An apparatus for estimating a value of a resistivity property of an earth formation intersected by a borehole, the apparatus comprising: an electrically conducting tubular (130;250;550) conveyable in the borehole; at least one transmitter (110,115) associated with the conducting tubular (130;250;550) configured to propagate an electromagnetic field in the earth formation; and at least one receiver (120,125) associated with the conducting tubular (130;250;550) configured to receive an electromagnetic signal resulting from interaction of an electromagnetic field with said earth formation; wherein the at least one transmitter (110,115) and at least one receiver (120,125) employ at least one of a plurality of antenna assemblies on the conducting tubular (130;250;550), each antenna assembly comprising: a recess in the conducting tubular (130;250;550) defined by at least one radially extending surface substantially perpendicular to a longitudinal axis of the conducting tubular (130;250;550) and non-radially extending surfaces; an antenna (240;540) in the recess; and conductive shielding (220;520a), the conductive shielding (220;520a) having a conductivity at least 30 times greater than a conductivity of the conducting tubular (130;250;550) and characterised by the conductive shielding (220;520a) covering the whole of each of the at least one radially extending surface. an electrically conducting tubular (130;250;550) conveyable in the borehole; at least one transmitter (110,115) associated with the conducting tubular (130;250;550) configured to propagate an electromagnetic field in the earth formation; and at least one receiver (120,125) associated with the conducting tubular (130;250;550) configured to receive an electromagnetic signal resulting from interaction of an electromagnetic field with said earth formation; wherein the at least one transmitter (110,115) and at least one receiver (120,125) employ at least one of a plurality of antenna assemblies on the conducting tubular (130;250;550), each antenna assembly comprising: a recess in the conducting tubular (130;250;550) defined by at least one radially extending surface substantially perpendicular to a longitudinal axis of the conducting tubular (130;250;550) and non-radially extending surfaces; an antenna (240;540) in the recess; and conductive shielding (220;520a), the conductive shielding (220;520a) having a conductivity at least 30 times greater than a conductivity of the conducting tubular (130;250;550) and characterised by the conductive shielding (220;520a) covering the whole of each of the at least one radially extending surface. a recess in the conducting tubular (130;250;550) defined by at least one radially extending surface substantially perpendicular to a longitudinal axis of the conducting tubular (130;250;550) and non-radially extending surfaces; an antenna (240;540) in the recess; and conductive shielding (220;520a), the conductive shielding (220;520a) having a conductivity at least 30 times greater than a conductivity of the conducting tubular (130;250;550) and characterised by the conductive shielding (220;520a) covering the whole of each of the at least one radially extending surface.