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The independent control of two orthogonal polarizations that possess dual functionalities is highly desirable in antenna and wireless communication technologies. Spin-decoupled metasurfaces with integrated dynamic and geometric phases have been proposed to generate two independent right-handed and left-handed circularly polarized (RCP and LCP, respectively) waves. However, the RCP and LCP phases are correlated by a linear equation of the dynamic and geometric phases. In this article, we propose a meta-atom in which the 1 b phase of two orthogonal polarizations can be controlled independently. Moreover, a high-gain broadband millimeter-wave multidimensional metasurface to generate an $x$ -polarized $l=0$ beam with a 10° beam deflection and a $y$ -polarized $l=+1$ beam independently is simulated, fabricated, and tested. The proposed metasurface operating over the frequency range of 16–28 GHz has the maximum gains of 28.7 and 23.8 dBi for the $l=0\,\,x$ -polarized waves and $l=+1\,\,y$ -polarized waves, respectively. Compared with spin-decoupled metasurfaces, the proposed metasurface provides a simpler design process to generate two independent vortex beams for the two orthogonal polarizations. The proposed vortex metasurface also has the advantages of dual polarization, high gain, wide relative bandwidth, and is broadband. The proposed metasurface has potential application in high-capacity communication systems. [ABSTRACT FROM AUTHOR]

A circularly-polarized (CP) traveling-wave endfire antenna featuring low profile, high gain, and simple feeding structure is presented in this communication. Offset parallel strips with proper dielectric loading are employed in a low-profile substrate to achieve two orthogonal electric field components with equal magnitude and 90° phase difference for CP endfire radiation. Meanwhile, periodic phase-loading technique is used to achieve a proper phase constant for high endfire gain. A prototype is designed and fabricated to verify the proposed method. Experimental results demonstrate CP endfire radiation within a frequency band of 9.78–10.09 GHz. The average endfire gain is 10.3 dBic with an average efficiency of 62.5%. [ABSTRACT FROM AUTHOR]

An extremely high scanning-rate beam-steering antenna based on coupled resonators is proposed in this communication. Coupling resonators in a controlled manner provides a sharp phase variation across a narrow frequency band, which contributes to the extremely high scanning rate. To steer the beam across broadside, alternating +90° and −90° impedance inverters are employed in the topology. Such a coupled-resonator array antenna is modeled and analyzed by coupling matrix technique, which was conventionally used in filter design. To illustrate the proposed technique, two examples with 50 and 100 MHz bandwidths are designed. Experimental validation is also provided for the 50 MHz bandwidth example, which demonstrates that the proposed antenna reaches a high relative scanning rate of $52.8^{\circ }/\%BW$ with efficiency of 75%. [ABSTRACT FROM AUTHOR]

In this article, we propose a traveling-wave endfire antenna based on the first higher-order transmission line (TL) mode, and it features wide bandwidth, high gain, and large aperture efficiency. We propose two essential conditions for the realization of the proposed wideband endfire antenna. First, the dispersion curve of the first higher-order mode should be made close to that of the air line across a wide frequency band. Second, the fundamental mode should be suppressed to allow single higher-order mode operation across a wide frequency band. Following these principles, we provide a design for an endfire antenna based on a periodically slotted parallel stripline, where the periodic meandered slots suppress the fundamental mode and hence allow single higher-order mode radiation. To verify the proposed approach, a prototype has been designed and fabricated. The antenna can achieve endfire radiation within a 1:2 frequency band (8.5–17.5 GHz), with an average gain of 10.7 dBi, and large aperture efficiency up to 6.38 dBi/ $\lambda ^{2}_{0}$. [ABSTRACT FROM AUTHOR]

