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Programmable metasurfaces enable fine‐grained real‐time modulation over electromagnetic (EM) waves in a digital manner, which have gained remarkable attention in antenna engineering and wireless communications. However, either a reflective or transmissive programmable metasurface requires an external feed source with significant distance to the metasurface, making the whole programmable device a relatively high profile as well as low efficiency as a result of the feed spillover losses. In this paper, an innovative design of radiation‐type programmable metasurface for dynamic modulation of radiant EM wave is presented, which perfectly combines the functions of 1‐bit phase shifter and efficient power radiator in the single unit framework. By employing the integrated series‐parallel hybrid microstrip network to stimulate the topside metasurface units, versatile capacities, including dynamic beam scanning and multimode vortex beam generation, are verified both numerically and experimentally. Due to the direct‐radiation characteristic of the metasurface design, the programmable metasurface possesses the aperture efficiency over 30% and a low profile reduced by almost two orders of magnitude, when comparing with the conventional reflective or transmissive programmable metasurfaces illuminated by the external feeds. The proposed design can offer a novel approach of programmable metasurface framework in dynamic radiant EM modulation for low‐profile conformal applications. [ABSTRACT FROM AUTHOR]

The electromagnetic scattering of an object is directly related to its physical geometry and material properties. While metasurfaces show excellent performances in mimicking material properties almost at well by flexibly designing meta‐atoms with arbitrary electromagnetic responses, their physical geometries are generally in a regular manner. The break of a metasurface's geometry will inevitably affect its electromagnetic scattering that introduces uncertainty in wavefront manipulation. Here, a general approach for highly efficient wavefront manipulation with irregular shaped metasurfaces is proposed. Such an approach establishes a universal iterative modulation relation between the metasurface and scattered field by introducing boundary constraints at the aperture, enabling to deal with the electromagnetic scattering from a metasurface with arbitrary spatial shape. In this way, the desired wavefront form can be engineered using meta‐atom sequences with arbitrarily shaped aperture. As a proof of concept, a flower‐shaped metasurface operating in the reflection mode is designed and experimentally demonstrated for reconstructing four random focuses with uniform and high‐efficiency intensity distribution at near‐field region, while the flower shaped field pattern can be extracted near the aperture plane. Such a method may pave a new route for advanced wavefront manipulation and electromagnetic concealment/camouflage applications. [ABSTRACT FROM AUTHOR]

An approach to achieve directional low‐profile UWB antenna by omnidirectional source with a reflector, is proposed. The general theoretical model about the direction and the phase conditions between the upward and reflected field are developed. A bow‐tie dipole source antenna is investigated first. To modify its radiation defect, proper phase equations between the original upward field and the reflected downward field are derived so that the aperture field becomes uniform enough to guarantee directional radiation. The concave‐shaped reflector is primarily adopted to satisfy the phase conditions. Then the concave‐shaped reflector is decorated with corrugated structure to realize good impedance matching within the wide band. Consequently, the split beams caused by multiple long linear currents with phase difference at high frequency is focussed while the directivity at low frequency is also improved. The prototype antenna was fabricated with a profile of 20.5 mm, about 0.156 λmax (maximum wavelength in the work band), and the measured impedance bandwidth of VSWR ≤ 2.2 is over 2.27–26 GHz. Both simulated and measured results demonstrate the stable directional patterns within the quintuple band (2–10.5 GHz). The realised gain is over 7 dBi within the band (2–10.5 GHz) and peak is over 12 dBi. [ABSTRACT FROM AUTHOR]

The recent development of metasurfaces offers a unique technique for the arbitrary control of electromagnetic waves by spatially manipulating their amplitudes and phases. However, real time control in metasurfaces typically depends solely on dynamical phase modulation, but lacks of the amplitude modulation. In this paper, the dynamical amplitude modulation is tried to combine with phase coding metasurface, for the dynamical manipulation of electromagnetic scattering at microwave frequencies. Such an active metasurface is achieved by placing a patterned graphene layer on binary metallic resonators. When applying bias voltages on the graphene layer, continuous reflection amplitude modulation can be achieved for the selected resonators while the others are not affected. By this merit, two degrees of freedom, preset phase coding and dynamical amplitude modulation, are obtained to control the electromagnetic wave. As an example, a metasurface that can dynamically and continuously control the scattering pattern from mirror reflection to diffusion scattering is shown. The above concepts and physical phenomena are confirmed by numerical simulations and experiments. [ABSTRACT FROM AUTHOR]

