D. Kettle

Offset balancing in pseudo-correlation radiometers for CMB measurements

Radiometeric CMB measurements need to be highly stable and this stability is best obtained with differential re- ceivers. The residual 1/f noise in the differential output is strongly dependent on the radiometer input offset which can be can- celled using various balancing strategies. In this paper we discuss a software method implemented in the PLANCK-LFI pseudo- correlation receivers which uses a tunable gain modulation factor, r, in the sky-load difference. Numerical simulations and experimental data show how proper tuning of the parameter r ensures a very stable differential output with knee frequencies of the order of few mHz. Various approaches to calculate r using the radiometer total power data are discussed with some examples relevant to PLANCK-LFI. Although the paper focuses on pseudo-correlation receivers and the examples are relative to PLANCK-LFI, the proposed method and its analysis is general and can be applied to a large class of differential radiometric receivers.

Very low-noise differential radiometer at 30 GHz for the PLANCK LFI

The PLANCK mission of the European Space Agency is devoted to produce sky maps of the cosmic microwave background radiation. The low-frequency instrument is a wide-band cryogenic microwave radiometer array operating at 30, 44, and 70 GHz. The design, test techniques, and performance of the complete differential radiometer at 30 GHz are presented. This elegant breadboard 30-GHz radiometer is composed of a front-end module (FEM) assembled at the Jodrell Bank Observatory, Cheshire, U.K., and a back-end module assembled at the Universidad de Cantabria, Cantabria, Spain, and Telecomunicacio/spl acute/, Universitat Polite/spl acute/cnica de Catalunya, Barcelona, Spain. The system noise temperature was excellent, mainly due to the very low noise performance of the FEM amplifiers, which achieved an average noise temperature of 9.4 K.

Design, development and verification of the 30 and 44 GHz front-end modules for the Planck Low Frequency Instrument

We give a description of the design, construction and testing of the 30 and 44 GHz Front End Modules (FEMs) for the Low Frequency Instrument (LFI) of the Planck mission to be launched in 2009. The scientific requirements of the mission determine the performance parameters to be met by the FEMs, including their linear polarization characteristics. The FEM design is that of a differential pseudo-correlation radiometer in which the signal from the sky is compared with a 4-K blackbody load. The Low Noise Amplifier (LNA) at the heart of the FEM is based on indium phosphide High Electron Mobility Transistors (HEMTs). The radiometer incorporates a novel phase-switch design which gives excellent amplitude and phase match across the band. The noise temperature requirements are met within the measurement errors at the two frequencies. For the most sensitive LNAs, the noise temperature at the band centre is 3 and 5 times the quantum limit at 30 and 44 GHz respectively. For some of the FEMs, the noise temperature is still falling as the ambient temperature is reduced to 20 K. Stability tests of the FEMs, including a measurement of the 1/f knee frequency, also meet mission requirements. The 30 and 44 GHz FEMs have met or bettered the mission requirements in all critical aspects. The most sensitive LNAs have reached new limits of noise temperature for HEMTs at their band centres. The FEMs have well-defined linear polarization characteristcs.

Noise properties of the Planck-LFI receivers

The Planck Low Frequency Instrument (LFI) radiometers have been tested extensively during several dedicated campaigns. The present paper reports the principal noise properties of the LFI radiometers. A brief description of the LFI radiometers is given along with details of the test campaigns relevant to determination of noise properties. Current estimates of flight sensitivities, 1/f parameters, and noise effective bandwidths are presented. The LFI receivers exhibit exceptional 1/f noise, and their white noise performance is sufficient for the science goals of Planck.

A lattice matched InP chip set for a Ka band radiometer

An extremely sensitive Ka band radiometer, operating at a temperature of approximately 15 Kelvin, is being developed for the EC funded FARADAY radio astronomy project. To maximize the sensitivity of the radiometer lattice-matched indium phosphide HEMT technology has been used: all of the active components of the radiometer, with the exception of the detectors, have been manufactured on a single wafer process. The radiometer, which uses the band 26 to 36 GHz, will be used to make radio maps of the sky from a 32 metre diameter radio telescope. Several new MMICs have been designed, including a 10 GHz bandwidth low noise amplifier with average noise temperature less than 20 K, and a 180/spl deg/ phase switch using low noise HEMTs as the switching elements. Design principles are described, together with a comparison of modelled and measured results.

A via-free left-handed Transmission Line with Radial Stubs

A novel via-free microstrip Left Handed (LH) Transmission Line (TL) utilizing Radial Stubs (RS) is proposed. The microstrip RS is approximated by a series combination of inductance and capacitance. The electrical equivalent circuit of LH TL unit cell including the equivalent inductance and capacitance of radial stub is discussed. The balanced and unbalanced LH TL is implemented in microstrip technology and backward waves are confirmed by both full wave simulations and experiments. Additionally an open-circuited Zeroth Order Resonators (ZOR) with their resonating properties in balanced and unbalanced left handed transmission lines are also verified by full wave simulations and experiments.

Advanced modelling of the Planck-LFI radiometers

The Low Frequency Instrument (LFI) is a radiometer array covering the 30-70 GHz spectral range on-board the ESA Planck satellite, launched on May 14th, 2009 to observe the cosmic microwave background (CMB) with unprecedented precision. In this paper we describe the development and validation of a software model of the LFI pseudo-correlation receivers which enables to reproduce and predict all the main system parameters of interest as measured at each of the 44 LFI detectors. These include system total gain, noise temperature, band-pass response, non-linear response. The LFI Advanced RF Model (LARFM) has been constructed by using commercial software tools and data of each radiometer component as measured at single unit level. The LARFM has been successfully used to reproduce the LFI behavior observed during the LFI ground-test campaign. The model is an essential element in the database of LFI data processing center and will be available for any detailed study of radiometer behaviour during the survey.

Cryogenic Performance of a Very Low Noise MMIC Ka-Band Radiometer Front-End

Radio telescopes have traditionally used a single receiver at the focus, effectively giving a one-pixel image of the sky. The One Centimetre Receiver Array (OCRA) is a three-stage programme to develop multi-pixel arrays to be mounted at the focus of large radio telescopes. OCRA-f is the second phase, funded under the EU FARADAY project, and consists of a 10-beam array installed on a 32-metre radio telescope in Poland. It will produce Ka-band radio maps of the sky, acting as a ten-pixel radio camera. The paper describes a state-of-the-art all-MMIC receiver front-end developed using the lattice-matched indium phosphide foundry process of NGST, California. The effect of leakage on system noise temperature is described. Finally measurements are presented yielding an overall noise temperature of less than 21 kelvin over a 10 GHz bandwidth at Ka band.

State of the art MMIC InP LNA realizations and applications in FARADAY array receivers

Historically radio telescope have mostly consisted of large dishes with a single feed system at the focus. Recently there has been a trend towards multi-beam systems to make more efficient radio maps of the sky. Three teams, funded under the EU FARADAY project, have designed receiver arrays developed using the lattice-matched indium phosphide foundry process of NGC, California. Receiver architecture and measured results are described

Bandstop filter using hybrid EBG structure

A hybrid EBG structure is realized by etching rectangular slots and circular patterns in the ground plane of the microstrip line. A method is proposed by which the ripples in the passband of the rectangular slots are minimized, without degradation of the stopband rejection, by introducing a circular pattern between the rectangular slots. This novel hybrid EBG structure has been designed, fabricated and measured in order to verify the present approach. The simulated and measured results of this hybrid EBG structure have good agreement.