This paper mathematically models the operation of Arrayed Waveguide Grating (AWG) based multiplexer (MUX) and demultiplexer (DEMUX) used in optical networks. In WDM networks, the optical MUX and DEMUX play a crucial role of managing the aggregation and segregation of wavelengths for networking applications. A simple and intuitive model of AWG based MUX design is discussed in this work. This model assumes that the device is linear, in which the principle of superposition is valid, and the primary emphasis is given to the optical power gain of the individual wavelengths. By using this model, one can exactly estimate the individual and overall power associated with each of the multiplexed wavelengths. The developed model was evaluated with experimental results using AWG based multiplexers. The experiments were repeated for different test cases with various power input levels and multiplexer configurations. It was found that the developed model provided a good approximation to the actual AWG mux/demux.

A new design for a compact and wideband circularly-polarized rectenna with high efficiency operating at X-band is proposed. A dual-slot coupled antenna excited by an H-shaped slot fed by a T-shaped microstrip is designed to yield wideband performance as a receiving array antenna. Rectifying circuit models for harmonic suppression circuit, impedance matching, DC-pass circuit, and DC return circuit at the input and output of the diode are built up and optimized to transfer the maximum power from the antenna to the load using an ADS circuit simulator. An RF-DC conversion efficiency of 71.9% is measured on the conditions of 300 load, and 50.1 mW RF input power at 9.5 GHz operating frequency. For the proposed wideband rectenna, the efficiency of more than 50% is measured over a 1 GHz frequency bandwidth. The measured gain, axial ratio, and return loss of the circularly polarized antenna with a 4-element array are 11.2 dBi, 1.1 dB, and -16.4 dB, respectively. The reflection coefficient of the array antenna is measured at less than -10 dB over a wide frequency range of about 2 GHz. Using this antenna as transmitting (TX) and receiving (RX) radiators, the free-space power transfer capability of the rectenna is tested in free space to turn on an LED at 25 cm distance.

In this paper, the feasibility of Substrate Integrated Waveguide (SIW) couplers, fabricated using single-layer TACONIC RF-35 dielectric substrate is investigated. The couplers have been produced employing a standard PCB process. The choice of the TACONIC RF-35 substrate as alternative to other conventional materials is motivated by its lower cost and high dielectric constant, allowing the reduction of the device size. The coupler requirements are 90-degree phase shift between the output and the coupled ports and frequency bandwidth from about 10.5 GHz to 12.5 GHz. The design and optimization of the couplers have been performed by using the software CST Microwave Studio©. Eight different coupler configurations have been designed and compared. The better three couplers have been fabricated and characterized. The proposed SIW directional couplers could be integrated within more complex planar circuits or utilized as stand-alone devices, because of their compact size. They exhibit good performance and could be employed in communication applications as broadcast signal distribution and as key elements for the construction of other microwave devices and systems.

An ultra wideband (UWB) monopole antenna with dual band-notch characteristic is proposed. Dual arm spiral resonators (DASR) are placed on both sides of the feed line to create band notches at 5.25 and 5.8 GHz for the upper and lower WLAN bands respectively. First the antenna is optimized individually for both upper and lower WLAN band-notch behaviors then embedded together for dual band-notch characteristic. The measured results ensure that two band notches are achieved, and the antenna can be used for UWB applications without any interference from WLAN band.

It is a common synchronization approach of the bistatic Synthetic Aperture Radar (BiSAR) with spaceborne/stationary configuration that obtains synchronization information from a direct signal. An easy and effective synchronization method is using the direct signal as a match filter to compress the echo for range compression. This method requires a high signal-to-noise ratio (SNR) of the direct signal, because the low SNR of the direct signal affects the synchronization result. Furthermore, it affects the imaging quality and bistatic-InSAR (BiInSAR) result seriously. Two factors affect the SNR of the direct signal: low gain and saturation. The transmitter and receiver antenna beam patterns cause the received direct signal's power variance during the exposure time. The requirement of high gain and no saturation cannot be satisfied simultaneously during the exposure time when the receiver sub-system does not have automatic gain control (AGC). In this paper, a modified synchronization approach is proposed. The proposed method not only tolerates the low gain and saturation, but also does not require the parameters of the transmitted signal, such as FM chirp rate, bandwidth and transmitted pulse length. The proposed method makes the gain design of the synchronization channel easy. The experiment results verifies the effectiveness of the proposed approach.

For microwave tomography applications, we show that the utilized incident field distribution can affect the achievable image quantitative accuracy and resolution. In particular, for the synthetic cases considered here, it is shown that the use of a focused incident field distribution within the imaging domain often results in either enhanced or equivalent image reconstruction as compared to the use of an omnidirectional incident field distribution.

