TUNING OF THE TUNNELING FREQUENCY IN FOAM EPSILON-NEAR-ZERO WAVEGUIDE WITH NARROWED CHANNEL

摘要

Epsilon-near-zero (ENZ) foam waveguide consists of input waveguides (1 and 1') filled with foam dielectric (3 and 3') which is mounted on a microwave substrate (4 and 4'). Microwave substrate (4 and 4') serves as a carrier of the foam dielectric and also as an ENZ channel (2). ENZ waveguide is coated with a metal foil on the outside (5 and 5"). Longitudinal slots (6 and 6') are etched in the metallization of the broad face of the channel (2) in order to shift down the tunneling frequency in respect to the case of ENZ channel without slots. The maximum shift of the tunneling frequency is limited with cut-off frequency of input waveguides. Similar frequency shift can be achieved with a longitudinal slot (7) etched on the wider side of the channel (2) and placed symmetrically in respect to input waveguides. When reducing the length of the slots by deposition of conductive paste onto the slot, the tunneling frequency increases up to the frequency without slots. In order to achieve discrete electronic tuning of the tunneling frequency, PIN diodes (9, 9' and 10, 10') are mounted across the slots, while for continuous tuning varactor diodes (11 and 11') are used. Foam ENZ wavegude is excited with coaxial connectors (8 and 8') that are matched in certain frequency range by changing their position and length of the pins.