\documentclass[10pt,twocolumn]{article}
\setlength{\topmargin}{-0.375in}
\setlength{\textheight}{9.0in}
\setlength{\oddsidemargin}{-0.1in}
\setlength{\textwidth}{6.5in}
\usepackage{graphicx,palatino,natbib}
\renewcommand{\baselinestretch}{1.05}
\newcommand{\kms}{km~s$^{-1}$}

\makeatletter
\renewcommand\section{\@startsection {section}{1}{\z@}%
                                   {-2.5ex \@plus -1ex \@minus -.2ex}%
                                   {2.3ex \@plus.2ex}%
                                   {\normalfont\large\bfseries}}
\renewcommand\subsection{\@startsection{subsection}{2}{\z@}%
                                     {-1.5ex\@plus -1ex \@minus -.2ex}%
                                     {1.2ex \@plus .2ex}%
                                     {\normalfont\large\itshape}}
\renewcommand\subsubsection{\@startsection{subsubsection}{3}{\z@}%
                                     {-1.2ex\@plus -1ex \@minus -.2ex}%
                                     {1.0ex \@plus .2ex}%
                                     {\normalfont\normalsize\itshape}}
\makeatother


\begin{document}
\thispagestyle{empty}
\twocolumn[
\Large 
\centerline {Third Annual Report for SuperCam:}
\large
\centerline {A SuperHeterodyne Camera for the Heinrich Hertz Telescope}
\centerline {AST-0421499}
\normalsize
\bigskip
]

\section{Summary}

SuperCam is a 64 pixel, superheterodyne camera designed for operation in the
astrophysically important 870~$\mu$m atmospheric window.  SuperCam
will be used to answer fundamental questions about the physics and
chemistry of molecular clouds in the Galaxy and their direct relation
to star and planet formation.  The advent of such a system will
provide an order of magnitude increase in mapping speed over what is
now available and revolutionize how observational astronomy is
performed in this important wavelength regime. Initially, SuperCam will be used
at the Arizona Radio Observatory (ARO) 10-meter Heinrich Hertz
Telescope (HHT) on Mt. Graham, Arizona to conduct a 
Galactic Plane survey in the $^{12}$CO and $^{13}$CO J=3$\rightarrow$2
lines. A long  
history of water vapor measurements ($>$10 years) indicate the
870~$\mu$m atmospheric window 
is available $\sim$50\% of the time from the HHT. Discussions are
underway for taking  
SuperCam to a comparable Atacama telescope to conduct the southern
portion of the Galactic Plane survey once the northern survey is complete.

Each component of Supercam has been modularized in units of {\bf
  1$\times$8 rows} of the full heterodyne array.  Thus, the mixer blocks, bias 
electronics, IF processors, and spectrometers are quantized into modules that
correspond to 8 detector ``pixels''  each.  This one-dimensional integration is
crucial to the realization of large heterodyne arrays and has been
successfully completed by the SuperCam team. 

After initial design work in 2004-5, we successfully tested a one pixel prototype of SuperCam (see
Puetz et al. 2006). Using this as a starting point, in 2006-7 our team
completed the baseline design of the optical, cryogenic, RF, and electronics
subsystems for the array.  A single-pixel end-to-end test of all SuperCam
technologies was successfully conducted in August, 2006.   In 2007
we have performed an end-to-end test of the 1$\times$8
  integrated SuperCam subsystems using the final cryostat
and spectrometer.  In the first 2/3rds of 2008, optimizations to the final mixer design, cryostat
layout, and integration plan with the HHT have taken place.   
{\bf The final production of mixers and bias electronics, and assembly
of the optical mounting framework is currently underway.  The project is on
schedule for completion by the end of 2008, with first light expected
at the HHT during the upcoming winter observing season. }

The following sections discuss the status of each component of SuperCam in more detail. 

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.47,angle=0]{../figures/supercam-b33.eps}
\caption{\label{beams} {\small The 64 beams of SuperCam overlaid upon
    the Horsehead Nebula (B33).  Each beam will measure a
    high-resolution spectrum (right).    }}
\end{figure}

\section{Optical System}

\begin{figure*}[!hbt]
\centering
\includegraphics[scale=0.8,angle=0]{figures/apex1.eps}
\includegraphics[scale=0.8,angle=0]{figures/apex2.eps}
\caption{\label{optics} {\small 3D CAD model showing 
SuperCam integrated in the HHT
    tertiary
    room, viewed (left) from behind and to the left, and (right) from 
    above.   }}
\end{figure*}

