In this paper, an electronically switchable ultra-wideband (UWB)/dual-band bandpass filter using defected ground structures (DGSs) is proposed. The proposed filter consists of meandered inter-digital coupled line sections, stepped impedance open stubs, coupled lines, and rectangular DGSs to realize high performance in the operation band with a compact size of 12.5 mm × 10 mm. The proposed filter is designed on an RT/Teflon substrate (ε_r = 2.2, h = 0.7874 mm). The main advantage of the proposed filter is the reconfiguration of ultra-wide bandpass filter to dual-band bandpass filter. UWB has passband from 3.6 GHz to 10.6 GHz with upper wide stopband attenuation better than 20 dB up to 18 GHz. The dual passbands extend from 3.8 GHz to 5 GHz and from 9.5 GHz to 10.8 GHz. This filter is able to provide interference immunity from unwanted radio signals, such as wireless local area networks (WLAN), worldwide interoperability for microwave access (WIMAX) that cohabit within the UWB spectrum, and X (Military) band of satellite from 7 GHz to 8 GHz. The state of filter can be changed by using switching matrix equipment (mini circuit, replacement of PIN diodes). To validate the design theory, an electronically switchable UWB/dual-band bandpass filter using DGSs is designed, fabricated, and measured. Good agreement is found between simulated and measured results.

Convolutional Neural Network (CNN) models applied to synthetic aperture radar automatic target recognition (SAR ATR) universally focus on two important issues: overfitting caused by lack of sufficient training data and independent variations like worse estimates of the aspect angle etc. To this end, we developed a lightweight CNN-based method named SARNet to accomplish the classification task. Firstly, a clock-wise data amplification approach is presented to generate adequate SAR images without requiring many raw SAR images, effectively avoiding overfitting in the course of training. Then a SARNet is devised to process the extracted features from SAR target images and work on classification tasks with parameters fine-tuning under comparative models. To enhance and structurally organize the representation of learned proposed model, various activation functions are explored in this paper. Furthermore, due to the pioneering conducted experiments, training samples in the MSTAR and extended MSTAR database are utilized to demonstrate the robustness and effectiveness of the lightweight model. Experimental results have shown that our proposed model has achieved a 98.30% state-of-the-art accuracy.

In this paper, an antenna composed of an inverted L-shaped feeding strip and a shorting strip with three branches for LTE/WWAN mobile phones is presented. With the help of novel ground plane slots, the proposed antenna can realize miniaturization (34×15 mm²) and multiband to cover LTE/WWAN bands. The measured bandwidth (3:1 VSWR) of the proposed antenna is 156 MHz (810-966 MHz) at the low band and 1937 MHz (1548-3485 MHz) at the high band. Moreover, the lowest measured radiation efficiency of the fabricated antenna is more than 54% in the whole operation band. The proposed antenna has been successfully fabricated and measured, and there is a good agreement between simulated and measured results.

In this paper, a 60-GHz broadband 8-by-1 gap-coupled microstrip antenna array is presented and experimentally investigated. The proposed antenna array has been implemented using a Miniature Hybrid Microwave Integrated Circuits (MHMIC) fabrication process on a thin ceramic substrate with ε_r = 9.9, and h = 127 μm. For a comprehensive characterization and to accurately evaluate losses, as well as manufacturing tolerances, the proposed antenna array structure has been implemented using two different feeding techniques. The first one adopts a grounded broadband via-hole less transition from coplanar to microstrip line (GCPW-to-MS), while the second one has involved a broadband waveguide (WR12) to microstrip transition, based on a ridged waveguide concept. The obtained results have demonstrated that the proposed gap-coupled array configuration provides an improved bandwidth (4.56%) and an enhanced gain (11.8 dBi), while maintaining a lower side-lobe level (13.4 dB). These outstanding performances make the proposed WR12 gap-coupled array structure a potential candidate for the future emerging 60-GHz short-range point-to-point wireless communication systems.

