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1. Reflectarray Concept for Interference Mitigation in Radio Astronomy

   https://doi.org/10.1109/USNC-URSI52151.2023.10237818  

   Hum, Sean V; Ellingson, Steven; Buehrer, R Michael (July 2023, IEEE)

   This paper proposes a composite reflectarray system for realizing a reflector antenna for radio astronomy applications. The system is equipped with a tunable reflectarray rim that enables nulls to be formed within the field of view and reduce the impact of interferers on the observations. Full-wave simulation results of a physical reflectarray system are presented to validate the concept. 

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2. Toward Electronically Reconfigurable Rims for Reflectors in Radio Astronomy

   https://doi.org/10.23919/URSIGASS57860.2023.10265427  

   Hum, Sean V; Ellingson, Steven; Buehrer, R Michael (August 2023, IEEE)

   This paper presents full-wave simulation results of a reflector-reflectarray hybrid antenna used as a spatial beamformer for mitigating interference in radio astronomy applications. Such antennas employ fixed reflectors with electronically tunable reflectarray along their rim to dynamically form nulls in the direction(s) of interferer(s). Results from realistic models of such antenas demonstrate their potential in producing nulls and potentially effectiveness in mitigating interference from satellites with the field of view of the instrument. 

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3. Weight Selection for Pattern Control of Paraboloidal Reflector Antennas with Reconfigurable Rim Scattering

   https://doi.org/10.1109/AERO55745.2023.10115669  

   Buehrer, R Michael; Ellingson, Steven W (March 2023, IEEE)

   It has been recently demonstrated that modifying the rim scattering of a paraboloidal reflector antenna through the use of reconfigurable elements along the rim facilitates sidelobe modification including cancelling sidelobes. In this work we investigate techniques for determining the unit-magnitude weights (i.e., weights which modify the phase of the scattered signals) to accomplish sidelobe cancellation at arbitrary angles from the reflector axis. Specifically, it is shown that despite the large search space and the non-convexity of the cost function, weights can be found with reasonable complexity which provide significant cancellation capability. First, the optimal weights without any magnitude constraints are found. Afterwards, algorithms are developed for determining the unit-modulus weights with both quantized and unquantized phases. Further, it is shown that weights can be obtained that both cancel sidelobes while providing a constant main lobe gain. A primary finding is that sufficiently deep nulls are possible with essentially no change in the main lobe with practical (binary or quaternary) phase-only weights. 

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4. Effect of Antenna Pattern on Time-Domain Canceling of Interference from Satellites

   https://doi.org/10.1109/USNC-URSI52151.2023.10237408  

   Sengupta, R; Ellingson, SW (July 2023, IEEE)

   Signals from satellites are a source of interference to radio telescopes. One possible scheme for mitigation of this interference is coherent time-domain canceling. Using a simple but broadly-applicable model for the antenna pattern, we show how the antenna pattern combined with the motion of the satellite limits the time available to compute an accurate estimate of the interference waveform, which subsequently limits the extent to which interference can be canceled in the output. We suggest a simple remedy to the problem. 

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5. UNDERSTANDING THE IMPACT OF SATELLITES ON RADIO ASTRONOMY OBSERVATIONS

   Peel, M; Eggl, S; Rawls, ML; Qui, H; Clements, DL (May 2025, European Space Agency Space Debris Office)

   Lemmens, S; Flohrer, T; Schmitz, F (Ed.)

   Radio telescopes observe extremely faint emission from astronomical objects, ranging from compact sources to large scale structures that can be seen across the whole sky. Satellites actively transmit at radio frequencies (particularly at 10±20 GHz, but usage of increasing broader frequency ranges are already planned for the future by satellite operators), and can appear as bright as the Sun in radio astronomy observations. Remote locations have historically enabled telescopes to avoid most interference, however this is no longer the case with dramatically increasing numbers of satellites that transmit everywhere on Earth. Even more remote locations such as the far side of the Moon may provide new radio astronomy observation opportunities, but only if they are protected from satellite transmissions. Improving our understanding of satellite transmissions on radio telescopes across the whole spectrum and beyond is urgently needed to overcome this new observational challenge, as part of ensuring the future access to dark and quiet skies. In this contribution we summarise the current status of observations of active satellites at radio frequencies, the implications for future astronomical observations, and the longer-term consequences of an increasing number of active satellites. This will include frequencies where satellites actively transmit, where they unintentionally also transmit, and considerations about thermal emission and other unintended emissions. This work is ongoing through the IAU CPS. 

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