1. Post-Correlation Interference Mitigation
M. Kesteven & R. Sault
Australia Telescope National Facility
IUCAF – Bonn, March, 2001

2. Post-Correlation RFI excision
Overview of the scheme
Application 1 - Single Dish
Application 2 - Synthesis Array
Problems/Limitations
Comparison with Adaptive Filters
Parametric Filter - Glonass excision

3. Features A Post-Correlation equivalent to an Adaptive Filter
Applicable to Single Dish observations
Applicable to Synthesis Array observations
Performance comparable to the Adaptive Filter
Can be implemented with current hardware

4. Adaptive Filter (schematic)

5. Post-Correlation Filter

6. Single Dish - Autocorrelation
Reference antenna
Parkes 64m

7. The Reference Antenna

8. Post-Correlation - Features
Tolerant to small number of sampler bits
Tolerant to multi-pathing interference
Tolerant to significant delays between the reference and the astronomy antenna
Tolerant to offset between the array tracking centre and the interference location
Only one reference antenna required even for an array filter

9. Post-Correlation Filter

10. Before and after spectra

11. ATCA MHz; 4 MHz BW

12. Before and after images

13. ARRAY - notes Require one Reference Antenna + conversion chain
Require Additional Correlator resources. Equivalent to adding one extra antenna to the array.
Enjoys all the flexibility of the observatory correlator
Makes no assumption as to similarity between antennas of the array. Interference may enter via different sidelobes in different antennas.
The corrections are based on the correlator output – therefore works with few-bit samplers.

14. Glonass Excision

15. Glonass Excision

16. Glonass excision

17. Post-Correlation - Theory
The correction spectrum Vc(f) is given by:

18. Post-Correlation Filter

19. Synthesis Array Filtering

20. Synthesis Array Filtering

21. Cleaned spectrum