Damir Muha

ENZ-based shortened horn antenna - an experimental study

Recent numerical study predicted phenomenon of a gain increase of a shortened horn antenna with the help of embedded double-thin-wire ENZ metamaterial slab. Here, we perform an experimental investigation of shortened horn antenna (length of which spans 52% of the length of optimal horn) with much simpler single-wire ENZ slab operated in 10 GHz band. Measurements revealed gain increase of more than 2 dB (comparing to the gain of a bare shortened horn) in 12% fractional bandwidth, with return loss better than -13 dB.

Practical realization of DB metasurface

In this Letter, experimental realization of recently proposed DB metasurface is presented. A compact DB unit cell is proposed and its operating principle is tested both numerically and experimentally. Practical realization of a single layer DB metasurface, composed of 16 DB unit cells, is presented. Prototyped DB metasurface was measured in a waveguide environment and obtained experimental results support theoretically predicted DB properties.

Exploiting Intrinsic Dispersion of Metamaterials for Designing Broadband Aperture Antennas: Theory and Experimental Verification

The intrinsic frequency dispersion has usually been considered as a relevant drawback of metamaterials, limiting their application to narrowband microwave components. However, we have recently demonstrated that a particular metamaterial-based lens, consisting of a combination of an epsilon-near-zero (ENZ) material and air, is able to enhance the gain of short horn antennas over a broad frequency range. This result was achieved by exploiting the dispersive nature of ENZ metamaterials. In this communication, we further discuss the latter aspect, giving more details about the physical mechanism enabling broadband operation of shortened horns loaded with ENZ-air lenses. The discussion is supported by a set of experimental results obtained on a fabricated prototype.

Influence of transmission line on stability of networks containing ideal negative capacitors

Majority of non-Foster-based metamaterials or antenna matching circuits are based on simple networks that contain parallel or series combination of positive and negative capacitor. It is well-known that these networks are stable, if the overall capacitance is positive. It is shown that this stability criterion becomes fundamentally different if a segment of a transmission line is inserted between the ideal positive capacitor and ideal negative capacitor. In parallel and series networks, the presence of a transmission line segment of any finite length (different from zero) causes instability. This counter-intuitive behavior is caused by the unstable system pole located at the positive real axis of a complex plane. However, it appears possible to remove that pole by a proper design of a practical negative capacitor and, therefore, assure stable operation.

Stability of Simple Lumped-Distributed Networks With Negative Capacitors

A majority of non-Foster antenna matching circuits and non-Foster metamaterials are based on a simple parallel combination of positive and negative capacitor. It is known that these networks are stable if the overall “mesh” capacitance is positive. Here, we show that this widely accepted criterion fails if a transmission line of any finite length (different from zero) is inserted between an ideal positive capacitor and an ideal negative capacitor. Such a network is always unstable, which appears to be a serious drawback. However, we also show that a realistic, band-limited negative capacitor can be designed in a way that assures stable operation.

Numerical and experimental investigation of horn antenna with embedded ENZ metamaterial lens

Recent numerical study indicated possibility of use of a double thin-wire metamaterial slab as a flat lens that can be embedded into a horn antenna. This led to the construction of the horn, the gain of which is almost equal to the gain of an optimal horn across the moderate bandwidth, but with the substantially shorter length (down to 52% of the original length). Here, we perform both numerical and experimental investigation of such shortened horn antenna operating in 10 GHz band. Simulation showed that both the single thin-wire media and double thin-wire media indeed increase the gain of the shortened horn antenna by 2 dB in 10% fractional bandwidth with return loss better than -13 dB. Qualitatively similar results were obtained for the lens made out of fictitious continuous ENZ material with Drude dispersion model, which indicates that theory of the continuous media can be used for the initial design. Finally, measurements of the gain of experiential antennas verified existence of the phenomenon of gain increase.

Experimental verification of broadband antennas loaded with metamaterials

The intrinsic frequency dispersion has been usually considered as a relevant drawback of metamaterials, limiting their application to narrowband microwave components. However, it has been recently demonstrated that a particular metamaterial-based lens, consisting of a combination of an epsilon-near-zero (ENZ) material and air, is able to enhance the gain of short horn antennas over a broad frequency range. This interesting result has been achieved by exploiting the dispersive nature of ENZ metamaterials. In this contribution, we further discuss the latter aspect, giving more details about the physical mechanism enabling broadband operation of shortened horns loaded with ENZ-air lenses. The discussion is supported by a set of experimental results obtained on a fabricated prototype.

Practical aspects of DB metasurfaces- a brief review

Recently proposed DB boundary is a hypothetical surface, on which vanishing of normal components of D and B vector occurs. This paper reviews metasurface-based implementations of a DB boundary proposed so far and highlights possible future research directions.

Self-seeded WDM-PON for next generation broadband access networks

Recent advances in the development of self-seeded WDM-PON communication systems employing modulation averaging are presented. Optical transmitter containing extended-cavity resonator with modulation-averaging reflector at the remote node improves the link margin and allows for a wider range of bias conditions at the transmitter. The developed modulation-averaging reflector is a passive optical device and therefore the remote nodes in our proposed WDM-PON system remain passive. Optimization of WDM-PON system components, in particular optimization of modulation-averaging reflector, is discussed in the paper.