This work presents extremely compact dual-mode and dual-band bandpass filter designs based on dual-resonance composite resonators developed by using integrated passive device (IPD) technology on a glass substrate. A dual-mode bandpass filter is also devised using a symmetric composite resonator with a perturbation element of grounding inductor to determine the filter bandwidth. Additionally, a feedback capacitive coupling path on the proposed dual-mode filter is implemented to produce three transmission-zero frequencies in the stopband. Furthermore, the proposed dual-band bandpass filter is designed in a high-density wiring transformer configuration with magnetic and electric mixed coupling. In addition to individually determining the fractional bandwidth of dual passbands, the magnetic and electric mixed coupling provides multiple transmission zeros to enhance the isolation between the two passbands and greatly improve the stopband rejection.

A coherent imaging system images a frame or an object onto a changing diffuser and projects the resulting pattern which generally contains speckles. Using a spatial light modulator (SLM) as the changing diffuser, the speckles in the pattern are suppressed without the need for any other mechanisms. With $M$ random phasor arrays being displayed in the SLM during the integration time of a detector, a suppression factor (C_f) of speckles, 1/√M, is achievable in the projected pattern, which is the sum of the intensity of M uncorrelated patterns. This paper shows both theoretically and in simulations that the C_f of the sum pattern was considerably reduced when two elementary patterns with fully developed speckles were negatively correlated. With the correlation coefficients of the elementary patterns found at [-0.3, -0.25], the C_f of the sum of 10 negatively-correlated speckle patterns was 48% lower than the C_f of the sum of 10\,uncorrelated speckle patterns. The negatively correlated patterns can be implemented using spatial light modulators or diffractive optical elements, and are used to suppress speckle noise in digital holography, laser projection display, and holographic display projections with relatively high efficiency.

This paper presents an inside-out axial-flux permanent-magnet brushless DC motor optimized by Finite Element Analysis (FEA) and Genetic Algorithm (GA) that uses sizing equation. The double-sided slotted-stator designed TORUS motor has sinusoidal back EMF waveform and maximum power density. The GA obtained the dimensions that gave the motor its highest power density. Field analysis of the dimensions was then put through FEA, to obtain and re-optimize the motor's characteristics. Possible design parameters were investigated via use of Commercial Vector Field Opera 14.0 software used in three-dimensional FEA simulation and of MATLAB 2010a in GA programming. Techniques such as modifying winding configuration and skewing the permanent magnets were explored to achieve the most-sinusoidal back-EMF waveform and minimized cogging torque. The desired technical specifications were matched by simulation results of the 3D FEA and the GA. The FEA and the GA simulation results comparison of the flux density in different parts of the designed motor at no-load condition agreed well.

A novel dual-mode bandpass filter (BPF) using stub-loaded defected ground open-loop resonator is proposed in this article. Defected arrow-shaped stub is loaded to a defected ground open-loop resonator, and two non-degenerate modes are excited for dual-mode characteristics. Based on even- and odd-mode theory, dual-mode characteristics of the resonator is analysed. Design equations for the defected-ground resonator are investigated. A two-pole dual-mode bandpass filter operating at 2.4 GHz with fractional bandwidth of 7.97% is designed, fabricated, and measured. Good agreement between simulated and measured results verifies the validity of this design methodology.

Transient electromagnetic topology (TEMT) method is presented briefly first and then three typical configurations, namely, a transmission line network, a wire penetrating a cavity aperture and then connecting to a device, and two systems connected by a shielded cable radiated by an electromagnetic pulse, are analyzed by using the TEMT method. The currents induced at the loads obtained by the TEMT method are compared with those from the experiment. The good agreement of the numerical results with the experimental ones validates the TEMT method.

