We present the design and validation of an isotropic field probe with geometry and frequency response shaped to correctly weight the aggregate contribution of the various frequency components of a broadband magnetic field in the band 100 kHz – 400 MHz according to the ICNIRP 2020 guidelines. The elementary sensor is a small strip loop printed on a thin dielectric substrate. The elementary sensor is initially analyzed via full-wave simulation from which a Thévenin equivalent model is extracted. Careful consideration of the frequency response of the loop and the power detector enabled the optimization of a canonical filtering topology to obtain the desired frequency response. Finally, the isotropic probe assembly consisting of a cubic arrangement of three elementary sensors is validated with respect to isotropy and isolation.