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In this article, the theory, design, and demonstration of wideband and low-profile dual-circularly polarized (dual-CP) transmit arrays (TAs) are reported, which support independent beamforming for left-/right-handed CP waves. This is achieved by utilizing an antenna–filter–antenna configuration for the TA unit cells with a profile of only about $0.11\lambda _{0}$ , which consists of receiving and transmitting stacked patches connected by two microstrip delay lines. By utilizing the phase delay lines and unit cell rotation, the dynamic phase and the Berry phase can be simultaneously exploited for providing continuous dual-CP transmissive phase compensation insensitive to the angle of incidence. The diffraction analysis of a linear gradient array of the proposed cells confirms its wideband performance of abnormal refraction. In addition, broadband CP planar feed arrays were designed and verified for functioning as low-profile feeds with symmetrical patterns for the TAs. As proof-of-concept examples, two $K$ -band dual-CP TAs integrated with the planar feeds were synthesized, fabricated, and measured, possessing a total profile of about $7.1\lambda _{0}$ . The two prototypes offer either symmetrical or asymmetrical dual-CP beams over a wide bandwidth. Their measured peak gain is higher than 22 dBic, while the joint $S_{11} dB, axial ratio < 2 dB, beam squinting

In this article, a compact triple-port dual-band triple-mode antenna enabled by a shielded mushroom structure with operational bands centered at 2.4 and 5.8 GHz is proposed possessing both pattern and polarization diversities. By tailoring the dispersive properties of the artificial transmission line (ATL) cells and structuring them into a multilayer architecture, the integrated antenna is capable of generating vertically polarized, $y$ -horizontally polarized, and $x$ -horizontally polarized radiation patterns simultaneously at two predefined bands with good port isolations and field orthogonality. The design concept and the analysis of the ATL cells in the form of shielded mushrooms are described, illustrating the dual-band operating principle of the antenna. A proof-of-concept antenna is designed with a footprint of $0.48\lambda _{0}^{2}$ and a profile of $0.07\lambda _{0}$ , where $\lambda _{0}$ is the free space wavelength at 2.4 GHz. The proposed antenna was fabricated and characterized, achieving measured $S_{11} dB bandwidths of 35 and 85 MHz in the two targeted bands, respectively, with mutual coupling smaller than −15 dB and envelope correlation coefficients below 0.01 for all three ports. Moreover, it is shown that the two operational bands of the antenna can be independently controlled, which reveals the unprecedented degrees-of-freedom in its design. The demonstrated dual-band triple-mode antenna is highly useful for dual-band multimode wireless devices and dual-band multiple-input multiple-out communication systems.

In this article, the theory, design, and validation of planar array antennas capable of producing dual-circularly-polarized (dual-CP) dual-beam radiation with a single feeding network are reported. Importantly, the properties of the formed CP beams with different handedness can be independently controlled. Such a capability is achieved by exploiting both the in-plane rotation-induced Berry phase and excitation phase for all the linearly polarized array elements, which can be regarded as a generalization of the well-known sequential rotation arrays. Microstrip patch arrays with such single-feed dual-CP dual-beam functionalities can be synthesized through a straightforward analytical approach that accurately predicts the radiation patterns for both right- and left-handed CP beams. The proposed technique and design methodology were verified by two proof-of-concept microstrip arrays consisting of $8 \times 8$ linearly polarized circular patch elements operating in the $K$ -band, one with uniform excitation amplitudes and the other with tapered excitations for sidelobe suppression. Both arrays were fabricated and measured, experimentally achieving a joint $S_{11} dB, axial ratio < 3 dB, and 3 dB gain bandwidth of more than 22.5%/20.0% and 16.7%/15.8%, respectively, for the right- and left-handed CP beams. Within this broad operational band, the beam squinting is on average within ±3°. The proposed dual-CP dual-beam arrays have fully planarized structures, low profiles, wide operational bandwidths, and high polarization purity, making them useful candidates for applications including satellite communications, point-to-multipoint communications, and so on.

