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This work generalizes the alternating projection approach (APA) to synthesize wideband frequency-invariant (FI) beam patterns for linear nonuniformly spaced arrays (NUSAs). Different from the conventional APA where excitation weights are synthesized for a desired pattern at single frequency, the generalized APA intends to find appropriate finite-impulse response (FIR) filter coefficients for each antenna element to provide the required wideband frequency-dependent excitation for a desired wideband FI pattern, and two modification techniques called mainlobe FI modification and wideband sidelobe control are introduced in each iteration to successively update the FI pattern performance. Several examples for synthesizing wideband FI beam patterns for NUSAs in different applications are conducted to verify the effectiveness and advantages of the proposed generalized APA.

A highly multifunctional antenna with multilinear polarizations (MLPs) and multibands (MBs) is proposed, which can operate over four reconfigurable frequency bands, each band having 16 switchable linear polarizations (LPs) at an 11.25° interval. The larger number of MLPs is achieved by developing an odd-even switching strategy for the independently controlled p-i-n diodes placed between the inner patch and outer sector patches. The diode control is enabled by a field programmable gate array (FPGA) with an engineered biasing network. Moreover, the reported antenna can switch among four continuous bands for each LP, covering a combined range larger than 35%. It is an attractive feature, yet a challenging task for an antenna with such a large number of MLPs. This is realized by utilizing a double-layer feeding strategy with appropriate sector-patch activation, which is particularly appealed to such a highly multifunctional antenna. Furthermore, the antenna has a rotational symmetry along the azimuthal direction and, hence, all the LPs show almost rotationally invariant pattern shapes and gains. The measured results are consistent with the simulated ones, commonly validating the effectiveness of our design.

A novel method of synthesizing shaped-beam cylindrical conformal array by rotating the antenna elements and optimizing their excitation phases is presented. Rotation of antennas on curved surface is mathematically described by rotating its vectorial active element pattern (VAEP) in its local coordinate system (LCS). Then the scalar patterns and polarization unit vectors of all the rotated VAEPs are properly transformed and then interpolated at a unified angle sampling grid in a common coordinate system, where they are summed to obtain an approximated array expression. With this expression, element rotations and phases can be optimized using the constriction factor particle swarm optimization (CF-PSO) to synthesize desired shaped-beam pattern with controlled sidelobe level (SLL) and cross-polarization level (XPL). However, since rotations on curved surface introduce considerable variations to the element curvature and mutual coupling (MC), the synthesized array pattern would have considerable errors. A refined strategy is adopted then to improve the synthesis accuracy. The proposed method uses uniform amplitude weighting, thus saving many unequal power dividers. Three typical shaped pattern synthesis examples are provided to show the effectiveness of the proposed method. A cylindrical array prototype with 24 rotated U-slot loaded patch antennas is fabricated and measured for practical validation.

Multiagent systems (MASs) are usually used in unmanned aerial vehicle formations, multi-manipulator coordinated, traffic vehicle control and other fields, which have attracted a lot of attention from scholars. In this research, with the help of the designed performance function, the nonlinear transformation of synchronization error is realized. And the synchronization error of MASs with given transient performance could converge to the predefined interval. According to the designed transformation function, a prescribed setting time consensus control is investigated with the advantages of Radial Basis Function Neural Networks (RBFNNs) in dealing with unknown functions. It guarantees that the MASs under consideration are uniformly bounded convergent. Furthermore, event-triggered mechanism is applied to relieve pressure of MASs' communication resources. Simulation results demonstrate its effectiveness.

A quasi-mixed-potential layered medium Green’s function (QMP-LMGF) is proposed for non-Galerkin surface integral equation (SIE) formulations in the modeling of homogeneous dielectric objects in layered medium. The formulation is derived based on the pilot vector potential approach. In this method, the field-type LMGF in the L-operator is decomposed into two parts, a “vector potential” term in a dyadic form, and a “scalar potential” term in a vector form, to represent the field components from current and charge sources, respectively. Since the proposed two potential terms (vector potential and scalar potential) do not satisfy the Lorenz gauge, we term them as quasi-mixed-potentials. The property of the two potentials is investigated to reveal that the proposed QMP-LMGF is compatible with the vector and scalar potentials in free space. Moreover, due to the continuity of the integration kernels across the interfaces, undesired line integrals are absent in the proposed QMP-LMGF when the objects are straddling different layers. Three popular non-Galerkin SIEs for dielectric objects in layered medium are studied, and the corresponding numerical results are demonstrated to validate the proposed method.

