This paper presents a numerical study of microwave scattering and emission from a foam-covered ocean surface. The foam layer is modeled as an inhomogeneous layer with randomly rough air-foam and foam-seawater boundaries. Kelvin's Tetrakaidecahedron structure is selected as the skeleton for simulating the air bubbles in the foam layer. The electromagnetic characteristics of the foam layer, including absorption and scattering coefficients for both vertical and horizontal polarizations, are calculated using a multilevel volume UV fast algorithm to accelerate the numerical computation of three dimensional Maxwell's equations. The surface scattering at air-foam and foam-seawater interfaces is determined using the integral equation model (IEM). The microwave emission from the foam-covered ocean surface, which accounts for multiple incoherent interactions within the foam layer and between the foam and interfaces, is modeled using the vector radiative transfer approach and numerically solved using the matrix doubling method. The model analyses of volume scattering and absorption of the foam layer reveal that the volume scattering coefficient of a foam layer increases with increasing water fraction at all selected frequencies, and its polarization dependence is negligible at a water fraction less than 2%. At 10.8 GHz and 18 GHz, the H-polarized scattering coe±cient is smaller than the V-polarized scattering coefficient for a larger water fraction; the opposite occurs at 36.5 GHz, at which V polarized scattering is weaker compared to H-polarized scattering. The model analyses of emission from a foam-covered ocean surface reveal that the emissivities at all selected operating frequencies have similar dependencies with water fraction and frequency, and they exhibit different sensitivities to water fractions. Moreover, the emissivities at high operating frequencies exhibit higher sensitivities to water fractions than the lower ones.

Based on the complex analysis of the Lossy Transmission Line Theory, which involves the result of a Generalized Smith Chart, a new version of the last one arises when trying to characterize the wave impedance along the Transmission Line by means of analytical complex functions. Among these functions, the complex logarithm of the reflection coefficient leads to the logarithmic-reflexion coefficient-plane and its parameterized version, the Logarithmic Generalized Smith Chart. This plane is specially useful for characterizing the Transmission Line along its extension. To validate these results, some examples will be presented providing physical interpretations to the behaviour of a lossy TL and pointing out some practical applications.

In this paper a method for a fast synthesis of planar, maximally thinned and steerable arrays is proposed and tested on several benchmarks available in literature. The method optimizes simultaneously the weight coefficients and sensor positions of a planar array without using global optimization schemes, properly exploiting convex optimization based algorithms. The resulting arrays are able to radiate a steerable beam pattern, satisfying a prescribed power mask and avoid to constraint the fitting of any a priori assigned reference field pattern. Although such a method takes into account the general case of sparse arrays, this letter is focused on the case of thinned arrays as a special case of sparse ones, since the initial grid to thin on has only half-wavelength distances. Such a feature allows a faster synthesis than in the general case of sparse arrays.

The modulational instability of a lower hybrid wave is investigated in a dusty plasma slab by developing a non-local theory of this four wave parametric interaction process. The immersed dust grains modify the dispersion relation and growth rate expression of low frequency unstable mode. A numerical analysis shows that the frequencies and growth rate of unstable mode is higher in dusty plasma than that in without dust grains. The growth rate of the unstable mode is proportional to pump amplitude and has strong dependence on pump frequency.

Digital manufacturing, or 3D printing, is a rapidly emerging technology that enables novel designs that incorporate complex geometries and even multiple materials. In electromagnetics and circuits, 3D printing allows the dielectrics to take on new and profound functionality. This paper introduces negative uniaxial metamaterials (NUMs) which are birefringent structures that can be used to manipulate electromagnetic fields at a very small scale. The NUMs presented here are composed of alternating layers of two different dielectrics. The physics of the NUMs are explained and simple analytical equations for the effective dielectric tensor are derived. Using these equations, the NUMs are optimized for strength of anisotropy and for space stretching derived from transformation optics. The analytical equations are validated through rigorous simulations and by laboratory measurements. Three NUMs where manufactured using 3D printing where each exhibited anisotropy in a different orientation for measurement purposes. All of the data from the analytical equations, simulations, and experiments are in excellent agreement confirming that the physics of the NUMs is well understood and that NUMs can be designed quickly and easily using just the analytical equations.