In this work, compact polarization-controllable dual-band antennas are designed, prototyped, and experimentally verified, which are composed of a planar monopole on top of a dual-layer truncated metasurface (MS) containing patches and nonbianisotropic complementary split ring resonators. By tailoring the dispersive properties of the MS, the relative phase difference of resonances associated with surface waves supported along two orthogonal horizontal directions can be independently engineered at two separate frequency bands, thereby giving rise to compact dual-band antennas with controllable polarization in each band. Three proof-of-concept example antennas with a form factor on the order of $0.3\lambda _{\mathbf {0}}\times 0.3 \lambda _{\mathbf {0}} \times 0.04 \lambda _{\mathbf {0}}$ were designed and measured. The first one provides circularly polarized (CP) radiation with the same sense of polarization in both bands, the second one offers linearly polarized (LP) radiation in the lower band and CP radiation in the higher band, while the last one achieves CP radiation in the lower band and LP radiation in the higher band. The measured results agree well with the simulation predictions, thus verifying the proposed concept and specific antenna designs.

In this article, the theory, design, and experimental verification of low-profile and wideband dual-circularly polarized (dual-CP) reflect-arrays (RAs) with independent handedness-based beamforming are reported. Such functionality is enabled by simultaneously exploiting the dynamic phase and Berry phase compensation techniques, which is illustrated mathematically by deriving the required conditions for the reflection coefficient matrix of the dual-CP RA phasing elements. Different from previously proposed multifunctional layer RAs for controlling waves with different handedness, here the independent dual-CP phase shifting is accomplished with only a single functional layer of elements. As proof-of-concept examples, rotated metal-backed dual-polarized aperture-coupled patches, with a profile of lower than $0.3\lambda _{0}$ , are designed, providing $2\,\,\times2$ bit dual-CP phase shifting that can offer independent beamforming of left-/right-handed CP (LHCP/RHCP) waves with an LHCP/RHCP feed antenna. Utilizing the proposed dual-CP elements, two specific dual-CP RAs operating in the Ka -band are synthesized, fabricated, and characterized, achieving either symmetrical or asymmetrical dual-CP beams over a wide bandwidth. The experimentally measured peak gain is higher than 28 dBic, while the joint axial ratio

In this article, a class of wideband transmit arrays (TAs), composed of cascaded anisotropic impedance surfaces (AISs), for circularly polarized (CP) multibeam generation from a single feed horn are reported. The dispersionless phase compensation is achieved by the Berry phase (BP) via imposing a spatially dependent rotation angle on the TA unit cells. A homogenized model for the BPTA unit cell is proposed and utilized for obtaining a wideband response by tailoring the dispersive properties of the AIS layers. Two modeling methods, an analytical vectorial field analysis and a full-wave strategy incorporating the homogenized model, were employed to efficiently evaluate the performance of the BPTAs. In order to validate the proposed unit cell and the modeling methodologies, a Q-band single-beam BPTA is demonstrated, which achieves a peak gain of 30.2 dBi and a 1 dB bandwidth of 11.1% within which the axial ratio is smaller than 2 dB. Furthermore, by employing the intersection approach for pattern synthesis, several Q-band BPTAs supporting multiple concurrent symmetric/asymmetric CP pencil beams and circular-shaped flat-top beams are designed. A BPTA prototype for producing quad CP pencil beams with unequal gain values was fabricated and characterized, yielding good performance with an overall operational bandwidth of about 11%. The proposed BPTAs are promising candidates for point-to-multipoint communication and point-to-multiregional coverage in wideband millimeter-wave communications for wireless and satellite applications.

