Kevin Shreve

Multilayer liquid crystal polymer based RF frontend module for millimeter wave imaging

In this paper we proposed an integrated RF front-end module by using multilayer liquid crystal polymer (LCP) substrates in millimeter wave frequency (mmW) range. The module consists of a linearly tapered slot antenna (LTSA), low noise amplifiers (LNA), as well as various passive components, including transmission lines, waveguides, filters, and their transitions. The active LNAs and their related bias circuits are integrated with RF circuits through wire-bonding process to achieve a gain of 12 dB centered at 94GHz. The fabricated devices are characterized and compared with simulated results, showing good agreement. The LTSA has a wide impedance bandwidth from 43 to 90 GHz and high radiation gain. The compact module holds tremendous promise in the high-performance applications, such as mmW imaging, and many other high density RF systems.

Transparent silicon solar cells: Design, fabrication, and analysis

Transparent silicon can lead to increased conversion efficiency in a multi-junction assembly by transmitting near and below band gap energy photons to a lower band gap solar cell. With semi-empirical calculations from Gray et.al. [1] potential efficiency gain from a lower band gap solar cell can be 4.9% absolute under concentration. The present work analyzes a 4-wire tandem system consisting of mono-crystalline silicon and a material of lower band gap filtered by a dichroic mirror under concentration. Optimization focuses on the thickness of the silicon, the band gap of the lower solar cell, and different levels of light concentration. Silicon devices are fabricated, tested outdoors, and analyzed to develop improved structures which are closer to the design goal for this transparent silicon solar cell of 8.2%. Devices fabricated for this work have high transparency to below band gap light and efficiency of 6.1% at 50X when filtered by the dichroic mirror. This compares favorably to the previously reported 5.4% for a transparent silicon solar cell as reported by Barnett et. al. [2].

Realization of a video-rate distributed aperture millimeter-wave imaging system using optical upconversion

Passive imaging using millimeter waves (mmWs) has many advantages and applications in the defense and security markets. All terrestrial bodies emit mmW radiation and these wavelengths are able to penetrate smoke, fog/clouds/marine layers, and even clothing. One primary obstacle to imaging in this spectrum is that longer wavelengths require larger apertures to achieve the resolutions desired for many applications. Accordingly, lens-based focal plane systems and scanning systems tend to require large aperture optics, which increase the achievable size and weight of such systems to beyond what can be supported by many applications. To overcome this limitation, a distributed aperture detection scheme is used in which the effective aperture size can be increased without the associated volumetric increase in imager size. This distributed aperture system is realized through conversion of the received mmW energy into sidebands on an optical carrier. This conversion serves, in essence, to scale the mmW sparse aperture array signals onto a complementary optical array. The side bands are subsequently stripped from the optical carrier and recombined to provide a real time snapshot of the mmW signal. Using this technique, we have constructed a real-time, video-rate imager operating at 75 GHz. A distributed aperture consisting of 220 upconversion channels is used to realize 2.5k pixels with passive sensitivity. Details of the construction and operation of this imager as well as field testing results will be presented herein.

Optical up-conversion enables capture of millimeter-wave video with an IR camera

Millimeter waves (mmWs) are electromagnetic signals with frequencies between 30GHz (10mm wavelength) and 300GHz (1mm wavelength). They are longer in wavelength than IR and terahertz signals but shorter than radio waves. Most objects naturally emit weak amounts of mmWs, much like IR radiation or heat. In addition, the atmosphere provides high thermal contrast for reflective objects at mmWs in all weather conditions, day and night. Signals at these long wavelengths are able to penetrate many materials, including clothing, most building materials, and atmospheric conditions such as fog (see Figure 1). However, unlike x-rays mmWs are completely safe and nonionizing to human tissue. These advantages have been driving the desire to develop a real-time imaging system that operates at mmWs for surveillance and security applications.1 Our eyes cannot ‘see’ mmW signals. To detect them, we at Phase Sensitive Innovations (PSI) Inc.3 and the University of Delaware (UD) have developed sensitive imaging systems capable of capturing imagery in the Q-band (33–50GHz) and W-band (75–110GHz) mmW regimes. These systems can be used for allweather navigation, situational awareness in degraded visual environments, and stand-off detection of contraband and improvised explosive devices. As an example, Figure 2 shows a picture of a UD laboratory taken with a W-band, single-pixel scanning imager. The imagery is intuitive and the modality can be completely covert, unlike radar or laser detection and ranging images. Figure 1. Atmospheric attenuation curves from 10GHz to 1THz under various levels of relative humidity (RH) and fog. Plot was generated using atmospheric codes developed for the North Atlantic Treaty Organization and notes some of the atmospheric ‘windows’ used for imaging.2

