This paper focuses on an efficient antenna selection strategy for a distributed massive MIMO system. The objective of the proposed algorithm is to attain ergodic achievable rate as much as possible with antenna selection in a constrained capacity limited system. In this proposed work, the initial selection of antenna set is based on channel amplitude and correlation which then follows an iterative approach in order to select the best subset of transmit antenna elements from the overall antenna set. The proposed scheme significantly outperforms, in terms of ergodic rate with low complexity, the prevailing transmit antenna selection methods. Simulation results show that the performance of the proposed antenna selection method is close to select all transmission with a minimum throughput loss. Thus the proposed method is best suited for a large scale distributed Massive MIMO system without degradation in system performance and is of low computational complexity.
Microwave Imaging (MI) is a new technique for detecting breast cancer using electrical property difference between the non-malignant and malignant tissues present in the breast. Numerous studies show that detecting the depth of the tumor is the essential measure in determining additional management. Developing evidence in many of the literature surveys illustrate that detecting tumor depth is a precise parameter for identifying the affected area. Thus, Ground Penetrating Radar (GPR) algorithm is applied successfully to detect the exact depth of the malignant tissue. Generally, GPR is originally conceived for archaeological investigations, building condition assessment, detection of buried mines, etc. But here an effort has been made to apply GPR to Radar-based breast cancer detection. The simulated bandwidth of the proposed UWB antenna starts at 2.4GHz and ends at 4.7 GHz. The electromagnetic wave reflected due to dielectric property variation is used by GPR algorithm to identify the depth of the tumor. Before applying a depth migration technique, preprocessing steps like Cartesian form transformation, Hermitian Signal Processing, and Inverse Fast Fourier Transform (IFFT) have to be followed in the backscattered signal to convert positive frequency data into time-domain data. Depth details can be noticed in the migrated image, after applying the migration procedure. Results show that GPR algorithm can be effectively used for detecting the tumor embedded in the depth of the breast tissue. To understand the effectiveness of this imaging scheme, an experimental analysis is done using a combination of wheat flour and water-petroleum jelly. The measured impedance bandwidth of the UWB antenna ranges from 2.8 GHz to 4.48 GHz. The observation is done for a known spherical tumor of diameter 13mm which is placed at different depths from the skin layer. While applying the algorithm in the received backscattered signal, we were able to detect correctly the tumor at a depth of 45mm embedded in the breast tissue. The experimental results are compared with simulation ones to validate the aptness of a microwave imaging approach for detecting the depth of the tumor.
In this paper, we extend our previously published hybrid analytical model for estimation of shielding effectiveness of a dual-cavity structure with an aperture array to generalize the model for a wider range of applications. The aperture array in the center and off-center, higher order modes, and multi-cavity are taken into consideration, respectively. At last, comparations of the results calculated by the extended hybrid analytical model with those obtained by the simulation software CST are given. The results show that the extended hybrid analytical model for shielding effectiveness prediction of a three-cavity structure with numerous apertures has high precision and high efficiency.
Stub-loaded step-impedance resonator (SLSIR) is a multi-mode resonator and can be applied to implement multi-band or wideband filters. In this paper, odd- and even mode impedance analysis is used to resonant properties of the SLSIR. Only two SLSIRs are applied to design a quint-band bandpass filter (BPF). To find the required five resonant modes, the frequency ratios of the high order modes to the fundamental mode of the SLSIR are calculated depending on the impedance ratio and the length ratio of the SLSIR. Several coupling types of the SLSIRs are considered first to have enough energy for all the five passbands. When forming the quint-band, a pair of the SLSIR are coupled electrically and connected with 0o feeding input/output structure. The center frequencies are designed at 1.38 GHz, 2.58 GHz, 3.69 GHz, 5.36 GHz, and 5.8 GHz, corresponding to the different communication applications. The filter is designed, fabricated, and measured. Simulated and experimental results are in agreement, verifying the design concept.