In this paper, the design and experimental validation of a novel miniaturized dual-band dual-circularly polarized (CP) metasurface (MS) antenna is reported. The proposed antenna is enabled by an engineered MS-based artificial ground that supports simultaneous dual-band functionality and dual-CP unidirectional radiation. The artificial ground is a highly truncated dual-layer MS containing an array of $2 \times 2$ unit cells. Each unit cell is comprised by a patch and a complementary split ring resonator (CSRR) printed on the top and bottom surfaces of the substrate, respectively. A printed feeding monopole antenna is integrated with the MS to form a low-profile dual-band dual-CP antenna with a thickness of $0.04{\lambda }_{0}$ , where ${\lambda }_{0}$ is the free-space wavelength at the first operational band. A dispersion analysis of the unit cell is carried out both analytically and numerically to illustrate the working principle of the proposed antenna. This reveals that the bianisotropic response and the orientation of the CSRRs jointly provide distinct dispersion behavior along two orthogonal directions of the dual-layer MS, enabling the desired dual-band dual-CP radiation. Moreover, the CSRRs also facilitate antenna miniaturization, yielding an overall footprint of only $0.33 \lambda _{0}\times 0.33\lambda _{0}$ . In order to verify the antenna design, a prototype is fabricated and tested, and strong agreement between simulated and measured results is observed, experimentally achieving a 50 MHz bandwidth, and a peak gain of 3.95 and 5.29 dBi at the two targeted bands with opposite handedness for the radiated waves.

This work was supported in part by the Spanish Ministry of Education through the Commission Fulbright Program “Salvador de Madariaga” under Grant PR X14/00320, in part by the Spanish and Andalusian Research Programs under Grant TEC2013-48414-C3-01 and Grant P12-TIC-1442, and in part by the Center for Nanoscale Science, NSF Materials Research Science a nd Engineering Center, under Award DMR-1420620, Since the pioneering work of Heinrich Hertz, perfect-electric conductor (PEC) loop antennas for RF appli- cations have been studied extensively. Meanwhile, nanoloops are promising in the optical regime for their applications in a wide range of emerging technologies. Unfortunately, analytical expressions for the radiation properties of conducting loops have not been extended to the optical regime. This paper presents closed-form expressions for the electric fields, total radiated power, directivity, and gain for thin-wire nanoloops operating in the terahertz, infrared and optical regimes. This is accomplished by extending the formulation for PEC loops to include the effects of dispersion and loss. The expressions derived for a gold nanoloop are implemented and the results agree well with full-wave computational simulations, but with a speed increase of more than 300 × . This allows the scientist or engineer to quickly prototype designs and gain a deeper understanding of the underlying physics. Moreover, through rapid numerical experimentation, these closed-form expressions made possible the discovery that broadband superdirectivity occurs naturally for nanoloops of a specific size and material composition. This is an unexpected and potentially transformative result that does not occur for PEC loops. Additionally, the Appendices give useful guidelines on how to efficiently compute the required integrals., Spanish Ministry of Education through the Commission Fulbright Program “Salvador de Madariaga” under Grant PR X14/00320, Spanish and Andalusian Research Programs under Grant TEC2013-48414-C3-01 and Grant P12-TIC-1442, Center for Nanoscale Science, NSF Materials Research Science a nd Engineering Center, under Award DMR-1420620

In this paper, a class of integrated metasurface (MS)-based planar antennas are proposed, which are fed by monopoles operating below their fundamental modes. Various interdigitated capacitor (IC) loading schemes for a metallic sheet backed MS are investigated, which provide footprint miniaturization and bandwidth enhancement. A linearly polarized (LP) MS-based antenna, loaded by ICs, provides a 15% impedance bandwidth and a gain higher than 6.67 dBi. The radiation mechanism and resonant frequency dependence were revealed via a dispersion analysis, which serves to explain the working principle of the proposed antenna. Next, a miniaturized antenna with doubly loaded ICs was introduced, achieving an impedance bandwidth of 10%, a gain above 6 dBi, and a more than 30% footprint reduction. A more advanced compact, circularly polarized (CP) MS-based antenna with a compact footprint, and improved 3-dB axial ratio (AR) bandwidth were also presented, by introducing triangular IC and diagonal slot loadings to the MS. It is demonstrated that this antenna achieves an impedance bandwidth of 16%, a gain above 5.5 dBi, and an AR ${ bandwidth of 10%. Three antenna prototypes were fabricated and measured, with good correspondence between the experimental results and simulation predictions, confirming the proposed design methodologies. These compact and well-performing MS-based antennas have promising potential for applications in modern wideband wireless systems.

