Design of multi-element antennas (MA) for small mobile terminals operating at higher frequencies remains challenging despite smaller antenna dimension and possibility of achieving electrically large separation between them. In this paper, the importance of the type of radiating elements operating at 3400-3600 MHz and their locations on the terminal chassis is highlighted. An isotropic radiation pattern that receives incoming signals from arbitrary directions is obtained by combining the radiation patterns of multiple antennas with localized chassis current distribution. Four MA configurations with two- and eight-element antennas are designed and evaluated experimentally in indoor propagation environments. Our proposed designs of MAs provide the highest MIMO channel capacity compared to their counterparts using antennas with less localized chassis current distribution, even in the presence of user's hand.

This paper presents a novel design of a circular ring defected ground structure (DGS) antenna for bandwidth enhancement using fuzzy logic approach. The ground plane of the antenna is defected by introducing circular ring sector type of defect beneath the circular ring patch. The position of the defect in the ground plane to attain the highest return loss and corresponding frequency is determined by using Fuzzy Interface System (FIS). The antenna resonates in X-band showing wideband characteristics with improved gain and reduced cross polar radiations. The return loss and analogous frequency obtained from simulated results and fuzzy system are compared and are in good agreement. The return loss and input impedance is measured experimentally and compared with the simulated results. Parameters like impedance bandwidth, VSWR and antenna gain are likewise calculated and discussed. The simulated results for the radiation pattern of the proposed design with polarization (Co-polar and Cross-polar) are also presented. The simulated impedance bandwidth of about 1.33 GHz (1.2 GHz experimentally) in X-band is obtained with a gain of 6.43 dB and also cross-polarized radiations have an isolation of 20 dB.

A simple wideband antenna with parasitic element is proposed in this paper. The printed antenna is comprised of an L-shape monopole and a parasitic element. By optimizing geometrical parameters of the parasitic element structure, a good impedance bandwidth which covers DVB (470 MHz~702 MHz) for return loss being higher than 5 dB and LTE/700(704 MHz~787 MHz), GSM850/900 (824 MHz~894 MHz/880 MHz~960 MHz) for return loss being higher than 10 dB is achieved. A fabricated antenna has a dimension of 150 mm×56 mm. The measured and simulated efficiency, gain and radiation pattern which is quasi omni-directional in the yoz plane make it to be a good candidate of mobile communicational terminals.

Just over a decade ago, wireless capsule endoscopy (WCE) was introduced as a novel alternative to conventional wire or probe endoscopy to examine disorders of the human gastrointestinal (GI) tract. Yet, the persistent inability of transmitting high-quality images due to limited data rate of the telemetry system continues to be an issue of major concern. Thus, high-data-rate telemetry systems are essential due to the widespread use of the WCE technique. In this paper, we present such a telemetry system that includes a highly-simplified receiver for the use in WCE. Unlike the conventional architecture of a radio frequency (RF) receiver, the architecture of the new receiver allows the direct conversion of analog RF signals to digital signals, eliminating the need for any frequency conversion in the analogue domain. Our receiver system consists of sub-blocks, a low-noise amplifier (LNA), a logarithmic amplifier (LA), a power detector (PD), and a comparator. The common-source cascode LNA was designed with its frequency spectrum centralized at 450 MHz, which was determined by electromagnetic (EM) simulation of the path loss in the GI tract of the human body. To ensure that the higher data rate, i.e., 100 Mbps, could be attained, the LNA was designed for a system bandwidth of 100 MHz, i.e., 400-500 MHz. The LNA and the three cascading blocks in combination have total gain of 80 dB to compensate for the losses in the weak signals that are received. The LNA and the LA, including the PD and the comparator, require 17-mA and 337-μA currents, respectively, from a 1.5-V, DC source.

