In this paper, a multiple-grid precorrected fast Fourier transform (MG-pFFT) based on the integral equation domain decomposition method (IE-DDM) is presented for multi-scale, dynamic electromagnetic scattering problems in half space. In the framework of the IE-DDM, the proposed method employs multiple auxiliary FFT grids in each domain. Numerical experiments validate the reduced complexity and accuracy of this method. It is also shown that the proposed method is an efficient and robust preconditioner for the original IE system in half space.

In this paper, a novel suspended stripline (SSL) bandpass filter using hybrid transmission line stepped impedance resonator (HTLSIR) is proposed. SSL has proven to be an excellent transmission-line system for realizing different types of filters. However, due to the effective permittivity being too close to unity, the size of the distributed elements is usually very large. The novel resonator introduced in this letter contains a section of hybrid transmission line which consist of the SSL and the microstrip line. The characteristics of the HTLSIR have been analyzed clearly. The novel SSL filter is designed, fabricated and tested. Both simulated and measured results are presented.

A highly efficient and robust scheme is proposed for analyzing electromagnetic scattering from electrically large arbitrary shaped conductors in a half space. This scheme is based on the electric field integral equation (EFIE) with a half-space Green’s function. The precorrected fast Fourier transform (p-FFT) is first extended to a half space for general three-dimensional scattering problems. A novel enhanced dual threshold incomplete LU factorization (ILUT) is then constructed as an effective preconditioner to improve the convergence of the half-space EFIE. Inspired by the idea of the improved electric field integral operator (IEFIO), the geometrical-optics current/principle value term of the magnetic field integral equation is used as a physical perturbation to stabilize the traditional ILUT perconditioning matrix. The high accuracy of EFIE is maintained, yet good calculating efficiency comparable to the combined field integral equation (CFIE) can be achieved. Furthermore, this approach can be applied to arbitrary geometrical structures including open surfaces and requires no extra types of Sommerfeld integrals needed in the half-space CFIE. Numerical examples are presented to demonstrate the high performance of the proposed solver among several other approaches in typical half-space problems.

A compact dual-wideband bandpass filter featuring two controllable center frequencies and passbands using a single side-coupled shorted λ/4 stepped-impedance resonator (SIR) is presented. The resonant frequencies of the two passbands can be adjusted by tuning the impedance ratio and length of the SIR. The bandwidth of the two passbands is determined by the coupling strength between the meandering feedlines and the resonator. The generation mechanism of filter’s transmission zeroes was investigated by equivalent models of the filter and the bending parts of the open-end meandering feedlines. Owing to the cross-coupling between the two open-end meandering feedlines and the phase shifted characteristic of the open-end meandering feedlines, several transmission zeroes can be generated to improve the selectivity. To verify the design concept, one dual-wideband bandpass filter has been designed, fabricated, and measured. The simulated and measured results are presented with good agreement.

A triple-mode microstrip square ring short stub-loaded stepped impedance resonator (SIR) is proposed for the design of bandpass filters (BPFs). The resonator possesses three resonances over the wide frequency band, which can be employed to implement a BPF with flat response. This kind of the filter is able to control spurious response by changing the structure of the resonator. For validation, a triple-mode BPF with central frequency of 2.55 GHz has been designed, fabricated and measured. Good agreement is observed between measured and simulated results.

In this paper, an efficient method is proposed to eliminate frequency splitting in nonradiative wireless power transfer via magnetic resonance coupling. In this method, two nonidentical resonant coils (NIRCs) are used as wireless power transmitter and receiver, respectively. According to the elliptic integral term in the analytical expression, the pole of the mutual inductance function with respect to transfer distance can be eliminated by using the two NIRCs, and hence overcoupling between transmitter and receiver with close transfer distance is avoided. Therefore, frequency splitting caused by overcoupling can be suppressed and stable output power can be achieved. The NIRCs are analytically calculated, numerically simulated and finally, fabricated and tested to verify the theory. All the calculated and experimental results show that frequency splitting is completely eliminated and uniform voltage across the load is achieved. Furthermore, lateral misalignment between the NIRCs barely introduces frequency splitting, and the suppression level of frequency splitting can also be controlled freely.

A novel fifth-order suspended stripline (SSL) low-loss bandpass filter with four transmission zeros is proposed. The technique of utilising only one cross-coupling structure introduces four transmission zeros to provide high selectivity. By adjusting the parameters of the coupling open loop, the performance of out-of-band of the filter can be changed. A detailed discussion of this effect of the coupling open loop is given. The highest out-of-band rejection of the filter is more than 70 dB. An SSL bandpass filter is designed, fabricated and measured. The measured results are in good agreement with the simulated results.