This communication enlightens design, simulation, fabrication and testing of a novel compact CSRR etched ultra-wideband (UWB) patch Antenna with quadruple Band refusal characteristics. To design the antenna, the dimensions are chosen as 28x18x0.8 mm³. The design was done on FR4 substrate of 4.4 dielectric constant, 0.02 loss tangent. The planned antenna contains chamfered bevel slot rectangular radiating material with a complementary split ring resonator (CSRR) etched on one side and an incomplete ground plane on the other side of the substrate. To understand band rejection characteristics, four circular slots with different radii are etched on the radiating material as CSRR to reject bands at Worldwide Interoperability for Microwave Access (WiMAX) at 3.5 GHz, Indian national satellite (INSAT) at 4.6 GHz, wireless local area network (WLAN) services at 5.8 GHz, and Wideband Global SATCOM (WGS) at 8.2 GHz. The rejected bands center frequencies are perfectly coupled at particular slots with different radii. This compact antenna is effective and useful for short areas and can be easily incorporated in small devices. The results show that the antenna has a bandwidth from 2.77 GHz to 13 GHz. This antenna gains a worthy harmony between the simulated and measured results.

A distinct feature of GNSS-R land reflectometry is that random rough surfaces are superimposed on many levels of elevations. The rms elevations are in tens of meters which are many times larger than the microwave wavelengths at GNSS frequencies. Such multiple elevations were not considered in the coherent model nor the incoherent model. In this paper, we studied the electromagnetic scattering of this new rough surface scattering problem using Kirchhoff integral as first-principle. A numerical Kirchhoff simulator is developed to calculate the electromagnetic scattering and the power ratio in the specular direction. The integration is carried out over a footprint of 10 km by 10 km with the specular point as the center. In integration the surface discretization is as small as 2cm by 2 cm so that a total of 2.5×10¹¹ patches are used. Parallel computing is implemented requiring a moderate amount of computer resources. The results of the power ratio of the numerical Kirchhoff simulator differ from the results of both the coherent model and incoherent model. The results show that the phase of the first Fresnel zone is random, and the power contributed by the first Fresnel zone is a small fraction of that over the 10 km by 10 km. The power ratios of the numerical Kirchhoff simulations are much larger than that of the incoherent model and smaller than the coherent model for small RMS heights. The results show that the multiple elevations in land have large effects on GNSS-R specular reflections.

In this article, a new class of dual-/tri-band bandpass filters (BPFs) using a quintuple-mode resonator (QMR) is proposed. The classic odd-/even-mode analysis method is used to analyze the two filters due to their symmetrical structure. Owing to characteristics of the QMR, the dual-/tri-band BPFs based on the same topology are designed. The bandwidths (BWs) of the passbands are controllable. A dual-band BPF with center frequencies of 2.1 GHz/3.43 GHz and a tri-band BPF with center frequencies of 2.35 GHz/3.44 GHz/5.2 GHz are designed, fabricated, and measured. The fabricated filters are compact in size, and measured results are in good agreement with the simulated ones.

Building of compact plasmonic integrated circuits based on domino spoof plasmons (DSPs) is an important requirement and still a challenge. In this work, we report the first demonstration of two kinds of channel domino plasmonic circuitries, which consist of an easy-to-manufacture periodic chain of metallic box-shaped elements inside two finite metallic plates. We reveal that only the channel DSPs itself rather than the hybrid TE₁₀ and DSPs modes is supported in the part of the channel domino plasmonic waveguide with or without the metallic vias on both sides. Two channel domino plasmonic filters based on the efficient transition structures are designed, and the simulated S-parameters and near electric field distributions show excellent transmission performance in broadband. Utilizing the lateral insensitive property of these two channel DSPs, two kinds of broadband plasmonic power dividers/combiners are firstly implemented. Excellent transmission performance validates our optimizations and indicates that the proposed scheme can be easily extended to other bands. This work provides a new route for construction of deep-subwavelength DSP devices in application of high integration of microwave and terahertz circuits.

In this paper suppression of higher order modes of a microstrip antenna array is investigated. The array consists of two radiating elements which are fed by a corporate type microstrip feeding network. They array provides resonance at 5.2 GHz frequency for its fundamental mode (TM10 mode). Beside this fundamental mode, two harmonics at 10.4 GHz (1st harmonic) and 15.05 GHz (2nd harmonic) and few sub-harmonics at 7.8 GHz (TM12), 8.8 GHz (TM22), and 13.3 GHz (TM32) are excited. In order to suppress 1st harmonic, a pair of half wavelength open ended stubs (pair of stub-A) whereas for 2nd harmonic a pair of quarter wavelength open ended stubs (pair of stub-B) are employed. From the simulated results it is noticed that the 1st and 2nd harmonics are successfully suppressed, and the sub-harmonics are also suppressed. Prototypes of the antenna arrays are fabricated and measured. Measured results have good agreement with simulated ones.

