Design and Realization of Fully-digital Microwave and Mm-wave Multi-beam Arrays with FPGA/RF-SOC Signal Processing

There has been a constant increase in data-traffic and device-connections in mobile wireless communications, which led the fifth generation (5G) implementations to exploit mm-wave bands at 24/28 GHz. The next-generation wireless access point (6G and beyond) will need to adopt large-scale transceiver arrays with a combination of multi-input-multi-output (MIMO) theory and fully digital multi-beam beamforming. The resulting high gain array factors will overcome the high path losses at mm-wave bands, and the simultaneous multi-beams will exploit the multi-directional channels due to multi-path effects and improve the signal-to-noise ratio. Such access points will be based on electronic systems which heavily depend on the integration of RF electronics with digital signal processing performed in Field programmable gate arrays (FPGA)/ RF-system-on-chip (SoC). This dissertation is directed towards the investigation and realization of fully-digital phased arrays that can produce wideband simultaneous multi-beams with FPGA or RF-SoC digital back-ends. The first proposed approach is a spatial bandpass (SBP) IIR filter-based beamformer, and is based on the concepts of space-time network resonance. A 2.4 GHz, 16-element array receiver, has been built for real-time experimental verification of this approach. The second and third approaches are respectively based on Discrete Fourier Transform (DFT) theory, and a lens plus focal planar array theory. Lens based approach is essentially an analog model of DFT. These two approaches are verified for a 28 GHz 800 MHz mm-wave implementation with RF-SoC as the digital back-end. It has been shown that for all proposed multibeam beamformer implementations, the measured beams are well aligned with those of the simulated. The proposed approaches differ in terms of their architectures, hardware complexity and costs, which will be discussed as this dissertation opens up. This dissertation also presents an application of multi-beam approaches for RF directional sensing applications to explore white spaces within the spatio-temporal spectral regions. A real-time directional sensing system is proposed to capture the white spaces within the 2.4 GHz Wi-Fi band. Further, this dissertation investigates the effect of electro-magnetic (EM) mutual coupling in antenna arrays on the real-time performance of fully-digital transceivers. Different algorithms are proposed to uncouple the mutual coupling in digital domain. The first one is based on finding the MC transfer function from the measured S-parameters of the antenna array and employing it in a Frost FIR filter in the beamforming backend. The second proposed method uses fast algorithms to realize the inverse of mutual coupling matrix via tridiagonal Toeplitz matrices having sparse factors. A 5.8 GHz 32-element array and 1-7 GHz 7-element tightly coupled dipole array (TCDA) have been employed to demonstrate the proof-of-concept of these algorithms

Frequency-Multiplexed Array Digitization for MIMO Receivers: 4-Antennas/ADC at 28 GHz on Xilinx ZCU-1285 RF SoC

Communications at mm-wave frequencies and above rely heavily on beamforming antenna arrays. Typically, hundreds, if not thousands, of independent antenna channels are used to achieve high SNR for throughput and increased capacity. Using a dedicated ADC per antenna receiver is preferable but it\u27s not practical for very large arrays due to unreasonable cost and complexity. Frequency division multiplexing (FDM) is a well-known technique for combining multiple signals into a single wideband channel. In a first of its kind measurements, this paper explores FDM for combining multiple antenna outputs at IF into a single wideband signal that can be sampled and digitized using a high-speed wideband ADC. The sampled signals are sub-band filtered and digitally down-converted to obtain individual antenna channels. A prototype receiver was realized with a uniform linear array consisting of 4 elements with 250 MHz bandwidth per channel at 28 GHz carrier frequency. Each of the receiver chains were frequency-multiplexed at an intermediate frequency of 1 GHz to avoid the requirement for multiple, precise local oscillators (LOs). Combined narrowband receiver outputs were sampled using a single ADC with digital front-end operating on a Xilinx ZCU-1285 RF SoC FPGA to synthesize 4 digital beams. The approach allows $M$ -fold increase in spatial degrees of freedom per ADC, for temporal oversampling by a factor of $M$

Feasibility and systems definition study for Microwave Multi-Application Payload (MMAP)

