In this paper, a systematic design of Fabry-Perot cavity antennas based on leaky waves is proposed in the THz range. The use of different topologies for the synthesis of homogenized metasurfaces ...shows that a specific fishnetlike unit cell is particularly suitable for the design of efficient THz radiating devices. Accurate full-wave simulations highlight the advantages and disadvantages of the proposed geometries, thoroughly considering the bounds dictated by technological constraints and the homogenization limit as well. The radiative performance of different designs for achieving theoretical directivities ranging from 15 to 30 dB is evaluated with reliable analytical and numerical methods, and completely validated with full-wave simulations. The relevant results corroborate the proposed systematic design, consolidating the validity and the usefulness of the leaky-wave approach, well established at microwave frequencies, to the more challenging and still unexplored THz range.
We propose the design and testing of a 2-D Fabry-Perot structure based on a multilayer (ML) slab arrangement fed by a circular array of simple sources. Such a class of planar leaky-wave (LW) antenna ...can be made of low-loss commercial laminates, and it is bounded on top by a subwavelength 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 TM 1 leaky mode, which is a perturbed version of the guided-wave supported by the corresponding parallel-plate waveguide. An accurate dispersive analysis for the ML 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 LW-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.
Expanding the bandwidth of resonator cavity antennas is challenging, and most studies have focused on using positive phase gradient partially reflective surfaces. Although multi-layer partially ...reflective surfaces can provide bandwidth enhancement, they have the weaknesses of extremely high design complexity and thresholds in bandwidth improvement. Here, a new approach is proposed to significantly enhance the 3 dB gain bandwidth of the resonator cavity antenna while maintaining high gain and low profile. The method begins by utilizing an open resonator with a spherically modified ground to activate multiple resonances akin to Laguerre-Gaussian beam modes. Positive phase gradients are then added to the frequency band between each resonant mode for phase optimization, all provided by a simple metasurface. The proposed approach has been verified across multiple designs and the antenna prototype of one design has been selected for fabricating. The measurements agree very well with simulations, showing a 3-dB gain bandwidth of about 40%, a peak gain of 19 dBi, and a side-lobe level of around -10 dB. This work demonstrates a new low-profile, high-gain, wideband, low-design complexity antenna for various wireless system.
A simple model allowing us to predict beam steering characteristics in a Fabry-Perot (FP) cavity antenna is presented in this letter. The structure consists of a ground plane and a phase-modulated ...metasurface used as a partially reflective surface (PRS). The aim of this letter is to present a simple model that allows calculating the necessary phase modulation for a desired beam-steering angle. Furthermore, phase-modulated metasurfaces are designed by varying the PRS inductance, and the model is validated both numerically and experimentally on antennas designed to operate around 2.25 GHz.
Directive pencil beams scannable in both elevation and azimuth are obtained through a planar phased array placed inside a Fabry-Perot cavity. The key element of the proposed approach is the ...exploitation of a conical element pattern (EP) with high directivity in elevation, obtained through the excitation of a dominant, weakly attenuated cylindrical TM leaky wave of azimuthal order <inline-formula> <tex-math notation="LaTeX">n = 0 </tex-math></inline-formula> by means of a simple coaxial probe. Then, a highly reduced number <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula> of such sources are arranged to form a phased array radiating directive pencil beams. Beam-angle reconfigurability with continuous scanning both in azimuth and elevation inside a wide solid angular range is achieved by varying the array phasing and the operating frequency. An investigation on the features of truncated cylindrical leaky waves is first developed to properly characterize the EP. Then, conventional array theory is exploited to calculate the pattern of the entire array. The radiation efficiency is also evaluated accounting for the spurious surface wave related to the undesired excitation of the quasi-TEM mode. The proposed array design provides a simple and inexpensive innovative solution for obtaining a high-gain pencil beam continuously scanning in the 3-D space without suffering gain losses. In the presented implementation, the elevation angular scan, which is generally constrained by the wideband capability of the feeding system, by the requirements on the sidelobe level, and by the cutoff of the relevant leaky mode, ranges from about 21° to about 68°. Possible applications are envisaged for the next generation of wireless power transfer devices, for advanced radar and surveillance systems, earth observation, as well as for ceiling-mounted indoor localization and tracking.