We engineer very low aspect ratio Aluminum (Al) based periodic plasmonic nanostructures with period ≈ resonance wavelength for enhanced refractive index and thickness sensing, which offer to access complete ultraviolet-visible-near infrared spectral range for SPR sensors. Al-based periodic nanostructures on top of a thin homogeneous Al metal coated on a BK-7 glass substrate were designed by systematic variation of geometrical parameters using Rigorous Coupled Wave Analysis and finite elements full wave solver, while, taking into account applicable fabrication constraints. The reason of adding a thin layer of homogeneous Al metal between the nanostructure and glass substrate was to convert the signature of Surface Plasmons (SPs) from transmission dips to transmission peaks, using ±1st order diffraction mode. The shift in SP mode excited on the nanostructure-analyte interface was used to measure the variation in refractive index, and the number of waveguide modes with the increase in the thickness of the analyte was used to capture the variation in thickness of the analyte. The proposed nanostructures of period 400 nm and an aspect ratio of 0.1 offered a sensitivity of 400 nm/RIU and full width at half maximum of 18 nm resulting in a figure of merit of 22. These plasmonic nanostructures have potential to be used as refractive index and thickness sensor due to a high figure of merit, high localization of the field, and very low aspect ratio that is needed to maintain laminar flow of analyte.

In order to obtain a wideband sum-and-difference network, a novel ridged substrate integrated waveguide (RSIW) magic-T is designed. The proposed magic-T is composed of a five-layer RSIW structure. The signal input from the coaxial H-plane port is transmitted to RSIW through a stripline and split into two in-phase and equal signals at the output ports on the top and bottom layers because of the vertically symmetric structure. An E-plane SIW power divider is utilized to realize the E-plane input/output port of the magic-T. A remarkable bandwidth improvement is achieved due to the ridged structure and the wide bandwidth of a ladder-shape stripline optimized by genetic algorithm (GA). Measured results indicate that the magic-T has a fractional bandwidth (FBW) of 78.7% (6.4-14.7 GHz) with return loss better than 18.1 dB and great isolation characteristics.

Global Navigation Satellite System Reflectometry (GNSSR) can be used to derive information about the composition or the properties of ground surfaces, by analyzing signals emitted by GNSS satellites and reflected from the ground. If the received power is measured with linearly polarized antennas, under the condition of smooth surface, the reflected signal is proportional to the modulus of the perpendicular and parallel polarization Fresnel coefficients, which depend on the incidence angle θ, and on the dielectric constant ε of the soil. In general, ε is a complex number; for non-dispersive soils, the imaginary part of ε can be neglected, and a real value of ε is sought. We solve the real-valued problem explicitly giving formulas that can be used to determine the dielectric constant ε and we compare the analytical solution with experimental data in the case of sand soil.

A novel null steering method in a multi-mode circular microstrip patch antenna is presented in this letter. A stacked patch configuration, capable of exciting three different radiating modes, namely TM₁₁, TM₂₁, and TM₃₁, is investigated. When two or three modes are excited simultaneously, up to three nulls can be formed in the upper hemisphere, and by tuning the amplitude ratio of these modes, a continuous null steering pattern is realized. It is shown that a full hemispherical null steering of ±90° range can be achieved using the proposed method. The null steering capability with different dielectric permittivities is also presented.

By etching a half-wavelength hook-shaped slot on the ground and adding quarter-wavelength rectangle-shaped strips in the patch, a novel triple band-notched ultra-wideband (UWB) antenna is proposed. The triple band-notches are used to prevent interferences from existing bands at 3.3-3.9 GHz, 5.15-5.35 GHz, and 5.725-5.825 GHz. Fed by coplanar waveguide, the antenna is printed on a 30*30 mm² substrate. The parameters affecting antenna performance are simulated and analyzed. The simulated and measured results show that the proposed antenna achieves a wide bandwidth from 3 GHz to 11 GHz with triple band-notches. Radiation patterns and gain are also investigated and analyzed.

