An optimum polarization-space-time joint domain processing (PST-JDP) technique is proposed for clutter suppression which adequately adopts the three-domain information including the polarization, space and Doppler frequency information of the radar echo. The study shows that the polarization information together with the space and Doppler frequency information are effective to significantly enhance the clutter suppression performance for airborne radar. Several new techniques, (i.e., the covariance matrix eigendecomposition, the spectral analysis and the resolution grid method), are utilized for deriving the performance of the optimum PST-JDP. The main factors which affect on the performance of clutter rejection are the clutter degree of polarization, statistical distance of polarization between target and clutter, Doppler frequency of target and input clutter-to-noise ratio. The new optimum PST-JDP method outperforms significantly the traditional optimum space-time processing technology, especially in the case of the slowly or tangentially moving target. The simulation verifies the correctness and efficiency of the model.
A change in the relative proportions of a mixture of rubber tire dust and rice husks will cause a change in the mixture's electrical permittivity and its ability to absorb electromagnetic energy. An open-ended, coaxial probe was used in conjunction with three dielectric mixture equations (the Kraszewski equation, the Landau equation and the Lichtenecker equation) to obtain the dielectric properties of a mixture of rubber tire dust and rice husks (RTDRH) over the frequency range of 7 GHz to 13 GHz. Lichtenecker's equation for dielectrics proved to be a useful practical formulation for determining the effective permittivity of homogeneous dielectric mixtures. The effectiveness of these dielectric mixture equations in determining the effective permittivity of RTDRH was investigated in this study. A newly developed mixture equation was derived based on these dielectric mixture equations, and it and the existing equations were assessed to determine their effectiveness in determining dielectric properties of such mixtures.
Simultaneous exposure to multiple electromagnetic signals with widely differing carrier frequencies is a reality of daily life, but its possible effects on health are unknown. In this study we exposed rats to non-thermal levels of 900 and 2450 MHz TEM-mode radiation, applied individually or simultaneously, and we obtained estimates of 1 g mean SAR (specific absorption rate) in various tissues using a numerical model of the rat and finite-difference time-domain software. The experimental system comprised a GTEM (gigahertz TEM) chamber connected to two vector signal generators, a signal mixer and amplifier, a directional coupler, a spectrum analyzer and a power meter. Tissue sections from rats sacrificed 24 h after exposure, and from negative controls and positive controls exposed to gamma radiation, were stained with haematoxylin-eosin for evaluation of general cell morphology and with DAPI (4',6-diamidino-2-phenylindole) for evaluation of apoptosis. Lesions, tissue destruction and apoptosis were only observed in positive controls. The results for rats exposed to either frequency, or to both simultaneously, were similar to those of unexposed negative controls. It remains to determine whether chronic exposure is similarly innocuous.
The introduction of various wearable textile radiators facilitates the realization of a fully wearable electronic system. However, the human body itself poses a serious fundamental challenge to its realization, mainly due to electromagnetic interaction with radiators placed in its proximity. Thus antenna performance in terms of reflection coefficient, bandwidth, radiation pattern and efficiency is expected to be severely influenced during on-body deployment. Besides addressing the need for a systematic on body evaluation procedure, this work presents an in-depth discussion on the measured degradation relative to free space operation. Considering a practical deployment scenario, the two antenna designs are first optimized in proximity of a human-emulating box using a commercial simulator. ShieldIt textile is chosen to build the antenna's conductive components, and this prototype is then benchmarked against another similarly dimensioned prototype constructed using conductively-homogeneous copper foil. For each material, two dual-band prototypes are fabricated, one resonating at 2.45 GHz and 5.2 GHz, and the other at 2.45 GHz and 5.8 GHz. Two realistic on-body deployment locations are chosen to be investigated, on the chest and back, considering two antenna orientations - one radiating away from the user, and the other radiating along the body. Free space and on-body reflection coefficient, bandwidth and radiation pattern are evaluated for each prototype in an anechoic chamber, while a reverberation chamber is utilized to determine their efficiency. All measurements were carried out using consistently the same human volunteer. Evaluations show that coupling distance and conductivity are the main factors in determining efficiency rather than on-body location, given that evaluations are carried out while the antenna keeps its planar form.
