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We present the development of a low-loss, high-power, and ferriteless balun that operates over 0.1-1.6 GHz bandwidth. The proposed balun employs a novel compensated circuit, a single quarter-wave semirigid coaxial cable and an on-board inductor on a thermoset ceramic board to achieve high power and ultrawide bandwidth performance. The experimental results show that the balun achieves a measured average insertion loss of less than 0.5 dB and return loss of better than 10 dB from 100 MHz to more than 1.6 GHz. Within the measured bandwidth, the amplitude and phase imbalances are within ±1 dB and ±5°, respectively. Multiphysics analysis and high-power measurements demonstrate that the balun can handle more than 600 W and above at 1.6 GHz. To the best of our knowledge, the reported balun has the highest measured power handling capability per the largest 16:1 bandwidth ratio to date.

Recent advances in radio-frequency system-on-chip technology have provided mm-wave fusion plasma diagnostics with the capability to overcome major challenges such as space inefficiency, inflexible installation, sensitivity, susceptibility to EMI, and prohibitively high cost of conventional discrete component assemblies as higher imaging resolution and data accuracy are achieved by increasing the number of channels. Nowadays, shrinking transistor gate lengths on fabrication techniques have enabled hundreds of GHz operation, which is suitable for millimeter-wave diagnostics on current and future tokamaks. The Davis Millimeter Wave Research Center (DMRC) has successfully developed V-band (55-75 GHz) transmitter and receiver chips for Microwave Imaging Reflectometer (MIR) instruments. The transmitter can illuminate 8 different frequencies simultaneously within 55-75 GHz. Moreover, the receiver has the capability to amplify the reflected signal (>30 dB) while offering 10-30× reduction in noise temperature compared to current MIR instruments. Plasma diagnostics requires ultra-wideband (more than 20 GHz) operation which is approximately nine times wider bandwidth than the recent commercial impetus for communication systems. Current efforts are underway for gallium-arsenide monolithic microwave integrated circuit receiver chips at W-band (75-110 GHz) and F-band (90-140 GHz) permitting measurements at higher toroidal magnetic fields.

We present the development of a low-loss, high-power, and ferriteless balun that operates over 0.1-1.6 GHz bandwidth. The proposed balun employs a novel compensated circuit, a single quarter-wave semirigid coaxial cable and an on-board inductor on a thermoset ceramic board to achieve high power and ultrawide bandwidth performance. The experimental results show that the balun achieves a measured average insertion loss of less than 0.5 dB and return loss of better than 10 dB from 100 MHz to more than 1.6 GHz. Within the measured bandwidth, the amplitude and phase imbalances are within ±1 dB and ±5°, respectively. Multiphysics analysis and high-power measurements demonstrate that the balun can handle more than 600 W and above at 1.6 GHz. To the best of our knowledge, the reported balun has the highest measured power handling capability per the largest 16:1 bandwidth ratio to date.

Recent advances in radio-frequency system-on-chip technology have provided mm-wave fusion plasma diagnostics with the capability to overcome major challenges such as space inefficiency, inflexible installation, sensitivity, susceptibility to EMI, and prohibitively high cost of conventional discrete component assemblies as higher imaging resolution and data accuracy are achieved by increasing the number of channels. Nowadays, shrinking transistor gate lengths on fabrication techniques have enabled hundreds of GHz operation, which is suitable for millimeter-wave diagnostics on current and future tokamaks. The Davis Millimeter Wave Research Center (DMRC) has successfully developed V-band (55-75 GHz) transmitter and receiver chips for Microwave Imaging Reflectometer (MIR) instruments. The transmitter can illuminate 8 different frequencies simultaneously within 55-75 GHz. Moreover, the receiver has the capability to amplify the reflected signal (>30 dB) while offering 10-30× reduction in noise temperature compared to current MIR instruments. Plasma diagnostics requires ultra-wideband (more than 20 GHz) operation which is approximately nine times wider bandwidth than the recent commercial impetus for communication systems. Current efforts are underway for gallium-arsenide monolithic microwave integrated circuit receiver chips at W-band (75-110 GHz) and F-band (90-140 GHz) permitting measurements at higher toroidal magnetic fields.