In this paper, radio wave propagation over irregular terrain is investigated in 200-600 MHz (VHF/UHF band). Measured results are compared with different path loss models such as Fresnel knife edge diffraction and uniform theory of diffraction (UTD). It is shown that, for low antenna heights, using a combination of the two-ray path loss model and knife-edge diffraction, great improvement in path loss prediction accuracy is achieved. The derived model is aimed to effectively predict path loss for near-ground and short-range communication applications.

A novel design for radar cross section (RCS) reduction of a bilateral Vivaldi antenna is presented. The method for RCS reduction is based on the wave-guiding characteristic of the substrate integrated waveguide (SIW) structure, which guides the incident energy to the lateral side of antenna plane. The bistatic RCS is controlled under the premise of reducing the monostatic RCS. Compared with the reference antenna, a significant monostatic RCS reduction is achieved over a wide frequency band ranging from 5 GHz to 12 GHz, and a remarkable monostatic RCS reduction at 7 GHz is as much as 34.73 dB without obvious radiation performance degradation. To verify the proposed strategy, prototypes of the reference and proposed antennas have been fabricated and measured. Good agreements between the simulated and measured results demonstrate that the proposed method preserves the radiation performances well and achieves an outstanding wideband RCS reduction.

DBS (Doppler Beam Sharpening) imaging for scene matching terminal guidance is investigated. An echo simulation method for DBS of missile-borne radar that considers environmental factors is presented. The transmission signals of missile-borne radar are studied first. Next, the method for the modeling of the echo signals is discussed with consideration of environmental influences including the objects on the ground, radome and the seasonal variations, especially undulation of the ground. The status of the surface of the earth as well as internal elements of the radar will influence the precision of the height measurement, thereby indirectly influencing the image matching. Undulating terrain can also cause changes in the electromagnetic characteristics that lie in the translation of image points; in addition, there is a close relationship between the position offset and the altitude of the image area. The operation flow of DBS is provided together with the method of generating reference images. Finally, an optical image of an airport and the simulation results using echoes are presented for validation.

A novel broadband circularly polarized planar monopole antenna fed by coplanar waveguide (CPW) is proposed and fabricated. The proposed antenna consists of a rectangular monopole, an inverted-L strip and an asymmetric ground plane with cutting a horizontal slit on the right ground plane. Firstly, a narrow circularly polarized (CP) radiation at the upper band can be achieved by utilizing the asymmetric ground plane. Then, an inverted-L strip is introduced to obtain broadband CP characteristic matched with wide impedance bandwidth. The measured results demonstrate that a 10-dB bandwidth of 58.8% from 4.8 to 8.8 GHz and a 3-dB axial-ratio bandwidth (ARBW) of 47.8% from 5.375 to 8.75 GHz can be achieved which can completely cover the WLAN (5.725-5.85 GHz) band. Additionally, a 10-dB impedance bandwidth of 24% (3.3-4.2 GHz) with linear polarization is also obtained which can completely cover the WiMAX (3.3-3.7 GHz) bands. In additional, to explain the mechanism of dual-band CP operation, the analysis of magnetic fields distributions and a parametric study of the design are given. Compared to other recent works, a simpler structure, wider axial ratio and impedance bandwidths and a more compact size are the key features of the proposed antenna.

In this article, a pair of T-shaped stepped-impedance-stubs plays a key role in the structure of a Wilkinson power divider. In the first step, to find a general relation between electrical lengths and characteristic impedances of the mentioned stubs and consequently how the operating frequency can be chosen, an equation based on a mathematical analysis is obtained. Then, by using this equation several miniaturized Wilkinson power dividers with the same configurations at different operating frequencies and capable of suppressing spurious frequencies are designed. Moreover, in each of these circuits 2nd to 16th unwanted frequencies are suppressed. The simulation results of the designed dividers are in good agreement with the expected responses predicted by the obtained equation. To validate the proposed method, a Wilkinson power divider at 0.85 GHz as a sample is fabricated, and 77.83% size reduction is obtained. Furthermore, the fabricated divider suppresses 3rd to 21st harmonics better than -20 dB.

