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We present a high efficiency backward wave oscillator (BWO) using an inhomogeneous slow wave structure (SWS). This SWS is based on a novel unit cell design that features mode dominance reversal and complete isolation of passbands. Inhomogeneity is introduced by varying the periods of the SWS cells in each section. The resulting SWS is then fabricated and cold-tested to determine its dispersion curve...
We present a low profile, wideband beam-steering antenna for continuous coverage of the K- and Ka-bands (18–40GHz). The array is based on the tightly coupled dipole principle and micro-electro mechanical systems (MEMS) phase shifters are integrated into each element for real-time beam forming. This topology leads to significant reduction in the size, weight, complexity, and cost of the phased array...
We present a tightly-coupled array antenna with integrated phase shifters with continuous coverage of K- and Ka-bands (18–40GHz). Micro-electro mechanical phase shifters were integrated with each antenna element to reduce power consumption, insertions-loss, size, cost and complexity of the beam-forming network. A 4×4 proof-of-concept array is designed, fabricated and measured at broadside. The major...
We present the fabrication, testing and validation of novel slow wave concepts for slow wave structures used in designing high power backward wave oscillators(BWO). A key aspect of the design is the reversal of the mode dominance to ensure mode purity. Cold test results of the designed homogeneous slow wave structure showed excellent agreement with simulated dispersion curves and validated mode dominance...
We present a multilayer mmW phased array topology that can be lithographically fabricated above transceiver substrates. The ultra-wideband array exhibits continuous impedance bandwidth of 35–70GHz and is isolated from the lossy substrate with a ground plane. As such, the total efficiency of the array is over 60% over the entire impedance bandwidth. Perhaps more importantly, the overall height of the...
We propose a THz spatial filter using frequency selective surfaces (FSS) integrated with bimaterial actuator for switching. The actuator consists of two materials that have different thermal expansion rates and can be designed based on temperature tuning. The goal for this design is to develop high performance reconfigurable filters operating in the THz band. The filter was fabricated using gold as...
In summary, we showed a novel approach to conduct difficult CP-gain measurements at mm-wave frequencies using a practical and simple yet affordable method. The proposed method eliminates the need of moving expensive equipment and also reduces the cost of alignment set-up or downconverter probes. Since there is no phase relation between the two steps of the measurements, the method proves to be increasingly...
We propose a bandwidth reconfigurable spatial filter using frequency selective surfaces (FSS) combined with phase-change materials (PCMs), vanadium dioxide (VO2) for advanced terahertz (THz) applications. The FSS filter is simulated using sapphire as substrate and employs circular loops FSS with VO2 rings in between. Simulations of this filter show bandwidth difference in the frequency range of 0...
Unused millimeter-wave (mmW) bands must be harnessed to sustain the explosive growth in wireless connectivity. By 2020, more than 50 billion wireless devices are projected to be connected (Rangan, et. al., IEEE Proc., vol. 102, no. 3, pp. 366–385, March 2014). In order to sustain the quality of service (QoS) for each device connected to this Internet of Things (IoT), new signaling, transceiver and...
There is an increasing need for high power microwave sources. Among this class of sources, Traveling Wave Tube Amplifiers (TWTA) are attractive for high power applications such for radars and long range satellite communications systems. Several important factors influence the performance of TWTs. Among them are: a suitable Slow Wave Structure (SWS) within the tube, beam focusing, attenuation, electron...
Millimeter wave antennas are of recent interest due to their commercial applications for high data-rate links. However, at mm-waves, losses are of major concern. To mitigate losses, slotted waveguide antennas have been proposed due to their small power loss and low cost. For airborne transceivers, such antennas typically perform beam steering via frequency scan. However, beam steering using frequency...
The sensitivity of THz waves to tissue hydration levels in excised specimen enables clinical, in-situ discrimination of cancerous vs. normal tissue regions (Z. D. Taylor et al., IEEE Trans. Terahertz Sci. Technol., 1(1), 201–219, 2011 and M. H. Arbab et al., J. Biomed. Opt., 18(7), 077004, 2013). However, previous studies on THz biomedical imaging of human tissue groups have been largely disconnected,...
Resonant tunneling diode (RTD) structures have the potential to counteract plasmonic losses and thus enhance the gain performance of terahertz (THz) devices. Of particular interest are nitride-based devices, as their high breakdown voltages and capability of large voltage swing gives distinct advantages over Si-based technologies. In this paper, several resonant tunneling diode (RTD) configurations...
High-data-rate, beam-agile, low-profile, compact, and low-power transceiver systems are required to address the air-to-air and satellite communications (SATCOM) connectivity requirements of unmanned assets in the battlefield. To this end, the Ka-band offers a key advantage for smaller size and lower profile antennas over the traditional X- and Ku-band antennas and phased arrays. More importantly,...
Reconfigurability is a vital feature of future RF, millimeter Wave and terahertz systems for sensing, imaging, wireless, and satellite communications. Indeed significant efforts have been devoted to develop tunable systems in the past among them are RF MEMS switches. But, in practice, these solutions have not been widely implemented due to a need for high voltage actuation, lack of flexibility for...
We propose a reconfigurable terahertz (THz) filter using frequency selective surfaces (FSS) combined with vanadium dioxide (VO2) phase change materials (PCMs) integrated with micro-heater for THz applications. The integration of novel material and micro-heater with our FSS design enables simultaneous control of temperature and conductivity of the PCM film leading to transmittance profile control of...
Generation of terahertz signals using solid-state devices has yet to be demonstrated above 1 THz. This paper presents modeling and optimization of a plasma mode High Electron Mobility Transistor (HEMT) for operation beyond 3 THz. In designing this structure, we examine geometrical and electrical parameters and their impact on the resonance frequency. Preliminary results show that as much as 20% of...
There has been growing interest in all-electronic sources in the terahertz frequencies. A compact THz source is obtainable, if plasma-oscillations in the 2DEG of a high electron mobility transistor (HEMT) are utilized. With this goal in mind, we develop a numerical tool which models such oscillations. We use hydrodynamic equations to model drifting plasma in the 2DEG, whereas the surrounding environment...
We propose phase-change materials (PCMs) to demonstrate the reconfigurablility of THz filter. Here vanadium dioxide (VO2) is studied since it shows insulator-to-metal transition properties at temperature of 70 °C. A broadband ON/OFF filter using frequency selective surfaces (FSS) integrated with VO2 is designed to improve selectivity of THz sensing devices. Simulation and measurement results show...
Millimeter wave and terahertz band antennas are of growing interest due to applications in radar, imaging and communications. Specifically, circularly polarized (CP) antennas find special interest in satellite communications and applications involving mobile transceivers. For mm-Wave and THz band, gain characterization for CP antennas is a difficult task due to phase errors in alignment. To avoid...
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