Work completed on three Shuttle/Spacelab experiments is examined: the Adaptive Multibeam Phased Array Antenna (AMPA) Experiment, Electromagnetic Environment Experiment (EEE) and Millimeter Wave Communications Experiment (MWCE). Results included the definition of operating modes, sequence of operation, radii of operation about several ground stations, signal format, foot prints of typical orbits and preliminary definition of ground and user terminals. Conceptual hardware designs, Spacelab interfaces, data handling methods, experiment testing and verification studies were included. The MWCE-MOD I was defined conceptually for a steerable high gain antenna

A Flexible RFIC Architecture for High-Sensitivity Reception and Compressed-Sampling Wideband Detection

Compressed sensing (CS) is a new signal processing approach that has disrupted the Shannon-Nyquist limit based design methodology and has opened promising avenues for building energy-efficient radio frequency integrated circuits (RFICs) for detecting and estimating particular classes (i.e. sparse) of signals. Whether in application domains where naturally occurring signals are sparse or where representations of signals subject to the fidelity limits or configuration settings of the radio equipment are often found to be sparse, the emergence of CS has forced us to re-imagine the radio receiver. While realizing some of the potential benefits promised by theory, CS-RFIC architectures proposed in earlier research were not particularly suitable for mass-market applications. This thesis demonstrates how to take a new signal processing technique all the way to the hardware level. So far, the main focus in literature has been how CS offers a significant advantage for signal processing. This work will show how CS techniques drive novel architectures down to the integrated circuit level. This requires close collaboration between communication system developers, integrated circuit designers and signal processing experts. The trans-disciplinary approach presented here has led to the unification of CS-inspired architectures for wideband signal detection with robust, legacy architectures for high-sensitivity signal reception. The result is a functionally flexible and rapidly reconfigurable CMOS RFIC compactly implemented on silicon with the potential to achieve the cost, size and power targets in mass-market applications. While the focus of this thesis is RF signal finding and reception in frequency, the CS-based RFIC design approach presented here is applicable to a wide range of other applications like direction-of-arrival and range finding. We begin by developing a signal-model driven approach for optimizing the performance of CS RF frontends (RFFEs). We consider sparse multiband signals with supports contained within a frequency span extending from fMIN to fMAX. The resulting quadrature analog-to-information converter (QAIC) is a flexible-bandwidth, blind sub-Nyquist sampling architecture optimized for energy consumption and sensitivity performance. The QAIC addresses key drawbacks of earlier CS RFFE architectures like the modulated wideband converter (MWC) that implement frequency spans extending from 0 to fMAX. While these earlier architectures, a direct implementation of CS signal processing theory, have several beneficial properties, the true cost of their proposed analog frontend significantly diminishes the sensitivity performance and energy savings that CS methods have the potential to deliver. They use periodic pseudo-random bit sequence (PRBS) generators where the clock frequency fPRBS scales up with the maximum signal frequency fMAX. In contrast, fPRBS in the QAIC RFFE scales up with the instantaneous bandwidth IBW, where IBW = ( fMAX − fMIN ). This results in significant performance advantages in terms of energy consumption and sensitivity performance. The QAIC uncouples fPRBS from fMAX by performing wideband quadrature downconversion ahead of analog mixing with PRBSs at an intermediate frequency (IF). However, the dual heterodyne architecture of the QAIC suffers from spurious responses at IF caused by gain and phase imbalance in its wideband downconverter. We then show how the direct RF-to-information converter (DRF2IC) compactly adds CS wideband detection to a direct conversion frequency-translational noise-cancelling (FTNC) receiver by introducing pseudo-random modulation of the local oscillator (LO) signals and by consolidating multiple CS measurements into one hardware branch. The DRF2IC inherits benefits of the FTNC receiver in signal reception mode. In CS wideband detection mode, the DRF2IC inherits key advantages from both the earlier lowpass CS architectures and the QAIC while avoiding the drawbacks of both. It uncouples fPRBS from fMAX in contrast with the MWC. In contrast with the QAIC, the DRF2IC employs a direct conversion RF chain with narrow bandwidth analog components at baseband thereby avoiding frequency-dependent gain and phase imbalance. The DRF2IC chip occupies 0.56mm2 area in 65nm CMOS. In reception mode, it consumes 46.5mW from 1.15V and delivers 40MHz RF bandwidth, 41.5dB conversion gain, 3.6dB noise figure (NF) and -2dBm blocker 1dB compression point (B1dB). In CS wideband detection mode, 66dB operational dynamic range, 40dB instantaneous dynamic range and 1.43GHz instantaneous bandwidth are demonstrated and 6 interferers each 10MHz wide scattered over a 1.27GHz span are detected in 1.2us consuming 58.5mW