The performance of a Concentric Circular Antenna Array (CCAA) with robust techniques is presented in this paper. A CCAA geometry is chosen because of its symmetrical configuration which enables the phased array antenna to scan azimuthally with minimal changes in its beam width and side-lobe levels. The performance of CCAA system is degraded, if there is any disparity occur between the original signal direction and the steering direction of the beamformer. This performance degradation problem due to look direction disparity can be improved by using robust techniques. This paper proposes a technique, named variable diagonal loading (VDL) technique for CCAA system and compare the performance of the proposed robust CCAA processor with existing CCAA processors. The proposed robust CCAA beamformer enhanced the output power 28.9 dB, 9.34 dB and 1.63 dB at 10 disparity angle compared to the CCAA standard capon beamformer (SCB), robust SCB and existing novel loading technique. Numerical examples are presented to analyze the performance of the proposed robust beamformer in different scenarios.

A novel Yagi-Uda-like transmitarray is proposed for circularly polarized (CP) operation. The element consists of multiple strips stacked in parallel for achieving broad transmission phase range. By employing the design concept for the Yagi-Uda director, the transmitarray elements are made to provide the functions of phase shifter and director simultaneously. By introducing rotational offset into the stacking strips, the element is found to be able to generate circular polarization. To demonstrate the working principle, an 8-layer unit element is simulated using the Floquet method to provide a transmission phase range of 412˚. The proposed 5×5 full-fledged CP transmitarray is able to produce an antenna gain of 16.2 dBi, a -1-dB bandwidth of 4%, an axial-ratio bandwidth of 7%, and an aperture efficiency of 40.4%. A simple curve-fitted design equation is also given.

A S-band monolithic integrated switched filter bank has been designed to realize tunable working center frequency, and a tuning range of 12.9% from 2.7 to 3.05 GHz was achieved with interval of 50 MHz. The switched filter bank is designed using 8 eighth-order step impedance resonators (SIR) band-pass filters arranged in parallel rows. Microelectromechanical Systems (MEMS) switched circuit is integrated above filters for monolithic design combined with low temperature co-fired ceramic (LTCC) technology. The SIR bandpass filters are designed to resist Electromagnetic Interference(EMI) between components and introduce cross coupling to bring two transmission zeros and better out-of-band rejection. The monolithic integrated switched filter bank is only 74 mm×24 mm×2.5 mm, which realizes the monolithic integration of the device and enhances the reliability. The measured results show that the insertion loss and out-of-band rejection are in good working condition.

Results are presented for the transverse deflection of an electron beam by a long, straight wire carrying direct current. The experimental deflections are compared with three calculation methods based on the Lorentz force law (field theory) and both the Weber (direct action) and Ritz (emission) force formulae. The Lorentz force calculation is the conventional approach expressed in terms of electric and magnetic field components. By contrast the force formulae of Weber and Ritz do not contain any field vectors relating to E or B. The Weber force is based on direct action whereas the Ritz force expression is based on an emission/ballistic principle and is formulated in terms of a dimensionless constant, λ. The experimental beam deflections are for low speed (non-relativistic) electrons. Good agreement between experiment and theory is demonstrated for each approach. In fact, for the case of an infinitely long wire, all three calculation methods give identical results. Finally, the three approaches are contrasted when applied to the case of high speed electrons.

Microwave engineering of high average-power (hundreds of kilowatts) devices often involves a transition from a waveguide to a device, typically a resonant cavity. This is a basic operation, which finds use in various application areas of significance to science and industry. At relatively low frequencies, L-band and below, it is convenient, sometimes essential, to couple the power between the waveguide and the cavity through a coaxial antenna, forming a power coupler. Power flow to the cavity in the fundamental mode leads to a Fundamental Power Coupler (FPC). High-order mode power generated in the cavity by a particle beam leads to a high-order mode power damper. Coupling a cryogenic device, such as a superconducting cavity to a room temperature power source (or damp) leads to additional constraints and challenges. We propose a new approach to this problem, wherein the coax line element is operated in a TE₁₁ mode rather than the conventional TEM mode. We will show that this method leads to a significant increase in the power handling capability of the coupler as well as a few other advantages. We describe the mode converter from the waveguide to the TE₁₁ coax line, outline the characteristics and performance limits of the coupler and provide a detailed worked out example in the challenging area of coupling to a superconducting accelerator cavity.

