Theory and design of “shortened” multiantenna microwave applicators with controllable SAR patterns

A “shortened” multiantenna hyperthermia applicator has been designed and tested at the Mallinckrodt Institute of Radiology at Washington University School of Medicine. By shortening the distance from antenna to aperture, an applicator is obtained that produces an SAR pattern that is essentially the same as produced by a monopole antenna. By placing several properly spaced probe antennas into the same “shortened” applicator, an applicator is obtained that produces a SAR distribution that is essentially a composite of small overlapping SAR patterns produced by weakly interacting incoherently driven antennas. Such a design significantly improves the applicator’s lateral heating efficiency and allows the independent control of temperatures in certain tumor areas by changing the input power to the respective antennas.