Proposed Versatile 1.2 to 14 GHzRadio Telescope ReceiverS. Weinreb, JPL/Caltech, Draft July 5, 2005

Contents

1. Introduction and intended applications

2. Block diagram

3. Description of new technology

4. Key technical issues

5. Schedule

6. Cost

Introduction

• Technology developments during the past few years have made possible an extremely versatile and sensitive radio astronomy receiver with an instantaneous frequency range of 1.2 to 14 GHz in one instrument.

• Advances in digital signal processing allow this entire frequency range to be analyzed during one integration period without frequency scanning.

• These revolutionary technology advances greatly expand and facilitate the science which can be performed with a 34m radio telescope.

Key Applications for the Proposed Receiver

SETI - The Kepler space instrument is expected to find 50 earth-like planets by 2011. There will be intense public and scientific interest in searching the microwave spectrum of these planets and the proposed receiver will be an ideal instrument to do so. Radio Spectral Lines - The receiver will be capable of measuring all the radio lines (hydrogen, OH, and HCN included) in the 1.2 to 14 GHz range simultaneously. Pulsar Studies – Pulsars emitting extremely short (< 1ns) pulses have recently been discovered and beckon for a wider bandwidth receiver to resolve the pulses. Spectral Index of Continuum Sources - In the past this has been performed by sampling the spectrum with different receivers and telescopes. This decade bandwidth receiver will allow the continuum spectral slope and curvature to be measured with accurate comparison of sources. Transient Phenomenon – Time variable signals such as those from Jupiter will be measured simultaneously over the decade bandwidth

New Technology to be Described in This Proposal

• Compact, efficient antenna feeds with decade or more frequency range have been developed at Chalmers University, Sweden

• Low noise amplifiers also with decade bandwidth, < 10K noise at cryogenic temperatures, and differential input have been developed at Caltech

• Microwave monolithic integrated circuits (MMIC’s) which facilitate downconversion to baseband.

• Digital signal processors capable of analyzing 10 GHz of more of bandwidth at affordable costs

Wideband Receiver Block Diagram

Measurements of a 1 to 13 GHz Model of a Dual Polarized Low-profile Log-periodic Feed for US-SKA

Rikard Olsson1, Per-Simon Kildal2 and Sander Weinreb3

1,2Chalmers University of Technology, Göteborg, Sweden3California Institute of Technology, Pasadena, California

Abstract

We present measured results for a dual polarized 1 to 13 GHz laboratory model of a feed for use in reflector antennas. The main goals of the laboratory model were achieved: it provides dual polarization and can provide more than a decade bandwidth. The aperture efficiency in a primary fed reflector system is greater than 56% over the entire band, and the input reflection coefficient of the feed is better than -5.5 dB. The results agree well with computed values.

Chalmers 1 to 13 GHz Feed

Feed is currently being integrated with cryogenic LNA’s at Caltech.

Chalmers Feed Study Computed Results

• Calculated pattern gives 57% prime focus efficiency, 3K spillover, and 0.3K mesh leakage in 12/16m symmetric antenna from 0.5 to 1.5 GHz

• Gain is 10.5 +/- 0.5 dB and reflection coefficient better than 6 dB over 1:12 frequency range. Provides 65% efficiency at half-angles of 42O to 55O

Computed and Measured Antenna Patterns from 1 to 14.8 GHz

Computed and Measured Loss Reflection Lossfrom 1 to 13 GHz

Efficiency of the Chalmers Feed

TABLE I SUMMARY OF MEASURED AND CALCULATED SUB EFFICIENCIES FROM 1 TO 13 GHZ

Cause of efficiency BEST

CALCULATED [DB]

BEST MEASURED

[DB]

WORST

CALCULATED [DB]

WORST MEASURED

[DB] Spill-over, esp -0.20 -0.20 -0.76 -1.37 Illumination, eill -0.43 -0.31 -1.13 -1.25 Polarization, epol -0.00 -0.08 -0.18 -0.54 Phase, e -0.00 N/A -0.22 N/A Aperture, eap -1.15 -1.03 -2.25 -2.54 Reflections, erefl -0.06 -0.02 -1.44 -1.45 Total, etot -1.29 -1.25 -3.05 -3.39

Breadboard Feed/LNA Cryogenic SystemUnder Construction at Caltech

MMIC Wideband Low Noise Amplifiers

Three-stage LNA in 2mm chip

Low-cost assembly MMIC packageAmplifier provides 5K noise from 4 to 12 GHz when cooled to 12K

Active Balun Function - Needed for Wideband Feeds

Wideband Feed with Output Balanced with Respect to

Ground

Active

Balun-

+

A Microwave Low-Noise Cryogenic Differential Amplifier

•Wideband antenna feeds have balanced output which cannot connect to a low-noise amplifier without a passive balun

•Passive baluns are large, lossy, and add noise to the system

WBAL2, 0.5-11 GHz active balun

differential pair stage

• 2*1.6 mm chip size

• CMRR=gm*Rs (low frequencies)

• Requires matched components

• Same noise as a common source stage

INOUT

Active Balun-LNA on Carrier

Output microstripWBAL2 NGST

InP HEMT MMIC Input lines from feed

Measured Active Balun

Noise and Gain at 15K

Noise peaks above 12 GHz are believed due to resonance in

an input coupling capacitor and can be

eliminated,

Downconverter Bank Block Diagram

Key Technical Issues

• Antenna efficiency and noise temperature– DSS28 has F/D of 0.3 which results in an 160O subtended

angle at prime focus. With current Chalmers feed this would result in low spillover but with taper efficiency < 50%.

– A Cassegrain system with an optimum subreflector for the wideband feed should be investigated

• Continuum receiver sensitivity– Theoretical ΔT with Tsys = 30K, 1 GHz bandwidth, and 1

second integration time is .001K. It is difficult to achieve this theoretical sensitivity with a total power radiometer because of gain fluctuations and atmospheric noise fluctuation.

• Digital spectrometer architecture– 1 GHz bandwidth is available with both autocorrelator and

FFT processing. – Final mixing can either be I/Q or conventional baseband

Receiver Schedule

Cost Estimate

Cost Item Org Year 1 Year 2 Year 3 TotalTotal Burdened Labor 390 320 190 900

Receiver engineer JPL 150 150 50Optics engineer JPL 50 30 20Technical support JPL 100 50 40RF technician CIT 40 40 30Grad students CIT 50 50 50

Total Burdened Materials 330 240 20 590Feed improvements Chalmers 120 80 20MMIC processing NGST 150 0Cryocoolers (3) CTI 20 40Dewar parts MVI 10 20Downconverter parts Many 30 100

Total 720 560 210 1490