An alternative, field-based formulation of transformation optics is proposed. Field transformations are expressed in the language of boundary conditions for the electromagnetic fields facilitated through the introduction of generalized potential functions. It is shown that the field-based approach is equivalent to the conventional coordinate-transformation approach but is preferable when looking for specific field distribution. A set of example devices such as invisibility cloaks, concentrators, rotators, and transformation optics lenses capable of creating light beams with predetermined field distribution (e.g., Gaussian and sinusoidal) is studied to validate the effectiveness of the field-based formulation. As for the boundary conditions for the cloaked region the absence of the normal component of the Poynting vector is justified. In the frames of the field-based approach the physical reasons behind infinite components (singularities) of the material parameters of transformation optics devices are straightforwardly revealed.
In this article, a coupled-fed planar printed antenna mounted on the compact no-ground portion of the system circuit board of a mobile phone with a low profile of 10\,mm is proposed and studied. The presented antenna is formed by a double-branch feeding strip, a shorted coupling strip with two open-ended loops of different lengths, and a slotted ground structure consisting of two monopole slots, yet it has a size only 15×50 mm2. Two wide operating bandwidths of 698--960\,MHz and 1710-2690 MHz can be achieved by these radiating strips, which provide multiple resonant modes at about 750, 1000, 1750, 2300 and 2900 MHz. In addition, with the presence of the two narrow slots and a chip inductor (L = 1.5 nH), in this study, the printed antenna can lead to much widened bandwidths in both the antenna's lower and upper bands to cover LTE700/GSM850/900 and DCS1800/PCS1900/UMTS2100/LTE2300/2500, respectively. Good radiation efficiency and antenna gain for frequencies over the desired operating bands are obtained. Detailed design considerations of the proposed antenna are described, and both experimental and simulated results are also presented and discussed.
A simple geometrical Asian-hand model with human tissue properties posed at two common talk-mode positions is proposed for comparative study. The newly designed hand is formed by measuring adult female hand at open-hand position before being posed into the presented styles. Four human hand tissues are included; skin, bone, muscle, and tendon, and also three homogeneous set of hands using specific anthropomorphic mannequin (SAM) hand phantom dielectric properties. A candy-bar type mobile phone with Planar Inverted-F Antenna (PIFA) is used to radiate dual-band frequency of GSM900/1800 in the vicinity of the SAM head phantom. The mobile phone casing is made out of plastic and only two components were considered: the FR-4 ground plane and PIFA. The specific absorption rate (SAR) averaged over a mass of 10 gram and 1gram is calculated after obtaining the power loss density and electric field value from simulation in CST Studio Suite 2011. The SAR and return loss results of six hand structures, including the SAM hand phantom are compared. The antenna performance with the inclusion of hand does not decrease as much as 1800 MHz in 900 MHz range, but absorbs energy more in the hands for 1800MHz compared to 900 MHz SAR values.
This paper presents a low voltage wideband down-conversion mixer using current-mode approach for multi-standard receivers. The proposed mixer uses a current mirror amplifier with an embedded passive switching core to achieve mixing function, which can combine the advantages of active and passive mixers simultaneously. The mixer is implemented using a 0.18 μm CMOS technology and covers frequency band from 0.5 GHz to 4.0 GHz. A comparison with conventional CMOS down-conversion mixer shows that this current-mode mixer has advantages of large conversion gain, low noise figure and high linearity. Over the entire bandwidth, the mixer features a conversion gain of 8.0~8.7 dB, a double-sideband (DSB) noise figure of 6.7~9.1 dB and an input third-order intercept point (IIP3) of 1.5~5.2 dBm, while consuming 8 mA from a 1.2 V supply voltage. The mixer occupies the active area of 0.43×0.46 mm2 including testing pads.
We have applied the phase unwrapping technique to resolve the phase ambiguity problem arising from complex expressions of scattering parameters, for reflection-only measurement configurations, since, at some instances, only one side of the sample under test is accessible for electromagnetic measurements. We considered two different measurement configurations for testing the applicability of the phase unwrapping technique as: 1) two identical samples with different lengths flushed by a short-circuit termination and 2) one sample shorted by a varying short-circuit termination. For each measurement configuration, the underlying expressions for the reflection scattering parameters are derived. For both cases, we evaluated the suitability of the phase unwrapping technique by considering a highly-dispersive medium (distilled water) as our test sample. We note that continuity of the real part of the complex wavelength is a key issue in the unwrapping technique for (one-port) reflection-only measurements.
