: MAMBO/MPO 018/02 : 1 : 26-AVRIL-02 MAMBO : A : 1 NOTE INTERNE

Transcription

1 Rév. : A Page : 1 NOTE INTERNE Project Office Emetteur: LERMA B.THOMAS Destinataire(s): LERMA B.GERMAIN A.DESCHAMPS G.BEAUDIN M.GHEUDIN Copie(s): LERMA A.RAISANEN Objet: Front-end Design Préparé par: B.THOMAS Validé par: G.BEAUDIN LERMA Observatoire de Paris 61 avene de l'observatoire Paris Tél. : fax :

2 Rév. : A Page : 2 Table of contents Submillimeter Wave Heterodyne Receiver Front-end Front-end unit design and development overview Receiver RF stage Feedhorn Mixer IF Low Noise Amplifier Local Oscillator/coupler Chain Key Functional allocation Key design parameters performances Verification tests and analyses Main procurements Major challenges and risk mitigation Ultra Stable Oscillator... 11

3 Rév. : A Page : 3 Glossary CFE : Customer Furnished Equipment DSB : Double Side Band HBV : Heterojunction Barrier Varactor IF : Intermediate Frequency LNA : Low Noise Amplifier LO : Local Oscillator MHS : Millimeter Humidity Sounder MIRO : Microwave Instrument for the Rosetta Orbiter NEDT : Noise Equivalent Detection Temperature NF : Noise Factor. PLO : Phased-Locked Oscillator PLL : Phased-Locked Loop RF : Reference Frequency SHP : Sub-Harmonically Pumped SSB : Single Side Band TBC : To Be Confirmed TBD : To Be Defined USO : Ultra Stable Oscillator UVa : University of Virginia VDI : Virginia Diodes Inc.

4 Rév. : A Page : 4 Applicable Documents AD1 Reference Documents RD1 MIRO RAO : Part I : Scientific and technical Plan, ESA RO-EST-AO-000, August 1995, p18-30 RD2 Millimeter waves sounders critical technology, technical data package, RP/550/MT/ , ESA contract 9777/92/NL/PB-W.O.18, 03/12/98, IEMN, Observatoire de Paris, Chalmers University, ASTRIUM RD3 SAPHIR/MEGA-TROPIQUE Phase B, Performances Radiometriques, Draft n 2, 8/04/2002

5 Rév. : A Page : Submillimeter Wave Heterodyne Receiver Front-end The heterodyne receiver front-end has been designed in order to cover the frequency range from 324 GHz to 348 GHz to observe the main six molecular lines and two continuum windows within this range, with a very high sensitivity. The front-end sub-system is made of several units : the quasi-optics which separate the both polarizations of the observed signal and couple each polarization to one receiver head. The receivers : each receiver selects one part (upper or lower) of the total bandwidth in order to reduce the instantaneous bandwidth. A receiver is made of several units : - the sub-harmonic mixer performs the signal down-conversion in frequency, - the Local Oscillator, phased-locked on a USO, generates a stable monochromatic frequency line to pump the sub-harmonic mixer at half of the RF frequency, the Low Noise Amplifier amplifies the down-converted signal in the IF range without adding significant noise Front-end unit design and development overview The RFE (Receiver Front-End) is an indirect detection super-heterodyne receiver. The basic architecture of the front-end sub-system is described here after. It includes the quasi-optical module (polarising beam splitter, feed-horns), the RF receiver head - mixer, - Local Oscillator chain including a tripler, - a Gunn Oscillator and a Phase-Locked Loop), the first IF stage (Low Noise Amplifiers).

6 Rév. : A Page : 6 The following figure is a generic schematic of the Instrument, which emphasise the front-end unit : RF + IF part Receiver N GHz Quasi-optics RF + IF part Receiver N GHz Continuum CO 13CO HDO O3 H2O2 H2O Continuum CTSs Autocorrelators Surface Front end USO The aim of the front-end system is to down-convert the signal coming from the observed scene (frequency range of GHz) to a lower frequency (typically under 10 GHz) which allows the spectrometers to analyse it with high resolution. The use of two receiver heads is driven by several motivations : In order to get higher sensitivity, it is necessary to reduce the instantaneous bandwidth. One possibility is to separate the lower part of the band (extending from 324 to 336 GHz and covering five of the six lines to observe), and the upper part (extending from 336 to 348 GHz, and covering the CO line). Each receiver associated to one band includes a continuum channel providing data about the potential baseline slope over the entire frequency range. Since a receiver operates in one polarization only, informations concerning the surface can be recovered by observing both orthogonal polarizations by two receiver heads. The quasi-optical polarizer (made of free standing parallel strings) separates both polarizations with very low losses (typ. 0.1dB) from the observed signal and couple each one to the feedhorn of a receiver head. The redundancy can be useful in case of failure. If one of the receivers fails, the observations done with the other one still remains very interesting scientifically.

