A Switchable-Frequency Slot-Ring Antenna Element for Designing a Reconfigurable Array

A frequency-reconfigurable slot-ring antenna switching between L - and C -bands is presented. The aperture of an L -band slot-ring antenna can be reconfigured to a 2 × 2 C -band slot-ring antenna array by changing the states of 16 p-i-n diode switches. This antenna operates at 1.76/5.71 GHz with a fractional bandwidth of 8.6%/11.5% in the L / C -band operating states, respectively. The measured realized gain and radiation efficiency are 0.1/4.2 dBi and 66.6%/80.7%, respectively. The antenna element spacing at 5.71 GHz is 0.36λ 0 , which enables beamsteering without grating lobes. This shared-aperture antenna is scalable to a larger array with element spacing of less than half-wavelength in both frequency bands.