The traditional pattern synthesis method of space-borne array is to achieve a ``iso-flux'' beam coverage via approximating a desired pattern; however, the synthesized pattern may not optimize the whole satellite communication (SatCom) system performance. This paper analyzes the interference in multibeam SatCom system using CDMA, and establishes the relation model between user capacity and multibeam pattern. Additionally, a novel particle swarm optimization (PSO) based on simulated annealing (SA) pattern synthesis method is proposed, which chooses user capacity as synthesis objective function. The numerical analysis, which is performed for a hexagonal array with 19 stacked patch elements, confirms that user capacity is at least doubled with the ``max-gain-flux'' beam coverage implemented by our method, compared to the ``iso-flux'' coverage when communication outage probability is 10%.

A novel compact planar monopole antenna for UWB applications is proposed in this paper. The proposed novelty of the antenna is attributed to the addition of suitable beveled stubs to a basic circular geometry of the radiator as an improved impedance matching technique to achieve enhanced radiation performances. The feed circuit is a tapered microstrip line with a matching section over a semi-elliptical ground plane. The proposed antenna achieves sufficient impedance bandwidth for a VSWR<2 for frequencies from 3-15 GHz covering the entire UWB range (3.1-10.6 GHz), which is verified experimentally. Also this design achieves good gain, constant group delay and a near omni-directional radiation pattern over the UWB band. The UWB characteristics of the antenna are evaluated in frequency and time domains. Results reveal that the proposed antenna has flat transfer function, linear phase and good impulse response with virtually no ringing which are the essential requirements for an UWB antenna for efficient pulse transmission/reception. The simulated and measured results of these parameters are presented. The performance results of the novel antenna with other designs is also compared and presented.

Minimum side-zone power to center-zone power ratio (MSCR) method is presented to estimate array errors of azimuth multichannel synthetic aperture radar (SAR). Spaceborne azimuth multichannel SAR is one of the most promising candidates for achieving high-resolution wide-swath imaging. However, array errors brought in by instrument influences and aperture position errors need to be compensated. MSCR method is designed to obtain phase error estimates by minimizing side-zone power to center-zone power ratio, where the side-zone and the center-zone indicate the intervals far from and around Doppler centroid respectively. The proposed method achieves significantly improved performance on phase error estimation especially when signal to noise ratio is low. Experiment results confirm the validity and solidity of the method.

A new analytical technique to study the complex resonances of a rectangular patch in a multilayered medium is introduced. The problem is formulated as an electric field integral equation (EFIE) in the spectral domain and discretized by means of products of Chebyshev polynomials of first and second kind multiplied by their orthogonal weights in a Galerkin's scheme. The method is fast convergent, i.e., few expansion functions are needed to achieve accurate results, but leads to the numerical evaluation of infinite double integrals of oscillating and slowly decaying functions. To overcome this problem, suitable half-space contributions are pulled out of the kernels of such integrals in order to obtain exponentially decaying integrands. Moreover, the slowly converging integrals of the extracted contributions are expressed as combinations of quickly converging integrals by means of algebraic manipulations and an appropriate integration procedure in the complex plane.

A compact U-shaped defective ground structure (DGS) and an inverted U-shaped resonator are introduced in order to reduce the mutual coupling (MC) between two slotted microstrip antennas at two different resonance frequencies. The proposed DGS and resonator have the same electrical length and both are placed in between two patch antennas, as a technique to suppress the occurrence of MC at two different frequency bands. The DGS and the resonator offer stop bands at 2.45 GHz and 4.5 GHz respectively. Simulated results show a reduction in MC of 20 dB at 2.45 GHz band and 10 dB at 4.5 GHz band. We have developed experimental models that have proved this concept of MC reduction. Finally, the influence of other parameters of the proposed antenna at the presence of the combination of DGS and resonator in the array system has been studied. Prototype antennas for different combinations of DGS and resonator and two-element array integrated with DGS and resonator have been fabricated, measured and the idea has been verified. A good agreement is observed between measured and the simulated results.

Theoretical results on the electromagnetic wave diffraction from a periodic strip grating placed on a chiral medium are obtained. Analytical regularization method based on the solution to the vector Riemann-Hilbert boundary value problem was used to get robust numerical results in the resonant domain, where direct solution methods typically fail. It was shown that in the case of normal incidence of linearly polarized wave the cross-polarized field appears in the reflected field. For elliptically polarized incident wave the diffraction character essentially depends on the polarization direction of the incident wave. These diffraction peculiarities are more pronounced in the resonant domain. Influence of the dichroism caused by chiral medium losses is thoroughly studied. The combination of a chiral medium and a grating can be effectively used for a frequency and polarization selection and for a mode conversion.

The characteristics of periodic multilayered near-field superlenses are analyzed and optimized, using the dispersion relation derived from an effective medium theory and the transfer function in the spectral domain. The k'_z-k''_x and k_z-k_x contours are used to explain and predict the spectral width, amplitude and phase of the transfer function. Superlenses containing CsBr or active layers are proposed to reduce image distortion or to compensate for the propagation loss, respectively. The parameters of the superlenses can be optimized by simulations to resolve half-pitch features down to λ/36 using CsBr layers, and λ/20 using active layers.