A planar antenna array, which is closely placed with an infinitesimal distance of only 4 mm between array elements yet well decoupled by a deliberately designed small-size protruded ground, is presented. The well-designed protruded ground has two types of behaviors: reducing the coupling in between the array elements and improving impedance matching to enhance the bandwidth. At the lower bands of GSM850/900 and the upper bands of GSM1800/1900/UMTS/LTE2300/2500, the good radiation efficiencies of better than 43% and 50% respectively are obtained, and simultaneously the isolations of better than 10 dB are achieved in between the antenna elements. A prototype is made and tested, with S-parameters, radiation efficiency, radiation pattern, and envelope correlation coefficient (ECC) presented.

A compact ultra-wideband (UWB) planar antenna with reconfigurable band-notched characteristics is proposed in this paper. The proposed antenna covers the frequency band from 3GHz to 11GHz (S11 <= -10), with 114% fractional bandwidth. A T-shaped on the ground is used to widen the band of the antenna. Dual arc-shaped slots are embedded on the patch, to obtain the (WIMAX) 3.3-3.6 GHz and (WLAN) 5.1-5.9 GHz notched bands. The reconfigurable band-notched characteristics are achieved by adding PIN diode in the arc-shaped slot. When the PIN is conductive by adding DC voltage source, the notched band is disappeared with good UWB characteristic. The measured results have a good agreement with the simulated results. Because of its compact area and low cost, the proposed antenna is suitable for the UWB communication.

In this letter, two types of X-band ferrite-loaded isolators are proposed based on the substrate integrated waveguide (SIW) technology. First, a full-height E-plane ferrite slab is used to construct low-loss and high-isolation SIW isolators. The insertion loss is less than 2.2 dB and the isolation coefficient is larger than 30 dB within 400 MHz bandwidth. Then, a surface ferrite-loaded isolator is developed to simplify machining process. The ferrite slabs are mounted on the top and bottom surfaces of the SIW, but not inserted into rectangular holes within the SIW. The insertion loss is less than 3.2 dB ranging from 9.79 to 10.4 GHz. Both the return loss and isolation coefficient are better than 20 dB over the same frequency range.

This paper presents a high-gain on-chip antenna implemented in standard Si technology for millimeter-wave applications. A cubic dielectric resonator is mounted upon a `microstrip' form circular patch antenna. Different from other works, a very thin SiO2 layer which is of about 4μm thick is used, and the whole structure is rather simple, which means that it can be easily fabricated and scaled. The fabricated antenna occupies a size of 1.45 mm*0.9 mm. The simulation results indicate that the gain at 95 GHz and 99.4 GHz are 4.0 dBi and 4.6 dBi, respectively. And the peak efficiency and radiation efficiency of the proposed antenna reaches 62% and 72%. While the antenna efficiency and realized gain from 92.5 GHz to 95.8 GHz and from 98.7 GHz to 100.1 GHz for side-fire radiation are above 35% and 0 dBi.

In this paper, a novel focusing method in non-invasive microwave thermotherapy for breast cancer is proposed. Since the antennas used in the non-invasive microwave thermotherapy devices are no longer working as a far field transmitter, only its near field characteristics are critical to the performance of the system, design methods and principles have to be refreshed towards a better thermotherapy device. The method proposed in this paper focuses on the application of microstrip structure in these systems, is based on the nature of near field characteristic of microstrip antenna, thus to enhance the energy density of the target area. This novel device will achieve near field focusing effect by using single antenna, instead of antenna array, lenses or other methods that are usually utilized in communication systems. The focusing effect is verified and demonstrated by well-designed numerical experiments, and the results show that this method is very promising in the treatment of breast cancer.

A small-size low-profile narrow-frame antenna for seven-band WWAN/LTE operations in the internal smartphone applications is proposed. The greatest highlight of this proposed antenna is that its narrow edge has a width of only 5 mm, which is very novel for smartphone applications. Meanwhile, the proposed narrow-frame antenna has a small size of 5 × 40 mm2 and a low profile of 3 mm above the circuit board, which makes it very promising for slim smartphone applications. The proposed antenna is capable of covering GSM850/900/DCS/PCS/UMTS 2100/LTE2300/2500 operating bands. Detailed design considerations of the proposed antenna are described, and both experimental and simulation results are also presented and discussed.