Electromagnetic (EM) scattering properties from the ship wakes on the two-dimensional (2-D) perfect electric conductor (PEC) sea surfaces are studied by utilizing the small-slope approximation (SSA) theory. Considering the limitations of using the ideal plane EM wave incident upon a rough sea surface of the limited size, the expressions of the scattered field and scattering amplitude are derived by utilizing the modified tapered incident field. Based on a simplified segmented ocean spectrum model, the bistatic and monostatic normalized radar cross sections (NRCS) from the PEC sea surfaces with and without ship wakes are calculated, respectively. Meanwhile, the variation of scattering coefficient as scattering angles is given and compared under different polarization states. The results show that the scattering from the PEC sea surfaces with ship wakes is evidently different from that without them in bistatic and monostatic scattering. This provides a basis to extract ship wake characteristics. Also it shows that the SSA is a very effective analysis method to deal with the EM scattering from the rough sea surface. Finally, the effect of different tapered factors on backscattering coefficient is discussed, and it is concluded that an artificial reflection from the boundaries and a scattering upwarping from low-grazing incidence can be avoided just when the tapered factor is relatively smaller. This gives the theoretical basis for the analysis of EM scattering characteristics of ship wakes on the PEC sea surface.
A broadband circularly polarized patch antenna with high gain and wide axial ratio beamwidths is proposed for ultra-high-frequency (UHF) RF identification (RFID) applications in this paper. The antenna is composed of a square patch, a feed network printed on the bottom side of the substrates and an antenna radome. The CP radiation of the proposed antenna is excited by four cylinder probes which transmit four signals that have equal amplitude with quadrature phase difference (0˚, 90˚, 180˚, and 270˚) generated from the feed network. To obtain an optimum peak gain and a broad CP bandwidth, 100 Ω isolation resistor is omitted in the feed network for obtaining high radiation efficiency, and the effects of varying the feed positions and dimensions of the various parameters on the antenna performances are respectively investigated. Simulation results are compared with the measurements, and a good agreement is obtained. The measured results show that the proposed antenna can provide broad impendence bandwidth of 19.7% (815-993 MHz) (reflection coefficient less than -15 dB), a maximum gain of 9.65 dBi, and a 3-dB axial ratio (AR) bandwidth of about 11% (860-960 MHz). The results indicate that the proposed antenna is an excellent candidate for UHF RFID reader system. At last, read performance of the proposed antenna array in RFID systems is presented, which verify the superior features of the proposed antenna in practical RFID system applications.
The comparative evaluation based on the power speed density of several types of portable Permanent Magnet Generator (PMG) considered for agricultural applications is presented. These generators are purposely designed to be used in agriculture sectors and thereby it should be of lightweight, small in size and ease to use. Six different generator topologies are developed for investigation of such purposes. A number of design parameters are considered to analyze the performance characteristics for each type of developed PMG. Based on the power speed density factor that is used to describe better generator performance, the suitable PMG for the agricultural application is identified through a comprehensive evaluation.
The scattering of electromagnetic spherical wave by a perfectly conducting circular disk is studied by using the method of Kobayashi Potential (abbreviated as KP method). The formulation of the problem yields the dual integral equations (DIE). The spherical wave is produced by an arbitrarily oriented dipole. The unknowns are the induced surface current (or magnetic field) and the tangential components of the electric field on the disk. The solution for the surface current is expanded in terms of a set of functions which satisfy one of a pair (equations for the magnetic field) of Maxwell equations and the required edge condition on the surface of the disk. At this stage we have used the vector Hankel transform. Applying the projection solves the rest of the pair of equations. Thus the problem reduces to the matrix equations for the expansion coefficients. The matrix elements are given in terms of the infinite integrals with a single variable and these may be transformed into infinite series that are convenient for numerical computation. The far field patterns of the scattered wave are computed and compared with those computed based on the physical optics approximation. The agreement between them is fairly good.
General side-looking synthetic aperture radar (SAR) cannot obtain scattering information about the observed scenes which are constrained by lay over and shading effects. Downward-looking sparse linear array three-dimensional SAR (DLSLA 3D SAR) can be placed on small and mobile platform, allows for the acquisition of full 3D microwave images and overcomes the restrictions of shading and lay over effects in side-looking SAR. DLSLA 3D SAR can be developed for various applications, such as city planning, environmental monitoring, Digital Elevation Model (DEM) generation, disaster relief, surveillance and reconnaissance, etc. In this paper, we give the imaging geometry and dechirp echo signal model of DLSLA 3D SAR. The sparse linear array is composed of multiple transmitting and receiving array elements placed sparsely along cross-track dimension. The radar works on time-divided transmitting-receiving mode. Particularly, the platform motion impact on the echo signal during the time-divided transmitting-receiving procedure is considered. Then we analyse the wave propagation, along-track and cross-track dimensional echo signal bandwidth before and after dechrip processing. In the following we extend the projection-slice theorem which is widely used in computerized axial tomography (CAT) to DLSLA 3D SAR imaging. In consideration of the flying platform motion compensation during time-divided transmitting-receiving procedure and parallel implementation on multi-core CPU or Graphics processing units (GPU) processor, the convolution back-projection (CBP) imaging algorithm is proposed for DLSLA 3D SAR image reconstruction. At last, the focusing capabilities of our proposed imaging algorithm are investigated and verified by numerical simulations and theoretical analysis.
