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We present a multifilament current method (MFCM) to accurately and efficiently determine the cutoff wavenumbers (cutoff frequencies or eigenfrequencies) of homogeneous anisotropic material-filled metallic waveguides with arbitrary shapes. A set of $z$ -directed filamentary line sources placed outside of a waveguide are responsible for generating the simulated fields within the anisotropic material-filled waveguide in light of the derived 2-D anisotropic dyadic Green’s functions. Instead of solving an excitation-free eigenvalue problem, a substantial line source presented as an excitation is incorporated into the MFCM to formulate an eigenmode analyses technique without spurious eigenmodes. The internal field intensity response versus free space wavenumber are subsequently simulated, and a high magnitude response can be observed when an eigenmode is excited. In this case, the cutoff wavenumbers of physical eigenmodes are revealed by maximum locations of simulated field intensity response. Several numerical examples with different configurations on a waveguide are investigated. The simulated results are compared with those obtained from commercial software packages and an excellent agreement is achieved. In addition, the study of the oscillating phenomenon on magnitudes of filamentary sources and the ill-conditioning issue of constructed impedance matrix with respect to the placement of filamentary sources are also discussed. [ABSTRACT FROM AUTHOR]

The design of a 1 × 0.33 m dual-polarized reflectarray antenna (RA) operating in Ku-Band (17.2 GHz) for a synthetic aperture radar (SAR) mission using a 12 U CubeSat is presented. The SAR RA has larger electrical size, larger aspect ratio, and smaller focal to aperture length ratio (F/L) compared to existing CubeSat RAs designed for communication payloads. Electrically small unit cells accounting for large incidence angle variations, improving phase resolution, and preventing grating lobes are designed. To illuminate the RA with the desired elliptical beam, a compact aperture-coupled microstrip patch array antenna was designed. Tests done on a CubeSat mockup integrating the dual-polarization feed source and a five-panel reflectarray showed good agreement between the simulated and the measured beamwidths, with low sidelobe and cross polarizations levels. [ABSTRACT FROM AUTHOR]

We present a multifilament current method (MFCM) incorporated with generalized sheet transition condition (GSTC) to simulate 2-D cylindrical metasurfaces with arbitrary cross sections. The GSTC casts in the form of an impedance-type boundary condition to relate the tangential fields on two sides of a cylindrical metasurface. The MFCM is subsequently introduced and formulated by employing the GSTC. The doublet-current unit, including both electric and magnetic filamentary sources, is introduced in order to capture both co- and cross-polarized scattered and transmitted fields from the GSTC characterized cylindrical metasurfaces. Three illustrative examples are presented to validate the proposed simulation technique. The behaviors of filamentary sources in terms of scattered field singularities and the ill-conditioning issue of the constructed matrix are also discussed in detail. In comparison to existing numerical methods, the proposed technique has its merits on simplicity and conciseness. [ABSTRACT FROM AUTHOR]

The TM shielding effectiveness (SE) analyses of slotted carbon fiber reinforced polymer (CFRP)-based shells are presented in this letter. The multifilament doublet current method (MFDCM) is deployed to simulate the scattered and penetrated fields in the considered situation. The inner and outer regions of a slotted shell are separated by a hybrid boundary, which contains the material and slot parts. The material part is constituted of multilayered CFRP materials, whereas the slot part is a virtual boundary. A tensorial boundary condition (TBC) is then constructed to stand for the slotted shell with a chain matrix. The MFDCM is subsequently formulated by employing the TBC to estimate the EM performances of interests. Different slot angles of the shell and conductivity of the CFRP material are considered in our numerical calculations. Only transverse magnetic (TM) case is considered herein, yet the transverse electric (TE) situation can be handled straightforwardly with a similar formulation. [ABSTRACT FROM AUTHOR]