\subsection{ Telescope Matching Optics }

SuperCam will initially reside on the HHT.  The
goal of the instrument's optical system is to produce an 8$\times$8 array of
diffraction limited beams on the sky with $<$1\% overlap in their
power patterns (Figure~\ref{beams}). This can be achieved if the separation
between pixels in the instrument focal plane is 2.5$\;f\; \lambda$.  A
faster beam makes the focal plane more compact, but produces more
rapidly diverging beams.  The lower limit to the focal ratio is set by
the requirement that the emerging beams clear the cryostat window at
the 3$\omega$ level ($\omega$ is the Gaussian beam waist). For our
application an f/5 beam is a good compromise, yielding a pixel
separation of 11~mm in the focal plane. 

Trade studies were performed in 2007 and 2008 to determine the
optimal optical arrangement that allows SuperCam to be feasibly
installed into the HHT while minimizing impact on the observatory. 
For example, to eliminate the need to change secondary mirrors,
re-imaging optics are 
necessary to reduce the f/13.8 beam of the HHT to f/5.    Two optical
and mechanical systems placing Supercam inside and, alternately, on top of the
tertiary cabin, were fully explored and presented to the ARO staff. 

Recently, the go-ahead to fully develop the optical system that places
Supercam inside the tertiary cabin was achieved between the Supercam
and Arizona Radio Observatory (ARO) teams.  Figure~\ref{optics} shows 
a 3D CAD drawing of this optical system, which 
fulfills Supercam's design requirements and fits within the
tertiary room. The design was first made using Zemax and then optimized
with the more sophisticated ASAP optical design package.  

The dewar and optical system are mounted in a common frame capable
of being positioned in {\tt x} and {\tt y}, permitting the beams to be accurately
centered on the secondary. 


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.66,angle=0]{figures/lo-splitter.eps} 
\includegraphics[scale=0.66,angle=0]{figures/lo-splitter-zoom.eps}
\caption{\label{splitter} {\small 1x8 LO power splitter block, and
    zoom-in on a single waveguide junction}}
\end{figure}


\subsection{Local Oscillator (LO) Injection}

Several local oscillator (LO) injection schemes were considered,
including waveguide cross-guide couplers. The large number of pixels
makes waveguide coupling very cumbersome and difficult to
fabricate. We are fortunate that high-powered LO chains ($>$1mW) using
commercially available frequency multipliers permit simple,
quasi-optical coupling into the signal beam with a dielectric beam
splitter. In a ``standard'' quasi-optical beam splitter Mylar is often
used as the dielectric. In such instances of order 1\% of the LO power
is injected into the cryostat, with the balance being terminated in an
absorbing load. 


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.5,angle=0]{figures/machining.eps} 
\caption{\label{machining} {\small Fully machined extended feed horns
    for the mixers and LO power dividers, and split-block halves of the
    corporate 8x8 LO power divider, machined using
    the Kern micromilling machine purchased largely through this grant.}}
\end{figure}

An 8$\times$8 way waveguide, corporate power divider has been machined
(using the Kern micro-milling machine purchased largely through this
grant) to produce an independent LO beam for each pixel. One row of
the LO power splitter is shown in Figure~\ref{splitter} and all 8
splitters and extended feed horns are shown in
Figure~\ref{machining}.   The measured output power
from each horn is in excellent agreement with theory. After
encountering the mylar beamsplitter, the combined LO and signal beams
enter the cryostat through an AR-coated, crystalline quartz vacuum
window. They then pass through a cooled Goretex GR infrared filter before
entering an 8x8 array of feed horns.  


\begin{figure*}[!htb]
\centering
\includegraphics[scale=0.55,angle=0]{figures/1x8_prototype_sm.eps}
\caption{\label{mixerarray} {\small (left) Photograph of a completed 1x8 mixer
    array. }}
\end{figure*}



\section{ Mixer Arrays}
                                                  
\subsection{Design Approach}

SuperCam utilizes eight, 1$\times$8 rows of integrated mixer
arrays. For large ($>$25 pixels) format arrays like SuperCam, the
relative ease of assembly and low-cost of single-ended, DSB mixers
make them preferable over single-sideband
approaches. Figure~\ref{mixerarray} is a
photograph of the bottom half of a 1x8 mixer array that was machined
in 1 day using the Kern micro-milling machine at the UofA. The mixer
module is shown assembled with waveguide feed horns, IF MMIC modules,
and DC bias board. 

