Currently, more and more practical engineering applications place antenna system on the electrically large platform. This paper deals with the problem of antennas mounted on large platform from two aspects - radiation pattern and system electromagnetic compatibility (EMC). To achieve an accurate and effective computation, this paper applies Method of Moment (MoM) with Higher-order basis functions solver with large-scale parallel computation technique. And finally some real-life examples are presented to describe how to install antennas on the platform reasonably.

A feasible simulator, of which formulation and mechanism should be simple and time saving, is developed in this paper to overcome the difficulties of prediction on the EM scattering from three-dimensional (3-D) electrically very large ship-sea models. The work in this paper is twofold. First, the sea surfaces are supposed to be a combination of many locally-tilted slightly rough facets with two-scale profiles. The radar return from each local facet is associated to a semi-deterministic scheme which is established by combining the geometric optics limit of Kirchhoff Approximation (KA-GO) with the Bragg components of Bass-Fuks' two-scale model (BFTSM). Furthermore, we associate the complex reflective function of the respective facet by a so-called Phase-modified Facet Model (PMFM), in which the facet's phase is treated approximately as a combination of inherent part that follows a homogeneous random distribution and coherent part associated with the relative path-delay. Second, in companion with the semi-deterministic treatment of the sea scattering model, a hybrid approximate algorithm is proposed to deal with the composite scattering of electrically large ship-sea model, which is entirely evolved through facets (for the sea surface) and wedges (for the ship target). The method of equivalent currents (MEC) and a hybrid frame which combines the four path model (FPM) with the quasi-image method (QIM) are employed to calculate the scattering characteristics of the ship-like target and ship-sea interactions, respectively. The entire simulator is of comparatively significant computational efficiency, and suitable for providing a preliminary prediction on the instantaneous complex reflective functions and normalized radar cross sections (NRCS) mean levels for electrically very large ship-sea model.

This paper deals with adaptive array beamforming in the presence of errors due to steering vector mismatch and finite sample effect. Diagonal loading (DL) is one of the widely used techniques for dealing with these errors. However, the main drawback of DL techniques is that there is not an easy and reliable manner to determine the required loading factor. Recently, serval DL approaches proposed the so-called automatic scheme on computing the required loading factor. In this paper, we propose a fully data-dependent loading to overcome the difficulties. The novelty is that the proposed method does not require any additional sophisticated scheme to choose the required loading. The loading factor can be completely obtained from the received array data. Analytical formulas for evaluating the performance of the proposed method under random steering vector error are further derived. Simulation results are provided to confirm the validity of the proposed method and make comparison with the existing DL methods.

new circuit structure is proposed for design of dual-band bandpass filters with a wide upper stopband. The unit cell of the circuit consists of two two-port networks in shunt connection; one is a coupled-line section of λ/4 long followed by a transmission line segment of identical length, and the other has the same elements but cascaded in reverse order, where λ/4 is the wavelength at arithmetic mean frequency of the two passbands. Higher-order circuits can be obtained by directly cascading two or more such cells and show improved frequency selectivity. In addition to on both sides of the passbands, transmission zeros are also created in the rejection bands. Analysis of the unit cell circuit is formulated by the transmission line theory, and design curves for one- and two-cell circuits are provided. In realization, interdigital capacitors are incorporated with the λ/4 coupled sections for compensating the effect of unequal modal phase velocities on the filter performance in the rejection band. Two circuits are fabricated and measured to validate the analysis.

The wire-ground electromagnetic coupling structures are quite common in avionics system electromagnetic compatibility (EMC) analysis. The increasing complexities of physical structures make electromagnetic modeling an increasingly tough task, and computational efficiency is desirable. In this paper, a novel selective mesh approach is presented for partial element equivalent circuit (PEEC) modeling where intense coupling parts are meshed while the remaining parts are eliminated. With the proposed approach, the meshed ground plane is dependent on the length and height of the above wires. Relevant compact formulae for determining mesh boundaries are deduced, and a procedure of general mesh generation is also given. A numerical example is presented, and a validation check is accomplished, showing that the approach leads to a significant reduction in unknowns and thus computation time and consumed memories, while preserving the sufficient precision. This approach is especially useful for modeling the electromagnetic coupling of wires and reference ground, and it may also be beneficial for other equivalent circuit modeling techniques.

We characterize left-handed (LH) traveling-wave field effect transistors (TWFETs), which consist of two composite right- and left-handed (CRLH) transmission lines that are electromagnetically coupled by capacitances, inductances, and FET transconductances, for obtaining loss-free LH waves. In a device, two different propagation modes can support LH waves. We find that one of these modes gain wave amplitudes, while the other loses them. This amplitude gain can compensate wave attenuation resulting from electrode loss and substrate leakage. This study clarifies which mode gains amplitudes and the method of matched terminations, together with several experimental observations that validate the design criteria.

