In this review paper, a comprehensive study on the concept, theory, and applications of composite right/left-handed transmission lines (CRLH-TLs) by considering their use in antenna system designs have been provided. It is shown that CRLH-TLs with negative permittivity (e <; 0) and negative permeability (μ <; 0) have unique properties that do not occur naturally. Therefore, they are referred to as artificial structures called “metamaterials”. These artificial structures include series left-handed (LH) capacitances (C
 L
), shunt LH inductances (L
 L
), series right-handed (RH) inductances (LR), and shunt RH capacitances (CR) that are realized by slots or interdigital capacitors, stubs or via-holes, unwanted current flowing on the surface, and gap distance between the surface and ground-plane, respectively. In the most cases, it is also shown that structures based on CRLH metamaterial-TLs are superior than their conventional alternatives, since they have smaller dimensions, lower-profile, wider bandwidth, better radiation patterns, higher gain and efficiency, which make them easier and more cost-effective to manufacture and mass produce. Hence, a broad range of metamaterial-based design possibilities are introduced to highlight the improvement of the performance parameters that are rare and not often discussed in available literature. Therefore, this survey provides a wide overview of key early-stage concepts of metematerial-based designs as a thorough reference for specialist antennas and microwave circuits designers. To analyze the critical features of metamaterial theory and concept, several examples are used. Comparisons on the basis of physical size, bandwidth, materials, gain, efficiency, and radiation patterns are made for all the examples that are based on CRLH metamaterialTLs. As revealed in all the metematerial design examples, foot-print area decrement is an important issue of study that have a strong impact for the enlargement of the next generation wireless communication systems.

/pdf/a-comprehensive-survey-of-metamaterial-transmission-line-2yq6ozdmtb.pdf

A Comprehensive Survey of “Metamaterial Transmission-Line Based Antennas: Design, Challenges, and Applications”

This communication presents a reconfigurable antenna capable of independently reconfiguring the operating frequency, radiation pattern and polarization A switched grid of small metallic patches, known as pixel surface, is used as a parasitic layer to provide reconfiguration capabilities to existing antennas acting as driven element The parasitic pixel layer presents advantages such as low profile, integrability and cost-effective fabrication A fully operational prototype has been designed, fabricated and its compound reconfiguration capabilities have been characterized The prototype combines a patch antenna and a parasitic pixel surface consisting of 6 $\,\times\,$ 6 pixels, with an overall size of $06 \lambda \times 06 \lambda$ and 60 PIN-diode switches The antenna simultaneously tunes its operation frequency over a 25% frequency range, steers the radiation beam over ${\pm 30^\circ}$ in E and H-planes, and switches between four different polarizations ( ${\mathhat{\rm x}},$ ${\mathhat{\rm y}}$ , LHCP, RHCP) The average antenna gain among the different parameter combinations is 4 dB, reaching 6–7 dB for the most advantageous combinations The distance between the driven and the parasitic layers determines the tradeoff between frequency tuning range (12% to 25%) and radiation efficiency (45% to 55%)

Frequency, radiation pattern and polarization reconfigurable antenna using a parasitic pixel layer

Reconfigurable antennas play important roles in smart and adaptive systems and are the subject of many research studies. They offer several advantages such as multifunctional capabilities, minimized volume requirements, low front-end processing efforts with no need for a filtering element, good isolation, and sufficient out-of-band rejection; these make them well suited for use in wireless applications such as fourth generation (4G) and fifth generation (5G) mobile terminals. With the use of active materials such as microelectromechanical systems (MEMS), varactor or p-i-n (PIN) diodes, an antenna’s characteristics can be changed through altering the current flow on the antenna structure. If an antenna is to be reconfigurable into many different states, it needs to have an adequate number of active elements. However, a large number of high-quality active elements increases cost, and necessitates complex biasing networks and control circuitry. We review some recently proposed reconfigurable antenna designs suitable for use in wireless communications such as cognitive-ratio (CR), multiple-input multiple-output (MIMO), ultra-wideband (UWB), and 4G/5G mobile terminals. Several examples of antennas with different reconfigurability functions are analyzed and their performances are compared. Characteristics and fundamental properties of reconfigurable antennas with single and multiple reconfigurability modes are investigated.