High-gain single-feed antennas are desired for current and future wireless systems. Slot-based highly overmoded cavity antennas are one solution, but the fact that they can only radiate broadside beams limits their applications. An innovative phase-control technique is developed for slot-based resonant cavity antennas that utilizes a planar array of closely-spaced, appropriately-sized metallic patches integrated into the very near field of their slot arrays. It facilitates the design and realization of the phase distribution over their radiating aperture that is required for them to generate single and/or multiple tilted beams pointed at specified directions. A TE(10)(11)(0)-mode slot-based cavity antenna is selected as the pathfinder system. A TE110-mode single-slot cavity antenna that is equivalent to the half-wavelength subsection of that cavity is introduced initially to monitor the phase radiated from each slot. The phase control surface is then carefully engineered to facilitate tilted output beams from the base design. The approach is validated with two subsequent tilted-beam systems. The first system achieves a single beam tilted to 30° with respect to the broadside direction. The second system is extended to produce two independently-directed titled beams pointing at –10° and 20°, respectively. All of the measured results agree well with their simulated values.

A new approach for synthesizing wideband frequency-invariant (FI)-shaped patterns is presented. This method is a significant extension of the original iterative spatiotemporal Fourier transform (STFT) method that only deals with wideband FI pencil-beam patterns. Based on the original method, the wideband pattern can be regarded as a spatiotemporal spectral distribution, and the relationship between the spatiotemporal spectral distribution and finite-impulse-response (FIR) filter coefficients can be built as an STFT, which can be efficiently calculated by using 2-D fast Fourier transform (2-D-FFT). To achieve desired FI-shaped pattern performance, the spatiotemporal spectral distribution is iteratively adjusted by two new techniques called wideband pattern shaping and linear phase response (LPR)-based modification. Different from the constant phase response (CPR) processing in the original iterative STFT method, the LPR-based modification uses more relaxed phase requirements, thus releasing much more degrees of freedom. Numerical results show that the proposed method is effective even for very complicated pattern requirements, and it is very efficient in terms of both computation and storage. Besides, the proposed method can take into account the effects of frequency-variant antenna element patterns and mutual coupling in the periodic array structure.

A novel method is presented to efficiently synthesize linearly polarized shaped patterns for antenna arrays mounted on complex platforms surrounded with many scatters. The vectorial active element patterns (Vec. AEPs) are adopted to include the mutual coupling and complex platform effect. The vectorial least-square (LS) active element pattern expansion (Vec. LSAEPE) method is developed to approximate each Vec. AEP as the radiation from a virtual subarray with identical element patterns, so that the fast Fourier transform (FFT) can be utilized to efficiently perform the forward and backward transformations between the excitation distribution and the vectorial array pattern including mutual coupling. An energy-based weighted averaging method is introduced to merge the excitation vectors obtained from copolarization (CoP) and cross-polarization (XP) pattern synthesis in each iteration and consequently the obtained final excitation vector can simultaneously meet both the CoP and XP pattern requirements. The method is called the iterative Vec. LSAEPE-FFT significantly extends the FFT-based synthesis technique to be capable of controlling the CoP main lobe shape, sidelobe distribution, and the XP level. Three examples for synthesizing different shaped patterns for different antenna arrays on complex platforms are conducted to validate the effectiveness of the proposed method. A comparison with some other representative methods is also provided to verify the advantages of the proposed method in both accuracy and efficiency.

An efficient improved spectrum integral method (ISIM) is proposed to accelerate the scattering simulation of cuboid object by method of moment (MoM) in multiplanar layered medium (LM). The layered medium Green’s functions (LMGFs) are studied and decomposed into transmission and reflection terms, which hold the translational invariance and reverse translational invariance, respectively. By virtue of the (reverse) translational invariance of LMGF from the uniform square grids on the surface of the cuboid object, most of the coupling between the expanding basis functions and the testing basis functions can be represented by two kinds of submatrices, i.e., the Toeplitz matrix when transmission term is involved, and the conjugate Toeplitz matrix when reflection term is involved. Moreover, the submatrix coupling the expanding/testing basis functions defined on the edges with those defined on the parallel surfaces/edges is also extended to the (conjugate) Toeplitz matrixes. This will significantly alleviate the heavy computation and memory burden from the conventional SIM. With the improved operations on the basis functions associated with the edges of the cuboid object, the proposed ISIM in LM can reach the computational complexity as low as ${O}$ ( ${N} ^{1.5}$ log( N)) in the matrix vector production, while the computational complexity of matrix filling and the memory requirement are both ${O}$ ( ${N}^{1.5}$ ). Moreover, compared with conventional SIM, both theoretical analysis and numerical results demonstrate that the memory requirement and matrix filling time are dramatically decreased.