A full-space scanning leaky-wave antenna featuring small aperture size and relatively stable gain is proposed in this communication. We propose three key conditions for full-space scanning capability, including single-harmonic radiation, field cancellation suppression at endfire, and open stopband suppression at broadside. Results from a prototype based on paired stubs and crossover offset parallel striplines are provided to verify the proposed principle. Experimental results show that the main beam is able to continuously scan from backfire to endfire with stable gain around 9.1 dBi within the frequency range of 4.5–10.2 GHz. The antenna aperture is $6.85\lambda _{0}\times 0.1\lambda _{0}$ only. [ABSTRACT FROM AUTHOR]

This article proposes a general design technique for high-gain traveling-wave endfire antennas using a periodic arbitrary-phase loading technique. This work extends the periodic phase-reversal techniques reported in previous work to application scenarios where phase reversals are difficult to realize (e.g., single-layer circuits). It also relaxes the substrate permittivity requirement in phase-reversal techniques. To verify the proposed technique and theory, two design examples using different phases other than π are provided. Double-side parallel stripline and coplanar stripline are employed to provide vertical and horizontal polarizations, respectively. Double-side parallel stripline antenna achieves a maximum endfire gain of 15.6 dBi with vertical polarization. The coplanar-stripline antenna exhibits a maximum endfire gain of 16.6 dBi with horizontal polarization. The experimental results of these two examples validate the proposed technique. [ABSTRACT FROM AUTHOR]

A planar periodic leaky-wave antenna (PLWA) with continuous backward-to-forward beam-scanning capability and consistent gain is presented. The PLWA is made of a new type of periodically arranging meander line structures, in which the capacitive coupling between neighboring units plays the key role in achieving a high scanning rate. In detail, the beam-scanning rate of the proposed PLWA is efficiently tuned by varying the gap between two adjacent units, without considerably changing the working frequency band. To mitigate the open stopband (OSB) and to improve the impedance matching, several inductive open stubs are introduced into a single meander line unit cell to enhance the radiation. In the experiment, a prototype of the proposed PLWA was fabricated and measured. The simulated and measured beams show good agreement in terms of scanning range and radiation performance. A continuous beam scanning from −60° to +58° through broadside in the frequency band of 5.95–7.1 GHz is observed, and hence, a 102.6°/GHz scanning rate is realized in practice. Besides, the PLWA shows an average gain level of 11.96 dBi with a variation lower than 2 dB and a sidelobe below −10 dB at all the measured frequencies. The proposed PLWA may have potential applications in radar, microwave imaging, and wireless communication due to its compact structure, easy to fabricate, and dispersionless performance. [ABSTRACT FROM AUTHOR]

In this article, two configurations of novel dual-band half-mode substrate integrated waveguide (HMSIW) leaky-wave antennas are presented. The first proposed antenna radiates linearly polarized (LP) waves in the lower band and circularly polarized waves in the upper band when the unit cells are cascaded sequentially. The second antenna, where the sidewall via of the HMSIW unit cells is connected alternatingly, provides simultaneous dual beams with different polarization in the upper operational band in addition to the LP beam in the lower operational band. The unit cells of the two antennas are analyzed in terms of their dispersion behaviors. Finally, the performance of both the antennas is experimentally verified. [ABSTRACT FROM AUTHOR]

We present a multifilament current method (MFCM) incorporated with generalized sheet transition condition (GSTC) to simulate 2-D cylindrical metasurfaces with arbitrary cross sections. The GSTC casts in the form of an impedance-type boundary condition to relate the tangential fields on two sides of a cylindrical metasurface. The MFCM is subsequently introduced and formulated by employing the GSTC. The doublet-current unit, including both electric and magnetic filamentary sources, is introduced in order to capture both co- and cross-polarized scattered and transmitted fields from the GSTC characterized cylindrical metasurfaces. Three illustrative examples are presented to validate the proposed simulation technique. The behaviors of filamentary sources in terms of scattered field singularities and the ill-conditioning issue of the constructed matrix are also discussed in detail. In comparison to existing numerical methods, the proposed technique has its merits on simplicity and conciseness. [ABSTRACT FROM AUTHOR]

