Surface Wave Suppression Research Articles

Design of an Endfire Microstrip Antenna for Aircraft Collision Avoidance System

Traffic alert and collision avoidance system provides a solution to reduce the threat of mid-air collisions between civil aircraft. The endfire antenna is very much essential in such airborne system. In this letter, an antenna using planar elements is being developed, and the design of a prototype model for printed endfire microstrip antenna with four feeding ports is presented. An aerodynamically shaped conformal metamaterial lens-based radome is also designed to encapsulate the antenna inside an enclosure. Here, the suppression of surface wave in the antenna is taken place, which resulted in gain enhancement and also reduction of sidelobes. Hence, the shape of the radiation pattern is tuned as per requirement. The proposed antenna is capable of transmitting the electromagnetic waves toward $\text{360}^{\circ }$ surveillance region of the aircraft with proper excitation of its feeding ports. The proposed antenna and its radome have been designed and subsequently simulated using CST Microwave Studio EM tool. The antenna fabrication and measurement are also carried out to validate the simulated antenna performance and other antenna characteristics. Quite excellent similarity is attained among all the simulated and experimental results.

Low-Frequency Noise Suppression Method Based on Improved DnCNN in Desert Seismic Data

High-quality seismic data are the basis for stratigraphic imaging and interpretation, but the existence of random noise can greatly affect the quality of seismic data. At present, most understanding and processing of random noise still stay at the level of Gaussian white noise. With the reduction of resource, the acquired seismic data have lower signal-to-noise ratio and more complex noise natures. In particular, the random noise in the desert area has the characteristics of low frequency, non-Gaussian, nonstationary, high energy, and serious aliasing between effective signal and random noise in the frequency domain, which has brought great difficulties to the recovery of seismic events by conventional denoising methods. To solve this problem, an improved feed-forward denoising convolution neural network (DnCNN) is proposed to suppress random noise in desert seismic data. DnCNN has the characteristics of automatic feature extraction and blind denoising. According to the characteristics of desert noise, we modify the original DnCNN from the aspects of patch size, convolution kernel size, network depth, and training set to make it suitable for low-frequency and non-Gaussian desert noise suppression. Both simulation and practical experiments prove that the improved DnCNN has obvious advantages in terms of desert noise and surface wave suppression as well as effective signal amplitude preservation. In addition, the improved DnCNN, in contrast to existing methods, has considerable potential to benefit from large data sets. Therefore, we believe that it can open a new direction in the area of seismic data processing.

Wideband Radar Cross-Section Reduction on Checkerboard Metasurfaces With Surface Wave Suppression

In this letter, wideband radar cross-section (RCS) reduction on checkerboard metasurfaces with dual resonance and surface wave suppression is proposed. In addition to dual resonance, the surface wave suppression of the unit cells is applied to extend the −10 dB RCS reduction bandwidth limit of the upper frequency band that is generated by the surface wave. As a result, the proposed structure increases the high frequency of the −10 dB RCS reduction from 14.9 to 16.32 GHz. Fabricated checkerboard metasurfaces are shown, and simulation and measurement results are presented in this letter.

Surface Impedance Engineered Low-Profile Dual-Band Grooved-Dielectric Choke Ring for GNSS Applications

A novel low-profile grooved-dielectric choke ring with dual-band surface impedance resonance is proposed and experimentally demonstrated. The proposed structure is designed by engineering the surface impedance of a dielectric-based choke ring to introduce two resonant frequencies around the global navigation satellite system (GNSS) bands of L2 (1227.60 MHz) and L1 (1575.42 MHz). This provides capacitive surface impedances around both bands simultaneously, which is required for efficient surface wave suppression for higher multipath rejection performance. To demonstrate the proposed principle of surface impedance engineering, an in-house choke ring prototype of the proposed design is tested with the widely used Dorne and Margolin antenna. A high multipath rejection in both GNSS bands is experimentally confirmed with comparable performances to an otherwise bulky, heavy, and expensive conventional metallic choke ring.

Mutual Coupling Reduction in 4×1 Array Antennas Using Mushroom-Like Structures

Microstrip patch antennas are widely used in Telecommunication systems, because of their low manufacturing cost and low weight, but they have some disadvantages such as, low gain. For a long distance communication, antennas with very high gain are suitable. An easier way to improve the gain is a conception with array configuration, but the disadvantage of this design is the appearance of strong mutual coupling, which is a major drawback of this kind of antennas. The use of Electromagnetic Band Gap structures can reduce or suppress surface waves, then reducing the mutual coupling. This paper describes the use of Mushroom-like structures 4×1 to reduce mutual coupling between radiating elements. The effect of these structures is studied and demonstrated by plotting variations of return loss and transmission coefficient versus frequency, surface current and E-field distributions of the proposed array antennas are also investigated. Simulation results are performed with High Frequency Structural Simulator.

