'Sensitivity analysis for frequency-dependent objective functions' (Electromagnetic Waves, 2017), 'Adjoint Sensitivity Analysis of High Frequency Structures with MATLAB®', Chap. 4, pp. 99-132, DOI: 10.1049/SBEW525E_ch4
IET Digital Library, https://digital-library.theiet.org/;jsessionid=2eo85busccc4o.x-iet-live-01content/books/10.1049/sbew525e_ch4