A high temperature superconductor notch filter for the Sardinia Radio Telescope
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A High Temperature Superconductor filter operating in the C-band between 4200 and 5600 MHz has been developed for one of the radio astronomical receivers of the Sardinia Radio Telescope. The motivation was to attenuate an interference from a weather radar at 5640 MHz, whose power level exceeds the linear region of the first active stages of the receiver. A very sharp transition after the nominal maximum passband frequency is reached by combining a 6th order band-pass filter with a 6th order stop-band. This solution is competitive with an alternative layout based on a cascaded triplet filter. Three units of the filter have been measured with two different calibration approaches to investigate pros and cons of each, and data repeatability. The final performance figures of the filters are: ohmic losses of the order of 0.15–0.25 dB, matching better than −15 dB, and −30 dB attenuation at 5640 MHz. Finally, a more accurate model of the connection between external connector and microstrip shows a better agreement between simulations and experimental data.
KeywordsRadio Telescope Radio Frequency Interference High Temperature Superconductor Microwave Filters Scattering parameters Vector Network Analyser
The authors wish to thank Luca Carbonaro from the INAF - Arcetri Astrophysical Observatory for providing useful suggestions on the mechanical design and Richard Prestage from the Green Bank Observatory for his valuable comments on the contents of the article. Finally, the authors are grateful to the Italian company Galvanelettronica Electroplating for putting a lot of R&D efforts in the plating process of the titanium carriers.
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