This paper proposes a new mobile handset antenna structure to reduce the value of the specific absorption rate (SAR). The antenna is based on the PIFA structure and operates at dual-bands of 0.9 GHz and 1.8 GHz. The chassis current is reduced using a metallic shim-layer inserted between the patch and chassis. This shim-layer is connected to the handset chassis through posts whose number and positions are determined using optimization techniques. Sidewalls are attached to increase the gain of the antenna and reduce the radiation towards human head. Simulations in the cheek mode show that the SAR reduction factor (SRF) of the proposed structure averaged over 10-g is more than 75% at 0.9 GHz and 46% at 1.8 GHz. The SRF values obtained using simulations and measurements are found to be better than 51% and 76% at 0.9 GHz and 1.8 GHz, respectively.

The design of a thin tunable and steerable Fabry-Perot antenna is presented. The subwavelength structure is analyzed both by an efficient transmission line model and by full-wave simulations. The tunable antenna consists of a low profile resonant cavity made up of a Partially Reflecting Surface (PRS) placed in close proximity of a tunable high-impedance surface. The active ground plane is synthesized by loading the high-impedance surface with varactor diodes. Such design allows both tuning the high-gain operational frequency and obtaining a beam steering/shaping for each resonant frequency. The transmission line model here presented includes averaged analytical expressions for modelling the tunable high-impedance surface and the frequency selective surfaces. All the theoretical speculations are verified by full-wave simulations on a finite size structure.

The present study discusses some numerical techniques on the simultaneous use of the Fast Multipole Method (FMM) and specialpurpose computer (MDGRAPE-3) to make the impractically expensive calculation feasible without the loss of numerical accuracy. In the present calculations, the impingement of two identical inclined vortex rings has been studied, and the computation time has been reduced by a factor of 1000 at N=1.18 × 10⁶ where N is the number of vortex elements. The direct and MDGRAPE-3 calculations both have a scaling of O(N²), and the use of the FMM brings them both down to O(N). The global kinetic energy, enstrophy and energy spectra have been investigated to address the numerical accuracy and have good agreement with other similar works.

Communication technology is increasingly pervading everyday life. The rapid progress in wireless communication besides the increasing interest in wearable antennas and electronics in civil, medical, sport wear and military domains promises to replace wiredcommunication networks in the near future in which antennas are in more important role. Recently, there has been growing interest in the antenna community to merge between wearable systems technology, Ultra-Wideband (UWB) technology and textile technology. All these together have resulted in demand for flexible fabric antennas, which can be easily attached to a piece of clothing. In this paper, three different structures of UWB antennas using clothing materials and suitable for wearable application were fabricated and presented. The substrate of the designed antennas was made from jeans textile material, while radiating element and ground plane are made out of copper tape. The operating frequency of all three designs is between 3 GHz and 12 GHz. Measured results are compared with simulations and good agreement was observed.

A doubly balanced monolithic microwave passive mixer using novel configurations is designed and fabricated through a 0.15 μm GaAs pHEMT process. The configuration of the doubly balanced mixer (DBM) can eliminate the use of two dual baluns for application in the conventional star mixer, as well as make the mixer more compact and simplify IF extraction to obtain wider IF bandwidth up to 15 GHz. From the measured results, the fabricated DBM exhibits wideband performance, superior isolations and high dynamic range.

In this work, the analysis and design of wideband microstrip yagi and bi-yagi antenna arrays with photonic band gap (PBG) is presented. By using the bi-yagi planar array, a high directive gain and a high frontto-back ratio are achieved in comparison with that of the single microstrip yagi structure. The current distribution, the return loss, the radiation pattern, and the input impedance are calculated. For a single yagi, wide bandwidth up to 12.81% at 10.15 GHz is obtained. However, a high directive gain is achieved with the bi-yagi. The PBG structures force the antennas to have stop band at the higher end of the operating band. In addition, it increases the front-to back (F/B) ratio. The finite difference time domain (FDTD) with the perfect matched (PML) and a numerical package based on the method of moment (MOM) are used in the present analysis and design. A closed form based on an approximate equivalent circuit is used to get approximate dimensions of the PBG structures.

