A medical imaging system comprising: a microwave antenna array comprising a plurality of antennae which are spaced from one another, the plurality of antennae defining a transmitting antenna and receiving antennae, wherein the transmitting antenna is configured to transmit microwave signals so as to illuminate a body part of a patient and the receiving antennae are configured to receive the microwave signals following scattering within the body part; wherein the microwave antenna array has a plurality of configurations defining positions of the plurality of antennae relative to the body part, wherein in each configuration the plurality of antennae are located at positions which are unoccupied in the other configurations; the medical imaging system further comprising: an actuator configured to move the microwave antenna array between the plurality of configurations so as to position the plurality of antennae at previously unoccupied positions; and a processor configured to obtain a data set for the microwave signals produced in each of the plurality of configurations of the microwave antenna array and to generate an output indicative of the internal structure of the body part from a concatenation of the data sets; characterized in that: the physical spacing between the antennae is greater than half the wavelength of the microwave signal and an effective spacing between the antennae, defined as the spacing between the occupied positions across all configurations, is less than half the wavelength of the microwave signal; and in that the antennae are positioned in a formation formed from a regular tessellation of a polygon which is tilted with respect to a direction of movement of the antennae. a microwave antenna array comprising a plurality of antennae which are spaced from one another, the plurality of antennae defining a transmitting antenna and receiving antennae, wherein the transmitting antenna is configured to transmit microwave signals so as to illuminate a body part of a patient and the receiving antennae are configured to receive the microwave signals following scattering within the body part; wherein the microwave antenna array has a plurality of configurations defining positions of the plurality of antennae relative to the body part, wherein in each configuration the plurality of antennae are located at positions which are unoccupied in the other configurations; the medical imaging system further comprising: an actuator configured to move the microwave antenna array between the plurality of configurations so as to position the plurality of antennae at previously unoccupied positions; and a processor configured to obtain a data set for the microwave signals produced in each of the plurality of configurations of the microwave antenna array and to generate an output indicative of the internal structure of the body part from a concatenation of the data sets; characterized in that: the physical spacing between the antennae is greater than half the wavelength of the microwave signal and an effective spacing between the antennae, defined as the spacing between the occupied positions across all configurations, is less than half the wavelength of the microwave signal; and in that the antennae are positioned in a formation formed from a regular tessellation of a polygon which is tilted with respect to a direction of movement of the antennae. an actuator configured to move the microwave antenna array between the plurality of configurations so as to position the plurality of antennae at previously unoccupied positions; and a processor configured to obtain a data set for the microwave signals produced in each of the plurality of configurations of the microwave antenna array and to generate an output indicative of the internal structure of the body part from a concatenation of the data sets; characterized in that: the physical spacing between the antennae is greater than half the wavelength of the microwave signal and an effective spacing between the antennae, defined as the spacing between the occupied positions across all configurations, is less than half the wavelength of the microwave signal; and in that the antennae are positioned in a formation formed from a regular tessellation of a polygon which is tilted with respect to a direction of movement of the antennae. the physical spacing between the antennae is greater than half the wavelength of the microwave signal and an effective spacing between the antennae, defined as the spacing between the occupied positions across all configurations, is less than half the wavelength of the microwave signal; and in that the antennae are positioned in a formation formed from a regular tessellation of a polygon which is tilted with respect to a direction of movement of the antennae.