A novel compact dielectric loaded Exponentially Tapered Slot (ETS) antenna using Substrate Integrated Waveguide (SIW) technology is presented in this paper for Millimeter (Mm) wave wireless communication applications. The dielectric loaded ETS antenna and compact SIW feed are fabricated on a single substrate. The compact SIW feeding structure results in a considerable reduction in size and eliminates the unwanted radiations from feed. The proposed antenna is designed, fabricated, and investigated at 60 GHz. Furthermore, the proposed antenna design is simulated using electromagnetic software CST Microwave Studio and the comparison is made with Ansys HFSS to validate the design procedure. The measurement results are compared with simulated results.

A new sensor device is reported to measure the change in dielectric permittivity or refractive index of liquid samples. This novel device is extremely compact in nature and can be fabricated on a chip by integrated optical design method. The device works on change in surface plasmon (SP) amplitude to obtain permittivity values of samples adjacent to a specially designed metal-dielectric interface in a waveguide. The geometry of the interface has a distinct effect on sensitivity of measurement. The performance of the device is analyzed, and predicted through analytical and numerical calculations.

The electromagnetic scattering mechanism of radar targets in the high-frequency domain can be characterized exactly by geometrical theory of diffraction (GTD) model. In this paper, we propose a novel parameter estimation method for GTD model based on compressed sensing. The sparse characteristic of radar echoes is analyzed, and the parameter estimation problem is converted to one of sparse signal reconstruction. Furthermore, clustering and linear least-minimum-squares algorithms are utilized to improve the accuracy of the result. Compared with several modern spectral estimation techniques, the proposed method gives a more precise estimation of the GTD model parameters, especially the scattering centers. Simulations with synthetic and measured data in an anechoic chamber confirm the effectiveness of the method.

A bidirectional circularly polarized array of the same sense is proposed. The implementation is a combination of end-fire array, crossed dipoles, and composite right/left-handed transmission line (CRLH-TL). The proposed array consists of four dipoles spaced at a distance equal to λ₀/4 (λ₀ is the wavelength in free space at the center frequency). For the bidirectional circular polarization of the same sense, the four dipoles are fed in-phase in a series-fed structure. A feed line that exhibits 0° phase shift every λ₀/4 is needed. To satisfy the demand for the space distance and phase distribution in a series-fed array, the CRLH unit cell composed of lumped capacitors and inductors is employed and inserted in the feed line. Theoretical analysis is performed based on the balanced parallel stripline and design equations are presented for the determination of the lumped element parameters. The design method can be used in the design of the arrays with more elements. From the experimental results, the array offers a 4.2 dBic bidirectional circular polarization gain. The bandwidth between which the impedance matching is better than -10 dB and the axial-ratio is better than 3 dB is 300 MHz from 2.39 to 2.69 GHz.

Due to the fact that the imaging distance is similar to the dimension of synthetic aperture antenna in near-field, the Fourier imaging theory used in the traditional synthetic aperture imaging radiometer (SAIR), which is based on the far-field approximation, is invalid for near-field synthetic aperture imaging. This paper is devoted to establishing an accurate imaging algorithm for near-field millimeter wave SAIR. Firstly, the near-field synthetic aperture imaging theory is deduced and its relationship to the far-field imaging theory analyzed. Then, an accurate imaging algorithm based on the near-field imaging theory is established. In this method, the quadratic phase item and antenna pattern are taken into consideration, and the image reconstruction is performed by minimizing the Total-Variation norm of brightness temperature image, which reduces the influence of the visibility observation error and improves imaging precision. Finally, the effectiveness of the proposed imaging algorithm has been tested by means of several simulation experiments, and the superiority is also demonstrated by the comparison between it and the existing Fourier transform methods. The results demonstrate that the proposed method is an efficient, feasible imaging algorithm for near-field millimeter wave SAIR.

