A new configuration of printed non-directive surface-wave sources for advanced beam control

Planar antenna designs that utilize surface waves (SWs) for leaky wave (LW) excitation are investigated for millimeter wave frequencies of operation. Surface-wave launchers (SWLs) are employed as the antenna source generating cylindrical SWs for bound propagation on a grounded dielectric slab (GDS). By the addition of a segmented circular strip grating configuration, a partially reflecting surface (PRS) can be realized, providing suitable conditions for 2-D leaky-wave radiation. Directive pencil beam patterns at broadside, with gain values greater than 12 dBi at 19.5 GHz, can be achieved.

Planar antennas that achieve end-fire radiation by surface-wave (SW) edge diffraction are investigated. Specifically, Yagi-Uda like directive surface-wave launchers (SWLs) are utilized as the surface-wave antenna (SWA) feed, exciting cylindrical SWs on a grounded dielectric slab (GDS). With the design of a recessed ground plane, suitable conditions are achieved for far-field radiation at end-fire. In addition, a novel SWA offering end-fire beam steering is also presented by using a two element array of SWLs. Measured results suggest that the radiated beam pattern can be steered by 8deg from phi = -4deg to phi = +4deg in the far-field. In addition, highly directive beam patterns are observed from 18.5 - 22.7 GHz suggesting a relatively large radiating bandwidth. To the authors knowledge this is the first time such planar SWAs have been fabricated and measured.

A planar one-sided bull-eye leaky-wave antenna (LWA) is presented with suppressed open stopband (OSB). The antenna consists of a grounded dielectric slab (GDS) loaded on top with a periodic arrangement of double metallic strips, whilst a TM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> surface-wave launcher (SWL) feed system is adopted for cylindrical-wave excitation. The radial structure is also properly designed to suppress the OSB effect thus achieving reduced dispersion features when frequency scanning through broadside, as typically observed with 1-D periodic LWAs. A method-of-moments (MoM) dispersion analysis is also used to characterize the attenuation and phase propagation constants of the supported leaky-wave (LW) mode. The resulting single-layer LWA is lowcost and it is well-matched from about 18 GHz to 22 GHz. The planar 2-D design also radiates a directive pencil beam pattern with gain values reaching 15 dBi.

In this summary article, a simple surface wave launcher (SWL) in substrate integrated waveguide (SIW) technology is proposed. The launcher utilizes a conventional microstrip to SIW transition with the motivation of transferring power into the dominant TM 0 surface wave (SW) mode of a grounded dielectric slab (GDS). Moreover, by appropriate design of the SIW section and by applying field matching techniques using sub-wavelength microstrip patches while also conveniently separating some of the via conducting posts for one of the SIW side-walls, power can leak into the GDS with minimal losses for the generation of a bound and guided TM SW with a uniform phase front. The design approach is confirmed by numerical calculations and full-wave simulations for two feed systems which operate at 15 GHz, with and without the matching section. Our new approach for simple, microstrip-fed SW launching at microwave frequencies can also be useful for other SW-based guides, novel low-cost transitions, and new compact dividing/combing circuits for antenna feed systems as well as other SW structures which employ a common substrate.

A planar holographic antenna with novel metallic lens and straight strips is presented in this paper. The proposed holographic antenna utilizes surface wave launcher (SWL) as the surface wave excitation. The metallic lens consists of small rectangles arranged based on the surface refractive index of the unit cell. The spherical surface wave excited by SWL can be transformed to plane wave when passing through the metallic lens. Metallic straight strips are employed to achieve leaky wave radiation. Far field beam pattern results suggest that gain value of the main beam is as high as 18.37 dBi at 11.5 GHz. A good agreement between EM simulated and measured results evidently validates the proposed holographic antenna.

This second part of a three-paper sequence deals with the spatial domain parametrization and physical interpretation of the relevant asymptotic high-frequency Green's function for a semi-infinite phased array of parallel dipoles on an infinite stratified grounded dielectric slab. This array Green's function (AGF) has been previously derived using a spectral domain formulation; the relevant asymptotic solution contains contributions associated with Floquet waves (FWs), and corresponding surface, leaky and diffracted waves excited at the array edge. Both the truncated-FW series and the series of corresponding diffracted field contributions exhibit excellent convergence properties. In the present paper, through application of the Poisson summation, the AGF for a plane-stratified grounded dielectric slab is developed in terms of space domain FW-dependent Kirchhoff radiation integrals which are synthesized by superposition of periodicity-modulated phased line sources oriented parallel to the edge. The asymptotic evaluation of each Kirchhoff radiation integral leads to a grouping of various asymptotic terms, which provide physically appealing interpretations of a variety of wave processes, encompassing slab-modulated propagating (radiating) and evanescent (nonradiating) FWs, slab-guided surface waves (SWs) or leaky waves (LWs), and their edge-coupled phenomenologies. The present space domain parametrization leads to the same asymptotics as that from the spectral domain parametrization, but allows a clear description of the spatial wave interaction processes.

