Space-Time Digital Filtering of Radio Astronomy Signals using 3D Cone Filters Najith Liyanage 1, Len Bruton 2 and Pan Agathoklis 1 1 Department of Electrical and Computer Engineering University of Victoria, BC, Canada 2 Department of Electrical and Computer Engineering University of Calgary, Alberta, Canada RFI 2010, March 29-31, 2010, Groningen, The Netherlands

 MDSP Group, University of Calgary Dr Len Bruton,Leader MDSP Group Liaison Engineer, SKA T. K. Gunaratne, PhD student A. Madanayake, Pdf, moved to U of Akron  DSP Group, University of Victoria Dr Pan Agathoklis Najith Liyanage, M.A.Sc 2

Outline 1. Motivation  Pre-processing of signals in radio telescopes 2. Space-Time (ST) Signal Models and their Spectra  SOIs on Focal Plane Arrays (FPAs)  RFI Signals, and SOIs in Aperture Arrays (AAs)  Mutually Coupled (MC) Signals 3. 3D ST Filter Design 4. Mitigation of RFI Signals 5. 3D Space-Time Filtering: an Illustration using 3D simulation figures 6. Filtering of SOIs in the Presence of RFI and MC Signals on FPAs 3

 The Region of Support (ROS) of the SOI and inteference signals are analysed in the 3D frequency domain.  For FPA signals the ROS in the 3D frequency domain is a cone (frustal) which will be the pass band of the 3D filter.  Significant parts of the 3D spectra of the electromagnetic RFI signals and of the mutually-coupled LNA noise signals lie outside of the cone-shaped pass band of the 3D Filter.  The 3D ST Cone Filter operates on the digitized spatial array of antenna signals to significantly attenuate RFI and MC signals during preprocessing. 1.Motivation 4 Motivation

3D Cone Pre-FX FPA Filtering 3D EM celestial 3D EM RFI 3D MC EM noise w/e & LNA ADC 3D LNA electronic noise 3D Cone Pre-FX Filter 3D FT We design 1. Motivation 5

SOIs on FPAs 1GHz 4GHz 2.Signal Models 6 Focal Field Distribution [UC-FPFC] [7]

Radio Frequency Interferences (RFIs)  RFI: Interfering ST-PWs which do not fall in to the DOAs of SOIs Aperture Arrays Focal Plane Arrays 2.Signal Models 7 SOIs RFIs SOIs RFIs

2.Signal Models Synthesised BB RFI/SOI on AAs 3D Space-Time 3D ST Frequency Domain 8 PW-1 PW-2 PW-3

Mutually Coupled(MC) signals  MC Signal Types  Caused by RFI/SOI  The ST Propagation model  Circularly symmetric propagations with exponential damping in spatial dimensions 2.Signal Models 9 a= 6.29 (2dB)

Synthesised BB MC 10 2.Signal Models Inter-element attenuation of 2dB Inter-element attenuation of 5dB Inter-element attenuation of 20dB 3D ST Frequency Domain 3D Space-Time Domain

 Circularly symmetric cross-section  Linear phase  Analytic filter which is capable of easily defining the required passband angle 11 3.Cone Filter Design Cone filter approximation with L bands, each band consisting of a 1D linear phase FIR filter and a 2D zero phase circularly symmetric FIR filter.

RFI signals: PW-1 and PW-2 3D cone filter angle Energy of the input2222 Energy of the output Supp. efficiency (%) Mitigation of RFI signals (PW-1) ( θ 1,  1 )=(85,80) (PW-2) ( θ 2,  2 )=(90,10)

13 5.3D Space-Time filtering: an illustration using 3D simulations figures 3D ST 3D Frequency Output : 3D ST 3D ST Cone Filter Output : 3D Frequency AAs 3D ST filtering illustration

14 6.Filtering of SOIs in the presence of RFI and MC signals on FPAs SOI in the presence of RFI signals PW-1 and PW-2 and ST MC of 20dB inter-antenna attenuation (a=62.94) 3D cone filter angle ( ) Input SIR (dB) SIR of the filtered output (dB) SOI in the presence of RFI signals PW-1,PW-2 and ST MC (a=62.93). Where the energy of ST MC is 20dB higher than rest of the signals. 3D cone filter angle ( ) Input SIR (dB) SIR of the filtered output(dB) Equal RFI and MC signals Energy Dominant MC signals energy

Conclusions 15  3D space-time cone filtering methods have been proposed and investigated for enhancing the SNR of the far-field SOIs by  attenuating the RFI signals that propagate on or close to the surface of phased arrays, such as FPAs and dense AAs.  attenuating the MC noise signals that propagate on of FPAs  Numerical simulations, based on simulated broadband FPA data, show significant attenuation of over-the-horizon RFI signals and moderate attenuation of typical ST MC signals.

Relevant Publications 1.N Liyanage, L.T, Bruton, and P. Agathoklis, “On the Attenuation of Interference and Mutual Coupling in Antenna Arrays Using 3D Space-Time Filters”, IEEE PACRIM 2009, Victoria, Canada, May T. K. Gunaratne and L. T. Bruton, "Beamforming of broadband-bandpass plane waves using polyphase 2D FIR trapezoidal filters", in the IEEE Transactions on Circuits and Systems -I, Regular Papers, vol. 55, no. 3, April 2008, pp A. Madanayake and L.T. Bruton, "A Systolic-array Architecture for First-order 3D IIR Frequency-planar Filters", IEEE Trans. on Circuits and Systems-I: Regular Papers, Vol. 55, No. 6, July 2008, pp A. Madanayake and L.T. Bruton, "A Speed-optimized Systolic-array Processor Architecture for Spatio-temporal 2D IIR Broadband Beam Filters", IEEE Trans. on Circuits and Systems-I: Regular Papers, Vol. 55, No. 7, August 2008, pp