Matthew Sieth

Theory and Experiment of a Compact Waveguide Dual Circular Polarizer

A new compact and wide-band waveguide dual circular polarizer at Ka-band is presented and tested in this paper. This compact structure is composed of a three-port polarizing diplexer and a circular polarizer realized by a simple pair of large grooves. The polarizing diplexer includes two rectangular waveguides with a perpendicular H-plane junction, one circular waveguide coupled in E- plane. A cylindrical step and two pins are used to match this structure. For a LHCP or RHCP wave in the circular port, only one speciflc rectangular port outputs power and the other one is isolated. The accurate analysis and design of the circular polarizer are conducted by using full-wave electromagnetic simulation tools. The optimized dual circular polarizer has the advantage of compact size with a volume smaller than 1.5‚ 3 , broad bandwidth, uncomplicated structure, and is especially suitable for use at high frequencies such as Ka-band and above. The prototype of the polarizer has been manufactured and test, the experimental results are basically consistent with the theories.

Note: Cryogenic microstripline-on-Kapton microwave interconnects

Simple broadband microwave interconnects are needed for increasing the size of focal plane heterodyne radiometer arrays. We have measured loss and crosstalk for arrays of microstrip transmission lines in flex circuit technology at 297 and 77 K, finding good performance to at least 20 GHz. The dielectric constant of Kapton substrates changes very little from 297 to 77 K, and the electrical loss drops. The small cross-sectional area of metal in a printed circuit structure yields overall thermal conductivities similar to stainless steel coaxial cable. Operationally, the main performance tradeoffs are between crosstalk and thermal conductivity. We tested a patterned ground plane to reduce heat flux.

W-band heterodyne receiver module with 27 K noise temperature

We present noise temperature and gain measurements of a W-band heterodyne module populated with MMIC LNAs designed and fabricated using a 35 nm InP HEMT process. The module has a WR-10 waveguide input. GPPO connectors are used for the LO input and the I and Q IF outputs. The module is tested at both ambient (300 K) and cryogenic (25 K) temperatures. At 25 K physical temperature, the module has a noise temperature in the range of 27–45 K over the frequency band of 75–111 GHz. The module gain varies between 15 dB and 27 dB. The band-averaged module noise temperature of 350 K and 33 K were measured over 80–110 GHz for the physical temperature of 300 K and 25 K, respectively. The resulting cooling factor is 10.6.

Development of MMIC receivers for cosmic microwave background interferometry

We report on the development of some of the key technologies that will be needed for a large-format Cosmic Microwave Background (CMB) interferometer with many hundreds of wideband W-band (75-110 GHz) receivers. A scalable threebaseline prototype interferometer is being assembled as a technology demonstration for a future ground- or space-based instrument. Each of the prototype heterodyne receivers integrates two InPMonolithic Microwave Integrated Circuit (MMIC) low-noise amplifiers, a coupled-line bandpass filter, a subharmonic balanced diode mixer, and a 90° local oscillator phase switch into a single compact module that is suitable for mass production. Room temperature measurements indicate bandaveraged receiver noise temperatures of 500 K from 85-100 GHz. Cryogenic receiver noise temperatures are expected to be around 50 K.

Development of a 150 GHz MMIC module prototype for large-scale CMB radiation experiments

A prototype heterodyne amplifier module has been designed for operation from 140 to 170 GHz using Monolithic Millimeter- Wave Integrated Circuit (MMIC) low noise InP High Electron Mobility Transistor (HEMT) amplifiers. In the last few decades, astronomical instruments have made state-of-the-art measurements operating over the frequency range of 5-100 GHz, using HEMT amplifiers that offer low noise, low power dissipation, high reliability, and inherently wide bandwidths. Recent advances in low-noise MMIC amplifiers, coupled with industry-driven advances in high frequency signal interconnects and in the miniaturization and integration of many standard components, have improved the frequency range and scalability of receiver modules that are sensitive to a wide (20-25%) simultaneous bandwidth. HEMT-based receiver arrays with excellent noise and scalability are already starting to be manufactured around 100 GHz, but the advances in technology should make it possible to develop receiver modules with even higher operation frequency - up to 200 GHz. This paper discusses the design of a compact, scalable module centered on the 150 GHz atmospheric window using components known to operate well at these frequencies. Arrays equipped with hundreds of these modules can be optimized for many different astrophysical measurement techniques, including spectroscopy and interferometry.

