You are correct. 3G BTS systems used Stirling Cryocoolers[0] to cool superconducting microwave filters[1]. [0] https://en.wikipedia.org/wiki/Applications_of_th

You are correct. 3G BTS systems used Stirling Cryocoolers[0] to cool superconducting microwave filters[1]. [0] https://en.wikipedia.org/wiki/Applications_of_the_Stirling_engine#Stirling_cryocoolers https://en.wikipedia.org/wiki/Applications_of_the_Stirling_e... [1] http://home.eps.hw.ac.uk/~ceejh3/Journals/An%20HTS%20transceiver%20for%20third%20generation%20mobile%20communications.pdf http://home.eps.hw.ac.uk/~ceejh3/Journals/An%20HTS%20transce...