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This thesis describes the design of low noise amplifier (LNA) for the international Square Kilometre Array (SKA) project. LNAs in radio astronomy receivers play an important role of amplifying very weak signals from the Universe and the significance of the LNAs become more crucial in the SKA which is the largest and most sensitive radio telescope in the World. The aperture array (AA) system proposed for SKA is projected to deploy tens of millions of LNAs in a receiver system to survey large areas of the sky simultaneously over the frequency bands of 70-450MHz and 400-1400MHz. Hence LNA power efficiency has a significant implication in the SKA AA system due to the large number of the LNAs required. This thesis describes the design of 9 LNAs for the SKA. Seven LNAs with very low power consumption were designed, fabricated and characterised for SKA AA system using MIC technology by employing COTS components. Single ended and differential to single ended configurations were used for the lower frequency band of SKA AA system. Low noise figures (noise temperatures) of 0.6dB (43K) were achieved with high gain of more than 30dB at a power consumptions of less than 25mW for lower frequency band of AA. The LNAs designed to perform at 400-1400MHz have a very low power consumption of 28mW with an average noise figure (noise temperature) of 0.45dB (32K). Two MMIC LNAs based on low noise TQP13N pHEMT process of TriQuint Semiconductors with gate length of 130nm were designed for the low (0.7-1.8GHz) and high (8-10GHz) frequency ends of the SKA. The packaging and housing solutions of the SKA LNAs were implemented. The work described in this thesis shows low noise figures (noise temperatures) with high gains are achieved at a very low power consumption of less than 30mW for the MIC LNAs in the SKA AA system by using commercially available components.

The technique of microwave . limb sounding -from space represents a very powerful tool for determining the atmospheric processes involved in ozone depletion, the greenhouse effect, acid rain, etc.. Unfortunately, the technology involved in producing millimetric and submillimetric devices is highly complex, and miniature. The power levels and environmental conditions existing aboard spacecraft in present 'use, 5 differ from those required by the low noise heterodyne receivers employed by the Radio Astronomy community. Therefore, great effort has been spent in the design of radiometers with limited power and weight requirements, so that they can withstand the rigours of launch and operation in space. This thesis describes the design and construction of a subharmonically pumped, double diode mixer which is now used in an airborne atmospheric radiometer. The mixer power requirement and rugged nature make it an ideal option for space operation. The assembly of the millimetric circuit required the development, of novel techniques which enabled the incorporation of discrete circuit elements onto a single quartz substrate. This allowed the physical testing of the millimetric circuit independently of the RF block. A detailed investigation into the `whiskering' technique was carried out. It was thus possible to pinpoint errors that had previously occurred in assembly and which had resulted in the failure of a space flight device. With the adoption of quantified procedures, devices constructed using the `whiskering' technique were shown to be considerably more resilient than had previously been thought. The performance of the mixer is comparable with other designs using Schottky diodes at room temperature (-1200K DSB) and the local oscillator power requirement is easily met with a single solid state source. A simple theoretical analysis using the Seigel and Kerr program was undertaken in conjunction with RF measurements performed on a 65X scale model to determine steps required for further improvement.

This thesis presents instrumentation with which to measure the abundance of neutral hydrogen gas in the Universe. Measuring where the Universe’s hydrogen is, and tracing how its distribution evolves with time, holds the key to understanding how galaxies evolve, the nature of dark energy, and how the first cosmic structures formed. In particular, this thesis looks at instrumentation for 21-cm intensity mapping telescopes. In 21-cm intensity mapping, the collective emission of many galaxies is measured, without individual detections. This technique promises to allow detection of the baryonic acoustic oscillation peaks in the power spectrum of the Universe’s matter distribution. Such a detection would increase constraints on cosmological parameters. There are two main approaches to designing a 21-cm intensity mapping instruments: using a filled aperture instrument such as a single-dish telescope, or using a sparse aperture instrument such as an interferometric array of dipoles. This thesis investigates analogue components for a sparse aperture instrument operating at 1.0-1.5 GHz. As part of this work, a 16-element sparse aperture array was designed and constructed. To test the array’s performance, field testing was conducted; the results of which are presented here. In addition to this, I have designed a new digital spectrometer for redshifted hydrogen line science, named HISPEC. A copy of this spectrometer has been installed on the Parkes 64 m telescope, as a digital signal processor for the 21-cm multibeam receiver. HISPEC has increased instantaneous bandwidth, higher interchannel isolation, and improved quantization efficiency as compared to the existing backend, MBCORR. The HISPEC equipped multibeam receiver is an ideal instrument for 21-cm intensity mapping at redshifts z<0.2.

Low frequency radio astronomy has entered a second golden age driven by the development of a new class of large-N interferometric arrays. The low frequency array (LOFAR) and a number of redshifted HI Epoch of Reionization (EoR) arrays are currently undergoing commission and regularly observing. Future arrays of unprecedented sensitivity and resolutions at low frequencies, such as the square kilometer array (SKA) and the hydrogen epoch of reionization array (HERA), are in development. The combination of advancements in specialized field programmable gate array (FPGA) hardware for signal processing, computing and graphics processing unit (GPU) resources, and new imaging and calibration algorithms has opened up the oft underused radio band below 300 MHz. These interferometric arrays require efficient implementation of digital signal processing (DSP) hardware to compute the baseline correlations. FPGA technology provides an optimal platform to develop new correlators. The significant growth in data rates from these systems requires automated software to reduce the correlations in real time before storing the data products to disk. Low frequency, widefield observations introduce a number of unique calibration and imaging challenges. The efficient implementation of FX correlators using FPGA hardware is presented. Two correlators have been developed, one for the 32 element BEST-2 array at Medicina Observatory and the other for the 96 element LOFAR station at Chilbolton Observatory. In addition, calibration and imaging software has been developed for each system which makes use of the radio interferometry measurement equation (RIME) to derive calibrations. A process for generating sky maps from widefield LOFAR station observations is presented. Shapelets, a method of modelling extended structures such as resolved sources and beam patterns has been adapted for radio astronomy use to further improve system calibration. Scaling of computing technology allows for the development of larger correlator systems, which in turn allows for improvements in sensitivity and resolution. This requires new calibration techniques which account for a broad range of systematic effects. And, a deep integration between DSP hardware and software data reduction into a single backend.