Metamaterial advances for radar and communications

Metamaterial antennas have progressed considerably in the last few years. Kymeta has demonstrated December 2014 the transmission to satellites and back using 20 and 30 GHz antennas about the size of a laptop which use metamaterial resonators to effect the phase shifting. A clear explanation of how this antenna works is given. Echodyne and PARC, a Xerox Co., have developed metamaterial arrays for radar. The Army Research Laboratory in Adelphi MD has funded the development of a metamaterial 250-505 MHZ antenna with a λ/20 thickness. Complementing this a conventional tightly coupled dipole antenna (TCDA) has been developed which provides a 20:1 bandwidth with a λ/40 thickness. Target cloaking has been demonstrated at microwaves using metamaterials. With cloaking the electromagnetic wave signal transmitted by a radar goes around the target making it invisible. It has also been demonstrated at L-band with a 50% bandwidth using fractals. Stealthing by absorption using a thin flexible and stretchable metamaterials sheet has been demonstrated to give 6 dB absorption over the band from 8-10 GHz, larger absorption over a narrower band. Using fractals material <; 1 mm thick simulation gave a 10 dB reduction in backscatter from 2 to 20 GHz, ~20 dB reduction from 9 to 15 GHz. Good results were obtained for large incidence angles and both polarizations. Using metamaterial one can focus 6X beyond diffraction limit at 0.38 μm (Moore's Law marches on); 40X diffraction limit, λ/80, at 375 MHz. Has been used in cell phones to provide antennas 5X smaller (1/10^th λ) having 700 MHz-2.7 GHz bandwidth. Provided isolation between antennas having 2.5 cm separation equivalent to 1m separation. Used for phased array wide angle impedance matching (WAIM). It has been found that n-doped graphene has a negative index of refraction.