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