A phase-reversal technique is proposed in this article to overcome the gain-aperture tradeoff of endfire antennas. Such a tradeoff fundamentally forbids simultaneous high gain and small cross-section aperture. The phase-reversal technique breaks this tradeoff and hence allows one to design a high-gain endfire antenna with a small cross-section aperture. To illustrate the proposed phase-reversal technique, a crossover stripline structure is implemented. The antenna radiates into the endfire direction within 9.5–10.5 GHz and it achieves 13 dBi endfire radiation gain with only $0.047\lambda _{0}\,\,\times \,\,0.022\lambda _{0}$ cross-section aperture size. These results successfully validate the proposed phase-reversal technique. Such a high-gain and small-aperture endfire antenna is potentially useful for microwave imaging in lossy medium. [ABSTRACT FROM AUTHOR]

This article presents a 1-D frequency-diverse guided-wave imaging technique based on a surface-wave Goubau line. It employs frequency diversity to capture spatial information of the scatterers with an almost real-time speed, which is much faster than mechanical scanning or electronic scanning approaches. The surface-wave Goubau line is used because it provides more independent measurement modes than conventional transverse electromagnetic (TEM) transmission lines. Compressed sensing algorithms are employed to recover the spatial distributions when some sparse metal scatterers are placed above the line. The proposed technique is validated by four numerical examples and two experimental validations, where both narrow scatterers and wide scatterers are considered. It shows that the proposed technique is able to reconstruct scatterer position within an error of 1 mm, about 1/30 space wavelength at the center frequency 10 GHz. It is also able to identify two close scatterers until their distance reduces to 1 mm. This guided-wave technique, although applicable to very near-field detection only, can find broad applications in localization, field measurement, and fault detection. [ABSTRACT FROM AUTHOR]

A glide-symmetry Goubau line leaky-wave antenna for achieving both high scanning rate and wide scanning angle range is introduced. The novelty of the design is its combination of glide symmetry and a single-layer Goubau line. This combination leads to performance enhancement in both scanning rate and scanning angle range. Utilizing a corrugated Goubau line in a glide-symmetry fashion closes its stopband at the cutoff frequency while slowing down its group velocity. As the dispersion around the closed stopband is shifted to the fast-wave region by periodic profile modulation, the space harmonics exhibit high-scanning-rate radiation. In conjunction with this, the single-layer nature of the Goubau line allows the beam to scan from nearly endfire to backfire directions, leading to a wide scanning angle range. Numerical examples and experimental validation are provided to validate the proposed design. These show that the proposed antenna exhibits dual-band operation, where one band scans 152° within 2.2 GHz (corresponding to scanning rate of 69°/GHz) with 67% efficiency, while the second band scans 145° within 0.7 GHz (corresponding to scanning rate of 207°/GHz) with 26% efficiency. A tradeoff between scanning rate and efficiency always exists in high-scanning-rate leaky-wave antennas. One is able to freely choose the preferred scanning rate in this single antenna. A comparison with other related works shows that the proposed antenna exhibits the best performance. [ABSTRACT FROM AUTHOR]

The 1-D inverse scattering problem of super-resolving the location of discrete point shunt conductance or point impedance faults along transmission lines is considered. The results have applications to determine the structure of faults in transmission line components, such as connectors, when the available spectral information is not sufficient to obtain the spatial resolution required. The 1-D inverse scattering problem considered is formulated as a sparse reconstruction problem and convex optimization is applied to super-resolve the profile of discrete point faults in transmission lines. We extend previous results for super-resolution and prove that point faults can be super-resolved exactly with infinite precision in location when there are up to 4 point shunt conductance faults and 5–18 point shunt conductance faults if the faults are separated by $\lambda _{c}/2$ and $\lambda _{c}$ , respectively, where $\lambda _{c}$ is the minimum wavelength available in the system. This infinite precision is achieved for separations four times smaller than previous results. In addition, it is demonstrated that the location of up to 3 point impedance faults can be super-resolved exactly with infinite precision if they are separated by $\lambda _{c}/2$. Simulation and experimental results are used to demonstrate the effectiveness of the approach. [ABSTRACT FROM AUTHOR]