Argus: a 16-pixel millimeter-wave spectrometer for the Green Bank Telescope

We report on the development of Argus, a 16-pixel spectrometer, which will enable fast astronomical imaging over the 85–116 GHz band. Each pixel includes a compact heterodyne receiver module, which integrates two InP MMIC low-noise amplifiers, a coupled-line bandpass filter and a sub-harmonic Schottky diode mixer. The receiver signals are routed to and from the multi-chip MMIC modules with multilayer high frequency printed circuit boards, which includes LO splitters and IF amplifiers. Microstrip lines on flexible circuitry are used to transport signals between temperature stages. The spectrometer frontend is designed to be scalable, so that the array design can be reconfigured for future instruments with hundreds of pixels. Argus is scheduled to be commissioned at the Robert C. Byrd Green Bank Telescope in late 2014. Preliminary data for the first Argus pixels are presented.

Technology developments for a large-format heterodyne MMIC array at W-band

We report on the development of W-band (75–110 GHz) heterodyne receiver technology for large-format astronomical arrays. The receiver system is designed to be both mass producible, so that the designs could be scaled to thousands of receiver elements, and modular. Most of the receiver functionality is integrated into compact monolithic microwave integrated circuit (MMIC) amplifier-based multichip modules. The MMIC modules include a chain of InP MMIC low-noise amplifiers, coupled-line bandpass filters, and sub-harmonic Schottky diode mixers. The receiver signals will be routed to and from the MMIC modules on a multilayer high-frequency laminate, which includes splitters, amplifiers, and frequency triplers. A prototype MMIC module has exhibited a band-averaged noise temperature of 41 K from 82 to 100 GHz and a gain of 29 dB at 15 K, which is the state-of-the-art for heterodyne multichip modules.

Argus: A W-band 16-pixel focal plane array for the Green Bank Telescope

We are building Argus, a 16-pixel square-packed focal plane array that will cover the 75-115.3 GHz frequency range on the Robert C. Byrd Green Bank Telescope (GBT). The primary research area for Argus is the study of star formation within our Galaxy and nearby galaxies. Argus will map key molecules that trace star formation, including carbon monoxide (CO) and hydrogen cyanide (HCN). An additional key science area is astrochemistry, which will be addressed by observing complex molecules in the interstellar medium, and the study of formation of solar systems, which will be addressed by identifying dense pre-stellar cores and by observing comets in our solar system. Argus has a highly scalable architecture and will be a technology path finder for larger arrays. The array is modular in construction, which will allow easy replacement of malfunctioning and poorly performing components.

A W-band heterodyne receiver module prototype for focal plane arrays

A compact W-band heterodyne receiver module populated with MMIC LNAs designed and fabricated using a 35 nm InP HEMT process, and an IQ mixer designed and fabricated using the UMS Schottky diode process is developed as the prototype for Argus, a 16-pixel focal plane array to be deployed on the 100-meter Robert C. Byrd Green Bank Telescope in West Virginia to study star formation. The module has a WR-10 waveguide input. GPPO connectors are used for the LO input and the I and Q IF outputs. The module is tested at both ambient (300 K) and cryogenic (26 K) temperatures. A minimum receiver noise temperature of 27 K was achieved, with less than 45 K noise and more than 20 dB gain in the 85 GHz to 116 GHz band. The band-averaged noise temperature is 34 K and 249 K for a physical temperature of 26 K and 300 K, respectively. The IQ amplitude and phase balance shows image rejection better than 15 dB over 90 percent of the band with constant current operation of both mixers. Image rejection better than 25 dB is measured when optimized currents are used to drive the I and Q mixers.