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 (RF) 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 (EBG) 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 , 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 (RF) 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 (EBG) 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 , 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 . <EOS>