https://www.mdpi.com/2079-9292/8/2/128/pdf

Recent Developments of Reconfigurable Antennas for Current and Future Wireless Communication Systems

A simple compact planar pattern-reconfigurable antenna based on arc dipoles is proposed in this letter. The antenna consists of four identical arc dipoles and a broadband reconfigurable feeding network, which are printed on the bottom and top layers of the substrate, respectively. By switching the on/off states of the p-i-n diodes, which are integrated in the reconfigurable feeding network, four different modes with endfire radiation patterns can be obtained in the azimuthal plane. The antenna is simulated, fabricated, and measured. Experimental results indicate that the proposed antenna achieves a bandwidth of 33.6% (2.25–3.16 GHz) for impedance matching better than 10 dB. The measured average gain is 4.11 dBi. Furthermore, the radiation efficiency is up to 60%. The proposed antenna is suitable for WLAN applications in wireless communications.

A Simple Planar Pattern-Reconfigurable Antenna Based on Arc Dipoles

As demand for wireless connectivity increases, communication technology is moving toward integrating terrestrial networks with space networks. Creating this integrated space and terrestrial network (ISTN) is critically important for industries such as logistics, mining, agriculture, fisheries, and defense. However, a number of significant technological challenges must be overcome for ISTN through low-cost airborne platforms and high-data-rate backbone links.

Airplane-Aided Integrated Networking for 6G Wireless: Will It Work?

Pattern-reconfigurable antennas with multiple switchable beams, especially with both boresight and endfire directions, are highly desired for wireless communications. In this letter, a novel pattern-reconfigurable antenna is proposed that provides an efficient solution. By reconfiguring parasitic striplines placed around a radiating dipole and reflecting metal pieces under the dipole using p-i-n diodes, the antenna main beam can be switched to five directions in the elevation plane, approximately from $-90^{\circ }$ (left endfire), $-45^{\circ }$ , 0 $^{\circ }$ (boresight), $+45^{\circ }$ , to $+90^{\circ }$ (right endfire). The proposed antenna operates at 2.45 GHz with dimensions of about 0.57 $\lambda$ $\times\, 0.45\lambda$ $\times\, 0.28\lambda$ . An antenna prototype is fabricated and measured. For all five directional beams, the measured $|S_{11}|$ values are below $-$ 13 dB, and the measured realized gains range from 5.2 to 6.5 dBi. They agree reasonably well with the simulated ones.

/pdf/pattern-reconfigurable-antenna-with-five-switchable-beams-in-2p96gwh2jp.pdf

Pattern-Reconfigurable Antenna With Five Switchable Beams in Elevation Plane

For many leaky-wave antennas (LWAs), it is challenging to realize beam scanning through broadside. A problem is the presence of an open stopband (OSB), which restricts radiation in the broadside direction. In this paper, a novel substrate integrated waveguide (SIW)-based LWA is described to overcome the OSB problem and provide beam scanning continuously from the backward to the forward direction from a conventional periodic LWA. It is demonstrated that the $n =-1$ spatial harmonic can be excited efficiently from an SIW LWA and enables broadside radiation. However, it was found in our initial design that when the beam scans through the broadside, the cross-polarization level increases significantly compared to the beam close to the backfire direction. A technique is developed to reduce the cross-polarization level. As a result, a new antenna configuration is created. The antenna design has been realized and measured to validate the concept. The measured beam scanning range of the prototype is from −74° to +45° (119° of beam scanning) when the frequency sweeps from 7.625 to 11 GHz, and the measured cross-polarization level is 20.8 dB low at the main beam direction for the broadside beam.

