This paper describes the radio propagation measurement campaign in the sugarcane field representing a tall food grass characteristic which is one of the common types in outdoor agriculture environments. The measurement was conducted by using a channel sounder having a bandwidth of 45.6 MHz at 2.45 GHz with the aim at investigating the propagation channel characteristics which are useful in deploying of wireless sensor networks in the precision agriculture. By analogy to Ikegami model, the variation of path loss over the relative angles between the plant rows and the line-of-sight direction from the transmitter to the receiver is identified. Utilizing this knowledge, this work justifies the procedure of predicting the path loss at any point in the field by a few measurement efforts. Furthermore, the Rician K-factor and RMS delay spread are investigated in the vegetation depth shorter than 40 m. The result shows that the relationship between the Rician K-factor and its corresponding path loss value in each measurement point can be fitted with the log-linear line. This leads to the possibility of predicting K-factor at any points in the field. In addition, since the result of RMS delay spread is independent to the vegetation depth and the density of the plant, it is represented by the statistical model in which the Weibull distribution provides the best representation.

This paper presents single and dual notch ultra-wideband bandpass filters (UWB BPFs) to mitigate interference with coexisting wireless communication systems in ultra-wideband (UWB). The single and dual notch UWB BPF is developed by using signal interaction concept loaded with stub loaded resonator. The stub loaded resonator creates notches in the passband to avoid the interference with coexisting wireless communication systems. The notch frequency can be placed at the points of interest within passband by selecting a proper length of stub loaded resonator. Transmission zeros are introduced to enhance the selectivity of stopband. It presents UWB BPF with single notch at the frequency of 6.5 GHz and dual notch at the frequencies of 6.3 GHz and 8.0 GHz. The circuit size of proposed filters is 6 mm x 6 mm and 6 mm x 6 mm. The proposed filters exhibit good performance in terms of compact size, good fractional bandwidth and sharp selectivity. All the filters are simulated and fabricated on a Rogers R03010 substrate with relative permittivity of 10.2 and thickness of 1.28 mm. There is good agreement between simulated and measured results.

Ferrite toroids (or clamps) are widely used to reduce common-mode (CM) currents in power systems. The CM impedance of the ferrite depends on the frequency-dispersive permeability and permittivity of the ferrite, the geometry of the system, and the location of the ferrite in it. An analytical model was developed to predict the CM impedance of a wire harness above a return plane with a ferrite on it. The model is based on transmission line theory for a cable, a ferrite, and a return plane. The parameters of the model are calculated using a frequency-dependent quasistatic model for a ferrite toroid. This model accurately predicts the CM impedance of a mock harness within 3 dB up to 1 GHz. The proposed model is also applied to a real power system consisting of an inverter and a motor. Knowledge of the CM impedance of the system in the operating regime is critical to determining the impact of the ferrite on CM currents. The CM impedance is determined using the dual current clamp technique. The impact of the ferrite on the CM impedance and currents of the power inverter system was predicted within 3 dB, demonstrating the usefulness of the modelling approach for analysis of power systems.

Metasheets are ultra-thin sheets built from sub-wavelength resonators designed in order to achieve certain frequency-dependent transmission behaviour. A semi-analytical approach based on an equivalent circuit representation is proposed to calculate the microwave transmission through metasheets which consist of 2D periodic arrays of planar circular metal rings with and without substrate. The electromagnetic response of the metasheet can be controlled by changing the radius and periodicity of the circular rings. In the semi-analytical approach, the equations for impedances of the equivalent circuit are parameterized and fitted to match the values of transmission coefficients obtained by full-wave simulations at selected frequency points. Such an approach permits an optimization of the metasheet design with a very small number of full-wave numerical simulations. It is shown that the results of the semi-analytical approach match well with full-wave simulations and measurements within a reasonable range of radius and periodicity values.

The boundary element method is considered for solving scattering problems and is accelerated using the hierarchical matrix format. Thus, some matrix blocks chosen by geometrical criteria are approximated by low-rank matrices using a robust compression method. In this paper, we validate the use of the hybrid cross approximation which is quite new in this area, and we apply it to several examples. The validation is done on a conducting sphere, as well as less canonical objects such as the scattering by a rough (Weierstrass) surface or a plane.

