What are the challenges to be faced in microwave imaging. I am from rf and microwave antennas background. Does this topic involve signal processing and antennas both?
Try this http://eaton.math.rpi.edu/faculty/Cheney/CBMS/CBMSbookDec08.pdf and perhaps this https://udrc.eng.ed.ac.uk/sites/udrc.eng.ed.ac.uk/files/attachments/Introduction%20Radar%20signal%20processing.pdf
A microwave imaging system is composed of several devices. For instance, antenna(s), transceiver, processor. Also, a algorithm should be devised to construct the image.
You can only focus on the design of antenna for microwave imaging.