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Research Overview

The primary focus of the Adaptive Microwave & Antenna Systems (AMAS) research group at Colorado School of Mines is on design and development of adaptive microwave and antenna devices and systems for the next generation of wireless communication and radar systems. These systems need real-time reconfiguration and intelligent adaptive capabilities to maximize the communication throughput and efficiency while providing system resilience during unexpected radio communication interruptions. The research group is advised by Prof. Payam Nayeri.

Current Research Areas

Wireless Energy Harvesting (WEH) and Power Transfer (WPT)

Wireless transmission of energy has no bounds. In wireless power transfer (WPT), a transmitter connected to a power source beams the energy to one or more receivers wirelessly, where it is converted back to an electrical current and then used. On the other hand, with the birth of IoT and the growing popularity and applications of largescale, sensor-based wireless networks such as structural, health monitoring, human health monitoring, to name a couple, the need to adopt inexpensive, green communications strategies is of paramount importance. Most of these devices need to operate without batteries, and as such require an energy harvesting circuit that captures the wireless power. While WPT has been around for many years, several challenges still exist. For one, very few systems have been demonstrated that can harvest energy from freely available ambient RF sources. More importantly the efficiency of these systems is quite low and new methodologies to enhance them are required.

Active Antenna Arrays

Active electronically scanned arrays (ESAs) have power amplifiers with nonlinear responses. The nonlinearity of the amplifier power gives rise to undesired harmonics and intermodulation products which alter the radiation pattern of the array. The goal of this research is to develop new methodologies for accurate prediction of the system response under these nonlinear conditions, and mitigate the effects of these undesired responses on the radiation pattern of the active ESAs.

Multifunctional Microwave Circuits

The rapid developments in modern communication systems have imposed requirements such as small size, wide bandwidth, and multi-band operation for RF and microwave devices. The goal of this research is to develop new topologies and design theories for multifunctional microwave circuits and devices in modern communication systems.

Adaptive Beamforming with Software Defined Radios

Digital beamforming (DBF) is the holy grail of antenna array technology. By converting RF signals to bits at the antenna elements using software defined radios (SDRs), simultaneous multiple beams, adaptive nulling, direction finding, and multiple-input and multiple-output (MIMO) are possible in real-time. With the rapid development of antenna array systems, implementation of this advanced array technology opens the doors to numerous applications. Our goal is to develop a testbed for DBF experiments using SDR arrays. The developed testbed will then be used to evaluate and optimize the performance of advanced signal-processing-algorithms, as well as for educational purposes.

Wideband Antennas and Arrays

Over the past 3 decades, radio-frequency (RF) communications rapidly expanded way beyond our imagination. Modern communication systems need to transmit/receive very wideband signals and at higher data rates than ever before. On the receiver/transmitter side, the antenna plays a pivotal role. MIMO and antenna arrays offer several advantages over a single antenna and are generally considered a necessity for modern communication systems. The classic arrays use phase shifters to collimate the beam, however the term 'phased', implies narrow bandwidth. The solution to this system level problem is to use time-delay-units, as opposed to phase shifters, which shift the signal envelope, providing wide instantaneous signal bandwidth, and ensuring that pulse dispersion will not be observed due to bandwidth limitations. These types of arrays can be referred to as Timed Arrays. Timed arrays are a new research area in which traditional frequency domain analytical techniques do not apply. In order to properly use timed arrays in future RF systems, several fundamental issues need to be investigated. The objective of this research is to quantify these challenges and find solutions to fundamental issues in timed arrays, such as mutual coupling effects of very wide bandwidth signals, dispersion effects, spurious signal generation, techniques for mitigating wideband mutual coupling, and optimal time-delay-unit topologies in timed array architectures.