In this paper, a novel HMSIW slot antenna combines a significant bandwidth enhancement and small footprint for inter-satellite communications at C-band. The designed antenna has the capability of achieving a reduction of size with nearly 50% in comparison to conventional SIWs. The results show that the proposed antenna has a bandwidth of 4%, an average gain of 5.8 dB, and the radiation efficiency of η = 93% at 5 GHz.

A polarization matched 2×2 radiating array for electronically steered phased array antenna is presented. The antenna array is a multi-layer structure consisting of four square microstrip patch elements grown on each substrate to provide wide band operation at S-band. Dual polarizations of radiated wave from the antenna array have been achieved by feeding the array in series fed mode through horizontal and vertical ports. Designed 2×2 S-band dual polarized series fed antenna has been optimized on finite element based ANSYS HFSS full wave solver. Controlling the amplitude of RF signal at input ports, the polarization can be matched to the target antenna polarization, hence antenna can work as polarization matched antenna. Gain of the developed antenna is 13 dBi, and the return loss is better than 10 dB over the frequency range of 2.3 to 2.5 GHz. This antenna can be used as radiating array for electronically steered phased array for S-band SOTM (SATCOM On The Move) application where the polarization of the antenna changes with movement of host platform.

A novel compact ultra-wideband (UWB) multiple input multiple output (MIMO) slot antenna with band notch characteristics is presented for portable wireless UWB applications. The antenna comprises co-planar waveguide feed (CPW) and two radiating monopoles oriented in orthogonal orientation for providing orthogonal radiation patterns. A Minkowski fractal parasitic stub along with a Minkowski fractal grounded stub has been placed at 45° between the monopoles to reduce the coupling between them which in turn establish high isolation between the radiators. An excellent band notch characteristic is obtained at 5.5 GHz by etching a modified E-shaped compact slot on the radiators. At the centre of notched band, the efficiency and gain of the antenna drop significantly which indicates a good interference suppression. Results show that the designed antenna meets -10 dB impedance bandwidth and -17 dB isolation throughout the entire operating band (3.1-12 GHz). Novelty of this design lies in improving isolation using compact fractal structures which occupy less space than conventional isolation mechanisms in MIMO structures. The simulated and measured results show that the proposed antenna is convenient for MIMO diversity systems.

High-order fractal characteristics of low-resolution radar echoes provide a supplementary description of the dynamic characteristics of the echo structure of a target, which provides a new way for the classification and recognition of targets with low-resolution radars. On basis of introducing the definition of high-order fractal statistic-lacunarity as well as its calculation method and the lacunarity characteristics of a target echo under additive fractal clutter background, this paper analyzes the characteristics of the lancunarity parameter variation of target echoes from a surveillance radar at a VHF band, and puts forward a classification method for aircraft based on the feature of the echo lacunarity scale change rate from the viewpoint of pattern recognition. The target classification experiments using real recorded echo data show that, as a high-order fractal characteristic parameter, the lacunarity scale change rate can be used as an effective feature for aircraft target classification and recognition, and the proposed method has good classification performance.

A concept of an experimental simulator for studying longitudinal magnetic waves in dielectric samples and its electrodynamic justification are presented. The simulator is intended to control impact power and frequencies of wave processes. The simulator is realized as a two-channel junction consisting of perpendicularly crossed infinite rectangular waveguides with slot coupling. The simulation process is based on cyclic mechanical displacements of dielectric samples along the longitudinal axis of the waveguide in a quasistationary magnetic field localized in the slot region.