Dual-band dual-mode bandpass filters with good selectivity and wide upper-stop-band performance based on circular ring resonator is presented. The two first-order degenerate modes are excited and split to form the first passband ,while one of the third-order degenerate modes forms the second passband together with a second-order degenerate mode. After installing two parallel-coupled-line sections on a ring at the two ports with 90 degrees-separation,five transmission zeroes are produced for the rejections between the two passbands and in the stopband. A dual-band filter with the two transmission poles in each passband is designed and measured, the measured filter shows good agreement with the simulated.

A traveling-wave circularly-polarized microstrip array antenna is presented in this paper. It uses a circularly polarized dual-feed radiating element. The element is a rectangular patch with two chamfered corners. It is fed by microstrip lines, making it possible for the radiating element and feed lines to be realized and integrated in a single layer. A four-element array is designed, built and tested. Measured performance of the antenna is presented, where a good agreement between the simulated and measured results is obtained and demonstrated.

In this paper, an extension of the integral equation based on domain decomposition method (IE-DDM) is presented for dynamic electromagnetic scattering problems above a lossy half space. In the framework of the IE-DDM, the proposed method divides the composite object into several homogeneous sub-domains. Each sub-domain is properly described by a closed surface, and robin transmission condition is introduced to weakly enforce the continuity of tangential field across the touching-face between adjacent sub-domains. Multiple-grid precorrected fast Fourier transform (MG-pFFT) is adopted in each sub-domain independently to account for the self-interactions. Numerical experiments validate the accuracy and efficiency of this method.

This Chapter review the fast Fourier transform (FFT) technique and its application to computational electromagnetics, especially to the fast solver algorithms including the Conjugate Gradient Fast Fourier Transform (CG‐FFT) method, Precorrected Fast Fourier Transform (pFFT) method, Adaptive Integral Method (AIM), Greens Function Interpolation with FFT (GI‐FFT) method and Integral Equations with FFT (IE‐FFT) method. The basic ideas used in the FFT applications are addressed while the brief introduction to integral equation method is conducted. The general formulation and procedure in the integral equation method, surface integral equations, volume integral equations, solutions to integral equations, and their implementations of fast Fourier transform algorithm are also briefed together with fast convolution using fast Fourier transform. Fast integral equation method developed based on fast Fourier transform are reviewed where conjugate gradient fast Fourier transform method, and precorrected fast Fourier transform method (where projection operators and interpolation operators are also highlighted), adaptive integral method, Greens function interpolation with FFT approach and integral equations with FFT method are also described. While the matching schemes for gradients of Green's functions are addressed, accuracy and complexity, memory requirement and computational cost, and error controls and estimations are also discussed.

ABSTRACTA compact ultrawideband (UWB) planar bandpass filter (BPF) using quad‐T‐stub‐loaded ring resonator is presented. At this filter, two sets of the four high impedance lines at the two sides of the ring as the coupling fed structure are used to gain much stronger coupling effect. Compared with the conventional ring resonator filter, the bandwidth of the UWB BPF can be improved after we load four T‐shaped stubs on the ring resonator. That is because these stubs can increase the effective electrical lengths, and also lower the second and third resonant frequencies of the ring resonator at no expense of the size increase. Finally, a prototype of the proposed UWB BPF with 3 dB fractional bandwidth of 101% has been designed and fabricated. The measured results are in good agreement with the full‐wave simulations. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1988–1991, 2014

This paper presents a miniature and high gain on-chip V band microstrip antenna. A ground plane on the bottom metal layer M-1 has been approached to shield the wave from penetrating into the low-resistivity and high dielectric constant Si substrates to improve the antenna performance. Antenna parameters have been investigated to obtain an optimized antenna with 0.87 mm * 1.16 mm occupation. The measured and simulated return loss results and simulated radiation pattern results of proposed antenna have been presented. The performance of the proposed antenna as compared to other published on-chip antennas has also been demonstrated.

A function-reconfigurable double-helix printed antenna, inspired by DNA structures, is proposed. The antenna, consisting of two metal strips printed on a substrate, was designed, optimized, and fabricated. It was more stable than a metal-wire antenna. The antenna was demonstrated to have a remarkable functional reconfigurability with different lumped elements between the two helices. When the element is chosen as a capacitor, the antenna works as a broadband and high-gain antenna. When the element is an inductor, the antenna operates as a frequency-tunable antenna with a wide tuning range. While the antennas with both elements are circularly polarized, good performance of these antennas is exhibited.