Development of planar microstrip resonators for electron spin resonance spectroscopy Subhadip Roy, Sagnik Saha, Jit Sarkar and Chiranjib Mitra Eur. Phys. J. Appl. Phys., 90 3 (2020) 31001 Published online: 01 July 2020 DOI: 10.1051/epjap/2020200108