Metamaterial absorbers can perfectly absorb an incident wave in a narrow frequency band. In this paper, metamaterial absorbers are used to construct a terahertz modulator. By controlling the carrier density in the n-doped semiconductor spacer between a patterned metallic superstructure and a metallic ground with different applied voltage bias, the absorption varies sensitively, and the reflected wave amplitude acting as the modulated signal can be strongly modulated. Two types of modulators are investigated, one of which possesses an array of metallic crosses as the superstructure, and the other has a complementary superstructure. Compared with the former, the latter may give a better modulation performance.

A novel microstrip-fed slot antenna with triple-band operation in compact size is proposed. The proposed antenna structure consists of a L-shaped microstrip feed line and open-ended slot on the ground plane, having small overall size of 14 x 34 mm². The open-ended slot constructed of crossed double T-shaped slots is aimed to obtain resonant modes at 2.4/3.5 GHz. Meanwhile, with the use of a via-loaded metal patch connected to the edge of ground, the upper resonant frequency point at 5.8 GHz is achieved. The numerical and experimental results exhibit the designed antenna operates over triple frequency ranges, fulfilling the standards of 3.5-GHz WiMAX and 2.4/5.8-GHz WLAN. In addition, acceptable radiation characteristic is obtained over the operating bands.

We propose a metamaterial coplanar stop-band filter made of multi-turn rectangular spiral particles. Numerical and experimental results show the feasibility of devices with dimensions more than 10 times smaller than those in the literature and with good performances.

A low-cost, high isolation, printed loop-antenna system for multiple-input multiple-output (MIMO) applications in the 2.4 GHz WLAN band is presented. By feeding the orthogonal eigenmodes of the array, port decoupling (S₂₁< -20 dB) with tightly coupled elements (only 0.07λ separation) is obtained. The orthogonal eigenmodes are realized based on 180° coupler. Then decoupled external ports of the feed network may be matched independently by using conventional matching circuits. With this low-cost and high isolation characteristic, it is very suitable for being embedded inside a wireless access point (AP).

We present an empirical mixing model for rectangular cuboid metal inclusions in a host dielectric, suitable for replacing the detailed structure of a layer of on-chip interconnects with a homogeneous dielectric slab. Such an approximation is required to facilitate the accurate and efficient package-level electromagnetic modelling of complicated miniaturised systems, such as System-in-Package. Without such an approach, the direct inclusion of large areas of on-chip interconnect structures often results in intractable computation times. Our model allows us to predict the reflection (transmission) coefficient of impinging plane waves to within 3.5% (0.2%) error for incident angles up to 30^o off-normal, aspect ratios 0.6-3, metal fill factors 0.3-0.6, and host dielectric constants 1-11.7, over the frequency range 1-10 GHz.

An equivalent circuit model for single negative metamaterial (MTM) transmission line based on microstrip complementary electric inductive-capacitive resonator (CELC) is proposed for the first time. The verified circuit model gives strong support to the interpretation of all exhibited electromagnetic (EM) phenomena. The nonpure magnetic and electric resonances have been demonstrated by constitutive EM parameters. Based on the conclusions that have drawn, a more compact sub-wavelength particle based on Hilbert-shaped CELC (H-CELC) is proposed. The design procedures of the H-CELC-loaded MTM cell are derived based on the circuit model. For application, a bandstop filter covering one of the ISM bands 5.2 GHz by cascading two H-CELC cells is designed, fabricated and measured. Consistent results between simulation and measurement have confirmed the design. The established theory based on the proposed circuit model is of reference value for the design of novel bandstop devices.

