Meysam Moallem

Miniaturized-Element Frequency Selective Surfaces for Millimeter-Wave to Terahertz Applications

This paper presents a single-face, membrane-supported, miniaturized-element frequency selective surface (MEFSS) for image rejection of a J-band upconvertor mixer. In this design, a new miniaturized-element patch-wire MEFSS configuration is proposed to select the upper-side band (USB) response of a wave radiated from an upconvertor. The proposed MEFSS produces a single pole and an adjacent transmission zero to suppress the lower sideband. It is shown that the frequency response of this MEFSS can be predicted by an equivalent circuit model and that the location of pole and zero can be tuned independently with physical parameters. MEFSS elements are supported and protected by a 10 μm thick low-loss polymer membrane which allows flexible handling and minimizes substrate losses. Thickness of the metallic traces is increased to reduce the conductor loss. A salient feature of this design is low sensitivity of its frequency response to the angle of incidence and the absence of a harmonic response. This feature allows placement of the spatial filter in close proximity to radiating elements with spherical wavefronts. The membrane-supported MEFSS is fabricated using a microfabrication method with tolerances that allow such filter implementations up to terahertz frequencies. Performance of the fabricated device is experimentally verified using a free-space measurement setup. Experimental results show that the transmission response has 0.6 dB insertion loss in the passband (221-223 GHz) and more than 25 dB rejection out-of-band (206-208 GHz) which is in good agreement with full-wave simulation and its circuit model prediction.

A Broadband, Micromachined Rectangular Waveguide to Cavity-Backed Coplanar Waveguide Transition Using Impedance-Taper Technique

This paper presents a broadband fully micromachined transition from rectangular waveguide to cavity-backed CPW line for submillimeter-wave (sub-MMW) and terahertz applications. A cavity-backed CPW line (CBCBW) is a planar transmission line that is designed and optimized for minimum loss while providing 50- Ω characteristic impedance. This line is shown to provide less than 0.12 dB/mm loss over the entire J-band (220-325 GHz). The transition from CBCPW to waveguide is realized in three steps to achieve a broadband response with a topology amenable to silicon micromachining. The first step is a tapered transition from the CBCPW line to a 50- Ω reduced-height waveguide. The next two steps utilize a novel in-plane impedance tapering technique to transition from the reduced-height waveguide to the on-wafer regular height waveguide. The full transition has less than 0.9 dB of insertion loss and more than 13 dB of return loss over the entire J-band (39% bandwidth). Silicon micromachining technology is used to fabricate prototypes of back-to-back CBCPW line-to-waveguide transitions. A novel waveguide-probe measurement setup is introduced and utilized to evaluate the performance of the transitions and the CBCPW lines.

Polarimetric Study of MMW Imaging Radars for Indoor Navigation and Mapping

In this communication, the application of sub-millimeter-wave imaging radars for collision avoidance and navigation of autonomous platforms in indoor environments is investigated. The polarimetric backscattering phenomenology of walls and doorways are studied to aid the design and system specifications of such radar systems. Polarimetric backscatter measurements of different wall covers, such as dry-wall, concrete blocks, wood, etc., as a function of incidence angle are carried out using a network analyzer operating at J-band. Also an instrumentation radar operating at 215 GHz is setup to collect backscatter data from corridors in an indoor setting. At each radar position, radar range profiles for both vertical and horizontal polarizations as a function of angle are used to form polar images for obstacle detection. It is shown that horizontally polarized incident wave can generate higher backscatter level and less reflection from smooth walls at steep angles of incidence and thus is the preferred polarization for this application. The polar images at each location are then co-registered in a global coordinate matrix to form a complete map of the interior layout. Feature extraction and image processing methods are then applied to remove multipath and enhance the radar map of building interiors.

A single-layer metamaterial-based polarizer and bandpass frequency selective surface with an adjacent transmission zero

In this article, a high order bandpass miniaturized-element frequency selective surface (MEFSS) and a wire-grid polarizer are implemented on a single-layer substrate. This compact spatial filter and polarizer are designed to be incorporated in a 26 GHz UWB rangefinder radar. The spatial filter has a passband at 26 GHz and a transmission zero at 13 GHz. A new single-face miniaturized-element FSS has been proposed to produce the desired frequency response. An accurate circuit model has been developed for this structure to facilitate the filter synthesis process. The structure has been analyzed and optimized with a full-wave EM solver. A prototype of the designed structure has been fabricated and tested. Measurement results show low insertion loss in the passband (<0.5 dB) and high rejection at transmission zero (>20dB).

Optimally designed membrane-supported grounded CPW structure for submillimeter-wave applications

In this paper, a novel low loss CPW structure is presented. The line has less than 0.1 dB/mm insertion loss at 230 GHz, which is very small compared to previous CPW structures. The line can be used in millimeter- and submillimeter-wave MMIC applications as high-Q filters, resonators, corporate feed of antenna arrays, where high efficiency is a major issue.