7 Rév. : A Page : Receiver RF stage The RF sub-system is made of several units : Feedhorn The feed-horns, operating in the frequency range 335 GHz ± 10%, are directly connected to the SHP mixer blocks. They are scalar (corrugated) horns designed to have a low level of cross-polarization, a symmetrical radiation pattern, and a proper gaussian illumination of the reflector in order to guarantee low side lobes level (below 35 db TBC) Mixer The mixer unit, which performs the signal downconversion, is a fixed-tuned Sub-Harmonically Pumped mixer using a pair of integrated anti-parallel planar Schottky diodes. The SHP mixer, unlike a fundamental mixer, uses an LO corresponding to half of the RF signal frequency. This avoids the quasioptical injection of the RF and LO signal into the mixer, simplifying the front-end architecture (reliability increased, weight reduced). Horn Tripler co Coupler 57 GHz LO source (Gunn) Subharmonic mixer harmonic mixer PLL LNA GHz IF signal USO Spectral analysis module The planar Schottky diodes have been used, now since many years, for other space projects (Observatoire de Paris at ASTRIUM for MHS, at the JPL for MIRO), and demonstrated state-of-the-art performances in a wide range of millimeter and submillimeter wavelengths. The expected mixer performances are a noise temperature in DSB slightly over 1000 K, with conversion losses of 7 to 8 db. Moreover, the diodes will be integrated together with the passive elements (filtering metallic microstrips) on a monolithic quartz substrate, in order to have low parasitic elements unlike reported diodes on a metallized quartz substrate. Here is a schematic of the integrated circuit elements inside the mixer. 60 um UVa planar Schottky diodes Supplied by VDI.

8 Rév. : A Page : IF Low Noise Amplifier A low-noise amplifier (LNA) follows the mixer providing for the necessary gain to meet the IF output power requirements. It amplifies the IF signal which comes from the mixer output of approx. 30 db in the GHz band with a low noise factor of 1.3 db. The gain ripple over the band is 1.5 db. The gain stability is typically db/ C. A gain/temperature compensation system could be added afterwards Local Oscillator/coupler Chain. The Local Oscillator generates a monochromatic signal at 168 GHz (expected output power of approx. 10 mw) which will be input in the mixer to pump the SHP diodes. This is done by multiplying a Gunn source at 57 GHz with a frequency tripler. This one is based on HBV diodes technology which exhibits high efficiency and does not need any biasing and grounding. Here is a schematic of the tripler circuit design. Electric field (TE 10 mode) Output waveguide Signal at 168 GHz Quartz substrate 20 um Input waveguide Signal at 57 GHz HBV diode F out reject filter IEMN InP based HBV diodes The Gunn source, which outputs a 57 GHz monochromatic signal with 100 mw of output power, is phase-locked by a PLO, this one being phase-locked by an USO reference. The USO will be detailed in the next section.