A novel coplannar waveguide (CPW) cross-fed antenna which is wideband, high-gain and omnidirectional is proposed. After simulating the antenna model by CST MICROWAVE STUDIO®, the results show that this antenna not only has compact size, but also can effectively broaden operating band, improve gain and remain omnidirectional. In addition, adjusting antenna elements' dimension and spacing can control the central frequency position of operating band and bandwidth. The simulated results of antenna surface currents can be used to explain the reason of antenna possessing broadband and omnidirectional high-gain characteristics. A CPW cross-fed antenna operating at 2.4 GHz is designed and manufactured for measurement. The prototype is printed on a FR-4 epoxy resin board with 1 mm thickness. The experimental results indicate that the operating band is 2.35-2.85 GHz with reflection coefficient less than -10 dB (relative bandwidth 19.2%), and maximum gain in H-plane can achieve 5.2 dBi. Measured results well match the simulated ones. Moreover, the total antenna size is 187 mm × 22.5 mm (1.5λ×0.18λ), which can make it suitable in WLAN systems.

2.4/5.7-GHz dual-band Weaver-Hartley dual-conversion downconverters are demonstrated using 0.35-μm SiGe heterojunction bipolar transistor (HBT) technology with/without a correlated local oscillator (LO) generator. In the first implementation, the correlated LO generator consists of a divide-by-two frequency divider, a frequency doubler and a single-sideband upconverter and thus LO₁(=2.5×LO₂) signal is generated. As a result, the downconverter with the correlated LO signals has over 39 dB image-rejection ratios for the first/second image signals (IRR₁/IRR₂) of the dual-conversion system at both 2.4/5.7-GHz modes while the downconverter without the correlated LO generators has a 6-dB higher conversion gain and IRR₁/IRR₂ of more than 44 dB with the same dc power consumption (excluding the LO generator). On the other hand, a 10-GHz Weaver-Hartley downconverter is demonstrated with a resonant LC load at the first-stage mixer to improve the conversion gain at high frequencies. The downconverter achieves a conversion gain of 8 dB with IRR₁/IRR₂ better than 43/40 dB.

This paper presents a high-efficiency Ka-band solid-state power combining amplifier on the basis of a novel waveguide magic tee. By employing 16 low-power amplifier modules and compact waveguide power combining network with a low loss microstrip-to-waveguide transition, the output loss of the combining circuit is minimized, so a high combining efficiency larger than 85% from 34 to 36 GHz is obtained. Modular architecture is adopted in the combiner design. The single amplifier, bias circuit and heat sink are all fabricated separately, which add great flexibility to the system. Modular amplifiers can be premade and reserved in case any malfunctioning amplifier needs to be replaced. In addition, the improved power combining amplifier has the advantages of low loss, high isolation, compact structure, excellent heat-sink, etc.

The microwave to direct current (MW-DC) conversion efficiency of a rectifier drops significantly in a dual-frequency microwave power transmission (MPT) system. The measured data show that the MW-DC efficiency of a rectifier drops from 67% to 53% when the microwave source is switched from a continuous wave to a dual-tone waveform at the same power level. It is mainly due to the intermodulation effects resulted from a nonlinear component, e.g., the diode, in a rectifier. A novel rectifier is designed to improve the MW-DC efficiency by recycling the intermodulation power besides the harmonic power. With the novel configuration, the maximum MW-DC conversion efficiency of 62% can be achieved for a dual-tone waveform input at 17 dBm. It implies that more than one half of the intermodulation power has been recycled to DC power.

A low-profile unidirectional cavity-backed coplanar waveguide-fed uniplanar log-periodic slot antenna suitable for the ultra-wideband applications (3-18 GHz) is presented. Due to the inherent balanced structure compared with the unbalanced antennas, such as dipole or loop antenna, the impedance matching and radiation performances of the proposed antenna are quite stable and satisfactory. There is a potential advantage for low profile ultra-wideband unidirectional antennas, and this paper demonstrates a technique for transforming the bidirectional beam into a unidirectional beam by using a special cavity in this ultra-wideband antenna. Meanwhile, the multi-resolution time domain (MRTD) method is applied to analyze this antenna. Experimental results reveal that the cavity has a small affect on the S-parameter of the origin antenna, and remains the perfect reflection property within the desired operation band.