A novel electromagnetic modeling method for multidomain planar layered medium (MD-PLM) by surface integral equation (SIE) is proposed. The MD-PLM refers to the whole space that is separated into multiple PLM volumes, e.g., the infinite-sized PLM background with inserted finite PLM objects or multilayered parallel-plate structures. In the conventional SIE method for this scenario, only the exterior domain is considered as PLM that is modeled by layered medium Green’s functions (LMGFs), while the interior domain is treated by the multidomain homogeneous SIE. However, in this work, the surface equivalence formulation for this special scenario is reestablished by the LMGFs. Then, both the exterior and interior domains are considered as PLM that is modeled by the corresponding LMGFs and SIE in each subdomain. As a result, only the boundary of each sub-PLM domain is required to be discretized rather than the interfaces of each interior medium, which is different from the way in conventional SIE. Consequently, compared with the conventional SIEs, the proposed method can reduce a large quantity of unknowns and significantly increase the efficiency by reducing the memory consumption. By some numerical examples, the performance of this method is evaluated and compared with the conventional methods. The validity and efficiency of the newly proposed method are also well demonstrated in the examples.

A higher order current and charge integral equation (CCIE) approach is developed for accurate electromagnetic scattering analysis of dielectric objects for a wide frequency band, that is from extremely low frequency to microwave frequency. Compared to the conventional CCIE method, its accuracy has been considerably improved by expanding the currents and charges using high-order hierarchical vector basis functions and higher order orthogonal scalar polynomials, respectively. The proposed higher order approach retains whole-frequency-range stability as the traditional low-order counterpart, but characterized with enhanced accuracy and higher convergence rate. Moreover, the consistency of the basis functions’ expansion order in currents and charges is not mandatorily required, which further increase the flexibility in electromagnetic modeling. The scattered fields of penetrable objects are analyzed to validate the effectiveness of this new higher order CCIE, as well as investigate its accuracy, stability, and flexibility.

In this communication, a wideband low-profile antenna with switchable multilinear polarizations (MLPs) is proposed. An odd number of dipoles with trapezoidal-shaped arms printed on both sides of a substrate are adopted as reconfigurable radiators, which provides a much smaller polarization interval than using an adjacent even number of dipoles. The p-i-n diodes with simple dc biasing lines are loaded to reconfigure the polarization states. A circular-contoured artificial magnetic conductor (AMC) reflector using hexagon-patch cells is employed to reduce the antenna profile. The whole multiple dipole structure is rotationally invariant, which provides almost rotationally invariant antenna performance for different LPs. In addition, the antenna can be easily redesigned when adjusting the number of dipoles for different LPs. A seven-LP reconfigurable antenna working in 2.85–3.40 GHz is used as an example to give the detailed parameters’ study and performance analysis. Three antennas with five, seven, and nine reconfigurable LPs are designed and measured. With $0.035\lambda $ height, they achieve the measured overlapped bandwidths of 20.6%, 17.6%, and 15.9% for five, seven, and nine LPs, respectively, and their measured peak gains are ranging from 8.3 to 8.5 dBi.

The fast Fourier transform (FFT) via the least-square active element pattern expansion (LSAEPE) is generalized to speed up the computation of array patterns including mutual coupling and platform effect for time-modulated antenna arrays (TMAAs) at the central and sideband frequencies. By integrating the LSAEPE-FFT with differential evolution algorithm (DEA), the resulting DEA-LSAEPE-FFT method can realize efficient shaped pattern synthesis with accurate control of main lobe shape, sidelobe level (SLL) and sideband level (SBL). Two examples of synthesizing different shaped patterns for different TMAAs mounted on a nonuniform platform or with metal scatters are conducted to validate the effectiveness and robustness of the proposed method. Synthesis results show that the proposed method has much better accuracy performance than the conventional DEA-FFT while costing much less CPU time than that of using DEA combined with a direct summation.

