Auxiliary antenna-assisted interference mitigation for radio astronomy arrays

Abstract

Abstract-Interferometric image synthesis in radio astronomy is plagued by signal corruption from man-made sources. The very weak signals of interest can be overwhelmed by such interference. Recent work has proposed using array signal processing techniques of adaptive beamforming, adaptive filtering, and subspace projection to remove interference prior to image synthesis. In some practical scenarios, we have found poor cancellation performance when using such methods. Because signal-of-interest levels in radio astronomy (RA) are usually well below the noise, even interference to noise ratios (INR) less than unity can affect signal estimation. At these low INRs, it is difficult to estimate interference parameters or statistics with sufficient accuracy for high-performance adaptive cancellation or subspace projection. By adding a few (one to three) low-gain (relative to the primary telescope dishes) "auxiliary" antennas to an array, it is possible to overcome this problem. This paper will show that using such antennas (e.g. commercial-grade 3-m dishes) with an existing array can significantly improve interference rejection. New extensions to subspace projection spatial filtering methods are presented, along with analytical and simulated results for performance comparison.

Signal Processing for Phased Array Feeds in Radio Astronomical Telescopes

“…As contemporary science goals increasingly require observing sources outside the traditional protected spectrum bands, a critical need is developing to deal will ubiquitous man-made interfering signals such as satellite downlink transmissions [17], [18], radar systems [19], [20], air navigation aids [21], wireless communications [22], and digital television broadcasts. A variety of mitigation methods have been studied by us and others for single dish observation, including adaptive filtering using a reference antenna [18], [23]- [25], time blanking [19], [20], and parametric signal estimation and subtraction [17]. Also, array spatial filtering has been studied by us and others for synthesis imaging with large dish arrays and beamformed aperture arrays [23], [26]- [30].…”

“…A variety of mitigation methods have been studied by us and others for single dish observation, including adaptive filtering using a reference antenna [18], [23]- [25], time blanking [19], [20], and parametric signal estimation and subtraction [17]. Also, array spatial filtering has been studied by us and others for synthesis imaging with large dish arrays and beamformed aperture arrays [23], [26]- [30]. Post correlation interference mitigation has been used with the Parkes Telescope HIPASS horn feed array [31].…”

“…First, we have shown that use of auxiliary antennas steered to obtain high interference-to-noise ratio (INR) data can significantly improve cancellation depth when compared to other array processing algorithms [23]. Second, low order parametric models can be used to represent moving interference covariance structure evolution over windows longer than the STI stationarity time limit which typically bounds sample covariance integration.…”

Robust correlators

“…Methods using the spatial separation of the source of RFI and the radio source can effectively address this issue, see (Ellingson & Hampson 2003;Jeff et al 2005;Kesteven 2007;Cornwell et al 2004).…”

“…For example, for strong 100%-correlated RFI with an amplitude equal to 30.0σ, λ = 0.001 and ρ = 0.0, the output of Pearson's correlator is 0.349 and the output of the MAD-correlator is 0.001. For correlated RFI, other methods exploiting this correlation property can be more effective, see (Ellingson & Hampson 2003;Jeff et al 2005;Kesteven 2007;Cornwell et al 2004). …”