We showed that creating coupling between resonators through transverse electromagnetic transmission line directly tapped into both resonators provides a viable solution for the design of wideband microwave components where strong coupling values are required. However, more analysis is needed to explain the coupling mechanism and its limitation. In this work, we present the developed equivalent circuit model which is comprised only of lumped elements for comprehensive analysis of the tapped-in coupling between planar or cavity combline resonators. The effects of lumped elements which are in correspondence to physical parameters on coupling value and resonant center frequency are derived. The circuit model predicts that this coupling mechanism by adjusting the design parameters of coupling section simply realizes any required strength of coupling between resonators, i.e., from weak values close to zero up to strong values close to unity. Therefore, wideband filters are easily designed and their bandwidth can be controlled based on inter-resonator tapped-in coupling. This fact is validated through measurements for two-coupled resonators with unloaded resonant frequency of 1.45 GHz. The bandwidth is extended to 90% via tapped-in method. The total dimensions of structure are λ/4 × λ/18 × λ/72.

A non-canonical inhomogeneous background medium is one whose Green's function cannot be obtained by an analytical method. Electromagnetic scattering from objects embedded in a non-canonical inhomogeneous background medium is very challenging because of the computational complexity with the calculation of its Green's function and the multiple scattering between objects and the background. This work applies the Diagonal Tensor Approximation (DTA) to calculate the scattering from arbitrary objects in a noncanonical inhomogeneous background. Previously, the DTA has only been applied to a canonical background such as a homogeneous or layered background media. This approach employs a numerical method to obtain all Green's functions required in the calculation; an accurate DTA is used to calculate the scattering properties. In order to reduce the large number of simulations, we employ the symmetry and reciprocity in the Green's function calculation. Furthermore, considering that most realistic imaging measurements are made through a voltage probe usually represented by a wave port, we develop a method to convert the scattered field on the probe (the antenna) to the measured wave port voltage. Numerical results show that this method can obtain accurate scattering characteristics from arbitrary objects in a non-canonical inhomogeneous background medium in a microwave imaging system.

The diagonal loading method is a simple and efficient method to improve the robustness of beamformers. However, how to determine the ideal diagonal loading level has not been adequately addressed. In this paper, it is observed in the simulation that the peak of the main beam is moved with the diagonal loading level when there exists a Direction of Arrival (DOA) estimation error. Based on the observation, a novel diagonal loading method is proposed, and a tradeoff exists between the robustness and the interference suppression capability by controlling the peak location of the main beam. As long as the DOA estimation error is less than the half of the width of main beam, the proposed beamformer will not suppress the Signal of Interest (SOI) as interference. Numerical experiments prove the effectiveness of the proposed method.

This paper presents a system with experimental complement to a simulation work for early breast tumor detection. The experiments are conducted using commercial Ultrawide-Band (UWB) transceivers, Neural Network (NN) based Pattern Recognition (PR) software for imaging and proposed breast phantoms for homogenous and heterogeneous tissues. The proposed breast phantoms (homogeneous and heterogeneous) and tumor are constructed using available low cost materials and their mixtures with minimal effort. A specific glass is used as skin. All the materials and their mixtures are considered according to the ratio of the dielectric properties of the breast tissues. Experiments to detect tumor are performed in regular noisy room environment. The UWB signals are transmitted from one side of the breast phantom (for both cases) and received from opposite side diagonally repeatedly. Using discrete cosine transform (DCT) of these received signals, a Neural Network (NN) module is developed, trained and tested. The tumor existence, size and location detection rates for both cases are highly satisfactory, which are approximately: (i) 100%, 95.8% and 94.3% for homogeneous and (ii) 100%, 93.4% and 93.1% for heterogeneous cases respectively. This gives assurance of early detection and the practical usefulness of the developed system in near future.

