A diagnostic apparatus, comprising: a patch unit with integrated package having the form of a patch, including: an adhesive layer by means of which the patch unit can be affixed to a patient's skin; an antenna configured to be disposed on a thorax of a living body so as to direct radio frequency electromagnetic waves through a lung in the body and to output RF signals responsively to the waves that have passed through the lung, wherein the antenna comprises a planar antenna element printed on a front surface of a planar printed circuit board and a rear element behind the front surface and which is configured to serve as a reflective structure to reflect a backward wave from the planar antenna element in phase with a forward beam from the planar antenna element, the rear element comprising an electromagnetic bandgap structure made up of a periodic mesh of conductive patches connected to a ground plane by vias through a dielectric layer; a transceiver configured to generate driving signals for transmission by the antenna and filters and digitizes the reflected signals that the antenna receives from the patient's body; a processor which is configured to process the RF signals over time so as to measure RF path characteristic of the RF electromagnetic waves; a power module configured to provide power to the components of the patch unit; an ECG electrode and acquisition circuit (140, 150), which filters and digitizes ECG signals for input to processor; a user interface; and a communication interface for communication with a remote console, wherein: the path characteristic comprises an effective RF path length of the RF electromagnetic waves through the body, and based on the path characteristic, the processor is configured to assess a fluid content of the lung. an adhesive layer by means of which the patch unit can be affixed to a patient's skin; an antenna configured to be disposed on a thorax of a living body so as to direct radio frequency electromagnetic waves through a lung in the body and to output RF signals responsively to the waves that have passed through the lung, wherein the antenna comprises a planar antenna element printed on a front surface of a planar printed circuit board and a rear element behind the front surface and which is configured to serve as a reflective structure to reflect a backward wave from the planar antenna element in phase with a forward beam from the planar antenna element, the rear element comprising an electromagnetic bandgap structure made up of a periodic mesh of conductive patches connected to a ground plane by vias through a dielectric layer; a transceiver configured to generate driving signals for transmission by the antenna and filters and digitizes the reflected signals that the antenna receives from the patient's body; a processor which is configured to process the RF signals over time so as to measure RF path characteristic of the RF electromagnetic waves; a power module configured to provide power to the components of the patch unit; an ECG electrode and acquisition circuit (140, 150), which filters and digitizes ECG signals for input to processor; a user interface; and a communication interface for communication with a remote console, wherein: the path characteristic comprises an effective RF path length of the RF electromagnetic waves through the body, and based on the path characteristic, the processor is configured to assess a fluid content of the lung. the path characteristic comprises an effective RF path length of the RF electromagnetic waves through the body, and based on the path characteristic, the processor is configured to assess a fluid content of the lung.