A fast method for circular SAR three-dimensional imaging system by near-field elevation scanning is proposed in this paper. It is based on cylindrical spectrum theory which exploits the Fourier decomposition of the targets distribution instead of point by point imaging in earlier works. The proposed method sets up the relationship between the target image and the scattering field in spatial frequency domain. This leads to overcome the problem of computational inefficiency which was observed previously in projection-slice theorem. The near-field scattering is firstly analyzed by relating the return signal to the near-field focus function. The near-field focus function is then transformed to spatial frequency domain and evaluated by the method of stationary phase. Finally, the imaging result is given by three-dimensional inverse Fourier transformation from spatial frequency domain of targets. The proposed method is validated by the simulation results of distributed targets. In addition, experimental validation was also achieved in microwave chamber at X-band with targets placed on the turntable.
A general multiobjective optimization and design procedure of a Luneberg lens antenna (LLA) with a compact multiband multi-polarized feed-system for a broadband satellite communication terminal is presented. The LLA utilizes a compact multiband feed horn, consisting of an inner dielectric loaded circular horn for the K/Ka-band (dual-circular polarization) and a coaxial waveguide with axially corrugated flange for the Ku-band (dual-linear polarization). Measurements show good agreement with simulations. Moreover, an efficient multiobjective evolutionary algorithm based on decomposition (MOEA/D) with differential evolution operator and objective normalization technique is firstly coupled with the vector spherical wave function expansions (VSWE) for the optimal design of a 7-layer 650 mm diameter LLA, which provides higher aperture efficiency at Ku/K/Ka-band simultaneously. The frequency dependence of the LLA is also investigated. Finally, the gain and sidelobe level of a 5-layer design are jointly evaluated and compared with previous works. The proposed design procedure provides much better radiation performances and greater design freedom to the designers, as a group of Pareto-optimal LLA solutions can be obtained with just one simulation.
This paper addresses the problem of detecting multiple point-like targets in the presence of steering vector mismatches and Gaussian disturbance with unknown covariance matrix. To this end, we first model the actual useful signal as a vector belonging to a proper cone whose axis coincides with the whitened direction of the nominal array response. Then we develop two robust adaptive detectors resorting to the two-step GLRT-based design procedure without assignment of a distinct set of secondary data. The performance assessment has been conducted by Monte Carlo simulation, also in comparison to previously proposed detectors, and confirms the effectiveness of the newly proposed ones. In the last part of the work, in order to restore the detection performance of the newly proposed detectors in the presence of a large number of range cells contaminated by useful signals, we consider two adaptive detectors which resort to the structure information of the disturbance covariance matrix, and show that the a-priori information on the covariance structure can lead to a noticeable performance improvement.
In this paper, a new simple equivalent circuit model for analysis of dispersion and interaction impedance characteristics of ridge-loaded folded-waveguide slow-wave structure is presented. In order to make the computational results more accurately, the effects of the presence of the beam-hole and discontinuity due to the waveguide bend and the narrow side dimension change of this kind of structure were considered. The dispersion characteristics and the interaction impedance are numerical calculated and discussed. The analytical results agree very well with those obtained by the 3-D electromagnetic high-frequency simulation software. It is indicated that the equivalent circuit methods are reliable and high efficiency.
A generalized two-way coupled-line power divider with extended ports for dual band is proposed in this paper. The power divider is composed of two section coupled-lines, one conventional transmission line, and an isolation resistor, and employs extension of a transmission line or coupled-line at each port. The design equations are obtained based on even- and odd-mode analysis, and analytical ideal closed-form scattering parameter expressions derived. Because the traditional ring structure is a special case of coupled line, four cases of this generalized power divider are discussed and compared. In addition, the six power dividers simulated results of three special cases are shown. Finally, three fabricated power dividers measurements are used to certify this proposed structure and corresponding design parameters.
