Antenna Gain and Source calibration
Jim Gibson and Jack Welch
Antenna gain Measurement using Standard Horn
• Horn Gain from Shelkunoff and Frijs
• Horn at Edge of 6m BIMA Antenna
• Transfer Switches Between Feed and Horn
• Jupiter is the Signal Source
• Used BIMA 6m Antenna in Array
Jupiter Flux Measured with Calibrated Antenna
• Temperature Scale from Ambient and LN Loads
• Many On/Off Measurements of Jupiter
• Many Tipping Curves for Extinction
• Tb = 145.12K +/-2K
• Corrected for Synchrotron Emission: Tb=143.7+/-2K
Calibrating ALMA Images
• Calibrate Planets as often as Necessary
• Transfer Planetary Fluxes to Phase Calibrators. Use 2 or 3.
• Accurate Extinction Needed Here
• Scale ALMA Images to the Phase Calibrator Images. Little Extinction Correction Needed
Future Plans
• Transfer 28.5 Jovian Flux to Mars and MWC349
• Repeat the Calibration at 90 GHz with Mars/Venus
• Generate Overall Scale for MWC349
• Test the Accuracy of Tipping Curves
• Test Stephane’s Idea at 90 GHz
Tipping Experiments
• Compare with an Interferometric Extinction Curve on a Stable Day
• Compare with Model Atmospheric Calculations
• Try it with the Standard Gain Horn; It’s Pattern is Cleaner and can be Calculated