A compact multiple input multiple output (MIMO) antenna with WLAN band-notch filtering function for portable wireless ultra-wideband (UWB) systems is proposed in this paper. The overall size of the antenna is 26 x 40 x 0.8 mm³, and it is fabricated on a low-cost FR4 substrate. The antenna comprises two identical planar monopole antenna elements, namely PM1 and PM2, which are fed by a 50-ohm coplanar waveguide. The PM1 and PM2 are positioned perpendicular to each other to minimize the mutual coupling between them. To further reduce the mutual coupling and to increase the impedance bandwidth, a long rectangular strip is protruded from the ground plane between the PM1 and PM2. To create the band-notch characteristics at WLAN band from 5 to 5.9 GHz, an inverted U-shaped slot is etched on the feed line. The simulated and measured results show that the proposed antenna achieves good impedance bandwidth (S₁₁ ≤ -10 dB) from 2.2 to 11.4 GHz and mutual coupling (S₂₁) of < -20 dB. The measured peak gain of 2.4 to 7.5 dBi and radiation efficiency above 90% are obtained except at notch band. The measured envelope correlation coefficient (ECC) of 0.008 in the whole operating band and omnidirectional radiation characteristics demonstrate that the proposed MIMO antenna is a suitable candidate for portable UWB systems.

Compressed sensing (CS) relies on the sparse priorin posed on the signal to solve the ill-posed recovery problem in an under-determined linear system (ULS). Motivated by the theory, this paper proposes a new algorithm called regularized re-weighted inverse trigonometric smoothed function approximating L₀-norm minimization (RRITSL0) algorithm, where the inverse trigonometric (IT) function, iteratively re-weighted scheme and regularization mechanism constitute the core of the proposed RRITSL0 algorithm. Compared with other state-of-the-art functions, our proposed IT function cluster can better approximate the L₀-norm, thus improving the reconstruction accuracy. And the new re-weighted scheme we adopted can promote sparsity and speed up convergence. Moreover, the regularization mechanism makes the RRITSL0 algorithm more robust against noise. The performance of the proposed algorithm is verified via numerical experiments with additive noise. Furthermore, the experiments prove the superiority of the RRITSL0 algorithm in magnetic resonance (MR) image recovery.

Compact antenna test range (CATR) is one of the most commonly used antenna measurement techniques, particularly in the microwave/millimetre wave range. A conventional industry standard for the quiet zone of a CATR is ±0.5 dB amplitude variation and ±5º phase variation to conduct measurement with acceptable accuracy. Such a high standard, however, has not been rigorously verified in theory. And it is in contrast to 22.5º phase variation condition for the far-field method. Being inspired by many measurements, where the quiet zone is not up to the industry standard while satisfactory results are still obtained, this paper systematically investigates the effect of quiet zone performance on the radiation pattern measurement. It aims at searching for a guideline specifications for the construction of a CATR. Theoretical models have been built to predict the quiet zone performance on the antenna pattern measurement, particularly on the main beam. Many factors have been considered, such as amplitude and phase ripple, amplitude/phase taper, and electrical size. In coupling with experimental study, it is shown that a much more relaxed condition can be followed depending on the required measurement accuracy.

In indoor scenario, radar echoes are interfered by clutter from walls, ceilings, floors, and other indoor objects. Therefore, clutter suppressing is one of the key problems for indoor radar. This paper focuses on the problem of clutter suppressing for a secondary radar system which can be used in indoor localization. A clutter suppressing method based on orthogonal polarization character is presented. The orthogonal polarization character here is achieved by a designed transceiver, which can transpond electromagnetic waves in vertical polarization if and only if the received signal is in horizontal polarization. Thus the newly introduced polarization character can be used to discriminate target from clutter. Clutter is suppressed after calculating scattering similarity parameters via Pauli decomposition. Simulations and an experiment are conducted to demonstrate the proposed method. Compared with previous methods, the proposed method can distinguish stationary target with both static and varying clutters. Therefore, it is more practical for applications.

Existence of symmetric complex waves in a dielectric rod (DR) - a dielectric waveguide of circular cross section - is proved by analyzing functional properties of the dispersion equations (DEs) using the theory of functions of several complex variables and validating the existence of complex roots of DE. A closed-form iteration procedure for calculating the roots in the complex domain supplied with efficient choice of initial approximation is proposed. Numerical modeling is performed with the help of a parameter-differentiation method applied to the analytical and numerical solution of DEs.