Metasurfaces have been extensively studied for generating electromagnetic waves carrying orbital angular momentum (OAM). In particular, programmable metasurfaces enable real‐time switching between multiple OAM modes in a digital manner. However, the current programmable metasurfaces are mostly based on reflective mode, which suffer from low efficiency as well as serious feed blockage. In this paper, a transmissive programmable metasurface is presented for the highly efficient generation of multimode convergent OAM beams. The proposed transmissive metasurface is composed of electronically reconfigurable units with 1‐bit phase resolution (0/π), which are obtained by integrating two PIN diodes in the radiating layer for current direction modulation. Through the antisymmetry configuration of the two PIN diodes, nearly uniform transmission magnitudes but inversed phase states in a wide band can be obtained. The simulation results show that the proposed reconfigurable unit can achieve good 1‐bit phase tuning, with minimum insertion loss of 0.2 dB and 2 dB transmission bandwidth of more than 10%. Through the dynamic modulation of the quantized code distributions on the metasurface, programmable multimode OAM beams can thus be constructed. Both simulated and measured results verify the effectiveness of the proposed design. [ABSTRACT FROM AUTHOR]

A compact tri‐band bandpass filter is presented in this article, whose three passbands are realized by the lowest three resonant modes of a new structure of symmetrical stub‐loaded square ring resonator. The filter features a compact size of 0.049 λg2 (λg is the guided wavelength) as well as a high selectivity with nine transmission zeros. In addition, by using the odd‐ and even‐mode analysis, its center frequencies can be easily tuned to the desired frequencies by the identical‐number parameters, namely, the lengths of short‐, open‐, and square ring‐stubs. To validate the proposed design, a tri‐band bandpass filter with center frequencies of 2.4, 3.5, and 5.2 GHz was designed, simulated, and measured. The measurement results agree well with the simulation results. [ABSTRACT FROM AUTHOR]

A topological method for the design and optimization of planar circularly polarized (CP) directional antenna with low profile was presented. By inserting two parasitic layers, generated by particle swarm optimization, between the equiangular spiral antenna and the ground, a low-profile wideband CP antenna with directional radiation pattern and high gain is achieved. The optimized antenna shows an impedance matching band (S11<-10 dB) of 4–12 GHz with a whole-band stable directional pattern in 4–11.5 GHz, and the antenna gain peak is 8 dBi, which work well in the available band. Measured return loss, antenna gain, and far field patterns agree well with simulation results. [ABSTRACT FROM AUTHOR]

A broadband dual circularly polarized magnetoelectric dipole antenna (MEDA) fed by a miniaturized six-branch hybrid coupler (SBHC) is presented in this paper. First, a dual linearly polarized MEDA with a bandwidth of 73.3% is developed based on the previous design with a bandwidth of 52%. The SBHC, with a miniaturized size of 53%, is designed on a printed circuit board underneath the ground of the MEDA, which possesses an efficient bandwidth of 80.7% to generate the antenna for dual circular polarization. Measurement results show that the proposed dual circularly polarized MEDA achieves an impedance bandwidth of 84.5%, an axial-ratio bandwidth of 81.8%, and a nearly symmetrical, stable unidirectional radiation pattern with an average gain of 8 dBic over its impedance bandwidth. [ABSTRACT FROM AUTHOR]

This Letter presents a grating ridged waveguide V‐shaped slot array antenna for satellite communication (SATCOM) receiving antenna applications. A special grating ridged waveguide, V‐shaped slots and a matching section are applied in the proposed antenna design, so that the antenna provides an extra filtering response with a high radiation polarisation purity in a compact structure. For demonstration, a referential normal ridged waveguide V‐shaped slot array antenna is designed and compared. The simulation results show that the proposed antenna not only operates well in the working frequencies (12.25–12.75 GHz) but also provides the antenna gains of lower than −17.8dB compared with those of the referential antenna in the interference frequencies (14.0–14.5 GHz). [ABSTRACT FROM AUTHOR]

