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Near ground radio wave propagation is examined in a tropical plantation experimentally at VHF and UHF bands. The propagation loss with forest depth is empirically analyzed using an integrated model combining both the foliage induced effect and the ground effect. Several well-known empirical foliage models are compared and analyzed. It is observed that the fitted ITU-R model taking into account the ground reflection, can provide a close approximation to the path loss in a tropical palm plantation. However, the accuracy of this model becomes poor when lateral wave dominates in the VHF band. A modification to the ITU-R model is then proposed taking into consideration the lateral wave effect. The modified model is verified using measured and published data, and found to have higher accuracy for large foliage depth in the VHF band as compared to the existing empirical foliage models. Index Terms--Forest, lateral wave, near ground, path loss, VHF and UHF.

In this paper, an E-shaped patterned ground microstrip bandstop resonant cell is proposed. In comparison to other bandstop resonators, it provides the advantages of a high-Q factor, and a sharp transition knee within a small circuit area. This resonant cell is applied to the design of a tunable bandstop resonator. Due to the unique E-shaped pattern etched in the ground plane, the proposed resonant cell is able to provide tuning function within a small circuit area. Index Terms--Defected ground structure, patterned ground structures, slotted ground structures, tunable bandstop filters, tunable bandstop resonators.

In this paper, a novel high-performance compact dual planar electromagnetic bandgap (DP-EBG) microstrip low-pass filter with a U-shaped geometry is proposed. By employing the unique DP-EBG configuration and the U-shaped geometry of the microstrip line (MLIN), the proposed structure achieves a wide stopband with high attenuation and a high selectivity within a small circuit area. Its passband ripple level is low due to the U-shaped geometry and the electromagnetic bandgap (EBG) structure with square patches inserted at the bends of the MLIN. The Chebyshev tapering technique is used to taper components of the proposed structure in order to eliminate ripples caused by the EBG periodicity. The structure was fabricated and the measured results are in good agreement with the simulated results. This novel design demonstrates superior low-pass filtering functionality and can easily be applied to monolithic circuits. Index Terms--Electromagnetic bandgap (EBG), low-pass filters, planar passive filters, tapering techniques.

In this paper, the designs of two novel tapered dual-plane compact electromagnetic bandgap (C-EBG) microstrip filter structures are presented. With the dual-plane configuration, the proposed structure displays an ultrawide stopband with high attenuation within a small circuit area. Chebyshev distribution is adopted to eliminate ripples in the passband caused by the periodicity of the EBG structure. This gives rise to a compact EBG structure that exhibits excellent transmission and rejection characteristics in the passband and the stopband, respectively. The proposed structures are implemented and the measurement results are found to be in good agreement with the simulation results, verifying the excellent stopband and passband performance obtained using the proposed configuration. These novel structures are easy to fabricate and are promising structures that have wide applications for compact and high performance circuit component designs in microwave circuits. Index Terms--Bandstop filters, dual-plane, electromagnetic bandgap (EBG) structures, low sidelobe array theory, microstrip filters, tapering functions, tapering techniques.

The Numerical Electromagnetic Code (NEC) is one of the most popular tools for electromagnetic simulation of wireframe structures. The application of NEC is often limited to small to medium sized problems due to its full matrix nature. In this papery an approach by using the wavelet transform to increase the efficiency and capability of NEC is presented. In the approach, a sparse moment matrix equation can be produced and solved by efficient sparse solver instead of solving full matrix equation in the original NEC. Under close examination, structures with less singularities are found to have much better accuracy and higher compression rates. Index terms - Numerical analysis, wavelet transforms, wire antennas, wire scatters.

The horizontal orientation angle and the vertical inclination angle of an elongated subsurface object are key parameters for object identification and imaging in ground-penetrating radar (GPR) applications. Conventional methods can only extract the horizontal orientation angle or estimate both angles in narrow ranges due to limited polarimetric information and detection capability. To address these issues, this letter, for the first time, explores the possibility of leveraging neural networks with multipolarimetric GPR data to estimate both angles of an elongated subsurface object in the entire spatial range. Based on the polarization-sensitive characteristic of an elongated object, we propose a multipolarization aggregation and selection network (MASNet), which takes the multipolarimetric radargrams as inputs, integrates their characteristics in the feature space, and selects discriminative features of reflected signal patterns for accurate orientation estimation. Numerical results show that our proposed MASNet achieves high estimation accuracy with an angle estimation error of less than 5°. The promising results obtained by the proposed method encourage one to think of new solutions for GPR-related tasks by integrating multipolarization information with deep learning techniques. The data and code implemented in the letter can be found at https://haihan-sun.github.io/GPR.html. [ABSTRACT FROM AUTHOR]

In studies of surface-enhanced Raman scattering (SERS), individual metal nanoparticle and particle assemblies introduce enhancement of electromagnetic fields. However, the contributions to enhancement due to the substrate supporting the particles are yet to be studied analytically. In this communication, we present an analytical method to investigate the effect of a substrate with realistic layers in SERS. The proposed method quantifies the effect of a substrate on the electric field on the nanoparticles surface in SERS experiments. By applying the proposed method, optimal constructions of a substrate can be obtained to maximize the surface electric field while a poorly constructed one can be avoided. The maximization can lead to a high Raman enhancement factor. The method is verified using numerical simulations. [ABSTRACT FROM AUTHOR]