A novel band-stop filter with wide upper pass-band performance is proposed and discussed in this paper. This band-stop filter includes two three-section transmission-line stubs and a parallel coupled-line section. Because three-section transmission-line stubs and coupled-line section are used, this filter not only features good band-stop filtering property, but also has wide upper pass band. In order to verify this new filter circuit structure and its corresponding design theory, three groups of numerical examples are demonstrated. Finally, two practical band-stop filters using common microstrip technology are designed, simulated and measured. The simulated and measured results indicate that both the coupled-line section with weak coupling and two three-section stubs can improve the upper pass-band performance. Furthermore, the measured results of the second fabricated microstrip band-stop filter (Filter B) show that the 20-dB insertion-loss band-stop bandwidth at 0.46 GHz is 90 MHz and the 1.2-dB transmission coefficient upper pass band is from 0.66 GHz to 2.52 GHz. Thus, the highest pass-band frequency is extended to larger than five times of the operating center frequency of stop band.

A novel Gysel power divider based on patch type structure is presented in this paper. The proposed power divider possesses broad bandwidth, small physical occupation and arbitrary power division. More than 30% bandwidth enhancement is achieved based on the -15 dB input return loss criteria, while 55% size reduction is realized compared with conventional Gysel power divider. What's more, flat dividing is obtained in the design without using additional transmission line sections. Based on the novel structure, a design procedure of power dividers with unequal power division ratios is provided without using narrow microstrip line. To verify the design approach, the proposed power dividers with equal and unequal (2:1 and 4:1) power divisions at the centre frequency 1.5 GHz are fabricated and measured. The results demonstrate that the design can fulfil our goals.

The performance of traditional beamformers tends to degrade due to inaccurate estimation of covariance matrix and imprecise knowledge of array steering vector. The inaccurate estimation of covariance matrix can be attributed to limited data samples and the presence of desired signal in the training data. The mismatch between the actual and presumed steering vectors can be due to the error in the position (geometry) and/or in the look direction estimate. In this paper, we propose a differential evolution (DE) based robust adaptive beamforming that is able to achieve near optimal performance even in the presence of geometry error. Initially, we estimate an optimal steering vector by maximizing and minimizing the signal power in and out of the desired signal's angular range, respectively. Then, we estimate the look direction and reconstruct the covariance matrix. Based on the obtained steering vector, estimate for look direction and reconstructed covariance matrix, near optimal output SINR, can be obtained with the increase in the input SNR without observing any saturation even in the presence of geometry error. Numerical simulations are presented to demonstrate the efficacy of the proposed algorithm.

Focusing bistatic synthetic aperture radar (SAR) data in frequency domain requires two-dimensional (2D) point target reference spectrum (PTRS). Loffeld's bistatic formula (LBF) and the Method of Series Reversion (MSR) have been introduced recently to compute PTRS of bistatic SAR. In this paper, firstly we generalize the original LBF (OLBF) by introducing the Doppler contribution functions of transmitter and receiver. Thus, OLBF and its derivatives (e.g., extended LBF) can be viewed as special forms of the generalized LBF with constant Doppler contributions. Based on this, secondly the ideal LBF (ILBF) with no computing error, except the error resulting from the principle of stationary phase, is also presented. The ILBF reveals that the theoretical PTRS of bistatic SAR consists of only two monostatic terms, but it does not include bistatic deformation term in comparison with OLBF. It supplies us with a target when we deduce the PTRS for bistatic SAR. Finally, to get the precise analytical PTRS for general bistatic SAR, an approximated ILBF (AILBF) is proposed. It expresses the Doppler contributions of the transmitter and receiver as power series and can approach the ILBF very well. AILBF can keep the precision as MSR and inherit a simple form from LBF. In addition, error limit for the validity of bistatic PTRS is also given. The results in this paper can be used to develop imaging algorithms for extreme bistatic (e.g., spaceborne/airborne) and high squint (e.g., bistatic forward-looking) cases.