Chapter 12. Standing Wave Removal

Table of Contents

12.1. Introduction to Standing Wave Removal
12.2. Modified Passband Calibration Method
12.3. Sine Wave Fitting Method (fitHifiFringe)
12.3.1. Introduction to fitHifiFringe
12.3.2. Running fitHifiFringe
12.3.3. Example of using fitHifiFringe
12.4. Electrical Standing Wave correction in HEB bands
12.4.1. Introduction
12.4.2. Catalogue
12.4.3. Spline Model
12.4.4. Removal
12.4.5. Demonstration

Last updated: 15 September, 2015

12.1. Introduction to Standing Wave Removal

At many locations in the HIFI instrument, standing waves are generated. The standard (SPG) pipeline and AOTs are designed to minimise the amplitude of these waves in Level 2 spectra. However, for certain observing modes, some mixer bands, and some observation characteristics (sky signal strength, signal-to-noise level) particular residual waves may still be present:

  1. All bands: a 98 MHz wave from the cold black body to mixer cavity

  2. All bands: a 92 MHz wave from the hot black body to mixer cavity

  3. All bands: a 100 MHz wave from the local oscillator unit to mixer cavity

  4. Diplexer bands (3,4,6,7): a 620 MHz wave from the diplexer rooftop to mixer cavity

  5. HEB bands (6,7): a ~320 MHz wave from within the HEB mixers

Depending on the science application, the user may want to remove these waves. Different techniques may need to be applied for the different waves. These are described in the next sections.