The signal/LO beams are gathered by the feed horns and launched into
half-height rectangular waveguide. The waveguide carries the energy
around a 90 degree bend to the SIS junction (fabricated by Arthur
Lichtenberger at the University of Virginia) and fixed backshort. The first single pixel
mixer prototype (Puetz et al 2006) utilized the same quartz substrate
SIS devices used in Desert STAR.   {\bf In 2007 and 2008,  the
SIS junctions were fabricated with beam leads on thin silicon (SOI)
substrates, making device mounting more straightforward and
reliable.  This was a singificant departure from the initial design,
but its successful implementation represents a fully scalable design
for SIS array receivers from 200-1400 GHz.}  

The 4-6 GHz intermediate frequency (IF)
output of each junction is then wire bonded to the input of a custom,
low-noise, MMIC amplifier module designed by Sandy Weinreb and his
group.  A close-up of the module design and performance data are
provided in Figure~\ref{MMIC}.
The module produces $>$30dB gain at a noise temperature of $\sim$5K over
SuperCam's IF range (nominally 4-6 GHz). Besides having excellent
performance, the MMIC module has a power dissipation of 4-8mW which
permits it to be integrated directly into the mixer block, adjacent to
the SIS junction as shown in Figure~\ref{mixerarray}. The outputs of the MMIC modules
are wire bonded to a multilayer PC board that carries the signals via
microstrip to a 1x8 array of miniature, push-on (GPPO) connectors
located on the back of the module. DC bias for the SIS junctions, MMIC
modules, and electromagnets (required to suppress the Josephson
effect) are provided by multi-pin edge connectors and conveyed to the
components through underlying layers in the PC board. All electrical
connections to the 1x8 mixer subarray are made through connectors on
the rear of the unit, allowing it to be removed without disturbing the
cryogenic wiring harness. 

\subsection{Mixer Performance}

Single pixel test devices have demonstrated excellent RF
performance, as shown in Figures~\ref{single-perf} through
\ref{single-perf3}.   
The final design optimizations on the prototype 1x8 mixer block are being completed in
August-September 2008, with full-scale machining, assembly, and
testing to occur starting in October 2008.   Completion of all mixer
fabrication is expected near the end of 2008.


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.8,angle=0]{figures/soi-ivcurve.eps}
\caption{\label{single-perf} {\small  Sample I-V curve of a Supercam SOI
    SIS mixer and RF performance at 336 GHz using a synthesized LO
    source. The 70K DSB noise temperature is within 10K of the modeled
performance. }}
\end{figure}

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.75,angle=0]{figures/RF-perf.eps}
\caption{\label{single-perf3} {\small  The RF performance of Supercam
    mixers is excellent over the broad tuning range of an available synthesized LO
    source.  The degradation seen at 370 GHz represents amplitude
    instability in the local oscillator, not the mixer.  Normal LO 
    operating points for the key project science programs, $^{12}$CO
    and $^{13}$CO surveys are 341 and 335~GHz, respectively.  }}
\end{figure}


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.65,angle=0]{figures/proto1.eps}
\includegraphics[scale=0.8,angle=0]{figures/mmic-perf.eps}
\caption{\label{MMIC} {\small (TOP) 4-6 GHz MMIC Module.   (BOTTOM)
    MMIC performance plots show $>$30 dB of gain from 1-14~GHz. }}
\end{figure}


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.8,angle=0]{figures/DewarMount.eps}
\caption{\label{mount} {\small SuperCam dewar and Virginia Diodes 
LO (with 1x8 power splitter)  in their combined support frame. }}
\end{figure}


\section{ Cryostat}

The SuperCam cryostat is shown with its LO system in
Figure~\ref{mount}.  The cryostat has a 150mm diameter AR coated, crystalline quartz
window, is 20 inches on a side, and utilizes two closed-cycle
refrigerators: a Sumitomo RDK-415D to cool the mixer array and a CTI
350 to take the heat load of the 64 stainless steel coaxial (0.085 in)
cables. Laboratory measurements indicate the system has a 50\%
margin in thermal load capacity. IF connections to the outside are
made via 64 SMA style, hermetic, bulk-head connectors. Twelve
55-pin hermetic connectors are used to convey DC bias signals in and out of
the cryostat. The cryostat was wired in 2007 for conducting tests with the
first 1x8 row of the array, and is currently being wired (Fall 2008) for the
remaining 7 rows.
 

