Thomas M. Comberiate

Ultra-Small, High-Frequency, and Substrate-Immune Microtube Inductors Transformed from 2D to 3D.

Monolithic on-chip inductors are key passive devices in radio frequency integrated circuits (RFICs). Currently, 70–80% of the on-wafer area of most RFIC chips is occupied by the sprawling planar spiral inductors, and its operation frequency is limited to a few GHz. With continuous scaling of the transistor technology, miniaturization and high frequency operation of inductors have become the bottleneck to meet future demands of wireless communication systems. Here we report on-chip self-rolled-up 3D microtube inductors with extremely small footprint, unprecedented high frequency performance and weak dependence on substrate conductivity. The serpentine metal strips are deposited on an oppositely strained silicon nitrides (SiNx) bilayer. After releasing from the sacrificial layer underneath, the metal/SiNx layer is scrolled into a 3D hollow tubular structure by the strain induced unidirectional self-rolled-up technology. Compared to the planar spiral inductors with similar inductances and quality (Q) factors, the footprint of tube inductors is reduced by as much as two orders of magnitude, and the frequency at peak Q factor improves more than 5 times on doped substrates. The self-rolled-up 3D nanotechnology platform employed here, that “processes in 2D but functions in 3D”, is positioned to serve as a global solution for extreme RFIC miniaturization with improved performance.

Microwave and millimeter-wave ranging for coherent distributed RF systems

Microwave and millimeter-wave ranging systems, waveforms, and experimental results are described for coherent distributed RF systems applications. Measured results show that coherent distributed systems operating at carrier frequencies with coherence at λ/10 are possible well into the millimeter-wave regime by using widely separated two-tone ranging waveforms. The two-tone waveform in the context of continuous-wave ranging is introduced. A method for overcoming the range-ambiguous output of the matched filter processing is described. Microwave and millimeter-wave ranging measurements are shown and compared to the Cramer-Rao lower bound for range accuracy.

Benefits of Digital Phased Array Radars

In this paper, an overview is given of the radar benefits of digital arrays in comparison with conventional phased arrays. Considered are passive and active phased arrays as well as subarray- and element-level digital arrays; their key differences are highlighted. A discussion of several radar attributes and performance measures follows to show the advantages and promise of element-level digital arrays as the newest generation architecture for radar and other electronic systems. Radar attributes considered are antenna patterns and beam control (including adaptive interference cancellation), dynamic range, in-band linearity, system phase noise, and angle measurement accuracy.

Modeling I/O buffers using X-parameters

X-parameters have been shown to have a wide array of applications in the modeling of nonlinear devices and systems. This work analyzes the large-signal portion of an X-parameter model of a buffer to determine the extent of its nonlinearity and use for modeling input/output buffers.

Using the latency insertion method (LIM) to generate X parameters

X parameters have been shown to have a wide array of applications in the modeling of nonlinear devices and systems. In this work, the polyharmonic distortion (PHD) model and the latency insertion method (LIM) are combined to generate X parameters describing the nonlinear relationship between power waves. This technique leverages the speed and convergence advantages of the LIM simulation method to generate frequency-domain models. Results are compared with those of other methods.

Open-Loop Coherent Distributed Arrays

The ability to cohere the wireless operations between separate, moving microwave systems enables significant increases in capability for remote sensing, radar, communications, and other microwave wireless applications. Open-loop coherent distributed arrays, which are distributed systems of nodes that coherently coordinate without external signal inputs from the destination, are introduced in this paper. A model of the signal received from a coherent distributed array is derived, and a statistical analysis of the variation in signal power in the presence of coordination errors is presented. Requirements on the tolerable errors for internode range measurement, beamsteering angle measurement, and internode clock phase synchronization are given as a function of the probability of achieving a given signal power. Approaches for achieving the necessary internode range and angle measurements are presented, and the experimental results of a novel one-way clock transfer approach to phase synchronization are shown. These examples demonstrate the feasibility of implementing coherent distributed arrays on moving platforms operating at frequencies extending into the microwave region.

Demonstration of a Coherent RF Repeater for Distributed Communications

In this letter, we demonstrate a coherent radio frequency repeater. The repeater adds the appropriate phase shift to amplify or null a signal generated by another platform and directed to a target point. It leverages a high-accuracy microwave ranging system to estimate the range between platforms and maintain phase coherence when the platforms are moved without additional feedback from the receiver. A continuous beamforming gain operation is achieved without phase or frequency locking the repeater to the transmitter. We include measurements of the stability of the ranging system and discuss potential sources of the variations that limit system performance. Results from outdoor experiments demonstrating successful amplification and nulling of an existing communications link with the repeater are provided.

A Distributed RF Transmitter Using One-Way Wireless Clock Transfer

A coherent distributed two-element radio-frequency (RF) transmitter implemented with wireless clock transfer is presented in this letter. This work represents the first demonstration, to the authors’ knowledge, of a distributed RF transmitter using one-way wireless clock transfer, where the slave node need not provide any information to the master node. Two 1-GHz transmitters were implemented and coherent gain above 90% of ideal signal summation was achieved with a probability of 0.97. Experimental results show near-ideal 6-dB gain from the two-transmitter system at a distance of 85 m.

Platform placement for sidelobe mitigation in mobile sparse arrays

The preferential placement of the platforms in a coherent RF network to suppress sidelobe energy close to the array mainbeam is analyzed in this work. A linear array consisting of nine platforms within a 9000λ array size is optimized with a genetic algorithm. A large set of platform layouts that achieve sidelobe suppression of nearly 3 dB exists. The layouts are tolerant to position error on the order of 10λ and suppression improves with increased waveform bandwidth.

A Coherent RF repeater for distributed communications

The quality of a communications link is fundamentally limited by its transmission power. In the case of a mobile or small platform, this limitation can be particularly crippling because of energy storage constraints. In addition, a single platform, especially one equipped with an omni-directional antenna, can be limited in its ability to control where its signal is broadcast spatially. The former challenge motivates the use of a repeater to boost or null the signal power at a target; the latter prompts the concept of having that repeater act as a cooperative platform in order to provide spatial diversity as well as additional power on target. Some cooperative distributed communication methods have been demonstrated (D. Brown, P. Bidigare, and U. Madhow, ICASSP 2012), but these rely on feedback from a receiver. In a noncooperative setting, repeaters can be used to sample a transmitted signal and noncoherently retransmit a modified version of it to degrade the performance of a receiver (D. Torrieri, IEEE J. Sel. Areas Commun., vol. 7, no. 4, pp. 569–575, May 1989).