In this paper, without using external power and active components, a design of pin coupled functional antenna tuner is presented. The tuner consists of two parts, a coupling pin and a tuning circuit. It is used to tune the bandwidth and antenna gain of the proposed slot patch antenna. The prototype, including a slot patch antenna and the tuner, was constructed and excited through a T-shape microstrip feed circuit resonated at 2.6 GHz. The impedance bandwidth BW (-10 dB return loss) of the slot patch antenna without coupling to the tuner was 3% referred to the operation frequency at 2.6 GHz. When the tuner was matched with the impedance 75 Ω through the coupling pin to the proposed antenna, the BW of the antenna was increased to 11% operated at 2.6 GHz. However, if the tuner was matched with the impedance 25 Ω to the proposed slot patch antenna, the impedance bandwidth of the antenna was increased 21% at operation frequency. Relatively uniform antenna gain was obtained when the matching impedance was decreased from 75 Ω to 20 Ω. In the meantime, the lower matching impedance corresponds to more reducing cross-polarization of the proposed slot patch antenna can be observed in the measured field patterns.

Wireless implantable body area network (WiBAN) is useful for monitoring vital human parameters in medical diagnosis such as breast cancer, heart attack and high blood pressure. The main objective of this paper is to design a small printed monopole antenna for WiBAN applications at 6.0 GHz. The small implantable antenna was tested in a lossy environment by being submerged into canola oil that mimics the dielectric properties of human breast fat tissue. The antenna performances were measured by using vector network analyzer (VNA) in order to evaluate the return loss and operating bandwidth of the antenna. The other parameters such as efficiency, radiation pattern and gain are evaluated by simulation of CST Studio 2012 software. When compared, there is good agreement between the simulation and measurement results. The simulated antenna gain and efficiency are 5.8 dBi and 97%, respectively, when submerged into canola oil. The antenna radiation pattern is directional, and it has 6 lobes implying its coverage in more directions which is of good benefit due to body movement. The antenna's polarization was tested by placing a wideband antenna at several degrees around the proposed antenna. The value of S₂₁ was also analyzed to investigate the path gain of the selected links.

This paper considers the radar scenes which contain numerous rapidly changing terrains, i.e., there are more than one clutter-edge in the environment. This kind of radar scenes incurs sharply degradation in the performance of the present adaptive constant false alarm rate (CFAR) detectors as the statistical characteristic of reference cells is highly heterogeneous. To solve this problem, we propose a homogenous reference cells selector to improve the performance of CFAR detector in highly heterogeneous environment. The selector is comprised of an M-N clutter-edge detector cascading a terrain classifier. The M-N clutter-edge detector is used to obtain multiple clutter-edges in heterogeneous environment. With the detected clutter-edges, the terrain classifier is derived to obtain identical distributed range cells. Based on the selector, a modified Log-t-CFAR detector is suggested. Finally, the performance of the proposed selector and CFAR detector is evaluated by measured data and computer simulation.

In this paper, a novel monolayer multi-octave bandwidth log-periodic microstrip antenna (LPMA) is presented. This antenna consists of a 50 Ω microstrip feed-line and fourteen rectangular patch elements. Twelve rectangular patch elements are fed by edge-coupling from the microstrip feed-line and two other patch elements are directly connected with the microstrip feed-line. A mixed microstrip line feed is applied to expand the bandwidth. Our measured results closely agree with the simulated results. These results show that the proposed antenna lends itself well to operation in the impedance bandwidth from 2 GHz to 8 GHz with a voltage standing-wave ratio (VSWR) less than 2.

In this study, a three-dimensional (3-D) structural model of an adult male body, including 12 kinds of tissues and organs, was analyzed using a 3-D model design application (i.e., 3ds Max). The standard model of Asians was used as reference. The electrical parameters of brain tissues at different electromagnetic frequencies were introduced to obtain the electromagnetic model. Computational electromagnetic software based on the finite-difference time-domain was used to calculate the model absorption of electromagnetic waves under ultra-wide band electromagnetic irradiation. The specific absorption rates (SARs) of the ensemble average and the model human tissue were also obtained. This study aims to provide a parameter for the development of electromagnetic radiation protection standards, and to discuss related research.