\section{IF Processors}

The 4-6~GHz IF signal emerging from the SuperCam dewar must be filtered, downconverted to
baseband, and amplified to 0~dBm to be properly conditioned for the
input of the spectrometer system.  The designed 
IF processor provides each channel
an initial 48 dB of gain, a variable (0-31 dB) digital attenuator, a
selectable 256~MHz or 512~MHz bandpass filter, a mixer conversion to
baseband, low-pass filter and 50 dB of baseband gain.   An additional 
circuit provides total-power measurement of the IF power for telescope
pointing and continuum measurements. 

Sander Weinreb and his graduate
students Joe Bardin and Glenn Jones have designed, constructed and
delivered fully-tested 2-channel and modular 1$\times$8 IF processor prototypes
for SuperCam.  The 2-channel prototype is now in operation at Dome~A,
Antarctica as part of the NSF-funded {\tt Pre-HEAT} robotic submillimeter
observatory (ANT-0735854).  The full 8x8 assembly of IF downconverter
modules have been constructed and only await final testing at Caltech
before delivery to Arizona in October 2008.
A picture of the 8-channel IF
processor module and a sample 512 MHz bandpass is shown in
Figure~\ref{IFproc}.  


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.75,angle=0]{figures/IFproc2.eps}
\includegraphics[scale=0.8,angle=0]{figures/IFproc1.eps}
\caption{\label{IFproc} {\small 8-channel IF processor module and
    sample bandpass}}
\end{figure}

\section{FFT-in-FPGA Spectrometer}

The science goals of the Supercam instrument drive the development of
the backend array spectrometer toward two distinct requirements.
First, sufficient kinematic resolution of molecular cloud
components in CO emission will only be achieved with frequency
resolution of finer than 512~KHz per channel, with 256~KHz
preferred. Secondly, the divergence of the velocity field of the inner Galaxy
requires a bandwidth of 256~MHz or greater at 345~GHz. 

{\bf Rapid advances in digital logic have made the spectrometer solution
even more powerful than envisioned originally. }  Though we had
originally baselined a 64$\times$128~MHz 2-bit autocorrelator system
from Spaceborne Inc., recent gains in high-speed ADCs and FPGAs have
made a direct-digitization spectrometer economically feasible.  In
this scenario, the entire IF signal is digitized in real time with high 8-bit
fidelity (using multiple Atmel 1Gs ADCs) and a Fast Fourier Transform
is then performed by a (Virtex4) FPGA.   
Omnisys Inc. was consigned to construct a prototype spectrometer card
and rack-mounted system
capable of processing a total of 2~GHz of bandwidth, software-selectable
between 8-input mode (256~MHz per input), 4 input mode (512~MHz each), and
2-input mode (1~GHz each).  The prototype spectrometer card, like the
prototype IF processor, was deployed to Dome~A, Antarctica in late
2007 as part of the
NSF-funded {\tt Pre-HEAT} remote submillimeter observatory (ANT-0735854).
{\bf The full 64-pixel spectrometer system was delivered in 2008.}
Initially, we will power-combine in pairs the beams
from an entire row to a single spectrometer card, yielding 256~MHz of
bandwidth per beam, and thus requiring 8 spectrometer cards in
total.   A future upgrade path will be to
install 8 more boards, for 512~MHz of bandwidth per channel.  
The performance of the spectrometer 
has proven to be exceptional, with Allan variance (spectroscopic
stability) times in excess of 600 seconds, including the analog IF
processing electronics.  

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.7,angle=0]{figures/speccard.eps}
\caption{\label{speccard} {\small SuperCam spectrometer card as
    constructed by Omnisys Inc.  The board features 2~GHz of
    bandwidth, software selectable between two 1~GHz inputs, four
    512~MHz inputs, or eight (power combined) 256~MHz inputs. }}
\end{figure}

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.8,angle=0]{figures/spectrometer.eps}
\caption{\label{specperf} {\small Completed and delivered polyphase filterbank
    spectrometer system from Omnisys AB.  Eight spectrometer cards
    provide 64 independent receivers with 256 MHz 
    of bandwidth in 1024 channels each, in a single PC-style case with 200
    watts of power consumption. }} 
\end{figure}

\section{Electronics}

The control electronics for the biasing of the SIS detector array, and
its attendant electromagnets and MMIC Low Noise Amplifiers is a
consolidation of the successful electronics implementations used for
previous DesertSTAR and PoleSTAR heterodyne arrays.  
Single channel preamp were integrated into 1$\times$8 preamp boards by
the University of Massachusetts/Amherst in 2005; all preamp 
boards for the full 8$\times$8 array were delivered in 2006.   