In this paper we show that the optical chirality of plasmonic chiral metamaterials can be manipulated by superchiral light. In particular, the handedness selective enhancement and switching effect of optical chirality, along with the delocalization of the corresponding chiral fields, are observed in the near-field regime of a gammadion nanostructure. Our results indicate that the interaction between superchiral light and planar chiral nanostructures can further improve accessibility for plasmonics based enantiomeric sensing and potentially enable chiroptical imaging systems that can be coherently controlled.

In this paper., a compact dual-band antenna based on substrate-integrated waveguide (SIW) technology is proposed. The antenna is comprised by three layers. The top layer is a SIW cavity-backed slot antenna while the middle layer is a quarter-mode SIW (QMSIW) antenna. A microstrip feeding line is configured on the bottom layer connecting to a vertically-oriented probe penetrating through the three layers to feed the antenna. Full-wave simulations show that two operational bands with unidirectional radiation along broadside direction are successfully achieved at 2.6 and 5.9 GHz. The fractional bandwidths are equal to 1.54% and 2.71 %., respectively. The overall size of the antenna is 33mm×43mm×5. 23mm, which is extremely compact. Moreover., parametric studies revealed that the two bands can be tuned separately by adjusting the appropriate design parameters.

The unique light-matter interaction in metamaterials, a type of artificial medium in which the geometrical features of subunits dominate their optical responses, have been utilized to achieve exotic material properties that are rare or nonexistent in natural materials. Furthermore, to extend their behaviors, active materials have been introduced into metamaterial systems to advance tunability, switchability and nonlinearity. Nevertheless, practical examples of versatile photonic metamaterials remain exceedingly rare for two main reasons. On the one hand, in sharp contrast to the broad material options available at lower frequencies, it is less common to find active media in the optical regime that can provide pronounced dielectric property changes under external stimuli, such as electric and magnetic fields. Vanadium dioxide (VO2), offering a large refractive index variation over a broad frequency range due to its near room temperature insulator-to-metal transition (IMT), has been favored in recent studies on tunable metamaterials. On the other hand, it turns out that regulating responses of hybrid metamaterials to external forces in an integrated manner is not a straightforward task. Recently, metamaterial-enabled devices (i.e., metadevices) with ‘self-sufficient’ or ‘self-contained’ electrical and optical properties have enabled complex functionalities. Here, we present a design methodology along with the associated experimental validation of a VO2 thin film integrated optical metamaterial absorber as a hybrid photonic platform for electrically driven multifunctional control, including reflectance switching, a rewritable memory process and manageable localized camouflage. The nanoengineered topologically continuous metal structure simultaneously supports the optical resonance and electrical functionality that actuates the phase transition in VO2 through the process of Joule heating. This work provides a universal approach to creating self-sufficient and highly-versatile nanophotonic systems.

In this paper, a switchable broadband polarizer based on the electric field directed reconfigurable assembly of gold nanowires (NWs) is presented. Taking advantage of the collective optical properties of the two-dimensional gold NW lattices, we have experimentally demonstrated that transmission of linear polarized light can be purposely controlled using a dual electrode design to reversibly rotate the lattice by 90° on-demand. In addition, our experiments reveal that the transmission control is closely related to the geometrical dimensions of the NWs as well as the applied electric field conditions.

In this paper, the design of a compact dual-band dual-polarized antenna with unidirectional radiation patterns is introduced. The metasurface, loaded with complementary split ring resonators (CSRRs) not only converts the linearly polarized (LP) signal radiated by the monopole antenna to a circularly polarized (CP) signal in the broadside direction, but also provides dual-band dual-polarized functionality. Based on full-wave simulations, it is found that the proposed antenna can achieve RHCP and LHCP within the first and the second operational band respectively with moderate gain performance around 6 dBi and high front-to-back ratio (FBR).

