A radar system, comprising: a transmitter station configured to emit probe signals of RF electromagnetic radiation into a region; and a receiver station configured to process return signals of RF electromagnetic radiation from the region, the return signals based on probe signals scattered from one or more objects in the region, the receiver station comprising: a photonic crystal receiver formed of dielectric material and comprising: an antenna structure configured to couple to a target RF electromagnetic radiation, the return signals of RF electromagnetic radiation comprising the target RF electromagnetic radiation; a photonic crystal structure having an elongated slot disposed therein and configured to concentrate the target RF electromagnetic radiation in the elongated slot; and a vapor disposed in the elongated slot; an optical system configured to generate spectroscopic data based on optical signals from the photonic crystal receiver, the spectroscopic data representing one or more properties of the target RF electromagnetic radiation; and a data processing subsystem configured to generate a time series of property data based on the spectroscopic data, the time series of property data representing one or more properties of the target RF electromagnetic radiation over time. a transmitter station configured to emit probe signals of RF electromagnetic radiation into a region; and a receiver station configured to process return signals of RF electromagnetic radiation from the region, the return signals based on probe signals scattered from one or more objects in the region, the receiver station comprising: a photonic crystal receiver formed of dielectric material and comprising: an antenna structure configured to couple to a target RF electromagnetic radiation, the return signals of RF electromagnetic radiation comprising the target RF electromagnetic radiation; a photonic crystal structure having an elongated slot disposed therein and configured to concentrate the target RF electromagnetic radiation in the elongated slot; and a vapor disposed in the elongated slot; an optical system configured to generate spectroscopic data based on optical signals from the photonic crystal receiver, the spectroscopic data representing one or more properties of the target RF electromagnetic radiation; and a data processing subsystem configured to generate a time series of property data based on the spectroscopic data, the time series of property data representing one or more properties of the target RF electromagnetic radiation over time. a photonic crystal receiver formed of dielectric material and comprising: an antenna structure configured to couple to a target RF electromagnetic radiation, the return signals of RF electromagnetic radiation comprising the target RF electromagnetic radiation; a photonic crystal structure having an elongated slot disposed therein and configured to concentrate the target RF electromagnetic radiation in the elongated slot; and a vapor disposed in the elongated slot; an antenna structure configured to couple to a target RF electromagnetic radiation, the return signals of RF electromagnetic radiation comprising the target RF electromagnetic radiation; a photonic crystal structure having an elongated slot disposed therein and configured to concentrate the target RF electromagnetic radiation in the elongated slot; and a vapor disposed in the elongated slot; an optical system configured to generate spectroscopic data based on optical signals from the photonic crystal receiver, the spectroscopic data representing one or more properties of the target RF electromagnetic radiation; and a data processing subsystem configured to generate a time series of property data based on the spectroscopic data, the time series of property data representing one or more properties of the target RF electromagnetic radiation over time.