Different optimization strategies to reduce the earth resistance in a high resistivity soil are discussed in this work and illustrated with a practical example. Finite Element simulations reproducing real-world conditions in terms of structure design and soil profiles have been made to evaluate the improvements that should be adopted to minimize earth resistance. We analyze an example of an earthing system of an array of four identical telescopes installed on high resistivity (k¢m order) soils with two different behaviors. In the first one, current dissipation occurs in an uniform soil. In the second one, a terrain with four layers of different resistivities is considered. This situation corresponds to a real world case of an observatory constructed in a volcanic terrain. It was found that the best strategy in each case differs: extend horizontal electrodes as far as possible from the foundation in the first case and combine these electrodes with buried vertical electrodes that connect with deep high conductive layers in the second. The results are discussed in terms of the achieved improvements depending on the modifications introduced in the main structure.
In this paper, a plasmonic sensor based on a metal-insulator-metal (MIM) waveguide with a slotted side-coupled elliptical cavity is proposed. The transmission characteristics of the cavity are analyzed theoretically, and the improvements of performance for the elliptical cavity structure compared to a single disk cavity are studied. The influence of structural parameters on the transmission spectra and sensing performances is investigated thoroughly. The achieved sensitivity for the first mode was S = 959 nm/RIU and S = 2380 nm/RIU for the second one. Its corresponding sensing resolution is 1.04 x 10-5RIU for mode 1 and 4.20 x 10-6RIU for mode 2, respectively, and high transmissions are achieved at the two resonant wavelengths of 898.8 nm and 1857.1 nm. The proposed plasmonic sensor is a good candidate for designing novel devices and applications, in the field of chemical and biological sensing, and also in the field of plasmonic filters, switches, etc.
Microwave radiometer is a high-sensitivity ``camera'', which realizes high-resolution imaging by receiving the natural radiation signal in microwave band from the observation scene. Due to the imperfection of the system hardware, the measured data include not only the radiated signal of interest but also the noise generated by the system hardware itself. These unexpected noises will affect the imaging performance of the system, especially for the synthetic aperture interferometric radiometer (SAIR). In this paper, the noise behavior of the SAIR system is analyzed and modeled for the first time. Based on the noise behavior model, a method is proposed to pick the optimal averaging time for imaging with high fidelity in the SAIR system. Some experiments are carried out to verify the correctness of the noise behavior model and the optimal averaging time picking method for SAIR. With the noise behavior model and the optimal averaging time picking method, it can provide an effective guide for the SAIR system design, error correction, and reconstruction.
Rigorous quantum formulation of the Parity-Time (PT) symmetry phenomenon in the RF/microwave regime for a pair of coupled coil resonators with lump elements has been presented. The coil resonator is described by the lump-element model that consists of an inductor (L), a resistor (R) and a capacitor (C). Rigorous quantum Hamiltonian for the coupled LRC coil resonators system has been derived through twice basis transforms of the original basis. The first basis transform rotates the original basis such that off-diagonal terms of the governing matrix of the equation system of the coupled coil resonators is reduced to constants. Then a second basis transform obtains the quantum Hamiltonian, including the diagonal effective complex frequencies and off-diagonal coupling terms, together with the transformed basis. With the obtained quantum Hamiltonian, the eigenvalues and eigenvectors of the coupled coil resonators can be obtained as usual as the quantum Hamiltonian. Finally, numerical simulation verifies the correctness of the theory. The quantum formulation of the coupled coil resonators can provide better guideline to design a better PT-symmetric system.
Placing microwave absorbing materials into a high-quality factor resonant cavity may in general reduce the large interior electromagnetic fields excited under external illumination. In this paper, we aim to combine two analytical models we previously developed: 1) an unmatched formulation for frequencies below the slot resonance to model shielding effectiveness versus frequency; and 2) a perturbation model approach to estimate the quality factor of cavities in the presence of absorbers. The resulting model realizes a toolkit with which design guidelines of the absorber's properties and location can be optimized over a frequency band. Analytic predictions of shielding effectiveness for three transverse magnetic modes for various locations of the absorber placed on the inside cavity wall show good agreement with both full-wave simulations and experiments, and validate the proposed model. This analysis opens new avenues for specialized ways to mitigate harmful fields within cavities.
