are then processed off-line in Matlab to reconstruct the image. The 33-pixel camera is demonstrated in hardware for point-source detection.}, booktitle={2019 IEEE MTT-S International Microwave Symposium (IMS)}, publisher={IEEE}, author={Chauhan, Vikas and Schonherr, Simon and Hong, Zhangjie and Floyd, Brian}, year={2019}, month={Jun}, pages={1015–1018} }
 @article{hong_schonherr_chauhan_floyd_2019, title={Free-Space Phased-Array Characterization and Calibration Using Code-Modulated Embedded Test}, volume={2019-June}, url={https://publons.com/publon/27738918/}, DOI={10.1109/mwsym.2019.8701098}, abstractNote={A phased-array self-test technique called code-modulated embedded test (CoMET) is used for free-space characterization and calibration of phased-array transceivers packaged with antennas. Orthogonal two-bit modulation is applied to all phase shifters to allow for parallel extraction of gain and phase of array elements using a simple power detector. Our array uses two commercially-available beamformers and a patch antenna array. At 10 GHz, CoMET-extracted gain, phase, and phase offset are accurate to within 0.4 dB and 4° compared to network analyzer measurements. CoMET is then used within a calibration-loop to equalize elemental gain and phase across the array for 7-bit phase resolution. After calibration, the maximum gain and phase offsets between elements are reduced from 3.5 dB and 70° to 1.1 dB and ~0°. Free-space beam patterns after calibration show significant improvement.}, journal={2019 IEEE MTT-S International Microwave Symposium (IMS)}, publisher={IEEE}, author={Hong, Zhangjie and Schonherr, Simon and Chauhan, Vikas and Floyd, Brian}, year={2019}, month={Jun}, pages={1225–1228} }
 @inproceedings{a 24-44 ghz uwb lna for 5g cellular frequency bands_2018, url={https://publons.com/publon/48243423/}, booktitle={Global Symposium on Millimeter Waves (GSMM)}, year={2018} }
 @inproceedings{chauhan_floyd_2018, title={A 24–44 GHz UWB LNA for 5G Cellular Frequency Bands}, ISBN={9781538645840}, url={http://dx.doi.org/10.1109/gsmm.2018.8439672}, DOI={10.1109/gsmm.2018.8439672}, abstractNote={This paper presents a 24–44 GHz ultra-wideband (UWB) low-noise amplifier (LNA); simultaneously covering all major 5G cellular frequency bands. The LNA has been designed in 45nm CMOS SOI technology, has a maximum gain of 20 dB with more than 65% 3dB bandwidth (24-47.5 GHz), and a noise figure less than 5.5 dB (typical 4.7 dB) in the band. A narrowband 28 GHz LNA is presented for comparison and evaluation of merits of a wideband design.}, booktitle={2018 11th Global Symposium on Millimeter Waves (GSMM)}, publisher={IEEE}, author={Chauhan, Vikas and Floyd, Brian}, year={2018}, month={May} }
 @article{greene_chauhan_floyd_2018, title={Built-In Test of Phased Arrays Using Code-Modulated Interferometry}, volume={66}, ISSN={["1557-9670"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85040060676&partnerID=MN8TOARS}, DOI={10.1109/tmtt.2017.2784373}, abstractNote={This paper presents a built-in self-test technique for phased arrays that applies code modulation to each element within the array to allow parallel in situ measurements and a built-in distribution network to allow injection or extraction of test signals. The aggregated test response is downconverted from radio-frequency or millimeter-wave frequencies using a direct (power) detector, resulting in a baseband interference signal composed of code-modulated complex cross correlations between all elemental signals. Using orthogonal code products, each cross correlation can be extracted from the interference signal, and then the full set of cross correlations can be used to obtain amplitude and phase data of each element. A four-element 60-GHz phased-array receiver front end that includes this code-modulated embedded test (CoMET) infrastructure has been fabricated in SiGe BiCMOS technology. The BIST overhead is less than 2% of the total die area. Comparisons between our built-in test technique and measurements using a vector network analyzer show that CoMET can be used to extract amplitude with 1 dB accuracy and phase with four degree accuracy. Furthermore, measurements confirm that CoMET can be used to extract the phase-step response of each element in parallel across all settings as well as phase offset introduced by the built-in test network.}, number={5}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Greene, Kevin and Chauhan, Vikas and Floyd, Brian}, year={2018}, month={May}, pages={2463–2479} }
 @inproceedings{greene_chauhan_floyd_2016, title={Code-modulated embedded test for phased arrays}, volume={2016-May}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84973922847&partnerID=MN8TOARS}, DOI={10.1109/vts.2016.7477274}, abstractNote={Millimeter wave (mm-wave) design has become the forefront for enabling multi-Gb/s wireless communications due to the abundance of available bandwidth at frequencies above 24 GHz. At these frequencies, phased arrays are used to meet link budgets by combining phase-adjusted responses of multiple antennas to form a high-gain, directive beam which is electrically steerable. Current requirements point to array sizes ranging from 8-32 elements, each of which must be measured and calibrated in terms of RF output power and phase to obtain the desired array performance. This paper will first review phased-array topologies and calibration requirements. We will then present a code modulated technique for manufacturing test of the array which uses only digital code modulators per element and a single global mm-wave squaring circuit in the form of a power detector. This approach allows measurement of full array performance with a single detector using minimum additional built-in-test hardware. Behavioral models indicate that this method can estimate the phase response within 1 degree and an output power within 0.2 dB for each individual element using global array measurements.}, booktitle={2016 ieee 34th vlsi test symposium (vts)}, author={Greene, K. and chauhan and Floyd, Brian}, year={2016} }
 @inproceedings{chauhan_greene_floyd_2016, title={Code-modulated interferometric imaging system using phased arrays}, volume={9830}, ISSN={["1996-756X"]}, url={http://dx.doi.org/10.1117/12.2234758}, DOI={10.1117/12.2234758}, abstractNote={Millimeter-wave (mm-wave) imaging provides compelling capabilities for security screening, navigation, and bio- medical applications. Traditional scanned or focal-plane mm-wave imagers are bulky and costly. In contrast, phased-array hardware developed for mass-market wireless communications and automotive radar promise to be extremely low cost. In this work, we present techniques which can allow low-cost phased-array receivers to be reconfigured or re-purposed as interferometric imagers, removing the need for custom hardware and thereby reducing cost. Since traditional phased arrays power combine incoming signals prior to digitization, orthogonal code-modulation is applied to each incoming signal using phase shifters within each front-end and two-bit codes. These code-modulated signals can then be combined and processed coherently through a shared hardware path. Once digitized, visibility functions can be recovered through squaring and code-demultiplexing operations. Pro- vided that codes are selected such that the product of two orthogonal codes is a third unique and orthogonal code, it is possible to demultiplex complex visibility functions directly. As such, the proposed system modulates incoming signals but demodulates desired correlations. In this work, we present the operation of the system, a validation of its operation using behavioral models of a traditional phased array, and a benchmarking of the code-modulated interferometer against traditional interferometer and focal-plane arrays.}, booktitle={Passive and Active Millimeter-Wave Imaging XIX}, publisher={SPIE}, author={Chauhan, Vikas and Greene, Kevin and Floyd, Brian}, editor={Wikner, David A. and Luukanen, Arttu R.Editors}, year={2016}, month={May} }