A Full-Wave Numerical Approach for Analyzing Rectangular Waveguides With Periodic Slots

Double-sided open periodic structures are analyzed using inhomogeneous plane wave scattering.The leaky and surface wave modes of several unit cells of different structures are computed using the poles of generalized reflection and transmission coefficients of inhomogeneous plane waves in the spectral domain.It is shown that the reflection and transmission coefficients of the zeroth order Floquet mode contain the poles of the Green's function of the complex stratified periodic structure.The properties of evanescent mode amplification as well as super resolution near field imaging in a wire medium are addressed.A balanced leaky wave antenna unit cell with double-sided radiation feature is introduced and it is shown that, in contrast to grounded structures, total absorption in lossless nonchiral double-sided open unit cells is not feasible as long as the behavior of the unit cell is well described by its fundamental mode.

This article concentrates on the high-power microwave (HPM) breakdown process and behaviors in air-filled rectangular waveguide under the external dc magnetic field. To solve the persuasive issue, a three-dimensional (3-D) multiphysics model coupling full-wave Maxwell’s equations with plasma fluid equations is established and solved by the spectral-element time-domain (SETD) method. In our simulation, the Galerkin’s method is employed for the space discretization and the central difference scheme is used for the temporal discretization during the SETD process. The numerical results reveal that the external dc magnetic field applied in breakdown volume can significantly enhance the breakdown threshold to suppress the HPM breakdown, which is beneficial for the propagation of HPM pulse in air-filled waveguide. Our research provides theoretical guidance for suppressing the impact of HPM breakdown for HPM devices protection.

This article introduces a novel transition between coplanar waveguide (CPW) and air-filled rectangular waveguide (RWG). A rectangular radiator etched with a semi-elliptic slot is connected to the center conductor of CPW to realize the transition, which broadens the bandwidth. This direct transition does not require intermediate transition or air-bridges. Moreover, the planar circuit of the transition can be designed with high- and low-permittivity materials (εr = 10.2 and 2.22), which offer more benefits in both PCB and MMIC design. Two back-to-back transition prototypes at X-band are designed, fabricated and measured. The 15 dB fractional bandwidths are expanded to 44.7% and 47.6% respectively, which have been demonstrated in both of the transitions (εr = 10.2 and 2.22). The measurement results agree well with simulation results, which validate the feasibility of this design.

The SAW reflection from a strip (Pt, Al) deposited on a half-infinite substrate (Z-cut AlN) is numerically studied. The strip-substrate contact forms an acoustic waveguide supporting leaky modes propagating faster than SAW on the free surface of the substrate. The excitation of a leaky mode by SAW leads to a singular behavior of the reflection and the transmission coefficients. The dependence is investigated of the magnitude and the phase of these coefficients on the angle of incidence, the frequency, the width and the thickness of the strip. Two types of leaky waveguide modes are considered: Love-wave type mode and LLSAW type mode.

In this paper, we propose a new metallic cylindrical antenna at terahertz frequencies using the concept of low-frequency spoof surface plasmon polaritons (SPPs). The antenna is developed by introducing an open hollow ring (OHR) in each unit cell of the conventional periodic subwavelength corrugated metallic wire (PSCMW). The new structure is referred to as the PSCMW-OHR. The dispersion properties of PSCMWs and PSCMW-OHRs, the near-field and far-field distributions, as well as the radiation efficiencies are numerically evaluated and compared. By analyzing the numerical results, we find that there are extra new propagation modes that exist in the annular groove of the PSCMW-OHR, aside from the normal transmission modes in the PSCMW. Moreover, the dispersion line of the new SPP mode exhibits a negative slope. Surprisingly and interestingly, after passing through the light line, the propagation gets into the radiation zone, where it becomes a leaky mode with a complex-valued propagation constant. We have found that the far-field radiation of propagation in the leaky mode can lead to frequency scanning effects with a scanning angle of 22°, and the radiation efficiency can be increased to 90%, provided that the total number of the periodic unit cells is large enough.

Rectangular waveguide slot arrays are commonly used in several microwave antenna systems. The slots are most often located in the broad wall of the rectangular waveguide, arranged longitudinally parallel with the waveguide axis, because this provides good control of the excitation of each slot over a large dynamic range by adjusting the offset of the slot from the center line of the waveguide. However, longitudinal slots can only radiate electrical fields that are transversely polarized with respect to the waveguide axis. If longitudinal (or dual) polarization is required, the slots (or half of them) must be located transverse to the waveguide axis. Transverse resonant slots in the broad wall are too strongly excited for use in large arrays, so transverse narrow slots in the narrow wall are preferred. In the latter case the slots are not excited unless they are tilted or coupled to tilted parasitic elements like wires or posts inside the waveguide. The purpose of the present paper is to analyse an untilted narrow wall slot excited by two tilted wires. An improved and extended analysis in which the slot extensions into the neighboring two broad walls are included, is described. The virtual cylinder method is applied to the calculation of the external admittances of the slot using wedge dyadic Green's functions and entire-domain basis functions in order to get good convergence of the integrals of the spectral domain formulations.

In this paper, we review the basic properties of resonant leaky mode elements implemented with periodic waveguide layers and consider their applicability in photonic devices and systems. Leaky waveguide modes can be exited when an incident light beam is coupled into the waveguide structure through an inscribed periodicity under phase-matching conditions. This results in generation of a guided-mode resonance field response in the spectrum. Device operation can be explained in terms of the photonic band structure and associated leaky-wave effects near the second stop band. Resonant devices such as bandpass/bandstop filters, polarizers, wideband reflectors, biosensors, tunable filters, and display pixels can be designed using this operational principle.