A new architecture is provided for the efficient generation of shaped beams and multiple shaped beams (in amplitude, phase, and polarization), with leaky-wave (LW) metasurfaces (MTSs). Those antennas are usually fed by a surface-wave (SW) launcher, which evenly illuminates the MTS versus azimuth, through a cylindrical SW. When the interest lies in generating pencil beams or particular types of shaped beams, the required radiating aperture field (linked to the Fourier transform of the desired radiation pattern) on the MTS is almost azimuthally symmetric in amplitude. However, for a wide class of shaped beams, the desired aperture field is far from being azimuthally symmetric. This leads to an MTS design in which some sectors exhibit a very small surface impedance modulation. Those sectors tend to leave the SW intact until it reaches the rim of the surface, where the power is either reflected or diffracted at the slab rim. We solve this efficiency problem by reducing the amount of power fed into some sectors, through the use of an array of feeding monopoles. The azimuthal illumination of the feeder should be designed to match the azimuthal asymmetry of the desired aperture field. The corresponding MTS surface impedance is then determined using a method of moments (MoM)-based synthesis technique. Several examples are provided to illustrate the concept. The improvement in terms of antenna efficiency is numerically demonstrated.

The launching of surface waves by discontinuities in microstrip circuits can cause extra coupling between adjacent devices. This paper gives measurements of the efficiency of an open circuit in microstrip to both launch and receive surface waves. The measurement technique is described in which the radiated waves from the open circuit are distinguished from the surface waves. These results are then applied to the linear resonator and the open-circuited tuning stub in microstrip circuits. In particular, how their position on the microstrip substrate can effect their performance. Finally, the paper discusses how the surface waves can be reduced to increase isolation.

In the history of antenna development, periodic structures have been extensively studied and applied. Typically, through the dispersion analysis, the propagation and radiation performances of periodic structures can be predicted. There is no doubt that dispersion relation plays a vital role in periodic structures based antenna designs.&#13;\n&#13;\nIn this thesis, a systematic study on dispersion engineering of periodic structures and its applications to antenna designs is presented. The unifying goal of this study is to change the antenna properties by manipulating the dispersion relations to meet various design requirements and address the bottleneck problems. In addition, several novel antenna designs with excellent performances are proposed and presented in this thesis.&#13;\n&#13;\nFirstly, a novel one dimensional multiple periodic (MP) structure is proposed. Different from the conventional periodic structures that have single periodicity, the proposed MP structure increases the periodicity by enclosing different unit cells (UCs) into each periodic element. Through the dispersion analysis, it is found that some new features can be offered by the MP structures. With the increase of the periodicity, the separation distance between the space harmonics are reduced and several new stopbands are opened up. The former feature will lead to excitations of multiple space harmonic modes in a certain frequency range. These new features are proved to be universal for both dispersive and non-dispersive materials. Regarding to each material, the analyses are performed from media and lumped circuit perspectives. The MP structures provide room to manipulate the dispersions. By proper adjusting the geometric parameters, the dispersion relations can be engineered. Furthermore, a general dispersion relation and a general Bragg condition for MP structures are also derived.&#13;\n&#13;\nSecondly, the proposed theory of MP structures is extended to two new designs of supercell (SC) based dual-beam leaky-wave antennas. By proper engineering the dispersion relations, two space harmonic modes (m= -1 and m= -2) are excited to form two radiation beams. The two designs improve the link quality of the communication system and address the problems that are dominated by the intrinsic characteristics of the links, such as the multipath effect and the mutual interference. The first antenna is based on the microstrip lines and operates in the microwave region. It validates the feasibility of the proposed theory. On the other hand, another antenna is realized by the dielectric grating and works in the millimeter-wave (MMW) region (60-GHz). It employs a symmetrically configured SC and have better radiation performance. Both two designs can realize beam steering in the same clockwise or anti-clockwise direction against the frequency, which is rarely discussed in the previous literatures. They are of very simple structures that are easy for manufactures.&#13;\n&#13;\nThirdly, a new collimated surface-wave (SW) excited high impedance surface (HIS) leaky-wave antenna is proposed. This antenna realizes a transformation from TM0 SW mode to m= -1 leaky-wave mode. A novel substrate-integrated waveguide (SIW) based planar parabolic reflector is designed as the SW launcher (SWL). Different from the previous literatures that the SWs propagate in a cylindric wave fashion, the proposed SWL can efficiently excite collimated SWs. On the other hand, the dispersion relation is engineered by introducing an additional secondary slit on the HIS to solve the bottleneck problem, open-stopband effect. Through proper design, the open-stopband effect is suppressed successfully in the design and implementation.&#13;\n&#13;\nFinally, two antenna designs that can operate in the near-field region by using the inductive coupling principle are proposed for radio frequency identification (RFID) applications. The first antenna works in dual frequency bands (HF/UHF bands) that have nearly 70 times frequency difference. The design is challenged by the impaired UHF bandwidth due to existence of the spiral coil that operates in the HF band. A novel meander lines based diagonal symmetric structure is designed to support multiple resonance modes to expand the impedance bandwidth under the large inductive circumstance of the coil. On the other hand, the second design starts from a segmented loop antenna that behaves as a magnetic dipole and has better performance than coil. In order to meet the requirement of compactness of the RFID tag antenna, the dispersion relation is engineered by adopting multiple identical radiators. The zeroth-order resonance frequency is reduced with same dimension by this method. As a result, the physical dimension of the antenna can be further reduced at the desired frequency. Through the dispersion engineering, the antenna miniaturization is realized.&#13;\n&#13;\nIn summary, this thesis contributes to 1) the development of novel periodic structures and their relevant theory for the new features, 2) addressing practical issues by engineering the dispersion relations and 3) providing a new procedure of using the dispersion engineering for antenna designs.

