Yogesh B. Karandikar

Cryogenic 2–13 GHz Eleven Feed for Reflector Antennas in Future Wideband Radio Telescopes

The system design of a cryogenic 2-13 GHz feed is considered with emphasis on its application in future wideband radio telescope systems. The feed is based on the so-called Eleven antenna and the design requires careful integration of various sub-designs in order to realize cryogenic operation. The various sub-designs include the electrical design of the Eleven antenna, design of the critical center puck, alternative solutions for integrating the Eleven antenna with low-noise amplifiers (LNAs), mechanical and cryogenic design and tests, and system noise temperature estimation and measurements. A great deal of simulated and measured results are presented throughout this paper, including the electrical, mechanical and cryogenic performance, and an assessment of the system noise temperature. The objective of this work is to present a good feed candidate that is well-suited for VLBI2010 and SKA radio telescopes. Further developments needed to completely fulfill the requirements for these future wideband radio telescopes are also discussed.

340 GHz Integrated Receiver in 250 nm InP DHBT Technology

A 340 GHz integrated receiver based on a 250 nm InP DHBT technology is presented in this paper. It consists of a 2 × 2 differential patch array antenna, a sub-harmonically pumped Gilbert mixer and an IF buffer amplifier. Performance of the integrated receiver is evaluated by setting up a RF link in the frequency band of 302-338 GHz. At 338 GHz RF and 170 GHz LO, the peak conversion gain of 11.8 and 14.0 dB is achieved with and without antenna, respectively. A double-sideband noise figure of 17 dB at room temperature is obtained from direct noise figure measurement .

Monolithically Integrated 200-GHz Double-Slot Antenna and Resistive Mixers in a GaAs-mHEMT MMIC Process

This paper presents the design and characterization of two resistive mixers integrated with a double-slot antenna in a 100-nm GaAs mHEMT technology. With RF frequency varying from 185 to 202 GHz, a typical conversion loss (L c) of 8.0 dB is measured for the single-ended mixer and a typical L c of 12.2 dB is obtained from one of the two IF outputs for the single-balanced mixer. Each mixer is integrated with a double-slot antenna and mounted on an Si lens. Incorporating the antenna gain and the conversion loss of the mixer, a typical receiver gain of 15.4 dB is achieved for the integrated antenna with single-ended mixer, and a typical receiver gain of 11.2 dB is obtained for the integrated antenna with single-balanced mixer by measuring one of the two IF outputs. In this paper, a novel method is also proposed and proved to evaluate a moderate to high noise figure (NF) device in millimeter/sub millimeter frequency band. The result shows that the single-ended mixer in this paper has an NF around 1.0 dB higher compared to its Lc, and the single-balanced one has an NF about 1.6 dB higher than its Lc at room-temperature operation.

A 340 GHz high Gaussicity smooth spline horn antenna for the STEAMR instrument

We present the design, fabrication and measurements of a smooth walled spline feed horn antenna for the satellite borne climate research instrument STEAMR operating at 340 GHz. A method has been developed which, for a certain desired beam waist, can be used to optimize the horn profile for high Gaussicity and ultra-low sidelobes. The simulated performance of the horn achieves a beam waist of 1.9 mm over the band 323-357 GHz with Gaussian coupling efficiency exceeding 98%. The peak cross-polar sidelobes are below -28 dB over the required frequency band. For cost effective manufacturing with high repeatability, the smooth wall spline profile is drilled in out from a metal block using a custom made broach. To validate the design and fabrication, planar measurements of the phase and amplitude have been performed and from measured E-field vital horn parameters have been extracted.

140-220 GHz Imaging Front-end Based on 250 nm InP/InGaAs/InP DHBT Process

This paper presents a pre-amplified detector receiver based on a 250 nm InP/InGaAs/InP double heterojunction bipolar transistor (DHBT) process available from the Teledyne scientific. The front end consists of a double slot antenna followed by a five stage low noise amplifier and a detector, all integrated onto the same circuit. Results of measured responsivity and noise are presented. The receiver is characterized through measuring its response to hot (293) and cold (78) K terminations. Measurements of the voltage noise spectrum at the video output of the receiver are presented and can be used to derive the temperature resolution of the receiver for a specific video bandwidth.