The Design of Low Power Ultra-Wideband Transceiver

Ph.DDOCTOR OF PHILOSOPH

Surpassing Fundamental Limits through Time Varying Electromagnetics

Surpassing the fundamental limits that govern all electromagnetic structures, such as reciprocity and the delay-bandwidth-size limit, will have a transformative impact on all applications based on electromagnetic circuits and systems. For instance, violating principles of reciprocity enables non-reciprocal components such as isolators and circulators, which find application in full-duplex wireless radios, radar, biomedical imaging, and quantum computing systems. Overcoming the delay-bandwidth-size limit enables ultra-broadband yet extremely-compact devices whose size is not fundamentally related to the wavelength at the operating frequency. The focus of this dissertation is on using time-variance as a new toolbox to overcome these fundamental limits and re-imagine circuit and system design. Traditional non-reciprocal components are realized using ferrite materials that loose their reciprocity under the application of external magnetic bias. However, the sheer volume, cost and weight of these magnet based non-reciprocal components coupled with their inability to be fabricated in conventional semiconductor processes, have limited their application to bulky and large-scale systems. Other approaches such as active-biased and non-linearity based non-reciprocity are compatible with semiconductor processes, however, they suffer from other poor linearity and noise performance. In this dissertation, using passive transistor switch as the modulating element, we have proposed the concept of spatio-temporal conductivity modulation and have demonstrated a gamut of non-reciprocal devices ranging from gyrators to isolators and circulators. Through novel circuit topologies, for the first time, we have demonstrated on-chip circulators with multi-watt input power handling, operation at high millimeter-wave frequencies, and tailor made circulators for emerging technologies such as simultaneous-transmit-and-receive MRI and quantum computing. Delay-bandwidth-size trade-off is another fundamental electromagnetic limit, that constrains the delay imparted by a medium or a device within a fixed footprint to be inversely proportional to the signal bandwidth. It is this limit that governs the size of any microwave passive devices to be inversely proportional to its operating frequency. As a part of this dissertation, through intelligent clocking of switched capacitor networks we overcame the delay-bandwidth-size limit, thus resulting in infinitesimal, yet broadband microwave devices. Here we proposed a new paradigm in wave propagation where the properties such as the propagation delay and characteristic impedance does not depend on the constituent elements/materials of the medium, but rather heavily rely on the user-defined modulation scheme, thereby opening huge opportunities for realizing highly-reconfigurable passives. Leveraging these concepts, we demonstrated wide range of reciprocal an non-reciprocal devices including ultra-compact delay elements, highly-reconfigurable microwave passives, ultra-wideband circulators with infinitesimal form-factors and dispersion-free chip scale floquet topological insulators. Application of these devices have also been evaluated in real-world systems through our demonstrations of wideband, full-duplex receivers leveraging switched capacitors based true-time-delay interference cancelers and floquet topological insulator based antenna interfaces for full-duplex phased-arrays and ultra-wideband beamformers. Furthermore, to cater the growing RF and microwave needs of future, large-scale quantum computing systems, we demonstrated a low-cryogenic, wideband circulator based on time modulation of superconducting devices. This superconducting circulator is expected to operate alongside the superconducting qubits, inside a dilution refrigerator at 10mK-100mK, thus enabling a tightly integrated quantum system. We also presented the design and implementation of a cryogenic-CMOS clock driver chip that will generate the clocks required by the superconducting circulator. Finally, we also demonstrated the design and implementation of a low-noise, low power consumption, 6GHz - 8GHz cryogenic downconversion receiver at 4K for cryogenic qubit readout

Scalable Array Transceivers with Wide Frequency Tuning Range for Next Generation Radios