A compact slot-coupled endfire radiation antenna based on a tapering spoof surface plasmon polaritons (SSPPs) structure with high efficiency is proposed in this paper. A narrow slot balun is designed to feed the SSPPs structure rather than to work as the primary radiator. Simulated results show that the odd SPP mode is successfully excited on the tapering SSPPs structure, which contributes to the endfire radiation. Due to the high confinement of SSPPs, the proposed antenna shows low RCS within the frequency band of 1.5 GHz-4 GHz and 5.6 GHz-8 GHz. A prototype is fabricated and tested. Simulated and measured results show good agreement that the proposed antenna can provide stable endfire radiation patterns within the frequency band of 2 GHz-3.4 GHz. The maximum gain reaches 8 dBi, and the average efficiency over this bandwidth is 80%. The high-efficiency endfire SSPPs antenna with balanced broad band and high gain has a promising application in communication systems and integrated circuits.

A novel beam scanning microstrip leaky wave antenna based on liquid crystal material is proposed in this paper. Based on the dielectric anisotropy of the liquid crystal, the main beam angle of the antenna pattern can be easily adjusted with the changing of external bias voltages. Good agreement between simulated and measured results is found for the presented leaky wave antenna. Both the simulation and test frequencies of the antenna are set at 12 GHz. Besides, the measured data show that when the dielectric constant of the liquid crystal changes from 2.4 to 2.52, about 10 degrees tuning range of the main beam angle is achieved.

In this letter, a methodology for the generation of received irradiance/power time series for a GEO downlink concentrated on small aperture receiver terminals is reported. The synthesizer takes into account the atmospheric phenomena that degrade the propagation of the optical signal and especially the turbulence effects. For modeling the scintillation effects, Kolmogorov spectrum is assumed, and the Rytov's approximation under weak turbulence is also used. The time series are generated using the theory of stochastic differential equations. Finally, the proposed synthesizer is compared in terms of first order statistics with experimental data from the ARTEMIS GEO optical satellite link campaign with very good agreement.

A compact multiple-input-multiple-output (MIMO) antenna with very high isolation is proposed for ultrawideband (UWB) applications. The antenna with a compact size of 30.1×20.5 mm² (0.31λ₀×0.λ₀) consists of two planar-monopole antenna elements. It is found that isolation of more than 25 dB can be achieved between two parallel monopole antenna elements. For the low frequency isolation, an efficient technique of bending the feed-line and applying a new protruded ground is introduced. To increase isolation, a design based on suppressing surface wave, near-field, and far-field coupling is applied. The simulation and measurement results of the proposed antenna with the good agreement are presented and show a bandwidth with S₁₁ ≤ -10 dB, S₁₂ ≤ -25 dB ranged from 3.1 to 10.6 GHz making the proposed antenna a good candidate for UWB MIMO systems.

In this paper, we present our experimental study of the effect of the external DC magnetic bias field on the nonlinear properties of meta-atom loaded with ferrite elements of different shapes. It is demonstrated experimentally that the adjustment of the resonance frequency of the meta-atom loaded with the ferrite elements of different shapes is possible not only by the input microwave power but also by the external DC magnetic bias field. It is shown that as the external DC magnetic bias field is increased to a certain value, the resonance curve of the nonlinear meta-atom demonstrates bistability. In addition, we achieve significant enhancement of the meta-atom nonlinearity using the nonlinear properties of both ferrite and varactor diode.

This paper presents a quickly converging optimization technique for synthesis of filters with constant and frequency-variant couplings (FVC). Unlike the works so far appeared in the literature, the proposed technique is not based on the direct optimization of scattering parameters with assigned topology, but it consists of two procedures. Firstly, an FVC coupling matrix with assigned topology is suitably transformed by means of scaling and rotations for obtaining the new coupling matrix with constant couplings. Then, the cost function is constructed as a least squares problem involving both the eigenvalues of the new coupling matrix with constant couplings and that of the transversal coupling matrix. The solution is found via the solvopt optimization method. Two numerical examples with different topologies and specifications are synthesized to show the validation of the method presented in this paper.