The use of surface waves for estimating shear elasticity in soft tissues is an emerging method. There are numerous examples of in vivo and ex vivo applications in literature. Most of these examples base their inversion methods on Rayleigh surface waves, Rayleigh–Lamb dispersion curves, or even the Timoshenko beam model. In this work, we show that there is a critical distance from the source where near-field effects prevent the use of these models. This distance is given by the interference of the Rayleigh surface wave with the so-called leaky surface wave, which arises as a complex solution of the Rayleigh secular equation for materials with large Poisson's ratio [Benech et al., JASA 142(5), 2017]. This leaky wave has been observed experimentally in geophysical applications, and here we show its existence in tissue-mimicking phantoms [Benech et al., J. Phys. Condens. Matter, 34 (2022)]. We then show that a similar behavior is observed in transversely isotropic solids such as skeletal muscle. Finally, we demonstrate two different applications. First, in estimating the elasticity of the concentric contraction of the biceps brachii in vivo. Second, in monitoring the enzymatic maturation process by aging in beef samples. We highlight the advantages of surface waves over traditional ultrasound elastography in these two applications.

In this paper, electronically steerable microstrip and leaky wave antennas using tunable ferroelectric material are proposed. These antennas are lightweight, low volume, low profile, and conformal. They have low fabrication costs and are easily mass produced. They are thin and do not perturb the aerodynamics of a host automobile or aircraft. Linear, circular, and dual polarization are achieved with simple changes in feed position. Beam steering is accomplished by varying the relative phase between radiating elements. In planar array, both horizontal and vertical beam can be combined to provide full scanning capabilities. Tunable ceramic phase shifters are used in these antennas. In microstrip antennas, they are deposited as thin films on the feed lines whereas in the leaky wave antennas they have been used as a traveling waveguide with a ground plane on one side and metallic periodic grating on the opposite side. The dielectric properties of the ferroelectric material are changed by a bias voltage applied to the waveguide which in turn controls the leaky wave direction of the antenna. A simple experiment is presented which shows a good agreement with the theoretical prediction.