A novel defected ground structure unit is presented in this paper. This structure is composed of a traditional dumbbell DGS and a pair of coupling stubs in the aperture. In contrast to a single finite attenuation pole characteristic offered by the conventional dumbbell DGS, the proposed DGS unit provides dual finite attenuation poles that can be independently controlled. By adjusting the position of the two attenuation poles, a much sharper skirt and wider stopband could be achieved. A 3.2 GHz lowpass filter utilizing four cascaded novel DGS units is designed, fabricated and measured. This lowpass filter achieves a wide stopband with over 30-dB attenuation up-to 30 GHz. The results obtained from simulation and measurement have good agreement.

In this work, theoretical analysis and numerical results are given for time-reversal (TR) focus gains of polarization-varying electromagnetic fields in a rectangular resonant cavity. To demonstrate the gains in different polarization states of the static transceivers and the ones of the rotatable transceivers, the 3 dB attenuation areas of TR angle gain (AG) and AG flatness are first calculated. The flat area is about equivalent to the range of two centrosymmetric octants in a three-dimensional Cartesian coordinate. Phase-frequency waterfalls verify the polarization-rotational rheology of the TR focus gain, in which uniform and smooth areas will contribute higher gain than uneven and rough areas.

In this paper, we propose a very simple technique that offers an extra degree of freedom to optimize the design of a tire dust-based absorber with reduced height. Cladding is a technique that is used to enhance the surface properties of a part, and it has been used in many applications for many years. In this technique, a clad layer is created on the core material, and the composition of the clad layer is adjusted to enhance the performance of the core material. We use a rice husk-clad layer to enhance the impedance matching characteristics of the low-loss, tire-dust core, microwave absorber. The overall design is a two-layer, geometrically-tapered, pyramidal structure composed of two lossy waste materials. Our main goal was to make the front surface less reflective (impedance matched), hence the material of the outer layer (clad) of the absorber was selected on the basis of the analysis of the dielectric properties of the candidate materials. Optimum thickness of the clad was obtained by using CST simulation software and found to be 12 mm, for which a reflectivity performance of less than -20 dB was achieved in the frequency range of 4 to 20 GHz. The results were found to be better than those provided by an earlier design of the absorber, which was composed of a mixture of tire dust and rice husks.

The design of an efficient quasi-optics Frequency Selective Surface (FSS) filter which is required to provide a -3 dB pass band from 405 GHz to 441 GHz is presented. For atmospheric remote sensing application, this space-borne spatial device consists of a silicon layer and a thin copper layer which is perforated with periodic arrays of resonant dipole slots and circular apertures. FSS unit cell has a dimension much smaller than its operating wavelength. Unique features of this complex dense FSS structure include wide pass band properties with superb performance of frequency response and incident angles independence for TE polarization. Floquet mode analysis and finite element method (FEM) models are used to establish the geometry of the periodic structure and predict its spectral response.

Azimuth multichannel is a promising technique of realizing high resolution and wide swath for synthetic aperture radar (SAR) imaging, which consequently leads to extremely high data rate on satellite downlink system and confronts serious ambiguity in subsequent processing due to its strict limitation of pulse repetition frequency (PRF). Ambiguity suppression performance of conventional spectrum construction is disappointing when the samples are approximately overlapped. To overcome these weaknesses, a novel sparse sampling scheme for displaced phase center antennas based on compressed sensing (CS) is proposed in this paper. The imaging strategy sparsely sampled in both range and azimuth direction, leading to a significant reduction of the system data amount beyond the Nyquist theorem, and then operated the CS technique in two dimensions to accomplish target reconstruction. Effectiveness of the proposed approach was validated through simulation and real data experiment. Simulation results and analysis indicated that the new imaging strategy could provide several favorable capability than conventional imaging algorithm such as less sampled data, better ambiguity suppression, higher resolution, and lower integrated side-lobe ratio (ISLR).

A new design of broadband circularly polarized antenna is proposed. The antenna is composed of a square patch and a horizontal L-shaped stripline that feeds the patch at two orthogonal directions by two probes. The L-shaped feeding structure provides excitements of approximately equal amplitude and 90° phase difference and then good circularly polarized characteristics are obtained. Measured results show that the proposed antenna has 10-dB impedance bandwidth of 14.3% (2.27-2.62 GHz) and 3-dB axial-ratio bandwidth of 13.1% (2.3-2.62 GHz). Moreover, the measured gain is over 7 dBic within the effective band.

