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Small resonant elliptical slot antennas have shown great potential as imaging array elements at microwave frequencies. For high-resolution 3D imaging applications it is desirable to extend the operational frequency bandwidth of these elements. One way to achieve this is by loading the slot with a varactor diode, and electronically tuning its resonant frequency. This communication presents the design, analysis, and implementation of a varactor diode-tuned elliptical slot antenna at K-band (18 GHz-26.5 GHz). The slot antenna is then used to produce single-frequency and wideband multi-frequency synthetic aperture radar (SAR) images of two targets located at different distances to show the efficacy of using this slot for wideband imaging.