Traditional long vector-based MUSIC methods require 4D spectral search, which suffers from heavy computational complexity. This paper develops a joint DOA and polarization estimation method named as dimensionality reduction MUSIC (DR-MUSIC) method for a passive radar direction finding (PRDRF) system using spatially separated single-component circular electromagnetic vector sensor array (SSSC-EVSA), where 4D spectral search is transformed into 2D spectral search by exploiting rank deficiency of the signal component of cost function. Polarization parameters are estimated via the generalized eigenvector of matrix pencil, which can be utilized for the recognition of radar and decoy. In addition, the estimation performance of the proposed DR-MUSIC method is also studied considering the phase inconsistency among multi-channels. Simulation results demonstrate the effectiveness of the DR-MUSIC method.

Angular log-periodic meander line (ALPML) traveling wave tube (TWT) is one kind of low voltage miniature TWT. In order to decrease high frequency loss, avoid charge accumulation and enhance coupling impedance, the conformal microstrip ALPML TWT based on silicon substrate is proposed in this paper, which means that the projections of silicon supporting structure and metallic microstrip meander line are same in the top view. The microfabrication technology DRIE can be used to fabricate this structure. Compared with the conventional microstrip ALPML TWT, the coupling impedance of conformal microstrip ALPML TWT increases 50%. The particle-in-cell (PIC) simulation results reveal that the output power of conformal microstrip ALPML TWT can reach 220 W at 35 GHz, while the efficiency is 20%. The 3-dB bandwidth reaches 14 GHz in the frequency range between 28 GHz and 41 GHz when the operating voltage and radial sheet beam current are 3600 V and 0.3 A, respectively.

We report on the experimental verification of the employment of equivalent parameters in a 2D finite element model to describe absorptivity of curve-shaped, large-scale metamaterial structures. Equivalent homogeneous optical parameters were retrieved from experimental measurements of flat metamaterial sheets with square resonators of 8 and 9 mm and used in a 2D FE model to obtain the absorptivity of curved structures with similar metamaterial unit cells. The curved structures were experimentally characterized and showed good agreement with the model. The tremendous simplification made possible by simulating complex structures as homogeneous materials makes the method very attractive for designing large-scale electromagnetic shields and absorbers.

The design of a low cost, short range radar sensor based upon a novel phase coded linear frequency waveform is discussed in this paper. The radar sensor utilizes a novel waveform that is produced using digital frequency synthesis techniques. Digital frequency synthesis techniques enable the generation of repeatable, highly linear frequency sweeps and provide a means for accurate application of phase codes to linear frequency modulations. The work presented contains analysis of the component linear frequency and phase code modulations that form the compound phase coded linear frequency modulation. The resulting compound phase coded linear frequency modulation is compared with the component modulations to demonstrate the performance improvement that can be achieved by the combining of radar waveform modulations enabled by modern digital frequency synthesis techniques. The compound phase coded linear frequency modulation waveform shows improved range resolution and suppression of range sidelobes over the individual component waveforms. The phase coded linear frequency modulation shows an improvement of 13 dB over the linear frequency modulation and is only 2 dB less than the phase code. It also achieves a 5 and 10 nanosecond narrower mainlobe autocorrelation peak than the phase code and linear frequency modulation, respectively. A notional signal processing architecture of the waveform is simulated to demonstrate the ability to process the compound waveform. Experimental data collected from a direct digital frequency synthesis based arbitrary waveform generator is compared with the simulated waveform. The compound waveform model and the experimental results show good agreement.

An airborne phased-multiple-input-multiple-output (Phased-MIMO) radar with collocated antenna array is a tradeoff of phased array radar and MIMO radar. Its transmitting array is divided into multiple subarrays that are allowed to be overlapped. In this letter, we mainly study the array partitioning scheme of the airborne Phased-MIMO radar with equal uniform linear subarrays that are fully overlapped on the basis of space-time adaptive processing (STAP). A mathematical formula is derived to determine the number of subarrays and the elements in each subarray according to the principle of maximum STAP signal-to-interference-plus-noise ratio (SINR). The SINR performances corresponding to different partitioning schemes are simulated and discussed to demonstrate the effectiveness of the proposed mathematical formula for array partitioning in the sense of maximum STAP SINR.