A novel circular arc fractus named Arched Bow-shaped Fractal Curve (ABFC) is originally proposed. Four ABFCs are connected end-to-end, forming so called Arched Bow-shaped Fractal Loop (ABFL). The loop antenna peculiarly presents multiband multimode characteristics with resonance compression. The normal mode, which is pertinent to the loop area and circumference, is found improved with the iterative procedure. Thus, an eight-turned wire helix of small pitch angle (α=3 °) with a circular disc ground called Arched Bow-shaped Fractal Helix (ABFH) antenna is shaped from K₂ ABFLs. It can unprecedentedly operate in multiband of axial and off-axial modes with dual-sensed circular polarizations and high gain. Four matched bands (|S₁₁|≤-10 dB) are obtained within 2 GHz-8 GHz, of which f₁=2.34 GHz (400 MHz, 17.09%; G=10.63 dBi; RHCP), f₂=4.24 GHz (770 MHz, 18.16%; G=12.43 dBi; LHCP), f₃=5.48 GHz (300 MHz, 5.47%; G=8.13 dBi; RHCP), and f₄=6.98 GHz (960 MHz, 13.75%; G=15.89 dBi; RHCP). The unique multiband multimode property has been theoretically analyzed with illustrations and can be attributed to existence of the fractal boundary, which particularly encloses multiple equivalent loops with considerable areas. These peculiarities make K₂ ABFH antenna a very attractive candidate for multiband circularly polarized antennas, especially for space applications, such as spacecrafts communication, remote sensing, and telemetry, where reduction of quantity, height and weight of antennas are urgently wanted. It can also be configured into large array for higher gain service like radars and radio astronomy.

In this paper, a compact tri-band impedance transformer by utilizing stubbed coupling line for matching a load at three arbitrary frequencies is proposed. The transformer is composed of two parts, and each part is constructed from parallel-coupled transmission lines. Two structures with different configurations of the proposed transformer have been given and analyzed. Then, the close-form equations for the transformer parameters are derived analytically, and the corresponding analytical design approach is verified by numerical examples. To certify the validity of design formulas, an impedance transformer is fabricated and measured at 0.9/1.8/3.2 GHz. Good experimental performances at each frequency are obtained, which are in good agreement with the simulated results.

Cooperative wide-band spectrum sensing has been considered to enable cognitive radio operation of wireless regional area networks (WRAN) in the UHF and VHF TV broadcasting bands. In this paper, cooperative compressed spectrum sensing is considered to enable fast sensing of the wide-band spectrum. The speed and accuracy of spectrum sensing are improved by further optimization of the compressed sensing receiver, which is done blindly without any prior knowledge of the sensed signal. Enhanced compressed spectrum sensing algorithms are proposed for the cases of individual spectrum sensing and cooperative spectrum sensing (CSS). The cooperative signal reconstruction process is modified to optimally combine the received measurements at the fusion center. A low complexity authentication mechanism, which is inherent to cooperative compressed spectrum sensing, is proposed to make the cognitive radio system immune to adversary attacks.

This article describes a time-domain transmission line model based on distributed parameters for transient analysis. This model is based directly on the differential equations for the basic transmission line without any previous simplification. The solution presented here for these differential equations results in a more detailed time-domain model than others models currently in use, and with certain structural similarities with the distributed parameter frequency-domain model for long transmission lines. The deduction of a general time-domain transmission line model for fundamental frequencies parameters and single-phase line are presented in this article, but the model can also be extended to cases with multiconductor and frequency-depended parameters. In order to validate the model, a comparative test is presented to facilitate the analysis about the main similarities and differences between this and other models.

The synthetic aperture radar (SAR) is a widely used instrument for high-resolution imaging from aircraft or satellite platforms. In the paper, the problem of the defocusing of multi-look SAR images by uncompensated phase errors presented in the received data is analyzed. It is shown that the phase errors on a multi-look processing interval can be effectively described in terms of local quadratic and local linear phase errors. Approximate analytical expressions are derived to describe the azimuth resolution degradation. Criteria for acceptable phase errors are given. The obtained results are verified by numerical simulations. The approach is illustrated by two typical motion errors: slow deflections of a SAR platform trajectory from a reference flight line and periodic trajectory deviations.

