W-Band GaAs HEMT MMIC Subharmonically Pumped Diode Mixers with 20 GHz IF Bandwidth

Two subharmonically pumped (SHP) diode mixers are designed for wideband W-band RF frequencies, fixed LO frequency operation. These mixers are fabricated on a 4-mil substrate using 0.1- µµµµm GaAs MMIC process. Both simulation and test results show that the mixers are with 12.25 and 11.75 dB average conversion losses, respectively. Both mixers have IF bandwidth wider than 20 GHz. The conversion loss flatness of the symmetric circuit is within ±1.25 dB. To our knowledge, these are the state-of-the-art result on low-conversion-loss wideband MMIC SHP diode mixers

W-Band GaAs HEMT MMIC Subharmonically Pumped Diode Mixers with 20 GHz IF Bandwidth

Two subharmonically pumped (SHP) diode mixers are designed for wideband W-band RF frequencies, fixed LO frequency operation. These mixers are fabricated on a 4-mil substrate using 0.1-µ µ µ µm GaAs MMIC process. Both simulation and test results show that the mixers are with 12.25 and 11.75 dB average conversion losses, respectively. Both mixers have IF bandwidth wider than 20 GHz. The conversion loss flatness of the symmetric circuit is within ± ± ± ±1.25 dB. To our knowledge, these are the state-of-the-art result on low-conversion-loss wideband MMIC SHP diode mixers

AMiBA: Broadband Heterodyne CMB Interferometry

The Y. T. Lee Array for Microwave Background (AMiBA) has reported the first science results on the detection of galaxy clusters via the Sunyaev Zel'dovich effect. The science objectives required small reflectors in order to sample large scale structures (20') while interferometry provided modest resolutions (2'). With these constraints, we designed for the best sensitivity by utilizing the maximum possible continuum bandwidth matched to the atmospheric window at 86-102GHz, with dual polarizations. A novel wide-band analog correlator was designed that is easily expandable for more interferometer elements. MMIC technology was used throughout as much as possible in order to miniaturize the components and to enhance mass production. These designs will find application in other upcoming astronomy projects. AMiBA is now in operations since 2006, and we are in the process to expand the array from 7 to 13 elements.Comment: 10 pages, 6 figures, ApJ in press; a version with high resolution figures available at http://www.asiaa.sinica.edu.tw/~keiichi/upfiles/AMiBA7/mtc_highreso.pd

The Yuan-Tseh Lee Array for Microwave Background Anisotropy

The Yuan-Tseh Lee Array for Microwave Background Anisotropy (AMiBA) is the first interferometer dedicated to studying the cosmic microwave background (CMB) radiation at 3mm wavelength. The choice of 3mm was made to minimize the contributions from foreground synchrotron radiation and Galactic dust emission. The initial configuration of seven 0.6m telescopes mounted on a 6-m hexapod platform was dedicated in October 2006 on Mauna Loa, Hawaii. Scientific operations began with the detection of a number of clusters of galaxies via the thermal Sunyaev-Zel'dovich effect. We compare our data with Subaru weak lensing data in order to study the structure of dark matter. We also compare our data with X-ray data in order to derive the Hubble constant.Comment: accepted for publication in ApJ (13 pages, 7 figures); a version with high resolution figures available at http://www.asiaa.sinica.edu.tw/~keiichi/upfiles/AMiBA7/pho_highreso.pd

OPTIMAL METHODOLOGIES IN INVERSE SCATTERING UTILIZING WAVELENGTH, POLARIZATION AND ANGULAR DIVERSITY

It is well-known that the scattered electromagnetic field produced by a scattering target subjected to coherent illumination obeys Maxwell\u27s equations. The scattered field is determined by the relative positions of scattering centers on the target. A scattering center is defined as target detail that contributes to the observed field. It has been of longstanding interest in electromagnetics to investigate and develop analytical methods and measurement systems that enable one to use the information in the measured scattered field to infer the target shape, size, orientation and material properties in the context of target identification and/or classification. This problem is described by the generic term inverse scattering which is to determine the boundary conditions at the scattering target given the received scattered wavefield over a range of aspect angles and frequencies that is normally determined by practical constraints. The aim of the work described in this dissertation is the study and development of an optimal data acquisition and processing scheme for use in microwave inverse scattering techniques employing trade-off between angular, frequency and polarization diversities to collect a maximum amount of information about the scattering target cost-effectively. Efficient data processing and terminal information presentation in the form of an image interpretable by the eye-brain system are also central to this study. The use of frequency diversity over an extremely broad spectrum in coherent scattering measurements as a means of acquiring more information about the scattering target has been the subject of vigorous study at the Electro-Optics and Microwave-Optics Laboratory of the University of Pennsylvania. This dissertation represents a continuation of this effort. A variety of methods aimed at making the data acquisition and processing more efficient and cost-effective are studied. In particular, methods of deriving a phase reference signal from the target being imaged (target derived reference--TDR concept) to affect coherent detection and imaging are studied and compared. The advantages of TDR are numerous such as simplification of data acquisition, allowing considerable thinning of the imaging aperture, and elimination of Doppler and atmospheric distortions. Also the role of polarization, a priori knowledge (such as target symmetry for example), and digital image processing in image enhancement are studied extensively in an approach based on close interaction of theoretical analysis and experimental verification. . . . (Author\u27s abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UM