Scalable array transceivers with wide frequency tuning range are attractive for next-generationradios. Key challenges for such radios include generation of LO signals with widefrequency tuning range, scalable synchronization between multiple array unit cells andtolerance to in-band and out-of-band interferers. This thesis presents approaches toaddress these challenges in commercial CMOS technologies.The first part focuses on a series resonant mode-switching VCO architecture thatachieves both state-of-art area and power efficiency with an octave frequency tuningrange from 6.4-14 GHz achieved 186-dB-188-dB Figure-of-Merit (FoM) in 65 nm CMOStechnology. The scalability of this approach towards achieving even larger FTR is alsodemonstrated by a triple-mode 2.2 GHz to 8.7 GHz (119% FTR) CMOS VCO.In the second part a scalable, single-wire coupled-PLL architecture for RF mm-wavearrays is presented. The proposed architecture preserves the simplicity of a daisy-chained LO distribution, compensates for phase offset due to interconnect, and provides phasenoise improvement commensurate to the number of coupled PLLs. Measurements on a28 GHz CMOS prototype demonstrate the feasibility of this scheme.The third part of this thesis presents filtering techniques for in-band blocker suppression.A spatial spectral notch filter design for MIMO digital beam forming arrays is proposedto relax the ADC dynamic range requirement. Orthogonal properties of Walsh functionsincorporated into passive N-path approach enables reconfigurable notches at multiplefrequencies and angles-of-incidence. A 0.3 GHz-1.4 GHz four-element array prototypeimplemented in 65 nm CMOS achieves > 15-dB notch filtering at RF input for twoblockers while causing < 3-dB NF degradation.Finally, a code-domain N-path receiver (RX) is proposed based on pseudo-random(PN) code-modulated LO pulses for simultaneous transmission and reception (STAR)applications. A combination of Walsh-Function and PN sequence is proposed to createcode-domain matched filter at the RF frontend which reflects unknown in-band blockersand rejects known in-band TX self-interference (SI) by using orthogonal codes at RXinput thereby maximizing the SNR of the received signals. The resulting prototype in65 nm is functional from 0.3 GHz-1.4 GHz with 35 dB gain and concurrently receivestwo code-modulated signals. Proposed transmitter (TX) SI mitigation approach resultsin 38.5 dB rejection for -11.8 dBm 1.46 Mb s QPSK modulated SI at RX input. TheRX achieves 23.7 dBm OP1dB for in-band SI, while consuming ∼35 mW and occupies0.31 mm2Keywords: Passive Mixers, dual band, TX self-Interferer, synchronisation, STAR, Code domain N-path receiver, mode switching, notch filter, Phase locked loops, Octave tuning range, CMOS, phase noise, VCO, large-scale 5G mm-wave arrays, resonator, Simultaneous transmit and receive, resonator band-switching, LO distribution, scalable coupled-PLL, N-path passive mixers, MIMO arrays, digital beamforming, CDMA, phased arrays, wide tuning range, Walsh Functio

Wideband two-dimensional and multiple beam phased arrays and microwave applications using piezoelectric transducers

Modern satellite, wireless communication, and radar systems often demand wideband performance for multi-channel operation and the ability to steer multiple beams for multiple moving targets. This dissertation covers a variety of topics to design low-cost and wideband antenna systems. The main areas of study are microwave devices controlled piezoelectric transducers (PETs) and wideband baluns and balanced microwave circuits using parallel-strip lines. Some focus has also been given to the design of Rotman lens for multiple beam generation and Vivaldi antenna arrays for wideband two-dimensional scanning. The dielectric perturbation technique controlled by PET is introduced to design a wideband phase shifter and a QPSK modulator, and to tune the resonant frequency of a slot dipole. The designed PET-controlled phase shifters are used for beam steering in a dual beam phased array using a bidirectional feeding scheme and a five-beam phased array using a microstrip Rotman lens. Vivaldi-type antennas are commonly used to achieve wideband performance. Very wideband performance can be achieved using an antipodal tapered slot antenna because of its inherent simple wideband transition from microstrip line to parallel-strip line. An antipodal tapered slot antenna and a phased array are designed to span 10 to 35 GHz. In addition, a 4??4 two-dimensional antenna array is designed using wideband antipodal tapered slot antennas, and two sets of PET-controlled phase shifters for E- and H-plane scanning are fabricated to steer the beam. As a microwave system using wideband antenna array, a new low-cost and wideband phased array radar is developed using a modulated pulse over 8 to 20 GHz band. The double-sided parallel-strip line as a balanced line is presented. The parallelstrip line offers much flexibility for microwave circuit designs. This transmission line makes it possible to realize a low impedance line and allows the design of a compact wideband balun and junction. Wideband transitions (or baluns) from parallel-strip line to microstrip line, a typical unbalanced transmission line, are realized to cover several octave bandwidth. Balanced microwave filters and a hybrid coupler are developed using the parallel-strip line