9 Rév. : A Page : Key Functional allocation Here is a summarising table of the whole front-end performances : Characteristics Min Max Comments RF band (GHz) IF band (GHz) TBC LNA band (GHz) 0,10 8,00 LNA gain (db) 34±1.5 Ampli LNA : Miteq AFS P-4 Performances State-of-the-art 1 Goal Quasi-optic losses (db) Reflector + grid + feedhorn LNA NF (db) can be optimized to 1.2 Mixer eq. DBS temp. (K) Hypothetic values Conv. losses DSB (db) Hypothetic values Conv. losses eq. SSB (db) Equal in lower & upper SB Receiver temp. DSB (K) Quasi-optics + mixer + IF System temp. SSB (K) Typ Min Antenna Temperature (K) Tsys. SSB at limb (K) Tsys. SSB at nadir (K) Tsys. SSB at cold calibrat. (K) Tsys. SSB at hot calibrat (K) The system noise temperature has been obtained considering the following equations : Receiver noise temperature DSB : T rec = (L quasi-optics -1)*T amb + L quasi-optics *T mixerdsb + L quasi-optics *CL mixerdsb *T IF System Temperature in SSB : T sys = 2*T rec + Ta + Ti 2*T rec +2*Ta L quasi-optics : Quasi-optic losses in linear value, T mixerdsb : DSB mixer noise temperature in K, CL mixerdsb : DSB mixer Conversion losses in linear value, T IF : IF Low Noise Amplifier noise temperature in K Ta : Antenna noise temperature. Temperature seen from the antenna at limb or surface for example. Ti : Antenna noise temperature at the image band. T amb : Receiver physical temperature. T amb = 298 K. 1 Articles published : «A fixed-tuned 400 GHz subharmonic mixer using planar Schottky diodes», J.L. Hesler & Al., Uva, March Performaces : Tmix DSB = 1120 K, L DSB = 8dB «Improved 240 GHz Subharmonically Pumped Planar Schottky Diode Mixers for Space Borne Applications» I.Mehdi & Al., IEEE MTT, Vol.46, Dec Performances : Tmix DSB = 600 K, L DSB = 6dB

10 Rév. : A Page : Key design parameters performances Key contributors to the power, weight and size budget can be found in the table bellow. Characteristics Typ Comments RF band (GHz) LO (GHz) & LO Freq. stability (khz) 10 System Noise Temp. SSB (K) 3500 SSB NEDT (K) 4.06 τ = 1s, B = 1 MHz, 10 cal. average IF bandwidth (GHz) TBC IF Output power (dbm) -44 T amb =300K, B IF =5 GHz IF Gain ripple (db) 1.5 IF Temperature stability (db/ C) 0.03 to 0.04 Temp range : -55 to +85 C IF level know (db) ±0.1 Sidelobes level (db) -30 Goal : -35 db Cross-polarization level (db) -25 Weight and mass budget Typ LO power budget (W) 10 Gunn + PLL IF amplifier power budget (W) 0.6 Total front-end mass (g) 3000±200 Based on MIRO instrument Verification tests and analyses All the RF measurement tests will be done by the industrial subcontractant. This one could benefit from test facilities at the Observatory of Paris and University of Helsinki. Several components in the receiver front-end need to be space-qualified : the integrated circuit including the antiparallel Schottky diodes pair has not yet been qualified. Nevertheless, discrete antiparallel diodes pair from the same company have already been used and qualified for space project as MHS. The tripler unit, including the HBV diodes also need to be space qualified Main procurements Here is the baseline for the complition of the several front-end sub-systems : Mixer development : Observatory of Paris and Astrium for the design, complition and tests - Virginia Diodes Inc. (planar Schottky diodes supply), Multiplier development : Observatory of Paris and Astrium for the design, complition and tests- IEMN (HBV diodes supply), LO source : CFE (baseline) : Gunn source : JPL (baseline), RPG Farran (backup solution) PLL : JPL (baseline), Omnisys - Farran (backup solution) USO : JPL (baseline), CEPE SOREP TEKELEC (backup solution). Low Noise Amplifier : Miteq (baseline), Chalmers (backup solution)

11 Rév. : A Page : Major challenges and risk mitigation The SHP mixer performances seems to be a challenging point. State-of-the-art performances for SHP mixer at 240 GHz and 400 GHz using the same technology and diodes are interpolated to give the mixer performances expected for, which are in this document. However, at this date, no such SHP mixers in this frequency band exist and still need to be developed Ultra Stable Oscillator In order to do spectroscopic observations, it is important to have an excellent stability on the RF signal down-conversion. This depends directly on the Local Oscillator, and therefore on the USO which is used as a reference oscillator. The precision is given by the max. resolution of the spectrometers. The best spectral resolution used to observe the targeted molecular lines around 345 GHz is 100 khz (TBC), and the desired stability is better than 1/10 th of the resolution, therefore the stability requirement is 10 / The USO used to get this precision is a quartz oscillator enclosed in an oven and thermally controlled.