A dual circularly polarized (CP) omnidirectional antenna based on slot array in coaxial cylinder structure is presented in this paper. It is constructed by perpendicular slot pairs around and along the axis of the coaxial cylinder to realize the omnidirectional CP property, and two ports are assigned in its two sides as left hand circularly polarized (LHCP) port and right hand circularly polarized (RHCP) port, respectively. The proposed antenna achieves a bandwidth of 16.4% ranging from 5.05 to 5.95 GHz with an isolation higher than 15 dB between the two CP ports, and the return loss (RL) is higher than 10 dB within the bandwidth in both of the two ports. From the measured results, the average axial ratio (AR) of the proposed antenna in omnidirectional plane is lower than 1.5 dB. [ABSTRACT FROM AUTHOR]

The electromagnetic properties of a toroidal coated nanoparticle (T-CNP) antenna with an active core (doped with rare earth erbium Er3+ ions) are investigated. It is demonstrated that the active T-CNP acts as a strong dipole radiator at its resonance frequency when it is excited by a plane wave or an electric Hertzian dipole (EHD) radiating element. It is shown that in comparison to being a passive structure, the plane wave scattering cross section of the T-CNP can be increased by nearly 108 dBsm at its resonance frequency when it is active. Moreover, it is further demonstrated that the maximum peak of the power radiated by an EHD element in the presence of a properly designed active T-CNP is more than 120 dB over its value when radiating in free space; that is, its Purcell factor is 1012. [ABSTRACT FROM AUTHOR]

A broadband single-feed circularly polarized patch antenna with wide beamwidth is presented. The patch is coupled to four asymmetric cross slots via a microstrip ring with eight matching segments underneath the ground plane, traversing through the arms of the cross slots in a serial manner. And a coupling slice instead of a resistive load is used as matching load of the microstrip ring for higher gain. Furthermore, a metal side wall surrounding the antenna is used to improve the isolation between adjacent elements in an array. Through optimizing the four asymmetric cross slots and eight matching segments, excellent performances are achieved by the proposed antenna, especially for the broadband and wide beamwidth. Measurement results show that the antenna has −10 dB reflection coefficient bandwidth of 29.7%, 3-dB axial-ratio bandwidth of 21.6%, and beamwidth of more than 90°. It can be considered as a good candidate for the element of arrays. [ABSTRACT FROM AUTHOR]

A novel phase gradient method for detecting orbital angular momentum modes is proposed. By utilising a two‐element time‐modulated array, the phase gradient of the received signal is estimated through analysing the modulated harmonic component. The bit error rate performances are evaluated using Monte‐Carlo simulation. Results show that the sensitivity strongly depends on the number of sampling modulation pulses. Compared with the conventional phase gradient receiver, the proposed method obviously enhances the performance of detection. [ABSTRACT FROM AUTHOR]

A novel CP horn antenna with switchable polarization by single port feeding is presented. The antenna is composed of a coaxial-waveguide converter and a balance-cavity, a horn, a square-to-circular waveguide transition, and a stepped-septum polarizer, which simplify the feeding and can work on the left-hand or right-hand circular polarizations by manual exchanging the mounting position of the coaxial-waveguide converter and the balance-cavity. The antenna achieves an impedance bandwidth (3.88~5.12 GHz) of 27.5% and a 3 dB-AR (Axial Ratio) bandwidth of 18.6%, with the 3 dB-AR beamwidth of about 149°, and the antenna gain is over 13.3 dB in the available band. [ABSTRACT FROM AUTHOR]

This paper provides an effective solution of generating OAM-carrying radio beams with all three polarizations: the linear, the left-hand circular, and the right-hand circular polarizations. Through reasonable configuration of phased antenna array using elements with three polarizations, the OAM radio waves with three polarizations for different states can be generated. The vectors of electric fields with different OAM states for all three polarizations are presented and analyzed in detail. The superposition of two coaxial OAM states is also carried out, and the general conclusion is provided. [ABSTRACT FROM AUTHOR]