The existence of exceptional bulk, quasi–bulk–surface and pseudo–surface waves in a crystal of arbitrary anisotropy coated with a solid layer of arbitrary anisotropy is considered. One–component exceptional bulk waves that exist on the mechanically free surface are shown to disappear on the plated surface. They give rise to quasi–bulk–surface and pseudo–surface waves. The connection between the appearance of quasi–bulk subsonic surface waves and the existence of subsonic ordinary (Rayleigh) surface waves is investigated. In the plated crystal, instead of one–component exceptional waves, there arise three–component exceptional waves which involve the limiting bulk wave and two inhomogeneous modes. It is shown that the presence of an overlay in a general manner provides the existence of high–velocity (supersonic) pure surface waves near the intermediate transonic state and the existence of leaky waves near the highest transonic state.

This paper investigates the utilisation of classical antennas as surface wave (SW) launchers. SWs have potential to provide multiplicative factors of increase in the capacity over the existing multi-pair copper wires thanks to their low-loss and extended bandwidth compared to the well-known differential mode signalling, which is operating at sub-GHz frequencies. Although specially designed devices are required for high SW launching efficiencies, classical antennas can be also utilised for launching and receiving SWs by fixing a simple copper wire between antennas. In this way, transmitted power from an antenna is guided along the wire such that the received power of point-to-point wireless communication links can be substantially improved. To prove our claims, we investigate launching and receiving SWs with double-ridged horn antennas from cellular frequencies up to milli-meter wave spectrum. According to the experimental and numerical results, the proposed solution can achieve 30-50dB enhancement in the received power at short to medium communication ranges (under 150m) compared to wireless communication scenarios. Exploiting SWs in the future telecommunication networks may enable substantially improved data rates multi-Gbps links up to Tbps on the last mile without the need of replacing the copper infrastructure with fibre-optic cables. The proposed solution has the potential to provide a cost-effective alternative for enabling high data rate backhaul links required for 6G and beyond communication technologies.

In this paper, a study of surface-wave (SW) excitation by means of a simple parallel-plate waveguide (PPW) for substrate integrated image guides (SIIGs) is proposed. As a proof of concept, a wideband, low profile and fully planar feeding network is designed. It consists of a surface-wave launcher (SWL) based on a truncated PPW with the addition of a sub-wavelength matching section. This method for SW excitation is intended to overcome the feeding limitations encountered when using SIIG-based antennas or other non-radiating structures at microwave frequencies. A comparison between the performance of the proposed excitation method and structures that can be found in the literature are reported showing an improved bandwidth of more than 50% with respect to previous studies. In addition, this simple feed system has a reduced volume of more than 95% when compared with other alternatives, demonstrating its compactness. Applications include new SW driven feeds, leaky-wave antennas, sensors, or novel passive structures.

This study focuses on advancements in three broad aspects of active surface wave methods: modeling, testing, and inversion. Transfer matrix, global matrix, and stiffness matrix methods were employed to comprehensively model layered structures with half-space boundary conditions for soil structures with increasing/anomalous stiffness profiles, or pavement structures with decreasing stiffness profiles and leaky waves. All three methods were programmed in MATLAB as forward algorithms. The finite element method was adopted to simulate surface wave testing for various half-space site structures with absorbing layers using increasing damping technique. An improved experimental dispersion analysis scheme was developed by scanning phase-velocity and intercept-time followed by a power-spectrum analysis to minimize side lobes and increase sharpness of dispersion images. The multichannel simulation with one receiver (MSOR) method was applied to capture the dispersion characteristics of soil sites. The reciprocity principle for surface Rayleigh waves was verified by comparing dispersion images from MSOR and multichannel analysis of surface waves (MASW) testing at the same site with the same testing system. A multichannel surface wave acquisition system was developed to improve the accuracy of measuring high-frequency and high-velocity dispersion data on pavement sites. A minimally-invasive multimodal surface wave (MMSW) method was proposed to measure multi-mode dispersion data of Rayleigh waves by using either embedded receivers at various depths to record surface wave motions generated from moving impacts on the ground surface or using a multichannel seismograph with an array of geophones on the soil surface for measuring surface wave motions caused by Standard Penetration Test hammer blows at various depths in a borehole. Stiffness matrix and finite element simulations of the MMSW method were employed to identify the critical geophone depths for optimum measurement of higher-mode motions. A hybrid genetic-simulated-annealing (GSA) algorithm was applied to solve multiple minimization and non-linear optimization problems to match the theoretical dispersion curves against their experimental counterparts. Results from simulation and real-world studies demonstrate that the advancements made in the three aspects of surface wave methods can improve the accuracy of surface wave testing results with higher resolution of experimental dispersion data, more complete multi-modal dispersion data, and higher certainty of inversion.