Mutual coupling reduction using complementary of SRR with wire MNG structure

AbstractMutual coupling has always been a drawback for array antennas with different configurations. Engineers are obliged to cope with negative effects of mutual coupling in designing procedure. The most important cause of the mutual coupling is surface wave propagation as it transfers the wave in undesirable directions. A method to reduce this effect is the suppression of surface waves using metamaterial structures. A known type of metamaterial used for this purpose is complementary of split ring resonator (CSRR). In this work, a structure consisting of CSRRs with wires is used to alleviate the effect of mutual coupling. The results are verified by calculating effective permeability and permittivity of the structure showing the Mu‐negative property. The calculation is also performed by Kramers‐Kronig relations. A 17 dB reduction in mutual coupling is achieved over a bandwidth range of 170 MHz.

Dispersive Rayleigh wave attenuation using inverse-dispersion method

Reflections provide the most valuable information about the stratigraphy in seismic exploration. On land reflections are always contaminated by surface waves, high amplitude, low frequency, and low velocity and also dispersive. All these characteristics enable surface wave to be separated from reflections. A particular complication is that surface waves are dispersive. Then, frequencies of surface waves and reflections are overlapped in the spectral domain, the same can be found in the f-k domain. Traditional processing from doing surgical muting may cause damage to the data such as waveform distortion and narrowing the spectral band of the signal, especially when the surface waves are strongly dispersive. In this paper, a new method named inversedispersion algorithm is presented to suppress surface waves that overlap with reflections in frequency. We use the linear Radon transform and Fourier transform to find the dispersion curve of surface wave. With the help of dispersion curve and offset information, phases of every trace are moved. The phase-moving step is named the inverse-dispersion method. After the inverse-dispersion step, surface waves with different frequencies are transformed to be nearly parallel and away from reflections, which are easily separated. As it should be, the phase is moved back after surface wave elimination. In this paper the method is tested on field data, showing a good result with excellent protection of the reflections.

Radiation pattern control of microstrip antenna in elevation and azimuth planes using EBG and pin diode.

An important issue in wireless communication systems, which is related to the antenna gain degradation in case of changing the main direction of the antenna radiation pattern, this variation is not approval in many communications systems. In order to improve antenna radiation performances, Electromagnetic band gap (EBG) - antenna with radiation pattern control capability is presented. Mushroom-like EBG structure for suppressing surface waves has been combined, with the switching diode to produce the radiation pattern control with improving antenna characteristics of gain, directivity and efficiency. EBG of several cells are surrounded the patch antenna and placed symmetrically for the two opposite sides, generating different radiation patterns control ability in both the elevation (E) (-20° < φ < 20°) and azimuth (Z) planes (−18° < θ < 18°). At the ground plane of antenna the diodes have been switched ON and OFF states, the EBG sector properties in stop band (connecting vias) and pass band (disconnecting vias) are altered. Using CST Microwave Studio (CST MWS) the results show the flexibility in radiation pattern control for the Z and E planes using only four diodes. Antenna directivity of 10 dBi, gain 9.86 dB and efficiency 96.5% at the operating frequency of 6 GHz, more results for all direction has been stated in Table1. Significantly, unlike a conventional beam steering, this method does not suffering from gain degradation and the main lobe gain is approximately constant for all steerig angles.

Simulation Analysis of Electromagnetic Surface Wave Suppression by Soft Surfaces, Including Effects of Resistive and Active Elements

The soft surface is defined by its anisotropic surface impedance, and it has the property of suppressing surface wave propagation for any polarization of the electric field. It can be used as a general design element for reducing scattering or controlling coupling between nearby antennas. In this letter, the suppression capabilities and bandwidth limitations of soft surfaces are analyzed using simulations to draw the following conclusions: First, a soft surface is as good as an ideal perfect magnetic conductor for suppressing vertically polarized surface currents; second, adding loss to the soft surface actually increases coupling between nearby antennas; third, the bandwidth of soft surfaces can be extended using active loading; and fourth, a soft surface boundary condition can suppress coupling below even the expected free-space wave coupling. Several simple examples are illustrated using simulations, including the effect of lossy substrates, designs for active loading, and the effects of soft surfaces on the contributions to coupling between nearby planar antennas.

