Broadband negative-capacitor-based enhanced transmission through subwavelength aperture

Summary form only given. The phenomenon of extraordinary transmission was firstly demonstrated at optical frequencies (D. E. Grupp, H. J. Lezec, T. Thio, and T. W. Ebbesen, Beyond the Bethe limit: Tunable enhanced light transmission through a single wavelength aperture, Advanced Mater., vol. 11, pp. 860-862, 1999), and later also explained by using theory of leaky waves. In the metamaterial community, it has been proposed to achieve this extraordinary transmission by use of the ENZ (or MNZ) fillings either in the aperture or as the aperture cover (A. Alù, F. Bilotti, N. Engheta, and L. Vegni, Metamaterial covers over a small aperture, IEEE Transactions on Antennas and Propagation, vol. 54, no. 6, pp. 1632-1643, June 2006). Unfortunately, all passive ENZ and MNZ materials (as well as the ENG, and MNG materials) suffer from inherent narrow operating bandwidth caused by basic energy-dispersion constraints. Recently, it has been shown possible to build ultra-broadband (bandwidth up to six octaves) active ENZ metamaterials that overcome fundamental dispersion constraints. These metamaterials are based on non-Foster negative capacitors (S. Hrabar, I. Krois, et al., Negative capacitor paves the way to ultra-broadband metamaterials´, Applied physics letters. Vol. 99, No. 25, 25403-1-25403-4, December 2011).Here, we show both numerically and experimentally that is possible to use very similar concept for broadband extraordinary transmission through the subwavelength aperture. The demonstrator comprises a simple air-filled microstrip line with a blocking metallic screen and it operates in 100 MHz RF band. The microstrip line is laid through the rectangular (subwaveleght) screen aperture. The aperture ´filling´ is a short monopole antenna loaded with a opamp based negative capacitor previously developed in our group (Muha, D., Hrabar, S., Krois, I.; Bonic, I. Kiricenko, A., Zaluski, D., Design of UHF Microstrip Non-Foster Leaky-wave Antenna, Proc. on ICECOM 2013.,- pp. 134138, Dubrovnik, 2013). It was envisaged that this simple inclusion should cause broadband ENZ effect, and therefore should yield broadband transmission enhancement (tunneling). As a first step, the full-wave simulations, complemented by time-domain SPICEbased stability analysis of a measurement setup were performed. These simulations predicted a stable enhancement of 4-5 dB within one octave bandwidth (70-140 MHz). This bandwidth is considerably wider than a 5 % wide (95-100 MHz) bandwidth, predicted for the case of an ordinary resonant ENZ inclusion (a short monopole loaded with an inductor). Manufacturing of the RF demonstrator is in progress and the preliminary experimental results will be presented at the conference.