This article presents a new application of microwave microscopy as a diagnostic of the painted lightning strike protection (LSP) mesh used in composite aircraft skins. A new flexible probe is presented. This probe can sweep over the surface of the composite skin and detect breaks in the LSP lying underneath. It is demonstrated that shielding of the probe feeding line leads to better balancing, and consequently highly improved immunity to the presence of nearby objects. With this new approach, it is possible to localize faults as small as one cut strand under the paint. Also, this technique features the possibility to measure the paint thickness with a resolution on the order of micrometers. [ABSTRACT FROM AUTHOR]

Implementation of the multifilament current method (MFCM) to analyze the scattering from homogeneous anisotropic cylinders is introduced. The ${z}$ -directed electric and magnetic line sources are used to associate with TM and TE polarizations, respectively. The radiation fields of a line source in unbounded space occupied with an anisotropic material are derived in detail. With the help of the derived fields, the application of the MFCM is expanded to anisotropic materials. The scattering field is then obtained in terms of these line sources. Monostatic and bistatic scattering widths of cylinders with and without sharp edge are investigated under different incident wave polarizations and material characteristics. Apart from homogeneous anisotropic cylinders, the scattering from an anisotropic shell-coated PEC cylinder is also straightforwardly analyzed without additional considerations in the formulation. The oscillation phenomenon of filament currents in representing the scattered fields and the ill-conditioned issue of the constructed matrix are also discussed in detail. Numerical results obtained with this proposed scheme are also in good agreement with published ones, whereas the proposed technique has its merits on simplicity and conciseness in comparison to the existing numerical methods. [ABSTRACT FROM AUTHOR]

The design, simulation, and measurement of a beam steerable slotted waveguide antenna operating in X band are presented. The proposed antenna consists of a standard rectangular waveguide (RWG) section with longitudinal slots in the broad wall. The beam steering in this configuration is achieved by rotating two dielectric slabs inside the waveguide and consequently changing the phase of the slots excitations. In order to confirm the usefulness of this concept, a nonresonant 20-slot waveguide array antenna with an element spacing of $d = 0.6\lambda _{0}$ has been designed, built, and measured. A 14° beam scanning from near broadside ($\theta = 4^{\circ }$) toward end-fire ($\theta = 18^{\circ }$) direction is observed. The gain varies from 18.33 to 19.11 dBi and the antenna efficiency from 95% to 79%. The sidelobe level is −14 dB at the design frequency of 9.35 GHz. The simulated and measured co-polarized realized gains are in good agreement. [ABSTRACT FROM AUTHOR]

We present in this paper, a multifilament doublet current method (MFDCM) combined with the tensorial impedance boundary condition (TIBC) to simulate and analyze scattering and shielding performances of carbon fiber composite (CFC) material-based cylindrical shells. The TIBC of a shell made up with the multilayered CFC material with an arbitrary fiber orientation in each layer is introduced and derived. The MFDCM is subsequently formulated by employing the TIBC to handle numerical calculations with the anisotropic lossy material, such as a multilayered CFC material, for the first time. Monostatic and bistatic echo widths are investigated with reference to different layer numbers, fiber orientations, and incident wave polarizations. These different scenarios are also taken into consideration in the shielding effectiveness (SE) prediction. Both TE and TM modes are excited within the cylindrical shell under arbitrary incident plane waves over a high frequency range. Results are in excellent agreement with published ones. The proposed method has its merits on simplicity and conciseness. Also it can be applied to handle shells of arbitrary smooth cross sections. [ABSTRACT FROM AUTHOR]

A simple and low-cost single substrate layer Luneburg lens-based beamforming network (BFN) operating in $W$ -band is proposed. A multibeam antenna is then realized using the novel BFN and fabricated using a low-cost printed circuit board process. The Luneburg lens is realized by drilling holes in a substrate, and to extend the refractive index variation, a high dielectric constant substrate is embedded at the lens center. The lens is excited by radially placed open-ended substrate integrated waveguides (SIWs) at the lens circumference, feeding a subset of antenna ports placed on the opposite side of the lens. The proposed BFN thus provides half-power beamwidth (HPBW) and beam steering angle flexibility for multibeam antennas. An antenna generating seven beams was prototyped at 79.5 GHz to validate this BFN, providing measured beam steering of approximately ±41° with a broadside HPBW of 10°. The bandwidth of the proposed BFN is determined by the single-mode operation of the SIW. The fabricated multibeam antenna impedance bandwidth is, however, about 2% at 79.5 GHz because of the radiating elements. The radiating elements are series fed slot arrays placed on SIWs. [ABSTRACT FROM AUTHOR]

