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In a previous work, we derived optimum conditions for the design of finite-size 1-D unidirectional leaky-wave antennas (LWAs) in the general case. The bandwidth and the gain–bandwidth figure of merit are, however, structure-specific and have not been discussed yet. A practical case that is widely investigated in the literature is that of 1-D unidirectional LWAs based on partially reflecting surfaces (PRSs). In this work, we not only evaluate these features for this specific class of antennas, but we also derive design rules for optimizing the PRS impedance and cavity height to get maximum gain. Numerical results and full-wave simulations are finally proposed for a realistic example based on a metal strip-grating structure, to validate the theoretical findings. [ABSTRACT FROM AUTHOR]

The numerical solution of the classical Sommerfeld problem is thoroughly discussed in this work. In particular, the computation of the vertical electric field excited by a vertical electric dipole (VED) is taken as a paradigm to discuss some different approaches that have been proposed in the literature (with some new variations included). A detailed study is carried out on the pros and cons of each method as well as their range of numerical efficiency in terms of frequency, ground losses, height of the dipole, and distance to the observation point. We finally propose a numerical implementation of the steepest descent method as a good overall method in terms of accuracy, computational efficiency, and extended range of validity. Asymptotic closed-form expressions for the far-field region are also provided. [ABSTRACT FROM AUTHOR]

In this article, empty substrate integrated waveguides (ESIW) technology is applied to design long slot leaky-wave antennas (LWAs). First, a uniform-aperture structure is presented and its limitations on forming the beam are studied. Then, a sinusoidal curve is employed to modify the geometry of guided-wave structure which divides the slot into a number of segments, making a periodic aperture. After that, a method is proposed to regulate the guided waves inside the ESIW. To this end, a modulation function is derived to simultaneously determine the local amplitude and segment length of the physical sinusoidal curve at each individual points on the structure. This results in manipulating the phase constant $(\beta)$ and leakage rate $(\alpha)$ across the aperture which ultimately controls both the tilt angle and sidelobe-level (SLL) of the constructed beam. The slot is placed on the centerline of the broad wall of the ESIW to reduce the cross polarization. The structure is designed to operate at 35 GHz with SLL = −30 dB and a backward tilt angle of $\theta _{m}=-20 ^\circ $. Finally, the proposed LWA is simulated and a fabricated design is measured. A good agreement is observed between the theoretical, simulated, and measured performance of the antenna. [ABSTRACT FROM AUTHOR]

The optimization of antenna parameters such as gain is an important aspect of all antenna design. In the context of leaky-wave antennas (LWAs), it is important to have accurate design rules for optimizing the gain of the antenna for practical finite-length structures. In this work, taking advantage of the recent formulas derived for the accurate evaluation of the beamwidth in finite-size 1-D unidirectional LWAs, we obtain optimum conditions for this general class of antennas. In particular, design rules for minimizing the beamwidth or maximizing the gain are obtained. The latter is evaluated with a fully analytical procedure through the definition of a correction function that improves the accuracy of the common gain–beamwidth relation. The effects of material losses are also discussed to show how they can affect the optimization procedure. These results apply to any 1-D unidirectional LWA, because no assumptions are made on the wavenumber dispersion, which is instead structure-specific. However, the optimization of two practical examples, namely a holey and a slitted LWA, is discussed to show practical application of the proposed design rules. [ABSTRACT FROM AUTHOR]

A tapered vertical line source over the surface of the earth or ocean is explored as a means of communication. Two types of tapers for the line source are explored. One is a “Zenneck-wave” taper and the other is an “optimum” taper. The Zenneck-wave taper is chosen to excite the Zenneck wave to the extent possible. The Zenneck wave is a “nonphysical wave” that propagates on a semiinfinite lossy earth. The wave is nonphysical in the sense that a simple source such as a dipole will not excite a field that resembles the Zenneck wave at large distances from the source. However, by using a tapered line source, a field that resembles the Zenneck wave can be produced along the surface of the earth or ocean out to some distance. The optimum taper is chosen to optimize the field at a given horizontal distance from the line source on the surface of the earth or ocean. The optimum line source can be used to produce a field along the surface of the earth or ocean that is nearly constant over a large range of distances, something that does not seem easily attainable with other types of sources. [ABSTRACT FROM AUTHOR]

A 2-D periodic leaky-wave antenna (LWA) is a planar structure that radiates from high-order space harmonics (Floquet waves) of a leaky mode that propagates radially outward on a structure. The structure chosen here consists of a 2-D periodic cross-shaped distribution of metal patches on top of a grounded dielectric substrate and is designed to produce a highly directive elliptical beam at broadside. The beam at broadside is produced by two high-order space harmonics of a leaky TM0 surface-wave mode that propagates radially outward from a dipole source. It is shown here that the structure can be truncated to the shape of a cross, maintaining similar radiation characteristics as the full structure, while reducing undesirable grating beams. The results from theoretical analysis, full-wave simulations, and measurements for a fabricated 2-D periodic cross LWA are presented here and are found to be in good agreement. [ABSTRACT FROM AUTHOR]

The radiation properties of wideband Fabry–Pérot cavity (FPC) antennas have been investigated by studying the non-Foster behavior of the reflection coefficient phase of the thick partially reflective surface (PRS) forming the cavity. In order to better understand the performance of such cavities, we show for the first time that the wideband behavior can be explained via a unique dispersion characteristic of the dominant excited leaky-waves (LWs) inside such cavities. We derive new formulas that demonstrate the role of the LWs in forming wideband FPC antennas when the reflective phase of the PRS exhibits an increase with frequency within the band of operation. [ABSTRACT FROM AUTHOR]

A novel localization algorithm, which considers nonline-of-sight (NLOS) propagation, is proposed in this paper. By introducing a transfer function that relates the field at a given receiver to the source as a function of frequency and position, the NLOS effect can be mitigated and the propagation channel can be calibrated back to free space. The simulation results demonstrate that the proposed algorithm performs much better than that using the usual line-of-sight time difference of arrival (TDOA) localization, and the accuracy is only limited by the sampling frequency. The measurements verify the improvement in using the improved TDOA method versus the usual TDOA method. [ABSTRACT FROM AUTHOR]