Effects due to aliasing on surface-wave extraction and suppression in frequency-velocity domain

Surface waves are treated as a kind of strong noise in petroleum seismic exploration. We can suppress surface waves by extracting them because of the different distribution features of surface waves and body waves in the frequency-velocity (f-v) domain. The accuracy of surface-wave extraction and suppression relies on high-resolution and high-accuracy imaging, however, while spatial aliasing will inevitably smear energy images in the f-v domain due to sparse sampling. It is crucial to analyze the effects due to spatial aliasing on surface-wave extraction and suppression. We use the reversible linear operator, high-resolution linear Radon transform, to extract and analyze the energy caused by spatial aliasing. Real-world and theoretical examples demonstrate that the retrieved surface-wave fields will be polluted by spurious body waves once the spatial aliasing energy in the f-v domain gets involved in surface-wave extraction, which will subsequently affect the quality of surface-wave suppression. We suggest that the surface-wave extraction range should be kept within Nyquist spatial sampling limits as much as possible. In addition, the results of synthetic data show that the spatial aliasing could cause mode misidentification since it is easy to be recognized as the higher modes of the surface waves in the f-v domain. In order to distinguish higher modes from spatial aliasing, we proposed using the asymptotic velocity of high modes at high frequencies and derived formulas to calculate the location of the energy due to spatial aliasing to correctly identify the high modes.

Advances in 6C seismology: Applications of combined translational and rotational motion measurements in global and exploration seismology

Over the past few decades, the potential of collocated measurements of 6C data (3C of translational and 3C of rotational motion) has been demonstrated in global seismology using high-sensitivity, observatory-based ring laser technology. Proposed applications of 6C seismology range from tomographic reconstruction of near-receiver structure to the reduction of nonuniqueness in seismic source inverse problems. Applications to exploration problems have so far been hampered by the lack of appropriate sensors, but several applications have been proposed and demonstrated with array-derived rotational motion estimates. With the recent availability of, for example, fiber-optic-based high-sensitivity rotational motion sensors, widespread applications of 6C techniques to exploration problems are in sight. Potential applications are based on, for example, the fact that the extended set of combined translational and rotational motion observations enables carrying out array-type processing with single-station recordings such as wavefield separation and surface-wave suppression. Furthermore, measuring the rotational component (curl) of the seismic wavefield enables direct isolation of the S-wave constituents and could significantly improve S-wave exploration. Rotational measurements provide estimates of the spatial wavefield gradient at the free surface that allow carrying out analyses such as local slowness estimation and wavefield reconstruction. Furthermore, rotational motion measurements can help to resolve wavefield infidelity introduced by seismic instruments that are not well-coupled to the ground.

Gain enhancement of patch antenna integrated with metamaterial inspired superstrate

The paper investigates single band planar resonant antenna inspired by phi-shaped slotted metamaterial superstrate and a square patch antenna is used as a primary radiator. The antenna is modeled using finite difference time domain method and resonates at S band. The antenna comprises of single layer symmetrical metamaterial superstrate which is used to suppress surface waves based on μ-negative characteristics. The effective material parameters of the metamaterial structure are extracted from S-parameters using Nicholson–Ross–Weir method. The antenna achieves −28.64dB reflection coefficient of 2.4GHz and also maintains good radiation characteristics with a peak measured gain of 7.94dB at its operating frequency. Due to its advantages, the antenna can be used for modern wireless communications.

A Circularly Polarized Rectenna Array Based on Substrate Integrated Waveguide Structure With Harmonic Suppression

A compact circularly polarized rectenna with harmonic suppression for wireless power transmission at 5.8 GHz is proposed in this letter. The substrate integrated waveguide structure is adopted for enhanced gain, unidirectional patterns, and surface wave suppression. A rectifier, which consists of a matching network, a diode, and a dc-pass filter, is integrated with the antenna at the back side. The proposed rectenna is fabricated and measured. It features 6.9 dB gain, 0.67 dB axial ratio, and 30 dB return loss. The conversion efficiency is 65.87% with a 700 Ω load. A rectenna array is also built for an increased aperture. It shows 61.49% conversion efficiency with 650 Ω load in measurement. Both the rectenna and array are satisfactory choices for wireless power transfer usage.

Modeling and optimization of EBG structure using response surface methodology for antenna applications

Electromagnetic Bandgap (EBG) structures are widely used with microstrip antennas for improving antenna efficiency due to their ability to suppress surface waves. To have proper control of surface wave band-gap, it is necessary to have efficient models of the dispersion characteristics of EBG in the irreducible Brillouin zone. A new methodology for optimization of a modified mushroom EBG is presented, based on Response Surface Modeling (RSM) along with Design of Experiments (DoE). Four geometrical parameters which control the surface wave band gap namely the patch width (w), gap between the patches (2g), via radius(r) and the slot width(s) are considered as independent factors and DoE is carried out using Finite Element Analysis (FEA) simulation. The lower (F1) and upper (F2) frequencies of the band gap are extracted from the dispersion characteristics. Mathematical models for F1 and F2 are developed using non-linear regression analysis. Analysis of Variance (ANOVA) is used to study the effect of EBG parameters on the stop band frequencies. The optimum EBG parameters for a stop band in 5–8 GHz frequency range are determined and are found to be: patch width, 6.48 mm, gap, 0.49 mm, via radius, 0.25 mm and slot width, 0.48 mm. The statistical model is validated by experimental results.