In this letter, a novel broadband dipole antenna for UHF RFID transponder, which offers global functionality across different regulatory areas is proposed. The proposed antenna has a measured bandwidth from 0.83 to 1 GHz (18.5%) where the power reflection coefficient is below -10 dB for conjugate matching with an EPC class 1 Gen 2 chip, which is sufficient to cover the whole band (0.86–0.96 GHz) regulated by EPC global class 1 Gen 2 protocol (ISO/IEC 18000 6c). Additionally, an equivalent circuit model for such kind of antenna is presented to illustrate the broadband impedance matching characteristic between the antenna and the chip. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2795–2798, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22877 [ABSTRACT FROM AUTHOR]

In this study, a spiral patch antenna operating millimeter-wave band is proposed. Using this spiral structure, the patch antenna is designed for circular polarization and wideband operation at about 30.8–36.9 GHz for millimeter-wave communication. Simulated and measured results for main parameters such as return loss, impedance bandwidth, radiation patterns, and gains are also discussed herein. The study shows that the modeling of such antennas, with simplicity in designing and feeding, can well meet millimeter-wave wireless communication. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2068–2071, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22648 [ABSTRACT FROM AUTHOR]

In this paper, by exploiting surrounding fractal UC-EBG ground plane, a 2 × 2 microstrip array capable of X-band operation is studied. Result of comparison shows that this microstrip array proposed has much lower RCS than that of 2 × 2 array with the standard ground at frequencies outside operating band within 2–18 GHz while its gain is improved in the operating band. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1418–1422, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22440 [ABSTRACT FROM AUTHOR]

A new structure of ultra-wide band (UWB) band pass filter is proposed in this letter. The proposed UWB filter consists of a low pass filter and a quasi-high pass filter. The low pass frequency characteristic is realized with a dumbbell defected ground structure (DGS) array and narrow slots, the corresponding cut-off frequency is tuned to 10.7 GHz by adjusting sizes of each dumbbell and their spacing. The quasi-high pass filter consists of two symmetrical inter-digital capacitors. The cut-off frequency is about 3.0 GHz. Combining these two structures we obtain a new structure of UWB band pass filter. An experimental UWB filter was fabricated, the measured results show that the insertion loss is less than 1.5 dB throughout the passband of 3.0–10.8 GHz, the variation of group delay less than 0.25 ns in this band, and a wide stopband bandwidth with 20 dB attenuation up-to 20.0 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1374–1377, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22471 [ABSTRACT FROM AUTHOR]

A planar structure backed with a cavity is analyzed by a spectral-domain--eigenfunction method. An appropriate basis function and an appropriate weighting function have been chosen, which greatly simplifies the process of the solution. Finally, the calculated radiation fields of the antenna are compared with the measured results. [ABSTRACT FROM AUTHOR]

A novel ultra-wideband elliptical slot antenna is proposed.An elliptical slot is rotated by 45° and excited by a circular patch. Tapered microstrip feeding is used for impedance matching. The structure has multiresonance feature over a wide frequency range, where the simulated bandwidth ratio exceeds 20:1. Due to the limitation of the SMA connector, the experiment on the prototype antenna demonstrated an impedance bandwidth (voltage standing wave ratio < 2) of 165%, or 2.54-26.6 GHZ, 10.5:1. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:308-310, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27288 [ABSTRACT FROM AUTHOR]

Metasurfaces offer unprecedented freedom to manipulate electromagnetic waves at deeply subwavelength scales. However, realizing a highly efficient metasurface, yet simple enough to conceptualize, design, and fabricate, is a challenging task. In this paper, a novel approach is proposed for designing meta‐atoms which can achieve full phase control in the range 0–2 π with high efficiency in the transmission mode. In particular, a bilayer meta‐atom is designed, exploiting nearly perfect polarization conversion of the two orthogonal transmissions, whose transmission efficiency reaches as high as 85%. The transmission phase control in the circular polarization basis is achieved with the axial rotation of the proposed meta‐atom based on Pancharatnam–Berry phase principle. These meta‐atoms are then wielded to construct metasurfaces for generating vortex beams carrying orbital angular momentum. The conversion efficiency as high as 75% and a transmission efficiency of 55% are achieved for the realized metasurfaces. [ABSTRACT FROM AUTHOR]