In this paper, a hybrid antenna array for 4G/5G smartphone applications is presented. The hybrid antenna system is composed of one array of two antenna elements for 4G application and another array of six antenna elements for 5G application. By loading PIN diodes and changing the on/off state of the PIN switch, then the resonance point will shift. The 2-antenna array broadens the bandwidth of 4G frequency band and is capable of covering GSM850/900/DCS1800/PCS1900/UMTS2100 and LTE2300/2500 operating bands. A U-shape monopole strip and an S-shape slot coupling technologies are also introduced, the 6-antenna array improves the impedance matching for the proposed 5G antenna array, and is capable of covering the 5G (3300 3600 MHz and 4800 5000 MHz), which can meet the demand of 5G application. Spatial and polarization diversity techniques are implemented on these antenna elements so that high isolation can be achieved. This hybrid antenna array is fabricated, and typically experimental results such as S11, isolation, radiation pattern, efficiency, and channel capacity are presented. The measured results are in good agreement with the simulated ones.
An eleven element log-periodic dipole-array (LPDA) antenna, occupying a surface area of only 90 x 52 mm2, printed on an ultra-thin flexible Kapton substrate of thickness 0.035 mm , is proposed. The antenna operates with a stricter 10 dB reflection coefficient bound in the frequency bands 2.75-3.53 GHz and 4-6.2 GHz. For a less stringent bound of 6 dB (which is acceptable for wearable applications), it operates in the wider range of 2.7-6.8 GHz. The antenna has an end-fire radiation pattern with a maximum measured gain of 6 dBi. The flexibility of the antenna is illustrated by reflection and radiation pattern measurements for three different radii, i.e., 50, 30, and 10 mm in both the convex and concave configurations. It is experimentally demonstrated that LPDA exhibits stable input-impedance characteristics and consistent radiation properties over the whole operating band under all bending conditions. The low cost, light weight, and flexible design, as well as the broadband performance in both concave and convex bent configurations, prove the suitability of the antenna for the contemporary flexible electronic devices.
Space-time adaptive antijamming problem has received significant attention recently for global navigation satellite system (GNSS). It can jointly utilize spatial filters and temporal filters to suppress interference signals. However, most of the works on space-time antijamming problem presented in the literature require a space-time two-dimension (2-D) array with multiple antennas and delay taps. In this paper, an effective adaptive antijamming method based on space-time a 2-D sparse array is proposed. The maximum array gain is utilized to construct a space-time 2-D sparse array. The space-time antijamming weight vector is given by minimizing the 2-D sparse array output power. Compared with the previous works, the presented method can have better antijamming performance than a space-time 2-D uniform array. Simulation results verify the effectiveness and feasibility of the proposed method.
A compact wideband bandpass filter (BPF) with stopband suppression by utilizing transversal signal interaction concepts is proposed in this article. Two transmission paths from Port I to Port II are separately constructed by multi-mode step impedance resonator (SIR) and shorted coupled lines. The proposed configuration generates two controllable transmission poles, and wideband characteristic can be realized. Moreover, multiple transmission zeros are implemented by signals superposition of two transmission paths and stub loaded fans resulting in steepness sideband and broad upper stopband suppression up to 100 GHz. For clarification, the designed wideband centered at 4.5 GHz with fractional bandwidth of 14.2% is designed, assembled and measured. The circuit size of prototype BPF only occupies 0.94 cm2, and the presented BPF is evaluated by test results and simulated predictions with good agreement.