Surface wave attenuation based polarization attributes in time-frequency domain for multicomponent seismic data

In the paper, we propose a surface wave suppression method in time-frequency domain based on the wavelet transform, considering the characteristic difference of polarization attributes, amplitude energy and apparent velocity between the effective signals and strong surface waves. First, we use the proposed method to obtain time–frequency spectra of seismic signals by using the wavelet transform and calculate the instantaneous polarizability at each point based on instantaneous polarization analysis. Then, we separate the surface wave area from the signal area based on the surface-wave apparent velocity and the average energy of the signal. Finally, we combine the polarizability, energy, and frequency characteristic to identify and suppress the signal noise. Model and field data are used to test the proposed filtering method.

Mutual Coupling Reduction of MIMO Antenna for Satellite Services and Radio Altimeter Applications

Ground irregularities also known as defected ground structures (DGS) is a freshly presented innovatory way in designing of patch antennas to boost up the performance of antenna constraints. This study presents a novel proposal of ground irregularities or defected ground structure is proposed for suppression of mutual coupling effects among 2x1 multiple input multiple output patch array designed on Roggers Duroid 5880. The two adjacent M shape structures surrounding Dumbbell Shaped structure and sandwiched between Dumbbell shape patterns showed the significant level of surface wave suppression up to -42dB while maintaining the gain of 4.7dB and 5.6dBi of directivity. The patch array operates at 4 to 4.3GHz for Fixed and Radio satellite services (FSS) and (RSS) and radio altimeter application systems.

Wideband and High-Gain Millimeter-Wave Antenna Based on FSS Fabry–Perot Cavity

A novel wideband and high-gain millimeter-wave antenna is presented. The wide 3 dB gain bandwidth is achieved by using Fabry–Perot cavity (FPC) and printed ridge-gap waveguide technologies. The FPC is formed by placing a dual-layer partially reflective surface (PRS) above a slot antenna operating at 60 GHz and fed by a printed ridge-gap waveguide for surface-wave suppression. The PRS is based on a 2-D printed unit cell, the unit cell composed of two different frequency-selective surfaces (FSS) provides a positive phase gradient over the desired frequency range. The impedance bandwidth of the proposed antenna is 18.4%, from 55.4 to 66.6 GHz. Moreover, the 3 dB gain bandwidth is 12.5%, from 58.6 to 66.4 GHz. A maximum gain of 16.8 dB is achieved; this is about 12.2 dB over the gain of the slot antenna only. Consistent radiation patterns are achieved over the operating bandwidth. Experimental and numerical results are presented to justify the improved antenna performance. This communication, to the best of our knowledge, is the first one to utilize a dual-layer printed FSS-based superstrate at 60 GHz to enhance the radiation characteristics of a printed ridge-gap waveguide-fed slot antenna.

Gain and side‐lobe improvement of W‐band microstrip array antenna with CSRR for radar applications

A new method for suppressing surface waves on a millimetre-wave microstrip array antenna is presented. A 10 × 2 patch array antenna is designed at 77 GHz for W-band radar applications. Complementary split ring resonator (CSRR) has been designed at 77 GHz, etched on the antenna ground plane. Simulation and experimental results are compared in terms of the gain and the side lobe level with and without CSRR. CSRR between series patch antenna array could suppress surface waves effectively so that this approach enhances the gain and reduces the side lobe level. The measured gain improvement in the antenna with CSRR is 2.5 dB. The side lobe level of the antenna with CSRR is reduced up to 3.5 dB lower than antenna without CSRR.

EBG Structures for Reduction of Mutual Coupling in Patch Antennas Arrays

An important issue in antenna array design is reduction of mutual coupling. In square microstrip antennas this reduction can be achieved by using electromagnetic band-gap (EBG) structures. They can help in the reduction of mutual coupling by using their capability of suppressing surface waves propagation in a given frequency range. In this paper, we analyze the isolation properties of different EBG structures are compare them in antennas arrays by simulations. A new configuration of a planar compact electromagnetic bandgap structure is investigated. Compared to the conventional EBG (mushroom structure), a size reduction of 67.2% is achieved. Simulation results show that a significant value of mutual coupling reduction, more than 6 dB, can be obtained by using the proposed structure.

Phase-shift- and phase-filtering-based surface-wave suppression method

Aliased surface waves are caused by large-space sampling intervals in threedimensional seismic exploration and most current surface-wave suppression methods fail to account for. Thus, we propose a surface-wave suppression method using phase-shift and phase-filtering, named the PSPF method, in which linear phase-shift is performed to solve the coupled problem of surface and reflected waves in the FKXKY domain and then used phase and FKXKY filtering to attenuate the surface-wave energy. Processing of model and field data suggest that the PSPF method can reduce the surface-wave energy while maintaining the low-frequency information of the reflected waves.