This paper deals with the modeling the radiation of the power electronics component: the MOSFET. First, the magnetic near field measurements are made to characterize the radiation of the component. The MOSFET under test is referenced by IRF640 used in DC-DC converter. Second, we have applied the electromagnetic inverse method based on the measured field at 20 MHz to create a model of radiation sources of the MOSFET. The obtained results show a good agreement between the magnetic near field cartography obtained by the developed model and those measured. Finally, the developed model was used to predict the magnetic field in another distance and it wasvalidated with measured cartography.

In this paper, we provide a new theoretical model describing mechanism of electromagnetic radiation (and scattering) by passive single- and double-stranded (bifilar) helices. The proposed model is derived from basic physical principles till the end formulas which were computer processed for predicting a polarization type of the wave scattered by a helix. Comparison of the two types of helical oscillators revealed radical differences in their scattering performance (intensity and polarization). Optimal parameters of the bifilar helix for transformation of the polarization state from linear to circular were found for a non-axial direction of the incident and scattered field. Key features of the proposed model were confirmed by computer simulations.

A broadband gradient index (GRIN) metamaterial lens for gain enhancement of circularly polarized antennas has been automatically designed, fabricated and investigated. The GRIN metamaterial lens consists of an isotropic dielectric plate with a corresponding distribution of deep-subwavelength drill holes each with the same diameter. Such drill holes have a negligible influence on both the polarization state and the spectral response of the electromagnetic wave transmitting through the resulting GRIN metamaterial lens. Therefore, the GRIN metamaterial lens is polarization-insensitive and can efficiently transform spherical waves into planar waves over a very broad frequency range keeping the initial polarization states (e.g. linear or circular) scarcely changed. In the following we have derived analytical formulas that enable the setup of distribution rules for the drill holes on the plate. Based on these formulas, the GRIN metamaterial lens can be automatically designed and easily fabricated using circuit board engraving machines. The proposed GRIN metamaterial lens has been tested by placing it on the aperture of a circularly polarized conical horn antenna. The agreement between simulation and measurement results shows that the gain of the horn antenna has been significantly increased within the whole X-band (i.e. from 8 GHz to 12 GHz) and the largest gain enhancement reaches up to 5.7 dB. In particular, the axial ratio of the horn antenna with the GRIN metamaterial lens is less than 1.6 dB.

Pipelines made of dielectric materials such as Polyethylene (PE) are becoming increasingly popular. With no suitable inspection technique for dielectric pipes, there is an urgent need to develop new technology for their inspection. This paper presents a novel pipe inspection technique using Electrical Capacitance Tomography (ECT) imaging. Traditionally ECT is used for industrial process tomography as a low resolution but fast tomographic imaging technique. Typically commercial ECT can provide a resolution of approximately 10 percent of the imaging region. In this paper a limited region tomography technique is developed take into account prior knowledge about the geometry of the pipe. This has signicantly enhanced the imaging resolution of the ECT system, making it a viable pipe inspection solution. The experimental results in this study demonstrate an interior wall loss area as small as 0.195 percent of the ECT cross sectional imaging region is repeatable and can be reliably detected. A narrowband pass filter method (NPFM) is used as a means to limit the region for the ECT algorithm. This results in an unprecedented resolution, making ECT a viable non-destructive evaluation (NDE) technique for plastic pipes. The NDE application of the ECT for PE pipes is demonstrated in this paper with several experimental results. A wall loss of depth of 1.5 mm could be detected for an ECT sensor array of 150 mm in diameter, showing a high resolution and high definition ECT (HD-ECT) imaging that has not been reported before.