In this letter, a compact and high selectivity broadband bandpass filter (BPF) is proposed using the dual-mode folded-T-type resonator and the short stub loaded parallel-coupling feed structure. The resonator can generate one even-mode and one odd-mode in the desired band. Two resonant frequencies can be adjusted easily to satisfy the bandwidth of the BPF. A parallel-coupling feed structure with a cross coupling has been applied to generate two transmission zeros in the lower and upper stopband. Furthermore, the loaded short stub can create two transmission zeros near the upper cut-off frequency and in the upper stopband. Simultaneity, the transmission zero in the lower stopband moves towards the cut-off frequency. One filter prototype with the fractional bandwidth 57% is fabricated for experimental verification of the predicted results. The size for the resonator is only 0.156λ_g×0.303λ_g in which λ_g is the guided wavelength of 50 Ω microstrip at the center frequency.

In order to use power splitter for communication and real world applications (e.g., telephony performances, antenna designs, wireless communications, digital communications, optical communications, CATV transmission systems, airborne systems), studying the nature and characteristics of the splitter is important. The purpose of this paper is to review and discuss various techniques aimed to develop the power splitters component and remove its interference. This paper further focuses on the review of future implementation techniques and performance comparison along with their applications. Some of the applications are illustrated at the end of the paper, and recommendation for further study is also outlined. This review serves as a comparative studies and reference beneficial for power splitter researchers and for future implementation of the technology. This review paper opens a corridor for researchers to perform future comparative studies between different architectures and models as a reference point for developing more powerful, flexible and efficient applications.

In this paper several Defected Microstrip Structure (DMS) are used to suppress the first and second spurious responses in microstrip hairpin filters. The DMSs are integrated in filter structure, and therefore this method keeps the filter size unchanged. The DMS interconnection disturbs the current distribution only across the strip, thereby giving a modified microstrip line with certain stop band. The undesired spurious harmonics are suppressed through multiple transmission zeros which are added at these frequencies by designed DMSs. Experimental results verify that 25 dB suppression for the first harmonic and 40 dB suppression for the second harmonic, respectively, without affecting the main passband response. There is a good agreement between the simulated and measured results.

A simple electromagnetically coupled broadband printed microstrip antenna suitable for multifunctional wireless communication bands is presented. V-slots and corner notches are employed in a rectangular patch to achieve broadband operation. The proposed antenna has a 2:1 VSWR bandwidth of 51% from 3.75 GHz to 6.33 GHz. The simulated and measured reflection characteristics of the antenna along with the radiation patterns and gain are presented and discussed.

Microwave properties for a bilayer structure made of the high-temperature superconducting and the ferromagnetic materials are theoretically investigated. The properties are explored through the effective surface impedance calculated by using the enhanced two-fluid model for high-temperature superconductors together with the transmission line theory. The calculated effective surface impedance will be numerically analyzed as a function of the frequency, the temperature, and the thicknesses of the constituent layers. It is found that, for a thinner superconducting film, the effective surface resistance is a strong function of the frequency, and the effective surface reactance exhibits a peak and a dip in the frequency-domain. In the study of the effect of thickness in ferromagnetic substrate, there is a peak frequency in the surface reactance for a thinner substrate. There is also a threshold thickness for the ferromagnetic substrate such that it behaves like a bulk substrate when its thickness is larger than this threshold value. In the temperature dependence of surface reactance, the peak near critical temperature is shifted to lower temperature and broadened as the film thickness decreases.

A new type of evanescent-mode substrate integrated waveguide (SIW) bandpass filter is presented in this paper, with complementary split ring resonators (CSRRs) introduced on the top or bottom metal planes of the waveguide. Both positive and negative couplings are obtained between the CSRRs by changing their locations and orientations. In comparison with conventional SIW filters, the proposed filters are compact since their passbands are below the cutoff frequency of SIW. A third- and a fourth-order cross-coupled filter prototypes were designed using standard PCB technology. They operate at the same central frequency of 3.8 GHz, with their fractional bandwidths of 15% and 20%. The proposed filters have a wide upper stopband as the cutoff frequency of TE10-mode in the SIW is much higher than the central frequency. Their good performance is demonstrated by both the simulated and measured S-parameters.