Substrate Integrated Waveguide-Based Periodic Backward-to-Forward Scanning Leaky-Wave Antenna With Low Cross-Polarization

A reconfigurable, wideband, and low-profile circular polarization (CP) antenna is presented. Its wideband CP reconfigurability is realized by incorporating RF switches into a cross-bowtie radiator. A compact, wide bandwidth, and polarization-independent artificial magnetic conductor ground plane is developed to minimize the overall profile of the antenna while maintaining its wide bandwidth. The simplicity of this single-element design facilitates the realization of a reconfigurable, wide bandwidth CP array that achieves higher directivity without changing its overall profile. Prototypes of the single element and of a $1 \times 4$ array of these elements were fabricated and tested. The measured results for both prototypes are in good agreement with their simulated values, validating their design principles. They are low profile with a height $\sim 0.05\lambda _{\mathrm {\mathbf {0}}}$ . The array exhibits a wide fractional operational bandwidth: 1.65 GHz (21.7%), and a high realized gain: 13 dBic. Since they would enhance their channel capacity and avoid polarization mismatch issues, these reconfigurable CP antenna systems are very suitable for modern wireless systems.

/pdf/reconfigurable-wideband-low-profile-circularly-polarized-48lh423cn4.pdf

Reconfigurable, Wideband, Low-Profile, Circularly Polarized Antenna and Array Enabled by an Artificial Magnetic Conductor Ground

A novel fixed-frequency beam-scanning leaky-wave antenna (LWA) based on a period-reconfigurable structure is presented. Operating at 5 GHz, the antenna consists of a slotted substrate integrated waveguide and 54 electrically small patches. Each patch element is etched with two dumbbell-shaped slots, and its operating state can be flexibly controlled by the biasing of the p-i-n diode on a parasitic strip. An ideal array model employing isotropic point sources is used for the analysis on the scanning mechanism, based on which a new method for suppressing the higher order space harmonics is developed. Using this method, the monoharmonic radiation range can be dramatically extended, and a wide-angle beam scanning can be achieved by manipulating the period length of the LWA. An FPGA controlling platform is designed for the electronic control of the antenna. The measured results validate that the proposed antenna achieves good performance of wide-angle scanning (125°) with a peak gain of 11.8 dBi at a fixed frequency.

/pdf/a-period-reconfigurable-leaky-wave-antenna-with-fixed-2w70ijg89u.pdf

A Period-Reconfigurable Leaky-Wave Antenna With Fixed-Frequency and Wide-Angle Beam Scanning

A novel multi-linear polarization (multi-LP) reconfigurable unidirectional circular patch antenna is proposed, which can switch among four LPs at every 45° rotation. The patch antenna is fed in the center and shorting posts are used to excite TM11 mode with LP. By controlling the connections between the four shorting posts and the ground plane using p-i-n diodes, four reconfigurable polarization states at $\phi =0 {^{\circ }}$ , $\phi =45 {^{\circ }}$ , $\phi =90 {^{\circ }}$ , or $\phi =135 {^{\circ }}$ can be realized. The size of this antenna is about $0.57\lambda \times 0.57\lambda \times 0.07\lambda $ at 2.45 GHz. It can be easily fabricated and has a simple biasing network. The measured overlapping impedance bandwidth for different polarizations under the condition $|\text{S}11| \leq -10$ dB is from 2.33 to 2.50 GHz, which agrees well with the simulated one. Moreover, the antenna maintains stable radiation patterns and the measured realized gains range from 5.3 to 5.9 dBi.

Shu-Lin Chen

Papers

Pattern-Reconfigurable Antenna With Five Switchable Beams in Elevation Plane

Substrate Integrated Waveguide-Based Periodic Backward-to-Forward Scanning Leaky-Wave Antenna With Low Cross-Polarization

Reconfigurable, Wideband, Low-Profile, Circularly Polarized Antenna and Array Enabled by an Artificial Magnetic Conductor Ground

A Period-Reconfigurable Leaky-Wave Antenna With Fixed-Frequency and Wide-Angle Beam Scanning

A Multi-linear Polarization Reconfigurable Unidirectional Patch Antenna