A tutorial overview is presented on the principles of operation, physical modeling, and design procedures for the class of planar radiators known as Fabry-Perot cavity antennas (FPCAs), with an emphasis on their characterization as 2D leaky-wave antennas (LWAs). After recalling their principal radiative features, alternative electromagnetic (EM) models are discussed, helping us to gain physical insight into the involved radiation mechanisms from different viewpoints. The leaky-wave approach appears particularly useful in this connection; it provides the framework for the subsequent review of design guidelines. Supplementary material that accompanies this article on IEEE Xplore addresses the main recent advances in the field, including wideband, reconfigurable, and array-based designs.

Bessel beams can be generated at microwaves by means of compact, planar devices based on Fabry-Perot cavity leaky-wave resonators. Most designs are based on the excitation of a single transverse magnetic/electric (TM/TE) leaky mode by means of a vertical electric/magnetic dipole source. In this work, we analyze the important case of a horizontal magnetic dipole which excites both TM and TE modes, developing an original theoretical framework suitable for resonant radiators. Analytical expressions are provided for the dominant leaky-wave aperture field. The near-field distribution is then evaluated through an accurate numerical integration of the radiating currents, and validated through full-wave simulations for the relevant case of a Bessel-beam launcher when excited by a waveguide-fed slot. Different designs are presented and analyzed in order to obtain TM, TE, and hybrid polarization, finding in all cases an excellent agreement between simulations and theoretical results. Finally, we evaluate and compare the wireless power transfer efficiency of two coupled TM-polarized, TE-polarized, or hybrid-polarized Bessel-beam launchers when a wireless link is established in the radiative near-field region. Interestingly, full-wave results demonstrate the superior performance of resonant Bessel-beam launchers in TM or TE polarization with respect to the nonresonant hybrid case.

In this paper, a general formula for the half-power beamwidth of one-dimensional leaky-wave antennas (1-D LWAs) is presented. With respect to previous beamwidth formulas found in the literature, the new formula allows for both arbitrary propagation wavenumber and length of the antenna. The pointing angle of the beam is allowed to be arbitrary, and may be near broadside or endfire, or any angle in between. The beamwidth is also allowed to be arbitrary, though a simpler approximate expression is obtained under the assumption of a narrow beam. Numerical results confirm the accuracy of the new beamwidth formula. Furthermore, it is shown that the previous existing formulas are approximate limiting cases of this more general result. This new formula will provide a very useful tool for obtaining more reliable results for the beamwidth of any type of 1-D LWA.

A multi-fed radially periodic two-dimensional leaky-wave antenna is proposed for the generation of a directional beam continuously scanning in elevation by changing the frequency, and over a discrete number of directions in azimuth when activating different elements of the feeding system. The structure is planar and constituted by a circular grounded dielectric slab loaded with microstrip rings, properly positioned around the sources to support the propagation of an angularly directional surface wave over a sector determined by the corresponding activated feeder. This produces a perturbation of the surface wave, resulting in the generation of a directional leaky wave over the aperture, whose complex propagation constant is described by a single fast backward spatial harmonic. The antenna radiation features are numerically investigated in conjunction with the dispersion analysis of the structure, validated through a conventional generalized-pencil-of-function approach. Full-wave simulations have been developed to design a practical feeder, which is constituted by a circular arrangement of commercial coaxial connectors. The proposed multi-port antenna is validated by means of measurements performed on a microwave manufactured prototype. The design represents an attractive simple and cost-effective solution to achieve a high-gain beam scanning over the three-dimensional space, alternative to more conventional phased-array design based on cumbersome and lossy feeding networks.

We propose the design and test of a 2-D Fabry-Perot structure based on a multilayer slab arrangement fed by a circular array of simple sources. Such a class of planar leaky-wave antenna can be made by low-loss commercial laminates and it is bounded on top by a sub-wavelength partially-reflecting surface. The antenna is designed to suppress undesired radiation from the quasi-TEM mode while leaking power by the excitation of a fast TM1 leaky mode, which is a perturbed version of the guided-wave supported by the corresponding parallel-plate waveguide. An accurate dispersive analysis for the multilayer structure is developed and an original feeding system is designed and optimized to provide the needed wideband impedance matching. Thanks to translational invariance enabled by the homogenized nature of the partially reflecting screen, the antenna is used as a radiating element in the design of a leaky-wave-enhanced phased array, constituted by an arrangement of vertical probes to generate directive pencil beams steerable at a single frequency in azimuth and by changing frequency in elevation.