Bandwidth and gain enhancement of composite right left handed metamaterial transmission line planar antenna employing a non foster impedance matching circuit board

Mohammad Alibakhshikenari,Raed A Abd-Alhameed,Ayman A Althuwayb,Francisco Falcone,Chan H See,Naser Ojaroudi Parchin,Leyre Azpilicueta,Bal S Virdee,Tayeb A Denidni,Ernesto Limiti,Isabelle Huynen

doi:10.1038/s41598-021-86973-x

Abstract

The paper demonstrates an effective technique to significantly enhance the bandwidth and radiation gain of an otherwise narrowband composite right/left-handed transmission-line (CRLH-TL) antenna using a non-Foster impedance matching circuit (NF-IMC) without affecting the antenna’s stability. This is achieved by using the negative reactance of the NF-IMC to counteract the input capacitance of the antenna. Series capacitance of the CRLH-TL unit-cell is created by etching a dielectric spiral slot inside a rectangular microstrip patch that is grounded through a spiraled microstrip inductance. The overall size of the antenna, including the NF-IMC at its lowest operating frequency is 0.335λ0 × 0.137λ0 × 0.003λ0, where λ0 is the free-space wavelength at 1.4 GHz. The performance of the antenna was verified through actual measurements. The stable bandwidth of the antenna for |S11|≤ − 18 dB is greater than 1 GHz (1.4–2.45 GHz), which is significantly wider than the CRLH-TL antenna without the proposed impedance matching circuit. In addition, with the proposed technique the measured radiation gain and efficiency of the antenna are increased on average by 3.2 dBi and 31.5% over the operating frequency band.

Highlights

The paper demonstrates an effective technique to significantly enhance the bandwidth and radiation gain of an otherwise narrowband composite right/left-handed transmission-line (CRLH-TL) antenna using a non-Foster impedance matching circuit (NF-Impedance matching circuits (IMCs)) without affecting the antenna’s stability
When creating a MTM the parasitic elements associated with transmission-lines (TLs), i.e. right-handed (RH) ( ε > 0, μ > 0 ), combine with the LH characteristics to create a MTM structure commonly referred to as composite right/left-handed transmission-line (CRLH-TL)[7]
In this paper we demonstrate that by combining the proposed non-Foster impedance matching circuit (NFIMC) with a narrowband CRLH-TL microstrip antenna it is possible to significantly enhance the antenna’s bandwidth and radiation gain performance without compromising its stability

Summary

CL max

As mentioned earlier the parasitic RH elements (C R & LR ) are unavoidable components in the transmission-line structure due to existence of the voltage gradient between the patch and ground plane, and the currents flowing on the surfaces, respectively[13] As these parameters effect the overall frequency range of the antenna it was necessary to optimize the structural parameters of the antenna unit-cell using ADS to realize the desired performance. The dispersion diagram of the CRLH-TL unit-cell depicted in Fig. 6 shows the LH and RH regions are 1.14 GHz < fLH < 1.41 GHz and 2.45 GHz < fRH < 3.6 GHz, respectively It shows the propagation constant of the CRLH-TL unit-cell is near zero in the frequency range of interest between 1.4 and 2.46 GHz. The simulation analysis in Fig. 7 reveals show the input impedance of the antenna is affected by the number of unit-cells. The input capacitance of the antenna was counteracted with the negative reactance generated by the NF-IMC and thereby overcome the inherent narrowband characteristic of the antenna

Fabricated prototype and measurements

Conclusions

Author contributions

Findings

Additional information