The model based on range and Doppler equations (RD model) is the most precise model for SAR geolocation, and therefore SAR geolocation based on this RD model has become more and more popular. Unfortunately, the RD method requires iterative solution, in most case, which is time-consuming and prone to poor optimization due to observation errors of parameters. In face of the huge mass of measured data from global SAR measurements, how to improve processing speed while maintaining geolocation accuracy is an important problem. This paper examines how to solve the RD geolocation equations for single, interferometric, and stereo SAR. First, the RD geolocation equations for the three kinds of systems are abstracted into a unified equation form. Second, it is determined that the RD geolocation equation can be approximated as a mapping relationship using polynomials. Then a fast solution method for the unified geolocation equation is proposed based on the Range Doppler Polynomial Coefficient Model (RDPC). Third, the accuracy loss of the RDPC model is analyzed, and the precision differences among the three kinds of system are compared. Finally, several groups of TerraSAR-X measured data for the three modes are processed using the fast algorithm. The results show that the fast algorithm greatly reduces the amount of calculation while the geolocation accuracy loss is small. Performance evaluation demonstrates that the proposed method is efficient and correct.

A new design methodology for multi-band rectangular microstrip antenna using a metamaterial-inspired technique is proposed. The methodology uses the metal disk with SRR-shaped slot placed horizontally between the patch and the ground plane. With the introduction of the split ring, sub-wavelength resonance can be achieved while the dominant mode of patch cavity remains the same, so the antenna can operate at multi resonant frequencies. Construction of the multi-band antenna requires only the sandwiching of two etched circuit boards. The antenna has the properties of low profile, easy fabrication and low cost. Dual-band and tri-band antennas are fabricated and measured, which validate the design methodology.

Composites of rice husks and carbon nanotubes (RHCNTs) are an innovation in improving the absorption of microwave signals. Rice husks, which are an agricultural waste material, have been found to possess a significant propensity for absorbing microwave signals. Studies have shown that both rice husks and carbon nanotubes (CNTs)have high percentages of carbon. Thus, in this paper, we present the results of our experimental study in which we varied the ratios of rice husks and CNTs in the composite materials and determined the dielectric properties of the composites and measured their abilities to absorb microwave signals. The experimental microwave absorber was fabricated using rice husks and CNTs, which increased the dielectric constant and the loss factor.Complex permittivity was measured using an Agilent dielectric probe.The RHCNT compositeswere investigated to determine their reflection loss and absorption performance as microwave absorbers. For the fabricated microwave absorber,we used the rectangular waveguide measurement technique to study reflection loss, transmission loss, and absorption performance in the frequency range of12.4 - 18 GHz. Carbon has an essential role in the absorber due to its ability reflect/absorb microwave signals.Thus, we compared the abilities of a pure rice-husk (PRH) absorber and RHCNT composites absorbers to absorb microwave signals.

In this work, a subharmonic frequency mixer for millimeter wave applications has been designed. The mixing and multiplication phenomena are simultaneously achieved via a nonlinear component consisting in a microstrip line gap covered by a graphene film coating. The circuit structure is made up of various filters, which have been optimized to ensure high port-to-port isolation. The nonlinear behavior of the subharmonic frequency mixer has been experimentally evaluated within the 39-40.5 GHz RF frequency band. The frequency downconversion is achieved by mixing the RF signal with the second harmonic component of a 17.9 GHz LO signal. Conversion losses are minimized by generating a return path for IF, through the use of a quarter wavelength open-ended stub.

A new broadband multiple-input multiple-output (MIMO) antenna with good isolation and compact size is proposed. The proposed antenna consists of two G-shaped elements in the upper layer and two inverted L protrude branches and a T slot etched in ground which is used to reduce the mutual coupling. This planar antenna has a bandwidth of 100% with |S₁₁| ≤ -10 dB from 2.26 to 6.78 GHz. The value of isolation between the two antenna elements is more than 22.5 dB in the whole band. The experimental results verify the simulations.

For ultra-wideband synthetic aperture radar (UWB SAR), there often exist a lot of clutters in the image, and the weak targets are easy to be masked by them. However, using the prior scattering knowledge of targets, enhanced imaging can be realized and beneficial improvements in image quality and detection performance can be expected. In this paper, an enhanced imaging method for body of revolution (BOR) has been researched. Since the BOR target has the unique feature of aspect-invariant characteristic, the aspect scattering entropy (ASE) is proposed to describe the diversity of aspect scattering and used in the BOR-enhanced imaging method. Then the application of the proposed method in landmine detection is discussed. The experimental results show that the BOR targets are effectively enhanced and the clutters are surpressed and thus the probability of landmine detection increases under the same false alarm rate.