We systematically analyze and describe a new type of traveling-wave endfire antenna based on an asymmetrically corrugated Goubau line that exhibits high efficiency and has a low profile. By proving that asymmetry is a necessary condition in addition to the Hanson–Woodyard condition for traveling-wave endfire radiation, we study the effect of asymmetric corrugation on the mode guide and coupling. We subsequently show that two different waves are independently guided along the two corrugated edges, whose phase difference leads to a transversally polarized dipole moment radiating in the endfire direction. A closed-form expression for the radiation pattern is derived based on the proposed analysis to approximately predict the antennas’ optimum length. To verify the proposed analysis and design principles, results from an experimental prototype operating at 13–15 GHz are also provided. The experimental results show that the antenna design has an average gain of 9.9 dBi and an average efficiency of 82%. The agreement between the predicted results and the final optimized results validates the proposed analysis. [ABSTRACT FROM AUTHOR]

Transient communication (TC) is an emerging paradigm that focuses on the information transmission and reception between physically transient transmitters and receivers. The TC systems may find important biomedical applications in body-centric medical imaging and sensing, as system degradability allows for minimal retrieval effort of wastes. In this paper, we propose an antenna-dependent geometrically based statistical model (GBSM) to characterize the TC channel. We first define the transient operational domain (TOD) of an antenna, which is an enclosed set including all the legitimate combinations of antenna operating frequencies and radiation angles. The TOD changes its shape over time caused by antenna degeneration. This in turn results in a time-variant scatterer region in the GBSM determined by the antenna beamwidth. Subsequently, we derive important TC channel parameters including the ensemble average transfer function and power azimuth spectrum, which take into account the effect of randomness in antenna deterioration on the propagation channel characteristics. Finally, we present the comprehensive experimental and numerical examples to demonstrate the principles of the proposed model. [ABSTRACT FROM AUTHOR]

In this communication, we propose a high scanning rate leaky-wave antenna (LWA) based on a slow-wave substrate integrated waveguide (SIW) structure. The slow-wave effect is introduced by etching periodical slots on the top surface of SIW. The LWA radiation is subsequently realized by introducing sinusoidal modulation to the slots profile. Such a structure significantly improves the scanning rate of LWA due to the small group velocity at the slow-wave region. Simulation and measured results indicate that the proposed LWA scans a wide angle in a narrow bandwidth near the cutoff frequency of surface plasmon polariton. Within the frequency band 13.5–13.9 GHz (3% relative bandwidth), the measured scanning angle is from 2° to 37° with the measured gain all above 9.2 dBi. [ABSTRACT FROM AUTHOR]

A physically transient (PT) antenna changes its properties over a predefined lifespan due to its time-varying dimension and shape. The PT antenna technology has attracted much attention in the areas of biomedical, environmental, and military applications. It is also a fundamental building block of transient communications, where certain components of the communication link are degradable. In this paper, we revisit the classical antenna figures-of-merit such as resonant frequency and input impedance, and propose a novel immersion-time-dependent description framework to characterize this class of antennas, taking into account their PT nature. Subsequently, we present the notions of average and outage antenna characteristics over all realizations of the random antenna degeneration process occurring in a solvent. To the best of our knowledge, this is the first attempt in the open literature to quantify stochastically the properties of a PT antenna. Finally, we look into the specific application scenario of a degradable circular patch to demonstrate the principles and applicability of the proposed methodology. The analytical approach may also find important applications in the design and evaluation of other PT wireless devices and systems. [ABSTRACT FROM PUBLISHER]