Similarly, a single 
6U electronics bias board controls all functions of an entire 8-pixel
row of Supercam.  Operation of the bias board
prototype has been completely validated.   
The final bias electronics boards are
currently being fabricated and assembled into their ultimate
electromagnetically-shielded 
rack-mounted case.  With all hardware-level software already written,
all that remains is the final development of the GUI array control
software, scheduled for completion this Fall.


\section{ Data Pipeline}

A schematic of the SuperCam data pipeline is shown in Figure~\ref{data}. The
spectrometer will have a dedicated, 1~Gb ethernet connection to a
data acquisition/spectrometer (DAS) control PC.  The DAS PC will have
two ethernet cards and a RAID5 array for local data storage and fault
tolerance.   Five 750 GB drives in a RAID0/1 array 
will provide $>$3 TB of storage.  During
the Galactic Plane survey the data rate will be 400 GB/day. The DAS
disk array will provide at least a week of raw storage at 90\% duty
cycle.  

The DAS PC will stream the raw data to a background process that will 
be responsible for regridding the data into a more manageable format; 
approximately 200 GB for the entire Supercam Galactic plane survey.
The data processing task will also be responsible for determining the
quality of the data and flagging bad OTF scans that need to be
repeated.   Quality will be assessed by evaluating the RMS
noise after subtracting the baseline from each spectrum  and comparing
with that expected from T$_{sys}$.  The data processing task
will spool pre-processed data images to the telescope control
computer(s) for the observer to see, upon request.  The HHT telescope
control computer in return will send data acquisition requests to the
DAS PC, thus closing the communications loop. 

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.75,angle=0]{figures/pipeline.eps}
\caption{\label{data} {\small Schematic of SuperCam data pipeline }}
\end{figure}

\begin{figure*}[!hbt]
\centering
\includegraphics[scale=1.4,angle=0]{figures/schedule.eps}
\caption{\label{schedule} {\small Gantt chart of remaining Supercam
    tasks for the remainder of 2008, before installation at the HHT. }}
\end{figure*}

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.8,angle=0]{figures/apexroom-connections.eps}
\caption{\label{interfaces} {\small Schematic of the streamlined interface between
    Supercam and the HHT: only power, cryogenic lines, digital control
    signals, and ethernet are needed.  }}
\end{figure}

\section{Integration and Testing}

Thorough integration and testing of the Supercam array is vital to its
successful implementation on the HHT and its long-term scientific impact.
Thus, end-to-end tests of the entire Supercam system has been a
continuous process since the inception of the program.   For example, 
the single-pixel Supercam prototypes underwent a complete
end-to-end test in 2006, 
from Supercam test mixer with integrated MMIC LNA, to
prototype IF processor and Omnisys FFT spectrometer (Puetz et al. 2006).  
The entire chain of IF
technologies were validated and assessed, with ``first spectral
light'' and stability tests of the IF chain system performed.
The same end-to-end analysis 
was performed for the 1$\times$8 mixer blocks in the SuperCam
cryostat in 2007, and will again be performed for the full 64-beam
system prior to deployment by the end of 2008.  The electrical and
mechanical interfaces between the HHT and Supercam have been
streamlined to the most necessary and simple interfaces possible
(Figure~\ref{interfaces}).  At the conclusion of lab tests,
integration of the optical system to the HHT telescope and data system
to the HHT telecope control system will be performed, so that first
light will be achieved during the winter of 2008-9.   A schedule of
remaining activities for Supercam is shown in Figure~\ref{schedule}.



\twocolumn[

\section*{References}

\begin{enumerate}

\item Puetz, P., Hedden, A., Gensheimer, P., Golish, D., Groppi, C.E.,
  Kulesa,  C., Narayanan, G., Lichtenberger, A., Kooi, J.W., Wadefalk,
  N., Weinreb, S., \& Walker, C.K.,  ``345 ~GHz Prototype SIS Mixer
  with Integrated MMIC LNA'',  {\it  International Journal of Infrared
  and Millimeter Waves}, 2006, in press

\medskip

Reprint at:  

{\tt http://soral.as.arizona.edu/supercam/puetz2006.pdf}

\item Mueller, E., \& Waldman, J., ``Power and Spatial Mode
  Measurements of Sideband Generated, Spatially Filtered,
  Submillimeter Radiation'', {\it IEEE Transactions on Microwave
    Theory and Techniques}, 42, 1891.


\end{enumerate}

]


\end{document}