In this paper, a novel bandwidth-enhanced ultra-wideband (UWB) tapered slot antenna, with Y-shaped corrugated edges, is proposed. In the double-slot structure, the two slots are separated by a V-shaped metal surface with straight edges, which is beneficial for improving the directivity of the antenna. Meanwhile, an exponential Y-shaped corrugated edge is designed. This novel corrugated edge not only can improve the impedance bandwidth of the antenna by extending the path of the current, but also can enhance the directivity by concentrating the energy near the tapered slot. The proposed antenna provides 167% fractional bandwidth from 2.5 GHz to 28 GHz. The gain of the antenna is more than 10 dB from 3.5 GHz to 25 GHz and more than 8 dB in the whole operating band.

In order to improve the performance of antenna array beamforming, a semi-virtual antenna array beamforming method is proposed based on covariance matrix expansion. The sample covariance matrix is expanded, and virtual array elements are formed. The performance of the semi-virtual antenna array beamforming method is as good as the virtual antenna array beamforming methods, which are better than the conventional adaptive beamforming methods. In addition, the computational complexity of the semi-virtual antenna array beamforming method, which is greatly reduced compared with the virtual antenna array beamforming methods, is equal to that of the conventional adaptive beamforming methods. The fast calculation method of the optimal weight vector of the semi-virtual antenna array beamforming method is given in this paper. The validity and applicability of the proposed method is verified by simulation results.

This paper proposes the concept of sparse appended with the space tapering technique for the synthesis of an antenna radiation pattern. The procedure experiments on a Circular Antenna Array (CAA) configuration comprising of directional element (1+cos(φ)). The sparse initiates the minimum number of active elements in the CAA, while the space tapering technique gives the complex excitations that yield a beam pattern with constraints such as Side Lobe Level (SLL) and Beam Width (BW) in relation to Dolph-Chebyshev radiation pattern. The phase mode analysis, which is an built-in procedure in the proposed technique explores the circular antenna array configuration characteristics. The simulation results justify the effectiveness of the proposed technique for obtaining the desired radiation pattern synthesis.

The measured raindrop size distribution (DSD) and the ITU-R model have been used to elucidate the regional and diurnal variations of rain attenuation in Indonesia, for Ku-band (13.6 GHz), Ka-band (35.6 GHz), and W-band (96 GHz) frequencies. The DSDs were measured by the Parsivel disdrometer at Kototabang (KT; 100.32˚E, 0.20˚S), Padang (PD; 100:21˚E, 0:57˚S), Pontianak (PT; 109:37˚E, 0:00˚S), Manado (MN; 124:92˚E, 1:55˚N) and Biak (BK; 136:10˚E, 1:18˚S). In general, PD, KT and PT have lower rain attenuation than those at MN and BK, for the same rainfall rate, due to lower concentration of small-sized drops at these sites as reported by a previous study. Considerable differences between the attenuation obtained from the DSD and the ITU-R model are observed at all locations, in particular for very heavy rainfall (R > 50 mm/h). For R < 50 mm/h, the specific rain attenuation of measured DSD is in fairly good agreement with that obtained from the ITU-R model. The specific rain attenuation obtained from the DSD shows diurnal variation, in agreement with a previous study at KT. The diurnal variation of rain attenuation is dependent on the frequency and rainfall rate. At KT and PT, the lowest rain attenuation for Ku-band is observed during 06:00-12:00 LT, but during this period the largest attenuation is observed for Ka- and W-bands. These phenomena may be due to the increasing role of small and medium-sized drops by increasing frequency.

An ultrathin absorptive/transmissive radome with dual passbands is presented in this paper. The total thickness of radome is only 5 mm. The dual passbands are located at around 1.05 GHz and 2.2 GHz, respectively. The absorbing band ranges from 6.28 GHz to 15.04 GHz for TE wave incidence and from 6.3 GHz to 15.16 GHz for TM wave incidence. Due to the miniaturized elements, the grating lobes are shifted out of absorbing band to higher frequency. Both numerical and experimental results are also given out.