In this paper, we report the analysis, design, and experimental validation of a conformal coating approach for achieving a highly-confined mode in a dielectric waveguide with a low dielectric constant. By controlling the surface electromagnetic response of the anisotropic impedance surface, it is shown that the original loose confinement of the guided mode of the dielectric waveguide can be dramatically improved over a broad bandwidth. The tensor impedance surface was further realized by an array of short dipole elements and characterized. The good agreement between simulated and measured results confirms the proposed concept and associated design methodology.

An electric current triggered multifunctional vanadium dioxide (VO 2 ) integrated photonic metamaterial is presented. In our metamaterial design, the nanoengineered topologically continuous metallic structure simultaneously supports the optical and electrical functionalities. Moreover, acting as part of the resonating structure, the VO 2 thin film enables the tunable nature of the device. By presenting a series of proof-of-concept studies, we demonstrate the proposed hybrid metamaterial as a new platform for multifunction electro-optic control including reflectance switching, a rewritable memory process and manageable localized camouflage. The design methodology introduced here provides a universal approach to creating self-sufficient and highly versatile nanophotonic systems.

In this paper, a compact dual-band dual-mode antenna based on metasurface technology is proposed. Through full-wave simulations, it is found that the proposed antenna can achieve broadside and end-fire radiation at two distinct operational frequency bands centered at 1.94 GHz and 2.50 GHz, respectively. The proposed antenna is a promising candidate for many emerging applications including on/off-body communication systems.

A compact and flexible circularly polarized (CP) wearable antenna is introduced for wireless body-area network systems at the 2.4 GHz industrial, scientific, and medical (ISM) band, which is implemented by employing a low-loss composite of polydimethylsiloxane (PDMS) and silver nanowires (AgNWs). The circularly polarized radiation is enabled by placing a planar linearly polarized loop monopole above a finite anisotropic artificial ground plane. By truncating the anisotropic artificial ground plane to contain only 2 by 2 unit cells, an integrated antenna with a compact form factor of 0.41 λ 0 × 0.41 λ 0 × 0.045 λ 0 is obtained, all while possessing an improved angular coverage of CP radiation. A flexible prototype was fabricated and characterized, experimentally achieving S 11

Cylindrical vector vortex beams, a particular class of higher-order Poincaré sphere beams, are generalized forms of waves carrying orbital angular momentum with inhomogeneous states-of-polarization on their wavefronts. Conventional methods as well as the more recently proposed segmented/interleaved shared-aperture metasurfaces for vortex beam generation are either severely limited by bulky optical setups or by restricted channel capacity with low efficiency and mode number. Here, a noninterleaved vortex multiplexing approach is proposed, which utilizes superimposed scattered waves with opposite spin states emanating from all meta-atoms in a coherent manner, counter-intuitively enabling ultrahigh-capacity, high-efficiency, and flexible generation of massive vortex beams with structured state-of-polarization. A series of exemplary prototypes, implemented by sub-wavelength-thick metasurfaces, are demonstrated experimentally, achieving kaleidoscopic vector vortex beams. This methodology holds great promise for structured wavefront shaping, vortex generation, and high information-capacity planar photonics, which may have a profound impact on transformative technological advances in fields including spin-Hall photonics, optical holography, compressive imaging, electromagnetic communication, and so on.

This chapter presents two new types of recently developed wearable antennas. It presents the transformational designs for lightweight conformal wearable antennas which are highly efficient while, at the same time, having a compact footprint and a low profile in the MBAN band. These designs are enabled by placing a planar monopole antenna on top of an extremely truncated metasurface, which yields a front-to-back ratio in the radiation pattern that is remarkably high for its size and effectively isolates the antenna from the loading effects of the human body. The chapter focuses on compact, planar circularly polarized (CP) wearable filtennas with both narrow and wide operational bandwidths. It discusses the antenna design strategy, simulations, and experimental results, as well as on-body performance evaluations of these wearable antennas. Bandwidth broadening techniques are illustrated by introducing various interdigital capacitor loading schemes into the metasurface. The integrated band selective functionality of the radiating modules is verified by experimental measurements.