A beam-steering technique in narrow-wall slotted ridge waveguide at X-band is proposed. An array of inclined slots cut in the narrow wall of a rectangular ridge waveguide is employed. Beam steering is achieved by rotating a dielectric slab inside the waveguide. The change of wavelength at different rotation angles of the slab is used as the phase shifter. To confirm the usefulness of this method, a short nonresonant 20-slot waveguide array antenna with an element spacing of $d= {{0.44}}\lambda _{0}$ has been designed, built, and tested. It is shown that the main beam can be steered from near broadside $(\theta = {{6^\circ)}}$ toward end fire $(\theta = {{42^\circ)}}$ by rotating the dielectric slab by 90°. A directivity variation of 2.8 dB and a half-power beamwidth increase of 3° are observed over this scan at the design frequency. The gain varies from 11.17 to 12.47 dB over the scanning range. Due to the relatively short length of the prototype, losses in the terminating load have limited the radiation efficiency to values between 43% and 86%. The E-plane radiation patterns measured at the operation frequency of 9.35 GHz and compared very well with the simulated results. [ABSTRACT FROM AUTHOR]

A focused beam and a shaped beam four-layer transmitarray (TA) antenna operating in the $K$ -band have been designed, fabricated, and measured. Four-layer unit cells allowing a transmission phase range of 360° are used. The gain of the beam-focusing TA is 30.3 dB at 19 GHz with an aperture efficiency of 34.9%. Compared with TAs proposed in the literature, the presented antenna bandwidth is almost two times larger with a −1 dB gain bandwidth of 18% and a −3 dB gain bandwidth of 25.5%. A second TA radiating a shaped beam was designed, and its measured pattern correlates well with theoretical calculations. The sensitivity of the proposed unit cells to fabrication errors and the effect of oblique incidence are also studied. [ABSTRACT FROM PUBLISHER]

This paper presents the design of a meander-line circular polarizer optimized for oblique incidence and for a direction off from the principal planes (\phi=\text0^\circ, \text90^\circ, \text180^\circ, or \text270^\circ). This polarizing screen converts linearly polarized (LP) waves into circularly polarized (CP) waves and vice versa. To illustrate the design process, a three-layer meander-line circular polarizer is designed for an oblique incidence angle of (\theta=\text40^\circ, \phi=\text45^\circ) and its performance is examined in detail over the 18–20 GHz band. Measurements and simulations are in good agreement. Moreover, the sensitivity of the results to frequency and incidence angle variations is studied. The results show that the bandwidth of the meander-line circular polarizer is maximum when it is designed for normal incidence or for an oblique incidence in the two principal planes because coupling between orthogonal modes is weaker. [ABSTRACT FROM PUBLISHER]

In this paper, several conformal leaky-wave antennas (CLWAs) are designed, which utilize backward radiating waves to focus the beam. They employ a metal strip grating (MSG) in order to introduce the required phase constant ($\beta$) on a curved aperture to compensate for the defocusing due to the curvature. The required $\beta$ is obtained by modulating the distance between adjacent strips/slots to scan the beam toward broadside. Using backward waves with a modulated MSG on a smoothly curved CLWA is a novel design. Using a backward wave allows for a doubling of the aperture size as compared to the forward-wave case. This, in turn, leads to a doubling of the directivity. A simple two-dimensional (2-D) Fourier-series model is used to explain the radiation physics. Full-wave analyses using the FEKO and HFSS software packages are carried out to design and analyze these CLWAs in 2-D and three-dimensional (3-D), and to verify the concept. A CLWA with a focused backward wave, supported by a modulated MSG, is fabricated and tested. The calculations and experimental results confirm that directive beaming is possible with a backward wave on a curved, modulated MSG. [ABSTRACT FROM PUBLISHER]