Video rate passive millimeter-wave imager utilizing optical upconversion with improved size, weight, and power

In this presentation we will discuss the performance and limitations of our 220 channel video rate passive millimeter wave imaging system based on a distributed aperture with optical upconversion architecture. We will cover our efforts to reduce the cost, size, weight, and power (CSWaP) requirements of our next generation imager. To this end, we have developed custom integrated circuit silicon-germanium (SiGe) low noise amplifiers that have been designed to efficiently couple with our high performance lithium niobate upconversion modules. We have also developed millimeter wave packaging and components in multilayer liquid crystal polymer (LCP) substrates which greatly improve the manufacturability of the upconversion modules. These structures include antennas, substrate integrated waveguides, filters, and substrates for InP and SiGe mmW amplifiers.

High fill factor RF aperture arrays for improved passive, real-time millimeter wave imaging

Sensors operating in the millimeter wave region of the electromagnetic spectrum provide valuable situational awareness in degraded visual environments, helpful in navigation of rotorcraft and fixed wing aircraft. Due to their relatively long wavelength, millimeter waves can pass through many types of visual obscurants, including smoke, fog, dust, blowing sand, etc. with low attenuation. Developed to take advantage of these capabilities, ourmillimeter wave imager employs a unique, enabling receiver architecture based on distributed aperture arrays and optical upconversion. We have reported previously on operation and performance of our passive millimeter wave imager, including field test results in DVE and other representative environments, as well as extensive flight testing on an H-1 rotorcraft. Herein we discuss efforts to improve RF and optical component hardware integration, with the goal to increase manufacturability and reduce c-SWaP of the system. These outcomes will allow us to increase aperture sizes and channel counts, thereby providing increased receiver sensitivity and overall improved image quality. These developments in turn will open up new application areas for the passive millimeter wave technology, as well as better serving existing ones.

Packaging of High-Gain Multichip Module in Multilayer LCP Substrates at

In this paper, we packaged a multichip module (MCM) in multilayer liquid crystal polymer (LCP) substrate using V-shaped wire bond and 3-D-printed housing. In the proposed module, two low-noise amplifiers (LNAs) are cascaded in series to obtain high gain and low noise figure, and multilayer circuit is designed to achieve high assembly density. To minimize mode mismatch between microstrip lines on LNA and LCP with low dielectric constant, V-shaped wire bond was designed for LNA integration, achieving low insertion loss and low reflection at

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-band. To verify this bonding design experimentally, a single-chip module was first integrated and characterized, successfully achieving a gain of more than 26.5 dB from 80 to 100 GHz. Then, the MCM was investigated and packaged, in which substrate integrated waveguides and via barriers are introduced to eliminate the potential substrate modes, and 3-D-printed plastic housing coated with gold is designed to capsulate the LNAs and isolate them in free space. The measured data demonstrate a high gain of 50 dB, a low noise figure of less than 6 dB, and linear phase from 80 to 97 GHz.

High-Power, Aperture Coupled Photonic Antenna

A high-power charge-compensated modified uni-travelling carrier photodetector is directly integrated into an aperture coupled patch antenna. The coupling technique offers not only good isolation between feed and radiating patch substrates but also wide operational bandwidth. The antenna is developed to operate at 22 GHz with 3-dB relative bandwidth of ~20%, over which the measured effective isotropic radiated power approaches 31 dBm. The photonic antenna is integrated with a lightweight, low form factor fiber-optic feed that demonstrates potential for future wireless communications applications. The antenna’s electrical and radiation characteristics are observed to be in good agreement with simulations.