A novel method based on alternating linear programming optimization is presented to synthesize sparse linear arrays with sum and difference patterns. This method can find the optimized element positions and excitations shared for both sum and difference patterns with accurate control of multiregion sidelobe distribution and difference pattern null slope. In addition, the constraints on the minimum element spacing and dynamic range ratio of the obtained excitations can be also appropriately incorporated into this alternating optimization process. Two synthesis examples with different pattern shape requirements are conducted to validate the effectiveness and advantages of the proposed method.

Array antennas with multipolarization function have important research value to improve the stable transmission of communication systems by supporting antenna diversity technology. In this letter, a millimeter-wave (mm-wave) quadri-polarization array antenna based on folded C-type substrate integrated waveguide is proposed. The operating principle is that the proposed differential feeding network can flexibly provide the required amplitude and phase difference, so that four mutually perpendicular single-branch slot array antennas can achieve multiple polarization characteristics. In addition, by removing the metal floor around the array antenna, the distortion of the antenna's main beam is suppressed. Simulation and experimental results show that the proposed quadri-polarization array antenna can provide orthogonal dual-linear polarization and dual-circular polarization radiation patterns. At the same time, it has the advantages of low profile and easy integration.

It is difficult to realize a traveling wavemode current on a single conductor loop to generate a wideband circularly polarized (CP) radiation wave using a single feeding structure. In this communication, with the help of the characteristic mode analysis, we cut a wide gap in the annular ring conductor patch and design the feeding structure with capacitive coupling effect on the patch. By this way, the annular patch is effectively distributed with traveling wave currents and a printed annular ring antenna operating in the 2.4 GHz band is constructed. The experimental results show that the proposed antenna can generate CP radiation with impedance and axial ratio bandwidths of 26% and 10.6%, respectively. Meanwhile, this antenna has a good structural tolerance capability.

This paper deals with event-triggered $H_\infty $ filtering problem for switched continuous-time systems with quantization. A multiple periodic sampling-based event-triggering strategy is adopted to select those “necessary” sampled signals to be transmitted. As a result, the amount of communication and the frequency of signal updates can be reduced significantly. Regarding the nonideal communication network, we consider network-induced delays and packet disorders, which are common during packet transmission through networks. In order to cope with packet disorders, an active packet loss approach is introduced. As such, a new time-delay system model is established, by which the filtering error system is modeled as a switched system with an interval time-varying delay. Then, by employing piecewise Lyapunov functional method and average dwell time technique, some criteria are derived to ensure that the filtering error system can achieve a prescribed level of $H_\infty $ performance. Moreover, the relationship between switching instants and the data updating instants in filter is discussed in detail, and the filter gains and event-triggering parameters can be jointly designed in terms of solutions to some linear matrix inequalities. Finally, numerical simulation is provided to verify the effectiveness of the proposed method.

IEEE This communication presents a novel method of synthesizing both sum and difference patterns by optimizing the element rotations and positions for linear dipole array. The common element rotations and positions are optimized by using the particle swarm optimization (PSO) method to produce sum and difference patterns with reduced sidelobe levels (SLLs) and cross-polarization levels (XPLs), and as steep slope as possible for the difference pattern at the target direction. Such method leads to a sum-and-difference array with sparsely distributed uniform amplitude elements, thus saving many antenna elements and unequal power dividers. Three examples for synthesizing sparse rotated dipole arrays with sum and difference patterns are provided. Synthesis results show that the obtained arrays with uniform amplitudes can produce satisfactory sum and difference patterns while saving about 34.69% ~ 42.27% of the antenna elements when compared with λ/2-spaced arrays occupying the same aperture.

In this article, a novel method is presented to synthesize multi-beam circularly polarized (CP) patterns with sidelobe level (SLL) and cross-polarization level (XPL) suppression for planar dipole arrays by optimizing both element rotations and excitation phases. Multiple sets of excitation phases are adopted as optimization variables other than the determined values according to the rotation angles in the conventional sequentially rotated technique (SRT) and the random sequentially rotated technique (RSRT), so as to improve the performance of the obtained CP multi-beam patterns. This releases many more degrees of synthesis freedom but leads to a new problem of demanding excessive computation resources for a planar rotated dipole array with multiple CP patterns. Then, a two-step rotation and phase optimization strategy is proposed to effectively solve this optimization problem. In the initial step, the common element rotations and approximated excitation phases composed of the common phase parts plus the beam focusing phase parts are found for multiple desired CP patterns with different beam directions. And then, a refining step is performed to refine the excitation phases individually for each CP beam for improved pattern performance. Four representative examples of synthesizing multi-beam patterns with both SLL and XPL suppression are provided to verify the effectiveness of the proposed method. Comparisons with the conventional SRT and RSRT are also provided to show the superiority of the proposed method.