Medical applications of microwaves (i.e. a possibility to use microwave energy and/or microwave technique and technology for therapeutical purposes) are a quite new and very rapidly developing field. Microwave thermotherapy is being used in medicine for cancer treatment and treatment of some other diseases since early eighties. This paper is a contribution to a theory of phase array applicators to be used for a microwave thermotherapy (microwave hyperthermia) in a cancer treatment. It deals with a study and theoretical evaluation of homogeneity of SAR distribution in cylindrical agar phantom for several different values of its radius. Discussed SAR distribution is in our case created by simulations of EM field exposure done by aid of four microwave stripline type TEM mode applicators of the same type.
A compact planar ultra-wideband (UWB) antenna with triple band notch characteristics is proposed in this paper. The antenna consists of a rectangular radiating patch and a modified partial ground plane, and has an overall dimension of 24 mm × 22 mm. Three resonant elements are placed above the ground plane to generate three notch frequency bands separately in the WiMAX, the lower WLAN and the upper WLAN frequency bands. The proposed antenna successfully simulate, prototyped and measured. Effects of the key deign parameters on band notch characteristics are also investigated. The realized antenna achieved an operating bandwidth (VSWR ≤ 2) ranges from 2.9 to more than 11 GHz with triple notched bands of 3.26-3.71 (12.9%), 5.15-5.37 (8.5%), and 5.78-5.95 (2.9%) GHz. Measured flat transfer function and constant group delay within the operating band except at notched bands makes the proposed antenna suitable for being used in practical UWB applications.
In bistatic synthetic aperture radar (SAR) with one stationary station, two-dimensional spatial variance is a major problem which should be handled. In this paper, an Inverse Scaled Fourier Transform (ISFT) imaging algorithm to deal with this problem is proposed. The approach linearizes the two-dimensional spatiallyvariant point target reference spectrum to derive the reflectivity pattern's spectrum. Based on this spectrum, an ISFT along range direction and a frequency shift along azimuth direction are used to achieve the two-dimensional spatial variance correction. This method is efficient as it only uses phase multiplication and FFTs. Numerical simulations verified the effectiveness of the method.
It has been demonstrated in previously published results that large fourth Stokes parameter may be generated from a rough surface over multi-layered media, where only the top interface is rough while the others are all flat boundaries. In this paper, we consider the four Stokes parameters in microwave emission from a two-layer rough surface. In this case, there are two rough boundaries. The rough surfaces vary in one horizontal direction so that the azimuthal asymmetry exists in the 3-D problem. Periodic boundary conditions were assumed. The results are compared with the previously published results from a rough surface over multi-layered media. It is shown that the ``two-layer'' periodic rough surfaces can reduce the vertical and horizontal brightness temperatures remarkably; the interactions between the two rough surfaces also enhance the third and fourth Stokes parameters, which disappear in new structure for the large dips in the vertical and horizontal brightness temperatures presented in the former Sastrugi structure. In particular, the fourth Stokes parameter can be larger than that in previous layered structure. In addition, for the case of sinusoidal rough surface without large slope with snow's permittivities, the top boundary rough only layered structure cannot support the large third and fourth Stokes parameters any longer while the two-layer rough surface structure can do still up to -34 K and 15 K, respectively. It is also found that the reason resulting in the large fourth Stokes parameter is caused by relative magnitude of permittivities of the two layers, all cases with large fourth Stokes parameter should satisfy the upper layer's permittivity larger than the lower one due to total internal reflection from the lower layer.
Low speed flux-modulated permanent magnet machines (FMPMs) which are based on `magnetic-gearing effect' have attracted increasing attention due to their high torque capability and simple structure. In order to assess the potentials of FMPMs in the application of low-speed direct-drive, two flux-modulated interior PM machines with distributed windings and concentrated windings are quantitatively compared by using finite element method. The results demonstrate that the machine with distributed windings can offer higher peak electromagnetic torques and lower torque ripples. Moreover, the machine with distributed windings also present stronger flux-weakening capability and lower power losses. The results also indicates that the magnetic saturation problem should be paid full attention when design flux-modulated interior PM machine with concentrated windings. If this problem can be well solved, the performance of machine with concentrated windings may be improved.
