1. A radar system for reconstructing an image by computing a weighted combination of per-frequency estimates, the radar system comprising: a heterogeneous wideband antenna array apparatus; and a data processing unit connected to the heterogeneous wideband antenna array apparatus; wherein the heterogeneous wideband antenna array apparatus includes: a first sub-array comprising one or more antenna elements congruent to a first antenna element which is optimized to operate within a first frequency range; and a second sub-array comprising one or more antenna elements congruent to a second antenna element which is optimized to operate within a second frequency range; and wherein: the first frequency range is different from the second frequency range; the first frequency range and the second frequency range overlap; the first antenna element is not congruent to the second antenna element; antenna elements of the first sub-array and antenna elements of the second sub-array are interleaved such that at least one antenna element of the antenna array apparatus is surrounded by antenna elements which are not congruent to the at least one antenna element; and wherein: the data processing unit is operative to: collect a plurality of microwave responses for a plurality of combinations of transmit antenna elements and receive antenna elements of the antenna array apparatus, respectively, wherein each combination includes a transmit antenna element and a receive antenna element; compute a plurality of per-frequency estimates of a frequency-domain transfer function based on the plurality of microwave responses for the plurality of combinations of transmit antenna elements and receive antenna elements of the antenna array apparatus, wherein each per-frequency estimate is based on a measurement using a transmit antenna element and a receive antenna element of the heterogeneous wideband antenna array apparatus at a specified frequency; compute a plurality of estimated reflectivities at a plurality of three-dimensional locations, wherein each estimated reflectivity is computed based on a combination of the per-frequency estimates of the frequency-domain transfer function weighted by a phasor, wherein the phasor is a function of the transmit antenna element and the receive antenna element at the specified frequency; and reconstruct an image according to a function of the plurality of estimated reflectivities.