This letter presents a compact 2-D Butler matrix (BM) realized by multilayer substrate integrated waveguide (SIW) technology. The 2-D BMs in the open literature suffer from either bulky size or poor integration with the radiation portion. Facing this issue, a new SIW 2-D BM is developed and realized in planar configuration easily integrated with the slot antenna array. The key point of this letter is to design planar 2-D components, including 2-D couplers, 2-D crossovers, and 2-D phase shifters, of the proposed SIW 2-D BM, which can perform coupling, intersection, or phase shifting in both E- and H-planes. The proposed SIW 2-D BM also has the merit of ease integration with radiation portion and it is used to build a compact 2-D multibeam antenna in this letter. Simulation, fabrication, and experiments are conducted to verify the performance of the realized 2-D multibeam antenna.

IEEE A refined extended alternating convex optimization (REACO) method is presented to synthesize multibeam sparse circular-arc antenna arrays with minimum element spacing control by considering real antenna array structure characteristics. This method consists of initial step and a few refining steps. At the initial step, an initial array with dense elements distributed on a circular-arc is considered, and its array manifold vector is described by rotating a simulated isolated element pattern (IEP) without considering element mutual coupling. The collective excitation coefficient vector (CECV) and its energy bound are introduced for each element, and consequently the common element positions for generating desired multibeam patterns can be found by minimizing the number of active CECVs under multiple constraints. This minimization problem is further formulated as performing a sequence of alternating convex optimization (ACO) in which the CECV and an auxiliary weighting vector are alternately chosen as the optimization variables, so that the mimimum element spacing constraint can be easily dealt with. Once the initial optimization step is finished, a few refining steps are performed in which the element positions and excitations are successively updated in each step by renewing the array manifold vector through rotating the simulated nearby active element patterns (AEPs) of the antenna array obtained at the previous step. In such a way, the mutual coupling can be incorporated into the multibeam sparse array synthesis. An example of synthesizing a sparse circular-arc conformal array with 23 beams covering the space from–63.25° to 63.25° is conducted to validate the effectiveness and advantage of the proposed method.

An effective method is presented to design the layout of spiral array with ultra-wideband (UWB) grating lobe suppression. In this method, the general array factor expression of spiral array is formulated. Then, the synthesis problem of spiral array layout is converted to an optimization problem of three geometric parameters: s, r and Δϕ. These parameters can determine the exact position of each element. The optimization problem is solved by particle swarm optimization (PSO) algorithm where the constraints of element spacing and array aperture are introduced. For different-sized spiral arrays, there are always only three variables that need to be optimized in the PSO algorithm, which allows the proposed method to handle the layout design of large-scale spiral arrays with UWB grating lobe suppression. Two examples with different synthesis requirements are conducted to verify the effectiveness and advantages of the proposed method.

© 2002-2011 IEEE. In this letter, a modified iterative fast Fourier transform (MI-FFT) technique is presented to synthesize thinned massive array for 5G millimeter-wave (mm-wave) communications. The periodicity of a scannable array factor for a uniformly spaced planar array is discussed and employed to reduce the complexity of array factor computation. A gradual array thinning strategy is introduced to prevent the iterative procedure from being trapped into an endless loop so that a better solution with lower sidelobe level (SLL) can be found. The beamwidth control is also added in the MI-FFT to control the pattern beamwidth. A thinned 128-element planar array with parasitic patch covered microstrip antenna elements is designed with the frequency band from 25.2 to 31.6 GHz. The 128-element positions are optimally selected from a prescribed larger layout by the proposed method, and consequently the obtained thinned array has a much lower SLL and narrower beamwidth than a conventional fully occupied 128-element array.

