Active negative refraction index (NRI) transmission line with gain

We have investigated microwave active negative refractive index (NRI) transmission line (also named composite right-hand / left-hand transmission line, or CRLH-TL) metamaterials incorporating gain devices to provide effective negative resistance. Our simulation and experimental results show that by inserting semiconductor tunnel diode at the unit cell level, the negative phase constant (i.e., left-handedness) of this kind of transmission lines is maintained while gain can be obtained (negative attenuation constant of transmission line) simultaneously. Important design aspects of the active metamaterial transmission lines are discussed. As a potential application, single unit-cell zeroth order resonator (ZOR) antennas based on the passive and active transmission lines are also discussed.