The anomalous dispersion observed in wideband Fabry-Perot Antennas formed by multiple coupled cavities is explained in terms of modal coupling between several leaky waves. In this way, the negative ...group velocity associated to the homogenized mode can be explained. Moreover, the enhancement in the radiation pattern bandwidth can also be described from the contribution of these coupled leaky waves to the total interference pattern. Theoretical dispersion results are reported for 1-D and 2-D Fabry-Perot Antennas with <inline-formula> <tex-math notation="LaTeX">N = </tex-math></inline-formula> 2 and <inline-formula> <tex-math notation="LaTeX">N = </tex-math></inline-formula> 3 coupled cavities operating in broadside and off-broadside scanned patterns. The theory is also corroborated with experimental results.
Radiation from cylindrical leaky waves (CLWs) supported by layered dielectric media is of interest in a variety of current applications. A comprehensive two-part study has been undertaken to ...investigate the generation and the radiation properties of CLWs with an arbitrary integer azimuthal order n. The first of this two-part sequence deals with the identification of continuous rings of canonical sources of electric and magnetic types, capable of exciting higher-order CLWs (HOCLWs) in planar open radial waveguides. The relevant far-field radiation formulas are then derived, generalizing those already available in the literature for cylindrical waves with azimuthal orders n=0 and n=1, i.e., those excited by elementary vertical or horizontal dipoles. Design guidelines for the practical excitation of HOCLWs through discrete sources, namely, circular phased arrays, are provided in the companion paper along with numerical validations and illustrative results in both the near-field and the far-field regions.
The generation of higher-order cylindrical leaky waves (HOCLWs) by means of canonical electric or magnetic ring sources was discussed in Part I, where radiation formulas for such waves were also ...presented. In the second part of this sequence, the practical excitation of HOCLWs in a Fabry-Perot cavity antenna is discussed considering the use of ring sources in a discrete form, i.e., circular phased arrays of vertical electric or horizontal magnetic dipoles. Design guidelines for dimensioning the source radius and the number of array elements are presented in order to excite the desired waves with negligible unwanted higher-order azimuthal harmonics and negligible spurious radiation from the quasi-TEM cavity mode. Numerical results are provided for circular arrays with traveling-wave azimuthal excitation, in order to validate the theory presented in Part I and Part II. Furthermore, the salient features of conical radiation from HOCLWs in the far-field region are illustrated and their potential to produce beams carrying orbital angular momentum (OAM) in the near field is demonstrated through full-wave simulations.
A novel methodology realizing multiband Fabry-Perot-Cavity Antenna (FPCA) is proposed. Different from single transmission-mode (T-mode) or reflection-mode (R-mode) FPCA, the R+T-mode FPCA employs ...hybrid excitation modes to the same FPC, reducing the requirement for multiband high-quality feed antennas. To verify this methodology, a triple-band FPCA integrated by two R-mode ones, operating at the middle and the high bands, and a T-mode one working at the low band is designed. A triband partially-reflective-surface (PRS) offering bidirectional asymmetric transmission for middle and high bands, and partial reflection for the low band, is proposed. Meanwhile, a triband artificial magnetic conductor is designed to fulfill the in-phase bouncing condition in a low-profile uni-cavity for all bands. One inter-cavity feed and two external ones are utilized to complete the hybrid excitation of the FP cavity. Finally, a proof-of-concept prototype is fabricated showing -3 dB gain bandwidths of 7.0% (3.02-3.24 GHz), 16.9% (5.38-6.37 GHz), and 10.0% (10.31-11.40 GHz). Beam-scanning ranges of ±35° and ±30° are also obtained for the middle and the high bands. The proposed methodology may readily realize an FPCA of even more frequency bands with limited aperture size and a low-profile resonant cavity.
Fabry-Perot cavity two-dimensional leaky-wave antennas with polarization-reconfigurable omnidirectional conical beam are proposed. The antenna cavity is bounded by an annular, locally periodic metal ...partially reflective surface, and is loaded by a dielectric or a wire-medium slab in order to suppress undesired radiation from the fundamental quasi-TEM mode. A suitable design of the partially reflective surface and of the loading slab, based on a dispersion analysis of the linearized structure, allows for equalizing the phase and attenuation constants of the first higher order TM 1 and TE 1 leaky modes around a given frequency. Omnidirectional beams with full polarization reconfigurability are then achieved through independent excitation of such modes with a pair of azimuthally independent sources. Preliminary designs, aimed at producing a conical beam with circular polarization, are presented and optimized with state-of-art simulation software.
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