Using single structure antennas to generate electromagnetic waves with orbital angular momentum (OAM) modes can greatly simplify the OAM application systems. However, at present, there is a lack of theoretical guidance for the realization of OAM modes using only a single antenna. In this communication, the characteristic mode theory (CMT) is applied to analyze the current wavemodes of the patch antenna. Then, the orthogonal degenerate modes are selected and the feeding structure is determined to obtain the desired OAM mode. For example, a third-order OAM radio wave is implemented by a ring patch antenna, and the performance of this OAM mode is explained by using the modal excitation coefficient. It is verified that the CMT is an effective analysis tool for a single antenna to achieve OAM modes.

© 1963-2012 IEEE. Based on transformation optics, a simple and efficient strategy to design 3-D electromagnetic and optical devices is proposed. Using this new method, the materials required are isotropic and free of any singularity or zero value as long as the transformed domains in the virtual and physical spaces are finite. Three electromagnetic devices are designed and illustrated to verify this method. In order to avoid using a magnetic material which is a significant barrier in fabrication, the results are also tested when absorbing the magnetic permeability of the transformed material inside the permittivity. This is the first time to guarantee the obtained materials are all isotropic by transformation optics in 3-D problems. Therefore, the proposed method offers great potential in designing novel 3-D electromagnetic and optical devices, which will make these designed 3-D devices easier to fabricate in practical implementations.

© 1963-2012 IEEE. In this article, a novel strategy based on refined joint element rotation/phase optimization is presented to obtain vectorial shaped power patterns for antenna arrays with arbitrary element structures including mutual coupling. The active element pattern (AEP) is used for each antenna element, and then the rotation of an element is approximately described by mathematically rotating its AEP under the assumption that the mutual coupling variation does not change the AEP considerably. Optimal element rotations and phases for an array can be found by solving a vectorial shaped pattern synthesis problem such that the obtained array pattern has the desired co-polarization mainlobe shape while maintaining constrained sidelobe and cross-polarization levels. However, due to the variation of mutual coupling, this synthesized pattern may deviate from the real array pattern. To reduce the pattern discrepancy, successive refined joint element rotation/phase optimizations are adopted. As the number of refining steps increases, the allowable element rotation range is set to be smaller and smaller so that the synthesized array pattern can get closer and closer to the real one. Such a shaped power pattern synthesis technique does not need nonuniform amplitude weighting, thus saving many unequal power dividers. Three examples for synthesizing rotated linear and planar arrays with different antenna structures and different pattern shape requirements are provided to validate the effectiveness and advantages of the proposed method.

Order reconfiguration of orbital angular momentum (OAM) is the foundation for wireless communications based on OAM state multiplexing. As the symmetry of a circular patch is disturbed by an arc segment, two degenerate modes can be synthesized under the single-fed condition to generate OAM waves. Due to arc segment independent of the radiation patch, its effective length is controlled by a switching diode to select different order degenerate modes for synthesis. Based on this idea, a reconfiguration of first-order and second-order OAM modes is achieved. In comparison, the performance of low-order OAM mode is better than that of high-order mode.

The surface-enhanced Raman spectroscopy (SERS) is a technique for the detection of analytes on the surface with an ultrahigh sensitivity down to the atomic-scale, yet the fabrication of SERS materials such as nanoparticles or arrays of coinage metals often involve multiple complex steps with the high cost and pollution, largely limiting the application of SERS. Here, we report a complex hierarchical metallic glassy (MG) nanostructure by simply replicating the surface microstructure of butterfly wings through vapor deposition technique. The MG nanostructure displays an excellent SERS effect and moreover, a superhydrophobicity and self-cleaning behavior. The SERS effect of the MG nanostructure is attributed to the intrinsic nanoscale structural heterogeneities on the MG surface, which provides a large number of hotspots for the localized electromagnetic field enhancement affirmed by the finite-difference time-domain (FDTD) simulation. Our works show that the MG could be a new potential SERS material with low cost and good durability, well extending the functional application of this kind of material.

A compact bandstop filter (BSF) using parallel-coupled lines and open stubs with four transmission poles (TPs) is proposed. Through theoretical equation deduction, the positions of these four TPs can be obtained. Good roll-off skirts and stopband suppression characteristics of the BSF can be realised with the help of multiple TPs. To improve transition band roll-off rates, another BSF with five TPs is designed, where a short-circuited T-stub is loaded on the middle of the above BSF circuit structure. For demonstration, two filter examples with centre frequencies at 2 and 1.8 GHz are implemented with generation of four and five TPs, respectively, for theoretically calculated certification. Good agreement between simulated and measured results validates the design method.