The size of an antenna should be relatively large in order to get high radiation directivity. However, in some applications, the antenna is restricted in small region, while high directivity is still required. In this paper, we propose the method of realizing antennae with large effective apertures using arbitrary shaped small PEC reflectors and small volumes of left-handed materials based on coordinate transformation. Using this method, antennae with effective large parabolic apertures are designed using both a small parabolic reflector and a planar reflector. This design method is validated by the numerical simulations based on the Finite Element Method (FEM).

In this study, an inverse microwave scattering model for sea ice has been developed for the purpose of sea ice thickness retrieval using radar backscatter data. The model is loosely based on the Radiative-Transfer-Thermodynamic Inverse Model for Sea Ice Thickness Retrieval from Time-Series Scattering Data. The developed inverse model is a combination of the Radiative Transfer Theory with Dense Medium Phase and Amplitude Correction Theory (RT-DMPACT) forward model and the Levenberg-Marquardt Optimization algorithm. Using input data from ground truth measurements carried out in Ross Island, Antarctica, together with radar backscatter data extracted from purchased satellite images, the sea ice thickness of an area is estimated using the inverse model developed. The estimated sea ice thickness is then compared with the ground truth measurement data to verify its accuracy. The results have shown good promise, with successful estimation of the sea ice thickness within ±0.15 m of the actual measurement. A theoretical analysis has also revealed that the model faces difficulty once the sea ice thickness exceeds 1.7m. This can be considered in the future development and improvement of the model.

We have investigated the possibility of building a singleband Dicke radiometer that is inexpensive, small-sized, stable, highly sensitive, and which consists of readily available microwave components. The selected frequency band is at 3.25--3.75 GHz which provides a reasonable compromise between spatial resolution (antenna size) and sensing depth for radiometry applications in lossy tissue. Foreseen applications of the instrument are non-invasive temperature monitoring for breast cancer detection and temperature monitoring during heating. We have found off-the-shelf microwave components that are sufficiently small (<5 mm×5 mm) and which offer satisfactory overall sensitivity. Two different Dicke radiometers have been realized: one is a conventional design with the Dicke switch at the front-end to select either the antenna or noise reference channels for amplification. The second design places a matched pair of low noise amplifiers in front of the Dicke switch to reduce system noise figure. Numerical simulations were performed to test the design conceptsbefore building prototype PCB front-end layouts of the radiometer. Both designs provide an overall power gain of approximately 50 dB over a 500 MHz bandwidth centered at 3.5 GHz. No stability problems were observed despite using triple-cascaded amplifier configurations to boost the thermal signals. The prototypes were tested for sensitivity after calibration in two different water baths. Experiments showed a superior sensitivity (36% higher) when implementing the low noise amplifier before the Dicke switch (close to the antenna) compared to the other design with the Dicke switch in front. Radiometer performance was also tested in a multilayered phantom during alternating heating and radiometric reading. Empirical tests showed that for the configuration with Dicke switch first, the switch had to be locked in the reference position during application of microwave heating to avoid damage to the active components (amplifiers and power meter). For the configuration with low noise amplifier up front, damage would occur to the active components of the radiometer if used in presence of the microwave heating antenna. Nevertheless, this design showed significantly improved sensitivity of measured temperatures and merits further investigation to determine methods of protecting the radiometer for amplifier first front ends.

The complete design of 35 GHz, 200 kW gyrotron for various material processing and heating applications is presented in this article. The components of the device, such as Magnetron Injection Gun, interaction cavity, collector and RF window, are designed for the TE03 mode. Various in-house developed codes (GCOMS, MIGSYN and MIGANS) and commercially available codes (MAGIC, EGUN and CST-MS) are used for the design purpose. A thorough sensitivity analysis of the gyrotron components are also carried out. The designed device shows the capability to generate more than 200 kW of output power with more than 40% of efficiency.