Two novel compact magic-T configurations designed as a two layer structure are proposed in this paper. They consist of a microstrip tee-junction and resonance circuit composed of a microstrip line combined with rectangular or radial stubs. These microstrip circuits are respectively printed at the top and bottom layers of the structure, and coupled via a slot located in the common ground plane. The microstrip patch and slot are placed parallel to each other forming novel microstrip-slotline transitions, which provide broadband operation of the magic-Ts. Transmission line equivalent circuits are used to explain the performance of the proposed hybrids. It is shown that magic-T with a radial stub demonstrates wider operation bandwidth and better performance than the structure with a rectangular stub. In order to validate their performance, the prototypes of both configurations were manufactured and measured. Experimental and simulation results show that the resulting magic-T using a radial resonator has a fractional bandwidth of over 40% for 0.2\,dB amplitude and 1° phase imbalance. The experimental results are in good agreement well with equivalent circuit and full-wave simulations.
In the paper, the analysis of electromagnetic wave scattering from frequency selective surface is presented. The surface is composed of periodically arranged posts. The multimodal scattering matrix of such structure is derived and the transmission and reflection characteristic for the structure with arbitrary plane wave illumination are calculated. The exact full-wave theory based on the mode-matching method is applied to develop an efficient theory to analyze such structures. The validity and accuracy of the approach are verified by comparing the results with those obtained from alternative methods.
Spatial beam compression of an electromagnetic wave is one of the fundamental techniques employed in microwaves and optics. As there are many ways to achieve this task using the combination of prisms and lenses, recent research suggests the parabolic gradient index photonic crystals (GRIN PC) for the design of spatial beam compressor owing to its functionalities. However, the fabrication of a graded media with the parabolic profile is a difficult challenge in practical realization. To an alternative, present work attempts this problem with respect to the triangular gradient index profile. The performance and aspects of the beam compression are investigated experimentally using the pillar type GRIN PC at the microwave length-scales. The utility of the device for an effective beam injection to the photonic-waveguide component is further demonstrated experimentally.
We calculate the optical force exerted on the nanoparticle close proximity to the surface of fishnet metamaterials based on metal/dielectric/metal films when irradiated at near infrared wavelength. These forces show the resonant frequencies similar to the magnetic resonant frequencies in the double negative index fishnet metamaterial. We also present that the optical force can be enhanced by optimizing the geometry of the fishnet to provide a stronger magnetic resonant dipole. In contrast to the other plasmonic nanostructure always obtaining trapping force using electrical resonant dipole, our presented structure utilizes the magnetic resonance to provide a gradient force, which is suitable for the optical trapping of the nanoscale particles at illumination intensities of just 1 mW/μm2, the optical force is sufficient to overcome the Earth's gravitational pull.
Magnetic Induction Tomography (MIT) is a relatively new and emerging type of tomography techniques that is able to map the conductivity distribution of an object. Its non-invasive and contactless features make it an attractive technique for many applications compared to the traditional contact electrode based electrical impedance tomography. Recently, MIT has become a promising monitoring technique in industrial process tomography, and the area of the research interest has moved from 2D to 3D because of the volumetric nature of electromagnetic field. Three dimensional MIT images provide more information on the conductivity distribution, especially in the axial direction. However, it has been reported that the reconstructed 3D images can be distorted when the imaging object is located at a less sensitive region. Although this distortion can be com- pensated by adjusting the regularisation criteria, this is not practical in real life applications as the prior information about the object's location is often unavailable. This paper presents a memory ecient 4D MIT algorithm which can maintain the image quality under the same regularisation circumstances. Instead of solving each set of measurement individually, the 4D algorithm takes advantage of the correlations between the image and its neighboring data frames to reconstruct 4D of conductivity movements. The 4D algorithm improves the image qualities by increasing the temporal resolution. It also overcomes some sensitivity issues of 3D MIT algorithms and can provide a smoother and stabler result. Several experimental results are presented for validating the propose algorithms.
In this paper, two radiation pattern-reconfigurable antennas are designed to operate over DCS 1800 frequency bands. The geometry of the proposed antennas is symmetric with respect to the vertical center line. The electrical shapes of the antennas are composed of a monopole-loaded loop and an open wire. The open wire functions as either a director or reflector for the two antennas. Depending on the switching state, the antennas can select between two beam directions with no input impedance difference. The sizes of each antenna are then optimized to achieve beam switching capability using PIN diodes and FETs. The reflection coefficients and gain patterns for two bias conditions using both switches are measured and compared with the simulated results. The measured results show that the proposed antennas can clearly alternate their beam directions using the switching components.