This study investigates the dynamic output feedback L ∞ control for network-based switched linear systems subject to communication delay and quantisation. To reasonably configure the network communication resources according to the dynamic and steady-state characteristics of the system, the performance dependent event-triggering strategies are proposed. Moreover, the quantiser and dynamic output feedback controllers are applied, and the time-delay closed-loop switched system models corresponding to the system dynamic and steady-state processes are developed using a transformation technique. Subsequently, by utilising the average dwell time and piecewise Lyapunov functional techniques, sufficient conditions are derived to render the state of the time-delay closed-loop switched system globally uniformly ultimately bounded with an L ∞ performance level. In particular, the coupling between the switching instants and the data updating instants in the actuator is analysed during the system performance analysis. Furthermore, the design conditions of the event-triggered dynamic output feedback controllers are presented. Finally, numerical simulations verify the effectiveness of the proposed approach.

© 1963-2012 IEEE. In this communication, we introduce a p-i-n-diode-based polarizer integrated with a dielectric resonator antenna (DRA) to realize a polarization reconfigurability. The p-i-n-diode-based polarizer is found to be effective in altering the electromagnetic-field distribution of the DRA, such that the polarization of the DRA can be actively changed. Unlike conventional p-i-n-diode-based reconfigurable antennas, the proposed active polarizer would not degrade radiation performance of the DRA. In this way, the antenna retains the high radiation efficiency with its simple excitation. The proposed antenna uses a simple and agile-switching mechanism to provide three switchable polarizations to the DRA including: a y -axis polarization (STATE 1), a +45° polarization (STATE 2), and a -45° polarization (STATE 3) across a wide effective bandwidth (overlapped bands of three states) of 15.0%. The radiation efficiencies maintain 65%-79% in each state throughout the effective operating band. Finally, the experimental results agree well with the theoretical analyses.

A circularly polarized multibeam antenna array based on magnetoelectric (ME) dipole is proposed, which is fed by a substrate integrated waveguide 5 × 6 Butler matrix. There are two points that are key to completing the design—the wide axial-ratio (AR) beamwidth antenna element and the appropriate beamforming network. By adjusting the shape of the radiation patch of ME dipole, the amplitude of the orthogonal field becomes flatter at a wide angle, and the phase difference is maintained at 90°; hence, an antenna element with a wide 3 dB AR beamwidth can be achieved. In order to ensure the generation of normal beam, a 5 × 6 Butler matrix using the 3 × 3 Butler matrix is selected as the beamforming network. The proposed structure operates in the range of 27.5–28.5 GHz and generates five circularly polarized beams that cover the range of ±40°. The gain of all these beams is approximately 12.5 dBi.

© 1963-2012 IEEE. In this paper, the stabilized biconjugate gradient fast Fourier transform (BCGS-FFT) method is used to solve the electromagnetic scattering problem for 3-D inhomogeneous uniaxial anisotropic objects embedded in a layered uniaxial medium. The optical axis of the background medium is perpendicular to the layer boundaries. However, the optical axis of the scatterer can be rotated through any angles. The electric field integral equation (EFIE) is formulated in the layered uniaxial anisotropic background medium. The volumetric roof-top function is used for the basis function as well as the testing function. The dyadic Green's functions (DGFs) for both the electric field and the magnetic vector potential are used to solve the EFIE, and the results as well as the performance are compared. Several numerical simulations are carried out to validate the accuracy and efficiency of the proposed method. The major new contribution of this paper is to extend the BCGS-FFT method to accommodate the uniaxial anisotropy of the layered background medium. Therefore, the DGFs for the layered uniaxial medium are evaluated before solving the EFIE. In addition, the DGF for the electric field is also used to solve the 3-D scattering problem through BCGS-FFT iterations, which is different from the previous work.

© 1963-2012 IEEE. Efficient 2-D full-waveform forward and inverse electromagnetic scattering solvers are presented in this communication. The combined field volume integral equation (CFVIE) is formulated in a layered medium. Different from the previous work, the mixed-order basis function is adopted in the discretization of the 2-D CFVIE. Meanwhile, the permittivity and permeability are simultaneously reconstructed in the inversion through the variational Born iteration method, which is enhanced with a self-adaptive regularization factor and applied to the multifrequency data. The proposed forward solver is validated by comparisons with the finite-element simulations.