Radar scattered time domain response can be modeled by natural poles using singularity expansion method (SEM) in resonance region. In this paper, limitation of the conventional Extinction pulse method is brought out, and a hybrid of conventional Extinction pulse and auto-regressive (AR) method is proposed for robust discrimination of radar targets. A new target discrimination number (TDN) is suggested, which gives very good discrimination margin for enhanced decision process. The Hybrid Extinction pulse technique is applied on the free space targets as well as subsurface canonical metallic targets and the result obtained shows good discrimination margin. The free space target response was obtained using FDTD simulation and the subsurface target response was obtained using frequency domain measurement done for the targets buried under dry sand.

An improved directional equiangular spiral antenna with wide CP band and high gain is proposed, in which the impedance bandwidth is 2~12 GHz, CP bandwidth 4.5~7 GHz, and gain 6~9.5 dBi. The antenna includes 4 layers. The top layer is equiangular spiral antenna, and the bottom layer is ground. The middle two layers are parasitic metal films with irregular rectangular holes, which are introduced to improve the performance of equiangular spiral antenna and reduce the profile. The measured results are in good agreement with the simulated ones.

The purpose of this paper is to describe a model predictive direct torque control (MPDTC) with load angle limitation for surface-mounted permanent magnet synchronous motor (SPMSM) drive system. In this paper, an exact discrete-time state-space model of SPMSM is presented, which improves the state prediction accuracy comparing to simple Euler approximation. A finite control set type MPDTC is used to select the optimum voltage vectors applying to the voltage source inverter (VSI). It makes full use of the inherent discrete nature of VSI, and according to the predefined cost function it chooses the optimal solution from the possible switching states. It has been found that with the proposed scheme SPMSM drives show adequate dynamic torque performance and considerable torque ripple reduction as compared to traditional direct torque control (t-DTC). With the load angle limitation in the cost function, the proposed scheme can prevent the PMSMs falling from synchronism.

A novel extremely compact Zeroth Order Resonator (ZOR) antenna with a chip inductor, for Digital Video Broadcasting-Handheld (DVB-H) application, is presented. The proposed antenna has a bowtie structure with an overall dimension of 0.0186λ₀ × 0.020λ₀ × 0.003λ₀ mm³ at 503 MHz. The zeroth resonance property makes the resonant frequency to be independent of the antenna dimension. The 3:1 VSWR bandwidth of the antenna is 39 MHz and offers an omnidirectional radiation pattern. A 99.1% reduction in the overall area of the structure is achieved compared to a conventional circular patch antenna operating at the same frequency.

MIMO reference antennas are proposed for over the air (OTA) measurement applications. The reference antennas could get rid of feeding cable interference and control envelope correlation coefficients (ECC) continuously by only changing the length of an etched slot on a dual-feed PIFA. If only the ECC is investigated, the MIMO reference antenna is optimized to have a small variation of total efficiency from 70% to 50% when the ECC increases from 0.1 to 0.88. The prototypes are fabricated and measured in a scattered field chamber (SFC). Measurements agree well with the simulations. A practical example of applying this kind of reference antenna is provided. If the MIMO performance is studied, the MIMO reference antenna is proposed to own a large variation of total efficiencies from 90% to 47% while the ECC increases from 0 to 0.98. The bandwidth of the proposed reference antennas depend on the size of the antennas. This method is valid for all the frequencies.

Gaussian beam techniques are efficient asymptotic methods for field radiation computation. In these techniques, the initial field is first expanded on a chosen surface in elementary Gaussian beams which can propagate and/or interact with surrounding structures. However, the expansion cannot take into account surface and leaky waves propagation. In this paper, we propose an appropriate hybridization method using surface equivalent currents to overcome this limitation. The equivalent current formulation is written on grounded dielectric slab in spectral domain and can model surface and leaky waves which propagate from the surface expansion. The hybridization is carried out on the expansion surface, on which the distribution of elementary Gaussian beams and equivalent currents must be chosen in a relevant way. We study the influence of hybridization parameters and define a set of them leading to good results for general cases.

This paper proposes a miniature microwave bandpass filter. It comprises quasi-lumped suspended substrate stripline resonators of a new type. Their common substrate consists of two contiguous dielectric layers. Every resonator in the filter has three parallel strip conductors. Two of them are placed on the outer substrate surfaces and the rest is placed inside the substrate. The filter of the sixth order was designed with the use of special optimization rules that are universal for all resonator filters. The substrate of the fabricated filter was made of RT/Duroid 5880 (ε_r = 2.2, tan δ =0.002) with thickness of 0.127 mm. It has dimensions of 12 mm x 45.5 mm. The measured passband has a center frequency of 1.01 GHz, 3-dB fractional bandwidth of 11%, and minimum insertion loss of 1.4 dB. The 100-dB upper stopband extends up to 10.5 GHz.