'Swept Spectrum Analyzers' (Telecommunications, 2001), 'Spectrum and Network Measurements', Chap. 5, pp. 93-106, DOI: 10.1049/SBTE005E_ch5
IET Digital Library, https://digital-library.theiet.org/;jsessionid=1opw9zi3x8ezw.x-iet-live-01content/books/10.1049/sbte005e_ch5