Metasurfaces, also known as metafilms, have recently been developed by researchers for various applications that exploit their exotic electromagnetic characteristics which cannot be found in nature. These applications include compact filter designs, electromagnetic cloaking and illusion coatings, miniaturized waveguides, and many new types of antennas with enhanced functionalities. Specifically, metasurfaces have been proven to be particularly beneficial in patch antenna designs. Among these designs, metasurfaces have been introduced as artificial ground planes and/or radiating components, which are comprised by unit cells arranged in a one-dimensional or two-dimensional periodic array configuration. By virtue of these metasurfaces, highly-directive radiating beam(s), compact antenna form factors, high radiation efficiency, and multiple frequency-bands/operational-modes along with other desired features of patch antennas can be realized. In this contribution, we demonstrate that a complementary split ring resonator loaded metasurface can be employed to design a compact dual-band antenna. The compact size of our proposed dual-band antenna is attributed to the well-known capability of complementary split ring resonators for miniaturizing numerous microwave devices, including patch antennas. Moreover, due to the self-resonance of the complementary split ring resonators, the resonant frequency associated with the dominant mode of the original patch antenna is split into two modes, thereby giving rise to a dual-band functionality. The novel metasurface-enabled patch antenna proposed here not only possesses compact size, but also realizes multiple operational bands, making it a promising candidate for today's highly-integrated communication systems.

Conducting loops have been rigorously analyzed in the microwave/RF regime due to their simplicity and versatility. In the terahertz, infrared and optical regimes nanoloops are extremely promising for a variety of applications, including as solar cells or optical sensors. However, due to the complex behavior of metals, a complete theoretical derivation of the radiation parameters of a nanoloop at these frequencies has not yet been performed. This paper will extend the formulation of thin-wire Perfect-Electric Conductor (PEC) loops to include the effects of loss and dispersion. Closed form expressions for the radiated fields, directivity and gain will be presented. The expressions involve integrals of Bessel and Lommel-Weber functions as well as Q-type integrals. Various series representations for these integrals will be presented along with guidelines on which are the most efficient. Validation of the equations will be provided through a comparison with full-wave solvers. While these simulations take on the order of hours, the analytical expressions can be evaluated on the order of seconds.

In this paper a novel two-layered metasurface (MS) based antenna is proposed and simulated results are presented. Using the proposed MS as an artificial ground plane for a monopole antenna, the integrated antenna realizes both size miniaturization and dual-band functionality. The footprint of the proposed integrated antenna is only 0. 06λq with two operation bands around 4.1 and 5.1 GHz.

Superdirectivity has been a topic of active research in antennas at radio frequencies since it was first postulated almost a hundred years ago. Despite its potential use in solar cells and optical communications, the topic of superdirectivity on the nano-scale is a relatively new field of study. Examples of superdirective nano-antennas include phased arrays and notched dielectric spheres. In this communication, we show that superdirectivity naturally occurs in a simple thin-wire nanoloop without the need for phase shifters or the introduction of inclusions. A closed-form expression for the directivity at end-fire will be presented which allow the designer to easily predict when this phenomenon will occur. The physical mechanism producing superdirectivity will be explored by studying the currents and performing a multipole expansion.

The development of nanoantennas is mostly done through time-consuming computer simulations. Nanoloop antennas, working in the terahertz, infrared and optical regimes, have used in a variety of applications, including as solar cells or optical sensors. In this paper we will present a theoretical analysis of thin-wire nanoloops, which leads to closed-form expressions to derive key antenna parameters: radiated electric fields, radiated power, radiation resistance, directivity and gain. Results for gold thin-wire nanoloops are validated with full-wave simulations, and the presentation includes a comparison with classical nanodimensional PEC loops, emphasizing the differences and similarities from a physical point of view. While full-wave simulations can take on the order of hours, the analytical expressions can be evaluated on the order of seconds, thus allowing a wider assessment of the usefulness of these nanoantennas in practical applications.

