Summary [current goals: Beam profile w/ forebaffle]

Requirement: Spillover < -80 dB (to detect 0.1-μK level polarization)

Progress:

[2006/2/11] Sidelobes

[2006/2/4] Ground pickup w/ forebaffle

[2005/10/11] Beam mapping with black/shiny forebaffle

[2004/12/16] Extension due to SPT

[2004/3] Moon considerations

[2004/3] Design / Design explanation / beam pattern / outer shield performance

[2004/2/11 VertexRSI] Design outline

Inner, Absorbing Baffle

2 segments: Upper (16.8 kg) & Lower (12.5 kg), fabrication

Absorbing surface (~4030 in²), Bands: 83-115, 130-180 GHz

Eccosorb	TE reflectivity (on aluminum)	thermal conductivity	-70°C snow
HR-10	<3% @ 100/150 GHz	~0.5 W/K/m2 @ 77K, Meyer et al	cover w/ Volara foam
ANW-72	5-15% @ 150 GHz	~0.027 W/m/K
BSR	20-30% @ 150 GHz	~0.8 W/m/K	adhesive
CRS/MFS	30~90% @ 100 GHz	~0.8 W/m/K	castable / rubbery

Bock Black (stycast + carbon lampblack): ~20% reflection w/o grooved surface. FIRAM-160

Clearing Snow ( n_snow=1.0, n_ice=1.78): Heat the shield to >1 K above ambient. ~50 W/K/m² x 3 m² ~ 150 W/K (outside insulated)

Heat Blankets / Self-Regulating Heat Cable Sorensen DCR150-12B.pdf (150V, 12A), ACBAR supplies

Outer, Reflective Screen (require double diffraction of ground radiation):

	OUTER FIXED (reflective Al)
Angle (snow!):	slope ~50°
Round edge:	curvature radius = 4" (10cm)
Height:	88" (224cm) (hide inner shield)
Top radius:	155" (395cm) (minimized by choice of inner shield length)
Base radius:	bottom radius ~150cm (gap w/ boot for snow to fall)

Drawings:

Purchases: Clamps

Tools:

Gemetrical Theory of Diffraction (Keller) for conductors

FEMLAB, WIPL-D, Grasp (/opt/local/packages/grasp8w-8.2-5-se/), NEC (moments method)

References:

1959 Keller: Rounded-edge screen shadow

1979 Janssen et al Measurements of low-sidelobe horn

1981 Mather Broad-band flared horn with low sidelobes

1982 Burnside & Chuang Aperture-matched horn design

1989 GSFC Measurements of low-sidelobe conical horn antennas (corrugated, 30-90 GHz)

1990 Kogut et al 7.5 GHz: flared shield, sidelobe measurements

1994 Bersanelli et al 2 GHz: E-plane corrugated, grnd radiation measurement

1996 Staggs et al 10.7 GHz: inner & outer screens measurements

1997 Wollack et al 27-44 GHz (SK): screen offset measurements

1998 Halverson et al DASI

2000 Raghunathan & Subrahmanyan 1.28 GHz: Al screen + corrugated edges

2001 O'Dell POLAR (thesis): Sprtz tests w/ hand-held microwave source

2002 Miller et al QMAP and MAT/TOCO: Al honeycomb baffle + Keller flare

2002 Leitch et al 26-36 GHz (DASI) Ground/Sun shields

2003 Keating et al 26-36 GHz (POLAR: Large Angular Scale)

2003 Coble et al 40/90 GHz (Python V): 12-panel ground shield offset

2003 Lyman Page et al MAP Optical Design & Characterization: GTD

2003 Farese et al 26-36 GHz (COMPASS: intermediate angular scales): inner & outer screens polarized offset