Dual-band Gain Enhancing Compact Gradient Index Lenses

Microwave lenses provide an effective method of improving the gain of legacy antenna systems without having to do a complete redesign. At microwave frequencies, lenses can take on several forms, but gradient index (GRIN) lenses have garnered considerable attention of late because of their broadband performance and ability to control electromagnetic radiation. While previous work explored the use of a GRIN lens to enhance gain, a new direction we investigate is the optimization of a lens that enhances gain at one band but appears invisible at a second band. In addition, considerable effort is made to reduce the overall lens size. To demonstrate the effectiveness of the approach, a ceramic GRIN lens is fabricated and demonstrates +4 dB higher gain across a 15.4% fractional bandwidth (FBW) at L-band while not interfering with the performance at a second operating band with a 12.6% FBW in C-band.