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Abstract and Figures

Decreasing the electric length of an antenna results in increasing its input reactance that becomes greater than its input resistance, resulting in a significant rise in its quality factor and in a drastic reduction of its potential operating bandwidth. For such small antennas, namely ESA for Electrically Small Antenna, passive matching is restricted by the gain-bandwidth theory, providing narrow bandwidths and/or poor gain. This limitation can be overtaken by using antenna matching networks based on non-Foster components. In previous studies, non-Foster components are used to cancel the reactance part of the ESA, and then passive matching may be introduced to transform the net input impedance toward 50Ω, which leads to an increase in the bandwidth. In this paper, a design methodology is put forward on three different topologies all based on combined passive and active matching networks. A described step-by-step design to decrease the antenna quality factor is discussed. A comparison is made between these topologies along with a discussion on their limitations and ability to increase the bandwidth and radiation efficiency of ESA. The third topology presented in this paper is a novel one that proposes a three-stage matching network and exhibits both the widest matched bandwidth and an increase in the efficiency of the whole system compared to previous approaches. In order to make this comparison, a new indicator to estimate the whole system radiated power efficiency is introduced and validated by comparison with a full EM simulation. Moreover, actual implementation of the two most interesting techniques are detailed and associated measured results are carefully compared to simulations.
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Methodology for broadband matching of electrically small antenna
using combined non-Foster and passive networks
Saadou Almokdad
1,2
Raafat Lababidi
1
Marc Le Roy
1
Sawsan Sadek
3
Andre
´Pe
´rennec
1
Denis Le Jeune
1
Received: 19 December 2019 / Revised: 27 April 2020 / Accepted: 2 June 2020 / Published online: 6 June 2020
Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
Decreasing the electric length of an antenna results in increasing its input reactance that becomes greater than its input
resistance, resulting in a significant rise in its quality factor and in a drastic reduction of its potential operating bandwidth.
For such small antennas, namely ESA for Electrically Small Antenna, passive matching is restricted by the gain-bandwidth
theory, providing narrow bandwidths and/or poor gain. This limitation can be overtaken by using antenna matching
networks based on non-Foster components. In previous studies, non-Foster components are used to cancel the reactance
part of the ESA, and then passive matching may be introduced to transform the net input impedance toward 50X, which
leads to an increase in the bandwidth. In this paper, a design methodology is put forward on three different topologies all
based on combined passive and active matching networks. A described step-by-step design to decrease the antenna quality
factor is discussed. A comparison is made between these topologies along with a discussion on their limitations and ability
to increase the bandwidth and radiation efficiency of ESA. The third topology presented in this paper is a novel one that
proposes a three-stage matching network and exhibits both the widest matched bandwidth and an increase in the efficiency
of the whole system compared to previous approaches. In order to make this comparison, a new indicator to estimate the
whole system radiated power efficiency is introduced and validated by comparison with a full EM simulation. Moreover,
actual implementation of the two most interesting techniques are detailed and associated measured results are carefully
compared to simulations.
Keywords Non-Foster Passive matching Quality factor Electrically small antenna
1 Introduction
The demand for wide-band small antennas is steadily
increasing for future wireless communication systems, due
to the need of compact multi-function and multi-standard
devices. Electrically small antennas (ESA) are thus
required due to the limited space available in the structures
such as electronic mobile devices (5G), IoT (Internet of
Things), medical equipment, etc. However, practical
application in today’s electronic systems is limited by their
fundamental tradeoff between bandwidth and efficiency
using passive impedance matching techniques [1]. Non-
Foster circuits (NFCs) are active circuits that promise to
break the fundamental tradeoffs between size, operating
frequency and bandwidth for electrically small antennas
[2], [3].
An antenna is considered to be an ESA when it satisfies
the following condition: ka \0.5, where k is the wave
number and a is the radius of a hypothetical sphere
enclosing the antenna [4].
Furthermore, ESAs famously suffer from high quality
factor Q because of their high reactance value compared to
their small resistive value, resulting in storing the input
power in their near field and a small portion radiates in
their far field [5]. Wheeler and Chu [6] have provided
&Saadou Almokdad
Saadou-ali-almokdad@hotmail.com
1
Lab-STICC (UMR CNRS 6285), UBO, ENSTA-Bretagne,
Brest, France
2
Doctoral School of Science and Technology, Lebanese
University, Hadath, Lebanon
3
Faculty of Technology, Lebanese University, Saida, Lebanon
123
Analog Integrated Circuits and Signal Processing (2020) 104:251–263
https://doi.org/10.1007/s10470-020-01672-3(0123456789().,-volV)(0123456789().,-volV)
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
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