Stability of tunnel diode based negative impedance circuit

Summary form only given. Recently there are increasing interests in incorporating negative impedance converter (NIC) circuits into electrically small antennas to surpass the Chu limit and into metamaterial unit structures to eliminate the strong dispersion. Most of the works are transistor based (e.g. Linvill´s NIC circuit) or operational amplifier based (at low frequency). Our previous work has demonstrated some challenging issues remain in these designs, such as the limitation on operation frequency, parasitics, noise and stability. An alternative method to realize NIC circuit is by combining negative resistances and passive lumped elements. The configuration is firstly proposed 80 years ago (L. C. Verman, Proc. IRE, 19, 676-681, 1931), however, without a stability analysis. The negative resistance can be implemented by tunnel diodes, which has the advantages of high operational frequency and low-noise level.