Slots in rectangular waveguides are often used at elements in linear array antennas. The polarisation of the radiated energy is usually linear. Circular polarisation can be obtained with compound slots in the broad wall. Experiments have shown that circular polarisation can be obtained from certain I-shaped slots in the narrow wall.

An earlier design procedure, valid for arrays of longitudinal slots fed by air-filled rectangular waveguide, is generalized to apply to the increasingly used practical case that the waveguide is dielectric-filled. This requires abandonment of the model of an equivalent array of loaded dipoles, which results in a surprisingly simpler and more direct derivation of the design equations. The new generalized procedure retains an important feature of the earlier approach in that it includes the effect of external mutual coupling.

In this report, the phenomena of low-frequency spoof surface plasmon polaritons (spoof SPPs) in a new metallic cylindrical antenna at terahertz (THz) frequencies are demonstrated. The antenna is designed as a periodic structure whose unit cell includes an open hollow ring (OHR) as compared with the conventional periodic subwavelength corrugated metallic wire (PSCMW) with cylindrical structure. Near- and far-field distributions, dispersion properties, and radiation efficiency are numerically evaluated and then compared for both PSCMW and PSCMW-OHR. It is indicated that when the dispersion line passes through the light line into a radiation zone, the field becomes a leaky mode. We find that the far-field radiation of the leaky mode can generate frequency scanning effects with a scanning angle of 23°, and the radiation efficiency can be increased to 90% as the number of periodic unit cells is large enough.

Periodic arrays of resonant dielectric nano- or microstructures provide perfect reflection across spectral bands whose extent is controllable by design. At resonance, the array yields this result even in a single subwavelength layer fashioned as a membrane or residing on a substrate. The resonance effect, known as guided-mode resonance, is basic to modulated films that are periodic in one dimension (1D) or in two dimensions (2D). It has been known for 40 years that these remarkable effects arise as incident light couples to leaky Bloch-type waveguide modes that propagate laterally while radiating energy. Perfect reflection by periodic lattices derives from the particle assembly and not from constituent particle resonance. We show that perfect reflection is independent of lattice particle shape in the sense that it arises for all particle shapes. The resonance wavelength of the Bloch-mode-mediated zero-order reflectance is primarily controlled by the period for a given lattice. This is because the period has direct, dominant impact on the homogenized effective-medium refractive index of the lattice that controls the effective mode index experienced by the mode generating the resonance. In recent years, the field of metamaterials has blossomed with a flood of attendant publications. A significant fraction of this output is focused on reflectors with claims that local Fabry-Perot or Mie resonance causes perfect reflection with the leaky Bloch-mode viewpoint ignored. In this paper, we advance key points showing the essentiality of lateral leaky Bloch modes while laying bare the shortcomings of the local mode explanations. The state of attendant technology with related applications is summarized. The take-home message is that it is the assembly of particles that delivers all the important effects including perfect reflection.

An accurate design technique of dual-mode microwave dielectric or air-filled rectangular waveguide filters is described. Dual-mode coupling is realized by a section of rectangular waveguide with square-corner-cut. The unequal couplings between dual-mode pairs of the cavities is provided by a section of evanescent mode waveguide. Rigorous analyses are applied to characterize the microwave junctions and to obtain the design parameters for the filter. The design procedure used to determine the dimensions of the waveguide junctions with a minimum of computational effort is described. The design is demonstrated by four-pole and six-pole dual-mode rectangular waveguide elliptic function filters. Excellent agreement between computer simulation and experimental results with absolutely no tuning justifies the design.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

We develop the concepts of net Goos–Hänchen (GH) shift and reshaping shift, and apply these concepts to lateral beam shift arising from k (wavenumber) domain dispersion. Specifically, our interest is in cases in which the traditional concept of GH shift loses its meaning. We analyzed the effects of finite beam size, complicated beam profiles, and phase modulations on GH shift. We experimentally examined the GH shift for surface plasmon polaritons and a leaky waveguide mode. The results agreed well with those from analyses based on the net GH shift and reshaping shift, indicating that these concepts are useful for extending the traditional concept of GH shift to complicated reflection systems.

A 2-D periodic leaky-wave antenna is studied to examine the mechanism of beam formation from leaky-wave modes and the properties of the leaky-wave modes. The structure consists of a grounded dielectric slab with a periodic arrangement of narrow rectangular patches of metal on the upper surface of the dielectric, excited by a slot in the ground plane. The dimensions of the unit cell and the size of the patches determine the phase constant and the attenuation (leakage) constant of the leaky modes supported by the structure. The narrow beam that is formed is found to be due to an aperture distribution mainly consisting of the radiating space harmonics (Floquet waves) of two different leaky modes, one determining the E-plane behavior and one determining the H-plane behavior. The beamwidth is larger in the H-plane than in the E-plane due to the larger leakage constant of the H-plane mode. It is found that the two leaky modes also have different field distributions, in addition to having very different leakage constants.

The design of an 8-element vertically polarised array for a 60 GHz radar application is described. The array consists of 10 E-plane step horns that are dielectric loaded to allow an element spacing of half wavelength. These horns are connected to 8 inputs (the end elements of the array are parasitic) by waveguide runs that include transitions from a dielectric-filled square waveguide to a standard air-filled WR-15 rectangular waveguide. This array has been fabricated and results obtained from measuring the radiation patterns, return loss and horn cross coupling are outlined.