The problem of reducing the number of elements in a broadband linear array with multiple simultaneous crossover frequency-invariant (FI) patterns is considered. Different from the single FI pattern array case, every element channel in the multiple FI pattern array is divided and followed by multiple finite-impulse-response (FIR) filters, and each of the multiple FIR filters has a set of coefficients. In this situation, a collective filter coefficient vector and its energy bound are introduced for each element, and then the problem of reducing the number of elements is transformed as minimizing the number of active collective filter coefficient vectors. In addition, the radiation characteristics including beam pointing direction, mainlobe FI property, sidelobe level, and space-frequency notching requirement for each of the multiple patterns can be formulated as multiple convex constraints. The whole synthesis method is implemented by performing an iterative second-order cone programming (SOCP). This method can be considered as a significant extension of the original SOCP for synthesizing broadband sparse array with single FI pattern. Numerical synthesis results show that the proposed method by synthesizing multiple discretized crossover FI patterns can save more elements than the original iterative SOCP by using a single continuously scannable FI pattern for covering the same space range. Moreover, even for multiple FI-patterns case with complicated space-frequency notching, the proposed method is still effective in the reduction of the number of elements.

High-selectivity single-ended and balanced bandpass filters (BPFs) using dual-mode ring resonators and coupled lines loaded with multiple stubs are proposed in this paper. With the help of the loaded short-circuited and open-circuited stubs, six deep transmission zeros (TZs) from 0 to 2f0 (f0: center frequency of the passband) can be realized in both of single-ended and balanced BPFs to improve the stopband suppressions. The functions of the loaded short/open stubs and calculated analysis of TZs’ positions have been presented. For further demonstration, two examples of single-ended BPF and balanced BPF with high common-mode suppression are designed and fabricated, whose center frequencies are both at 2.1 GHz. Their measured 3-dB fractional bandwidths are 23.7% and 24.7% (differential-mode), respectively. The simulated results and measurements of these two filters are in good agreement.

A simple multibeam antenna fed by a modified horn beam-forming network (BFN) is realized in substrate integrated waveguide technology. Compared with Rotman lens fed multibeam antenna, such an antenna has the merits of a simple architecture and design process. The modified horn BFN applied here is developed from a traditional horn BFN by adding multiple lateral feeds to perform the beam scanning property. The operation principle, design method, and performance of the multibeam antenna are illustrated sequentially. Fabrication and measurement are conducted to test the consistency between simulation and experiment.

IEEE This work generalizes the Fourier transform (FT)-based frequency-invariant beamforming (FIB) method to the synthesis of scanned frequency-invariant (FI) beam pattern with space-frequency notching for an array with non-isotropic elements. Wideband FI pattern characteristics are described by using multiple reference sub-band FI patterns that are obtained through an iterative single-frequency FT-based synthesis method. By applying fast Fourier transform (FFT) on the combination of these multiple reference sub-band FI patterns, a wideband excitation distribution can be generated. Based on this excitation distribution, we construct a new wideband excitation distribution that is conjugate-symmetric about zero frequency, so that real-valued finite-impulse-response (FIR) filter coefficients can be obtained by applying FFT on the constructed distribution. Two numerical examples are introduced to show the effectiveness and efficiency of the proposed method for synthesizing scanned FI beam patterns with complicated notching requirements.

© 1963-2012 IEEE. The evaluation of singular or near-singular integrals is one of the key techniques in the integral equation method. Based on the previously proposed double-arctan transformation (DAT) for the nearly hypersingular integrals in curved surface modeling, this work presents new transformation methods to improve the accuracy and stability of DAT for the following two situations, i.e., the field point is: 1) extremely close to the source surface and 2) extremely close to the boundary of the source surface. The original DAT fails in these two situations and, hence, limits its applications. The reasons that cause such an instability are studied. Two additional transformations are introduced to make the DAT stable for these two cases. For situation I, the exponential transformation (ET) is adopted to optimize the distribution of the Gaussian quadrature points. For situation II, the shape-function transformation (SFT) is further proposed to remove the nearly angular singularity. We denote the newly developed DAT with ET and SFT as the improved DAT (IDAT) in this communication. The typical testing cases are provided to validate the proposed method.