Compact beam scanning 240GHz radar for navigation and collision avoidance

Autonomous small robotic platforms require a suite of sensor to navigate and function in complex environment. Due to limited space, onboard power, and processing capability these sensors must be low mass, compact size, low power, and run with minimal processing resources. We are in the process of developing a compact and low-power imaging mm-wave radar system for small autonomous robotic platforms operating at Y-band to allow for navigation and obstacle detection in conditions that make the use of passive optical sensors difficult or impossible. The radar system is being fabricated and assembled using silicon micromachining technique with the overall mass of 5 grams, peak power of 200 mW, and operational power of 6.7 mW for one frame per second update rate, field of view of ± 25°, angular resolution of 2°, range resolution of 37.5cm, and range of 400m. The beam steering is accomplished by frequency scanning and the range resolution is obtained from the standard FMCW technique utilizing a chirped signal waveform with step discontinuities. This paper will present the overall architecture of this radar system in addition to the phenomenological investigation of scattering from obstacle in indoor environment. It is also shown how radar images taken from indoor scenes can be interpreted and utilized to create the interior layout of a building.

A spatial image rejection filter based on miniaturized-element FSS for J-band radar applications

In this article, a single-face, membrane-supported, miniaturized-element frequency selective surface (MEFSS) for suppressing the image response of a J-band upconvertor mixer is presented. In this design, a new miniaturized-element patch-wire MEFSS configuration is proposed to select the upper-side band (USB) response of a wave radiated from an upconvertor. The proposed MEFSS produces a single pole and an adjacent transmission zero to suppress the lower sideband. It is shown that the frequency response of this MEFSS can be designed readily using an equivalent circuit model. MEFSS elements are supported and protected by a 10μm thick low-loss polymer membrane which allows flexible handling and minimizes substrate losses. The membrane-supported MEFSS is fabricated using wafer microfabrication technology. Experimental results show that transmission response has 0.6 dB insertion loss in the passband (221-223 GHz) and more than 25 dB rejection out-of-band (206-208 GHz) which is in good agreement with full-wave simulation and its circuit model prediction.

Y-band radar assessment for indoor navigation and mapping

In this paper, the application of sub-millimeter-wave imaging radars for collision avoidance and navigation of autonomous platforms in indoor environments is investigated. The polarimetric scatter phenomenology of walls and doorways are studied to aid the designing and system specifications of such radar systems. An instrumentation radar operating at 215 GHz is setup to collect backscatter data from corridors in an indoor setting. The backscattered data as a function of azimuth angle are collected while the radar is moved along the corridors. At each radar position, radar range profiles for both vertical and horizontal polarizations as a function of angle are used to form polar images. These images can be generated real time for obstacle-detection and navigation of autonomous robots. It is shown that horizontally polarized incident wave can generate higher backscatter level from smooth walls at steep angles of incidence and thus is the preferred polarization configuration for this application. Using the coordinate radar positions at each point, the polar images at each location are then co-registered in a global coordinate matrix through a “see-and-remember” algorithm to form a complete map of the interior layout. A number of image processing techniques are applied to the raw radar range profile maps to enhance the image quality and to remove the undesired effects. A linear feature extraction method based on Hough transform is used to extract the rectilinear features (walls, doors, etc.) in the complete map. Algorithms are developed to eliminate the ghost targets resulted from multi-path in the hallways.

Y-band phenomenology of indoor environment

Nowadays radars are commonly used in many civilian and military applications where standoff sensing and detection is needed. With the advent of technology and shortage of available spectrum at lower bands the operating frequency of the radars are being pushed higher. There are of course certain advantages associated with higher frequencies; most importantly is the reduction in size and mass of the radar for certain angular resolution as the frequency goes higher. In recent years, millimeter-wave radars have been widely used in applications ranging from automotive collision avoidance [1] to guidance systems for aircraft landing [2] and target detection and tracking [3]. Ability to penetrate poor weather, dust, smoke, cloth and other low loss but optically opaque material makes millimeter-wave radars suitable for navigation and surveillance [4]. To examine the utilization of radars for any application a thorough understanding of interaction of electromagnetic wave with the intended target and its environment is needed. In the past 20 years significant effort has been directed towards development of models based on theory and experiments at Ka-band and W-band [5]. However, such studies are rare at higher MMW frequencies. Our research group is engaged in developing an ultra lightweight short range MMW radar system operating at Y-band frequencies for collision avoidance and navigation of micro autonomous robotic platforms. Enclosed spaces and indoor environments are intended domain of operations for such system. In this paper, phenomenology of indoor environment at 215 GHz is investigated. A stepped frequency 215 GHz instrumentation radar system capable of vertical and horizontal polarization transmission and reception is utilized to collect backscatter data in indoor environment as the radar is moved within the building. As will be shown, horizontal polarization measurements give a much more accurate mapping of the environment compared to the vertical polarization. Measurement results are then processed to eliminate noise and shadow images, in order to create a clear mapping of the building.

A novel non-contact s-parameter measurement method for sub-MMW multi-port on-wafer devices

The increasing interest in the development of micromachined components for sub-MMW and terahertz applications calls for a reliable and accurate measurement method for characterization of such components. The conventional on-wafer measurement technique using GSG probes, which require physical contact, are subject to wear and damage of the probe tips due to repeated use. This results in significant measurement errors at sub-MMW and higher frequencies. In addition, characterization of multi-port components using two-port measurement systems require independent measurements of pairs of ports one at a time while all the other ports are terminated with matched loads which are very difficult to realize at sub-MMW and terahertz bands.