In this paper a newly designed metasurface (MS) loaded miniaturized antenna is proposed and simulated. The double layered MS loaded with complementary split ring resonators (CSRRs) acts as the ground plane for a planar feeding monopole antenna. The antenna has a compact footprint of 0.11λ 0 2 and a thickness of 0.07 λ 0 . The simulation results show that a wide −10 dB S 11 bandwidth of 9% is realized. In addition, a broadside radiation with a high gain and a high front-to-back ratio are achieved within the targeted frequency band.

In this paper a metasurface-based circularly polarized antenna is designed and simulated. The metasurface (MS) loaded with interdigital capacitors and titled slots are proposed to convert linearly polarized (LP) signal from the feeding monopole into circularly polarized (CP) signal radiated at broadside. The MS based antenna has a compact footprint of 0.31λ 0 2 and a thickness of 0.07λ 0 . According to the full-wave simulation results, in spite of a small dimension, the antenna still achieves a gain of 5.7 dBi, a high front-to-back ratio, and an axial ratio < 3 dB within a wide bandwidth.

In this paper, the handedness dependent electromagnetically induced transparency (EIT) in a chiral metamaterial and its sensitivity to the coupling conditions are presented. A chiral metamaterial, consisting of an array of coupled cut-wire resonators (CWRs) supporting the radiative resonance, exhibits strong chiral responses around 4 GHz when excited by circularly polarized (LCP and RCP) waves. Split ring resonators (SRRs) are designed to support non-radiative resonances at the same frequencies. Through appropriately introducing SRRs into the CWR array, transmission peaks are observed in the EIT chiral system at the frequencies correspond to the stopbands of the CWR chiral metamaterial for both RCP and LCP excitations. Particularly, transmission peaks of −2.3 dB and −1.3 dB are observed around 3.75 GHz and 4.10 GHz, respectively, for RCP and LCP waves, in contrast to the corresponding −13 dB and −9.2 dB handedness dependent transmission dips. The sensitivities of the proposed chiral EIT effect on coupling between SRRs and the CWRs are also studied.

We provide the first experimental demonstration of the handedness dependent electromagnetically induced transparency (EIT) in chiral metamaterials during the interaction with circularly polarized waves. The observed chiral-sensitive EIT phenomena arise from the coherent excitation of a non-radiative mode in the component split ring resonators (SRRs) produced by the corresponding Born−Kuhn type (radiative) resonators that are responsible for the pronounced chirality. The coherent coupling, which is dominated by the bonding and antibonding resonances of the Born−Kuhn type resonators, leads to an extremely steep dispersion for a circularly polarized wave of predefined handedness. Accordingly, retrieved effective medium parameters from simulated results further reveal a difference of 80 in the group indices for left- and right-handed circularly polarized waves at frequencies within the EIT window, which can potentially result in handedness-sensitive pulse delays. These chiral metamaterials which enable a handedness dependent EIT effect may provide more degrees of freedom for designing circular polarization based communication devices.

In this paper, a compact footprint and low-profile metasurface-enabled unidirectional antenna that operates from 4.11GHz to 4.26GHz with a center frequency at 4.2GHz is presented. The miniaturized metasurface, which has a reflection phase of -150 degree at 4.2GHz, was made possible by interdigital capacitor loading, resulting in a unit cell with an electrical dimension of only 0.02λ 0 2 . A finite-sized metasurface with two by three elements was integrated with a planar microstrip fed monopole antenna, enabling a total antenna footprint of around 0.13λ 0 2 and a thickness of 0.05λ 0 . Full-wave simulations show that, even with such a small footprint, the antenna achieves a large front-to-back ratio and a high gain within the targeted operational frequency band.