Electron cyclotron emission (ECE) imaging is a passive radiometric technique that measures electron temperature fluctuations; and microwave imaging reflectometry (MIR) is an active radar imaging technique that measures electron density fluctuations. Microwave imaging diagnostic instruments employing these techniques have made important contributions to fusion science and have been adopted at major fusion facilities worldwide including DIII-D, EAST, ASDEX Upgrade, HL-2A, KSTAR, LHD, and J-TEXT. In this paper, we describe the development status of three major technological advancements: custom mm-wave integrated circuits (ICs), digital beamforming (DBF), and synthetic diagnostic modeling (SDM). These have the potential to greatly advance microwave fusion plasma imaging, enabling compact and low-noise transceiver systems with real-time, fast tracking ability to address critical fusion physics issues, including ELM suppression and disruptions in the ITER baseline scenario, naturally ELM-free states such as QH-mode, and energetic particle confinement (i.e. Alfvén eigenmode stability) in highperformance regimes that include steady-state and advanced tokamak scenarios. Furthermore, these systems are fully compatible with today's most challenging non-inductive heating and current drive systems and capable of operating in harsh environments, making them the ideal approach for diagnosing long-pulse and steady-state tokamaks.

We demonstrate the design of a linear and high efficient power amplifier (PA) by using different gate bias voltages for parallelly combined Gallium Nitride (GaN) high electron mobility transistors (HEMTs). The experimental results show that the linearized PA achieves the gain flatness of 0.3 dB over a 35 dB power range and has a measured sharp output power at 1 dB compression point (P1dB) of 38.5 dBm, less than 2 dB below the saturated power (PSAT). The measured adjacent channel power ratio (ACPR) of the proposed linearized PA shows up to 8 dB improvements over the PA biased ∼class A (47% Idss).

We demonstrate the design of a linear and high efficient power amplifier (PA) by using different gate bias voltages for parallelly combined Gallium Nitride (GaN) high electron mobility transistors (HEMTs). The experimental results show that the linearized PA achieves the gain flatness of 0.3 dB over a 35 dB power range and has a measured sharp output power at 1 dB compression point (P1dB) of 38.5 dBm, less than 2 dB below the saturated power (PSAT). The measured adjacent channel power ratio (ACPR) of the proposed linearized PA shows up to 8 dB improvements over the PA biased ∼class A (47% Idss).

Electron cyclotron emission (ECE) imaging is a passive radiometric technique that measures electron temperature fluctuations; and microwave imaging reflectometry (MIR) is an active radar imaging technique that measures electron density fluctuations. Microwave imaging diagnostic instruments employing these techniques have made important contributions to fusion science and have been adopted at major fusion facilities worldwide including DIII-D, EAST, ASDEX Upgrade, HL-2A, KSTAR, LHD, and J-TEXT. In this paper, we describe the development status of three major technological advancements: custom mm-wave integrated circuits (ICs), digital beamforming (DBF), and synthetic diagnostic modeling (SDM). These have the potential to greatly advance microwave fusion plasma imaging, enabling compact and low-noise transceiver systems with real-time, fast tracking ability to address critical fusion physics issues, including ELM suppression and disruptions in the ITER baseline scenario, naturally ELM-free states such as QH-mode, and energetic particle confinement (i.e. Alfvén eigenmode stability) in highperformance regimes that include steady-state and advanced tokamak scenarios. Furthermore, these systems are fully compatible with today's most challenging non-inductive heating and current drive systems and capable of operating in harsh environments, making them the ideal approach for diagnosing long-pulse and steady-state tokamaks.