A small-sized, low-cost, and planar integrated Bluetooth and ultrawideband (UWB) monopole antenna with band-notched characteristics in the 3.5 GHz WiMAX and 5.2/5.8 GHz WLAN band is proposed. It is fed by a microstrip line and built on a FR-4 substrate with a whole size of 18*30 mm². This proposed antenna consists of a slot on the edge of the radiation patch, which not only makes it achieve Bluetooth and UWB performance but also produces a high isolation between them. Additionally, two split rectangular ring resonators (SRRR) are placed close to the microstrip line to reject the WLAN band. Measured S₁₁ is ≤-10 dB over 2.28-2.52, 3.66-5.02, and 6.05-12 GHz. The group delay characteristic indicates good transient response in the working band. The antenna shows acceptable gain flatness with stable omnidirectional radiation patterns across the integrated Bluetooth and UWB (3.1-10.6 GHz) band.

A novel circularly polarized antenna with a circular radiating aperture and circular ground plane for broadband characteristics is presented in this paper. The vertical and horizontal components of the L-shaped probe are separated and placed at the front and back sides of the substrate. The antenna is excited by a microstrip line which is connected to the vertical component of the L-shaped probe and electromagnetically couples the signal to the horizontal component of the L-shaped probe. The concept of placing an appropriate stub in the slot, by observing the electric field vector behaviour in the slot, is proposed to enhance the axial ratio (AR) bandwidth by around 15%. The fabricated antenna shows wideband impedance and circular polarization characteristics of 48% along with a maximum gain of 6 dBic. The measured and simulated antenna characteristics are in good agreement.

The influence of semi-planar chiral metamaterial (CMM) structures on the important characteristics of circularly polarized (CP) antennas is investigated in this paper. Based on this idea, CP planar two-arm Archimedean spiral (ARSPL) antenna and helical antenna are designed and the effects of chiral covers on their gain (or directivity), axial-ratio (AR), and return loss are considered. The results demonstrate that this method is greatly effective and the addition of a semi-planar CMM cover at an optimized distance over the CP antenna, significantly improves its gain and axial ratio.

The plasma sheath communication blackout issue for hypersonic or reentry vehicles is addressed from a channel characteristic perspective. Different from previous research, this paper emphasizes the importance of plasma sheath channel in the study of plasma communication blackout, and the discussion on transmission and phase shift characteristic of plasma sheath channel and their effect on communication performance was made with detail. A mathematical plasma sheath channel model is proposed and following the roadmap about how to obtain channel characteristic parameter is given. Flow field simulation of a blunt conical body physical was made, and the electron density and collision frequency profile got from flow field result under different incident angle at Mach 10-20 are presented thoroughly. The performance for QPSK based communication system under the established plasma channel is evaluated finally. It is indicated in our research that channel attenuation feature variation regularity is consistent with that of incident wave or Mach number, but the phase shift variation regularity with incident frequency or Mach number appears fall into chaos because of multiple 360 degree removal of original phase shift from communication view and complicated ratio relationships among incident wave, plasma frequency and collision frequency. Communication simulations result show that bit error rate agree with phase shift chaos well and phase shift exert large influence on present typical racking, telemetry, and command system. Some useful implications obtained from this study to improve communication performance include high frequency, high power and further rapid acquisition/tracing phase-locked loop compensating large phase shift.

In this paper, a modified iterative fourier technique (MIFT) for thinning uniformly spaced linear arrays featuring a minimum sidelobe level as well as narrow beam is presented. Since IFT is a thinning procedure which has to be performed many trial times with different initial element distributions to get the optimum solution, it is, to some extent, time consuming. Moreover, in each trial of IFT, the number of iterations is usually low, which makes the method tend to be trapped in local solution even with a large number of trials. Therefore, the similar procedures for both MIFT and IFT are to derive the element excitations from the prescribed array factor using successive forward and backward Fourier transforms, and array thinning is accomplished by setting the amplitudes of a predetermined number of the largest element excitations to unity while the others to zero during each iteration cycle. Furthermore, in MIFT, based on the idea of gradual thinning which is inspired by perturbation theory, an adaptively changed fill factor is proposed to modify IFT with the purpose of accelerating computational speed and facilitating convergence. The immediate result caused by this modified fill factor can be embodied in two points. One point is that unlike the random number of iterations contained in different trials of IFT, the number of iterations in all trials of MIFT is a fixed value and only predetermined by the array inherent features (symmetrical or asymmetrical) and fill factor. Therefore, sufficient iterations are ensured in each trial to effectively help the algorithm avoid trapping. The other point is that when MIFT is performed, the array elements are gradually truncated, which maintains the most useful element excitations while maximally excludes the bad excitations, so that the optimum solution could be obtained through only a small number of trials and thereby substantially save computational cost. The effectiveness of MIFT will be demonstrated for various linear arrays and compared with the published reports.

A proximity-fed annular slot antenna for UWB applications with a band rejection using different techniques is presented. The proposed antenna provides an UWB performance in the frequency range of ≈2.84 to ≈8.2 GHz with relatively stable radiation parameters. Three different techniques to construct a resonant circuit for the proposed antenna are investigated to achieve the band-notch property in the band ≈5.11 to ≈5.69 GHz band which include the WLAN and HIPERLAN/2 services without degrading the UWB performance of the antenna. Three resonators are considered; a single complementary split ring resonator (CSRR), a complementary spiral loop resonator (CSLR) and a spurline slot. Furthermore, the band-notched resonance frequency and the bandwidth can be easily controlled by adjusting the dimensions of the resonator. The proposed antenna is simulated, fabricated and measured. The measured data show very good agreements with the simulated results. The proposed antenna provides almost omnidirectional patterns, relatively flat gain and high radiation efficiency over the entire UWB frequency excluding the rejected band.

