An electromagnetic (EM) probe for monitoring at least one biological tissue. The EM probe comprises a spiral antenna conductor (not shown) and an EM radiation absorbing layer (92) mounted along the antenna. The EM radiation absorbing layer has a plurality of substantially concentric frame shaped regions (93A-C) corresponding to portions of said spiral antenna having equal surface of antenna conductor, any of said plurality of concentric frame shaped regions has an EM radiation absorption coefficient different than any other of said neighbouring concentric frame shaped regions.