A subsection of the radiating spiral arm, placed in parallel, induces a bandstop response at a notch frequency proportional to the resonant length of the strip. Detailed parametric study on the effect of variation of design parameters for an Archimedean spiral antenna and the resonant parallel strip (RPS) is presented. Empirical analysis on phase velocity on the radiating spiral arms allows characterization of RPS in terms of its resonant length. Identified systematic relation between design parameters and filter response is applied to design an antenna for the 3.1-10.5 GHz operating band with the notch response over the IEEE 802.11a band, 5.15-5.95 GHz. Successful implementation is demonstrated through performance comparison between simulated and experimental results.

A subsection of the radiating spiral arm, placed in parallel, induces a bandstop response at a notch frequency proportional to the resonant length of the strip. Detailed parametric study on the effect of variation of design parameters for an Archimedean spiral antenna and the resonant parallel strip (RPS) is presented. Empirical analysis on phase velocity on the radiating spiral arms allows characterization of RPS in terms of its resonant length. Identified systematic relation between design parameters and filter response is applied to design an antenna for the 3.1-10.5 GHz operating band with the notch response over the IEEE 802.11a band, 5.15-5.95 GHz. Successful implementation is demonstrated through performance comparison between simulated and experimental results.

We present the design and development of a compact, broadband balun based on a quasi-lumped LC transformer. The balun is constructed on a multilayer liquid crystal polymer substrate. The balun has a wide range of operating frequency from 0.9 to 3.6 GHz. Within this operating band, the balun achieves a measured insertion loss of less than 1 dB, a measured return loss of better than 10 dB, a measured amplitude imbalance of less than 1 dB and a measured phase imbalance less than 7°. This balun has an extremely compact size of 2 × 2.5 mm2. Copyright © 2013 Wiley Periodicals, Inc.

We present the design and development of dual-polarized aperture coupled stacked patch antennas with substrate embedded air cavities. The antennas, targeted for operation in the W-band (75 - 110 GHz), are realized in amultilayer organic hybrid substrate utilizing both Kapton and liquid crystal polymer (LCP). Balanced and unbalanced feedlines are investigated in order to improve isolation and mitigate coupling between orthogonal polarized ports. Measured results for the single antenna element show good performance with a beamwidth of 90° and a 2.6:1 VSWR bandwidth of 23 GHz, and isolation of better than 17.8 dB. An eight-element linear array is also designed, fabricated and tested. The antenna array achieves a beamwidth of 13 with a 2.3:1VSWR bandwidth of 7.2 GHz. Pattern measurements were achieved utilizing a millimeter-wave diode detector circuit implemented directly on the antenna substrate. © 2013 IEEE.

We present the design and development of dual-polarized aperture coupled stacked patch antennas with substrate embedded air cavities. The antennas, targeted for operation in the W-band (75 - 110 GHz), are realized in amultilayer organic hybrid substrate utilizing both Kapton and liquid crystal polymer (LCP). Balanced and unbalanced feedlines are investigated in order to improve isolation and mitigate coupling between orthogonal polarized ports. Measured results for the single antenna element show good performance with a beamwidth of 90° and a 2.6:1 VSWR bandwidth of 23 GHz, and isolation of better than 17.8 dB. An eight-element linear array is also designed, fabricated and tested. The antenna array achieves a beamwidth of 13 with a 2.3:1VSWR bandwidth of 7.2 GHz. Pattern measurements were achieved utilizing a millimeter-wave diode detector circuit implemented directly on the antenna substrate. © 2013 IEEE.

We present the design and development of a compact, broadband balun based on a quasi-lumped LC transformer. The balun is constructed on a multilayer liquid crystal polymer substrate. The balun has a wide range of operating frequency from 0.9 to 3.6 GHz. Within this operating band, the balun achieves a measured insertion loss of less than 1 dB, a measured return loss of better than 10 dB, a measured amplitude imbalance of less than 1 dB and a measured phase imbalance less than 7°. This balun has an extremely compact size of 2 × 2.5 mm2. Copyright © 2013 Wiley Periodicals, Inc.