Mode Counting in Rectangular, Cylindrical, and Spherical Cavities With Application to Wireless Measurements in Reverberation Chambers

The accuracy of wireless measurements in a reverberation chamber depends on the mode density. Reverberation chambers are normally rectangular in shape, but could also be made cylindrical or spherical. In this paper, modes in classical rectangular, cylindrical, and spherical cavities are counted over large frequency ranges in order to determine the number of modes over a specific excitation bandwidth as a function of frequency, i.e., mode density. The cavities are then judged by these mode densities for applications to reverberation chambers.

Compact Integration of Sub-Harmonic Resistive Mixer with Differential Double Slot Antenna in G-Band Using 50nm InP-HEMT MMIC Process

Sub-Harmonic resistive HEMT based mixers in Gband have been designed and integrated with Double Slot Antenna in Differential Configuration for the first time. This novel topology shows compact integration of active devices between antenna ports while achieving 25 GHz bandwidth around 200 GHz. The dual-gate 50nm x 15um InP HEMT used in the design achieves the conversion loss of 15 dB with +3 dBm LO power drive. Furthermore, a similar topology when used as a Harmonic mixer using a single gate device offers 16.5 dB conversion loss for +4 dBm LO power. For compact integration, via hole matching on slot antenna is also presented.

Development of a coolable 2–14 GHz Eleven feed for future radio telescopes for SKA and VLBI 2010

The Eleven feed is a log-periodic array of parallel dipoles in Eleven (II) configuration. It exhibits constant beam width and phase center position over a decade bandwidth, and finds therefore application as a wideband feed for reflector antennas. The present paper gives a summary of the present performance of a 2–14 GHz Eleven feed that is under development for use as a feed for VLBI 2010 radio telescopes for geodesy. Previous reported Eleven feeds did not reach that high in frequency. The intention is also to develop a feed that can be integrated with a low noise amplifier inside a cryostat at temperature of 14K, and receive the waves focused by the primary reflector through an RF window in the cryostatic cavity. Thereby the lowest system noise temperature is ensured. The present model has successfully survived cooling to 14 K.

THz smooth-walled spline horn antennas: Design, manufacturing and measurements

We describe a versatile and cost-efficient method for producing smooth-walled spline horn antennas for applications in THz radiometry. Specifically, the development of four different horns for radiometer receiver applications at frequencies 120, 183, 340 and 874 GHz is presented. General methods for efficient optimization of the spline profiles have been developed which enable the horn designs to be tailored to each application. All four designs display high Gaussicity (typically ~98%). Manufacturing methods based on numerical milling in splitblocks, lathing and drilling have been tested and compared. Milled splitblock horns with integrated receiver circuits (Shottky mixers in this case) allow for lower losses in the receiver system at the expense of higher cross-polarization levels. The radiation pattern of three designs at 183, 340 and 874 GHz have been measured using planar and rotational scanners.

A compact 340 GHz 2x4 patch array with integrated subharmonic gilber core mixer as a building block for multi-pixel imaging frontends

For linear multi-pixel imaging systems, a linear stack of pixels comprising of an antenna and a heterodyne receiver are needed. Such pixels can be realized using MMIC processes. The main constraint for such multi-pixel system is a compact array of pixels giving high coupling to quasi-optics used for focusing. This paper addresses this trade-off and presents a novel solution based on beam synthesis of two consecutive subarrays. One such sub-array along with heterodyne receiver is described as half-pixel in this paper and it is realized using 2×4 patch array and Gilbert core sub-harmonic mixer using a 250nm DHBT process. The patch array has ohmic loss better than 8 dB and mixer conversion loss is 6-8 dB over 320-350 GHz RF band. The chip size is 1mm × 2mm and therefore for 7 simultaneous beams a MMIC of 8 half-pixels is foreseen.