The electromagnetic force between two misaligned coils (coils with parallel axes) with uniform current density distribution and rectangular cross section based on the derived semi-analytical expressions was presented. Using the semi-analytical expressions for magnetic force between filamentary misalignment circular coils we calculate the propulsive and the transverse magnetic force. In order to verify the validity of the expressions, we use the filament method with Grover's formula to calculate the magnetic force for two coils with parallel axes. The results obtained by two methods are in a very good agreement. In this paper, the derivation of the semi-analytical expressions and the calculation results of the magnetic force are introduced.

A compact triple-band monopole antenna with two different slots for WLAN and WiMAX applications is proposed and experimentally studied. The proposed antenna with a size of 30mm×25mm×1mm is excited by a 50Ω microstrip feed line. The designed antenna obtains three frequency bands through loading an inverted E-shaped slot and an inverted C-shaped slot which incise the surface current and change the path of the current on the rectangle patch. The obtained results show that the designed antenna has impedance bandwidths of 2.4 GHz, 5.8 GHz for WLAN and 3.5 GHz for WiMAX. The return loss, radiation patterns and peak antenna gains are presented using computer simulations and measurements.

We experimentally quantify the radiation of a small Ultra-Wideband (UWB) antenna placed on a human body. The measurements are performed for different antenna locations on the body, namely the head, torso and belt. First the antenna is measured in free space as reference, and then the influences of the body are investigated for different frequencies and antenna polarizations. We observe minimal signal blockage when the antenna is located on the head. It is around 5d B-10 dB loss for all polarizations. For the belt and torso, the blockage is 10 dB to 35 dB, for both polarizations.

The plane-wave synthesis is brought to the CATR. The feed scans in the focal plane and antenna pattern is measured several times in different feed positions. The corrected antenna pattern is obtained by weighting the measured patterns. The weight is obtained by the least squares method for the electric fields in the aperture plane of the test antenna. The fashion, number and spacing of feed scanning are investigated. By the plane-wave synthesis in the CATR, a larger antenna can be tested, and higher test accuracy can be obtained than that of the CATR. Lower test number and less test time are needed than the conventional plane-wave synthesis. The technique proposed in this paper is numerically investigated in an offset single paraboloid CATR and verified experimentally in a Cassegrain CATR at 100 GHz.

Target localization is one challenge in passive coherent location (PCL) radar system, and the time delay is the most important parameter in the location. The difficulty of time delay estimate (TDE) in PCL system is that the target signal is completely buried in direct path signal, multipath and clutter (DMC). The conventional clutter cancellation algorithms in matched filter (MF) are time consuming. In this paper, we propose a time delay estimate method based on blind source extraction (BSE) which directly extract the target signal from the mixed signals, thus a new passive coherent location system is built. In this model, the reference antenna is not needed any more. For low signal to interference plus noise ratio (SINR) and frequency overlapped signals in passive coherent location, we introduce the cyclostationarity to enhance the target signal. The experiments on FM broadcast signals show that the computational burden of the proposed algorithm is extremely small and the improved SNR satisfies the location requirements of PCL system.

This paper presents a novel tri-band unequal Wilkinson power divider. The proposed structure is derived from the conventional unequal Wilkinson power divider by replacing the quarter-wavelength branch lines and quarter-wavelength transformers with the extended T-shaped short stubs and three-section transformers respectively. The first and third operating frequencies of the proposed Wilkinson power divider can be flexibly controlled, while the second frequency is equal to the mean value of the other two frequencies. Both of the closed-form equations and design procedure are given. For verification, a tri-band unequal power divider with the power dividing ratio of 2:1 and operating frequencies of 1.3, 3.0 and 4.7 GHz is designed, fabricated and measured. The measurement results are in good agreement with the simulation ones. It is shown that the proposed power divider has simple topology and good performances in terms of insertion loss, port matching and isolation at all three operating frequency bands.

In this paper, a deterministic strategy to generate the aperiodicity, based on three geometric taper distributions is studied and validated. The method is applied to study arrays with average inter-elements spacing larger than a wavelength, exhibiting a reduction of the grating lobe level and requiring lower aperture size against a periodic structure with same directivity. Finally, a microstrip patch aperiodic array has been designed, manufactured and measured for an experimental validation of the concept, obtaining good agreement between simulated and measured radiation patterns. This manufactured antenna demonstrates experimentally the reduction of the grating lobes with a similar level to the side lobe.

In this paper, a rectifying antenna (rectenna) for energy scavenging applications is presented. The proposed device uses a modified bowtie antenna to collect the electromagnetic energy coming from UHF RFID systems, and RF Schottky diodes to convert it into DC power. Experimental results at 866 MHz demonstrating an RF-to-DC conversion efficiency of about 65% with an input power density of 60 μW/cm² will be presented and discussed.