C-BASS

Abstract:

In this paper, we will present the design and the simulation of a 230GHz finline Ultra-wide IF Bandwidth SIS mixer. This mixer will be used in a novel millimeter-wave heterodyne interferometer: GUBBINS. GUBBINS is designed to demonstrate high surface brightness mm-wave interferometry at modest spatial and spectrum resolution. Its observational targets are the spectrum of the Sunyaev-Zel'dovich effect in the brightness galaxy cluster[3]. The archetype of the mixer design described here is an antipodal finline SIS mixer designed by Paul Grimes in Oxford Experimental Cosmology group in 2008[1]. Here several improvement and modification are made to simplify the design and fabrication, and also enhance the IF bandwidth. An unilateral finline replaces the complicated antipodal finline. No RF bandpass filter is needed after finline. The tuning circuit design presented here aims to achieve wider RF coupling bandwidth, even though only a single junction is used. A multi-stage IF transformer follows the IF bonding pad matching the IF output of the mixer to the input of the IF amplifier, as well as reducing the impact of the parasitical capacitance introduced by the RF finline and RF radial stub.

Abstract:

We present the first, complete 230 GHz feedhorn array manufactured by direct drilling of smooth-walled horns into a single plate of aluminium. The horn design process, based on a genetic algorithm, is described and the fabrication process, via direct drilling using shaped drill bits, is presented. We present cross coupling and beam pattern measurements of a close-packed pair of the smooth-walled horns fabricated in a single block of aluminium. We also present a prototype 37 horn array, again fabricated by drilling into a single block. Our measurements show that our designs and fabrication techniques will be robust when applied to large focal arrays of horns consisting of hundreds or thousands of feedhorns. We expect our smooth-walled horn designs and novel manufacturing techniques will offer an attractive, low-cost alternate to traditional horn arrays consisting of electroformed corrugated horns.

Abstract:

In this paper, we consider the problem of optimum multi-domain real-time beamforming and high-precision beam pattern positioning in application to very large wideband array antennas, particularly to the Square Kilometre Array (SKA) aperture array antenna. We present a new structure for wideband space-frequency beamforming and beamsteering that maximizes detectability of cosmic signals over the array operational frequency range. © 2010 IEEE.

Abstract:

Gigahertz-frequency phased arrays that are integral to next-generation radio astronomy instruments, in particular the Square Kilometre Array (SKA) radio telescope, pose a significant signal processing challenge. We argue that the development of high-performance signal processing systems is critical, not only for the particular application to future radio astronomy instrumentation, but also to the entire field of ultra-wideband phased arrays in the gigahertz bandwidth range. To this end, we have developed a cycle-accurate simulator environment and programming language for a novel, massively multicore array processor, and prototyped on it representative digital frequency domain algorithms. The results of this analysis reveal beamforming as a low compute-to-I/O processing task, best suited to high- I/O-bandwidth, streaming signal processing systems. © 2010 IEEE.

Abstract:

Digital beamforming for the aperture array components of the Square Kilometre Array (SKA) poses considerable computational challenges. We propose a hierarchical scheme aimed at tackling them and introduce OSKAR, a beamforming simulator which implements these ideas and algorithms. The simulator continues to be developed to investigate possible designs for the custom devices envisaged for phase 1 of the SKA construction. © 2010 IEEE.