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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]

A frequency-diverse imaging system is proposed based on high-scanning-rate leaky-wave antennas (LWAs) that can provide image reconstruction across narrow bandwidths. Analytical, simulation, and experimental results are provided to characterize and demonstrate the performance of the system. The core of the approach relies on a high-scanning-rate LWA, and in this work, we propose a prototype design that can scan 70° within 500 MHz (corresponding to a scanning rate of 140°/GHz from 10 to 10.5 GHz), providing more independent measurements for the system than conventional approaches. In addition, compressive sensing with a wavelet transform is utilized to reduce the required frequency measurements across the frequency band to only 21. It is demonstrated that the proposed system can reconstruct scatterer’s width and thickness within an error of 3 mm (about 1/10 wavelength at 10 GHz) using only 21 measurements across a 500-MHz bandwidth within 10–10.5 GHz. It is also able to estimate the distance between two objects when their edge-to-edge separation is greater than 5 mm. [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]

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]

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]

In this letter, a wide-angle narrowband leaky-wave antenna (LWA) based on substrate integrated waveguide-spoof surface plasmon polariton (SIW-SSPP) structure is proposed. Periodic slots are etched on both the top and bottom surfaces of SIW to introduce an SSPP mode. The periodic slots on the top surface are sinusoidally modulated to realize bidirectional LWA radiation. The problem of open stopband is solved by the asymmetrical design of the top and bottom slots. Thus, a wide bidirectional scanning range from −60° to +63° is achieved. Besides, the relative bandwidth of the fabricated antenna is reduced to only 9% by introducing the slow-wave effect of SSPP. It means the proposed antenna has a large scanning rate, or equivalently beam scanning range/bandwidth ratio. [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]

This letter proposes a low-profile and highly efficient endfire radiating traveling-wave antenna based on spoof surface plasmon polaritons (SSPPs) transmission line. The aperture is approximately $0.32\lambda _0\times 0.01\lambda _0$ , where $\lambda _0$ is the space wavelength at the operational frequency 8 GHz. This antenna generates near-endfire radiation beams within 7.5–8.5 GHz. The maximum gain and total efficiency reach 9.2 dBi and $96\%$ , respectively. Measurement results are finally given to validate the proposed SSPPs antenna. [ABSTRACT FROM AUTHOR]

In this letter, a single-layer electronically steerable leaky-wave antenna based on the Goubau line is presented. The modulation units consist of metalines connected by periodically loaded switchable p-i-n diodes and its biasing circuit. These p-i-n diodes are used as switches to dynamically control the modulation periodicity, and the antenna featuring low profile can, therefore, provide tunable beam-scanning angles at a fixed frequency. Measured antenna prototype demonstrates beam-steering capability of 74° at 4.35 GHz. [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]