This letter presents a dual-band bandpass filter (BPF) using interdigital coupling lines with a new defected ground structure (DGS) pattern. Traditional DGS structures are mainly used to realize wide bandstop characteristics. In this letter, by introducing a pair of coupling stubs in the aperture of the DGS, a narrow passband can be achieved within a wide stopband, so a dual-band bandpass filter can be implemented. An equivalent circuit model is derived to describe the filter. And the circuit simulation result agrees well with the EM simulation one. The position and bandwidth of the two passbands can be designed and adjusted independently. In order to verify the theory, a dual-band bandpass filter is designed, fabricated and measured. The simulated and measured results are in good agreement.

A major challenge in UWB signal processing is the requirement for very high sampling rate under Shannon-Nyquist sampling theorem which exceeds the current ADC capacity. Radar signal is essentially a delayed and scaled version of the transmitted pulse, determined by sparse parameters such as time delays and amplitudes. A system for sampling UWB radar signal at an ultra-low sampling rate based on the Finite Rate of Innovation (FRI) and the estimation of time delays and amplitudes to detect UWB radar signal is presented in the paper. This sampling scheme which acquires the Fourier series coefficients often results in sparse parameter extraction for UWB radar signal detection. The parameters such as time-delays and amplitudes are estimated using the total variation norm minimization. With this system, the UWB radar signal can be accurately reconstructed and detected with overwhelming probability at the rate much lower than Nyquist rate. The simulation results show that the proposed approach offers very good recovery performances for noisy UWB radar signal using very small number of samples, which is effective for sampling and detecting UWB radar signal.

This paper presents a compact dual-band multiple input multiple output (MIMO) antenna with low mutual coupling, operating in the 2.4 GHz band (2.4-2.485 GHz) and 5.5 GHz band (5.15-5.85 GHz). The proposed antenna system consists of two antenna elements located at the top two corners of FR4 substrate (PCB). Each element dimension is reduced substantially by employing a folded structure and slots on the top patch plate, so that it takes up a small volume of 12 × 9 × 6 mm³. To enhance port-to-port isolation and efficiency of each antenna, an additional non-radiating folded shorting strip is connected between each antenna element and ground plane of PCB. The measured isolation values are lower than -28 dB over the lower WLAN band (2.4-2.485 GHz) and better than -26 dB (-30 dB in most of the band) across the higher WLAN band (5.15-5.85 GHz). The improvement in antenna's efficiency caused to raise up 1 dB of effective diversity gain of MIMO system. Furthermore S-parameters, radiation patterns and diversity performance characteristics are provided.

This paper proposes a new logging while drilling (LWD) method to evaluate rock moisture content and reservoir hydrocarbon saturation. Transient signal with broadband spectrum covering the sensitive range of fluids contained formation was used as excitation signal in the near-bit MWD system. Continuous measurement in the whole spectrum with both fluid type and saturation changes caused differences in frequency distribution of response signals and achieved integrated evaluation of formation hydrocarbon and water saturation. Linear system analysis was optimized by adding oil/water saturation parameters, and analytic calculating results were presented to verify the performance of the proposed transient MWD system. Compared with conventional wireline and LWD tools, the method presented in this paper provided higher resolution and signal intensity.

This paper presents the analysis of novelistic fractal optical antenna arrays in a conceptual manner. Fractal antennas are array antennas with converging and diverging growth of basic element or elements for multi-wideband capturing of the electromagnetic waves. Most of these antennas relay on two components for their characteristics. First one is the basic stage shape and second one is the number of stages of growth. For computing the direction of radiation the well-defined fractal array manifold and a good estimate of the covariance matrix of the fractal array response is needed.