In this paper, the application of gammadion chiral metamaterial for converting linearly polarized waves to circularly polarized waves is presented and using this a circular polarized antenna for wireless application is proposed. First of all, a traditional rectangular microstrip patch antenna has been designed at resonance frequency of 5.15 GHz, which gives linear polarization. The linearly polarized waves are allowed to feed gammadion chiral metamaterial, which is placed at a height of 33 mm above the reference antenna. The gammadion chiral metamaterial produces two special effects that are responsible for polarization rotation: circular dichroism and optical activity. As a result of these effects, the necessary conditions for circularly polarized radiation are fulfilled, and antenna is converted to the circularly polarized antenna. This method gets rid of designing of complicated feeding structure that is necessary for circular polarization. The role of gammadion chiral metamaterial to convert linear polarization to circular polarization has been described. The antenna is fabricated, and the measurement of return loss, axial ratio, etc. is also carried out. Simulation and measurement results agree with each other.
An auxiliary antenna array scheme for sidelobe interference cancellation of satellite communication system is proposed in this paper. Considering earth curvature, signal bandwidth and transmission loss, a precise model of satellite communication interference scenario is established. In order to improve anti-interference capability, the performance of the auxiliary antenna array is studied by the minimum mean square error (MMSE) criterion. Then, a 7-unit linear microstrip antenna array is manufactured as the auxiliary antenna array. The main contribution of this paper is the corresponding auxiliary antenna array analysis and design. Simulated and experimental results confirm that the proposed scheme can achieve a relatively high interference cancellation radio (ICR) of about 25 dB in a wide beam range.
A dual-band microstrip rectenna for wireless local area network (WLAN) applications is presented. It consists of a dual-band dual-polarized receiving antenna and a dual-band high efficiency rectifier. The receiving antenna includes a circular loop, a coplanar waveguide (CPW), and a microstrip line. To minimize mutual interference and ensure high isolation of more than 20 dB between the dual-polarized ports, a CPW is used to produce vertical polarization modes and the horizontal polarization modes is fed by a microstrip line. The horizontal excitation port is used for information receiving, while the vertical feeding port transfers enough wireless energy for rectifying. A co-simulation of HFSS and ADS is used for analysing the performance of rectenna. Measured results show that it has the -10 dB reflection coefficient bandwidths of 510 MHz (2.39-3.09 GHz) and 920 MHz (5.16-6.08 GHz) for rectifying Port 1, where the isolation between the ports is higher than 25 dB, and the cross polarization is less than -15 dB in two bands. The maximum microwave-direct current (mw-dc) conversion efficiencies of 67.7% and 57.03% at 2.45 GHz and 5.8 GHz are achieved with a 300 Ω load and 16 dBm receiving power.
A new hybrid double stator bearingless switched reluctance motor (HDSBSRM) realizes the decoupling of torque and suspension force from the structure, and the permanent magnet added in the inner stator further reduces the suspension power loss. For HDSBSRM, loss is the main cause of temperature rise. In order to ensure the stable suspension and rotation of the motor, loss of the Magnetic Bearing (MB) and motor are calculated and analyzed by finite element method (FEM). Based on the loss result, the temperature field is analyzed. The analysis of loss and temperature field provides important theoretical basis for the design of motor cooling system.
This paper proposes and demonstrates a compact integrated filtering antenna built on a square ring resonator coupled with a capacitors loaded microstrip line filter. A microstrip filter module is connected to feeding line of the conventional patch without adding extra space. Thus, the combined configuration possesses radiating and filtering functions simultaneously. The proposed filtenna has a fractional bandwidth (FBW) of 3% at center frequency 2.4 GHz with 2.5 dB of maximum gain. The obtained result shows that the proposed design shows good stopband gain rejection, good selectivity at band edges, and smooth passband gain. Furthermore, the introduced filtenna has advantages of a small size and a simple structure, which makes it ideal for interconnection with different wearable devices operating within 2.4 GHz wireless system range.
A new miniaturized and ultra-thin non-resonant element-class of convoluted frequency selective surface (FSS) structure with reduced overall thickness is presented and empirically verified. The proposed FSS structure, which could be capable of providing a first order narrow band pass response for X band applications, is made up of three metallic layers separated from one another by two dielectric substrates. The outer layers are made up of convoluted inductive grids， and the inner layer is a non-resonant structure composed of convoluted square slot array. A first-order band pass response FSS with a centre frequency of 10.5 GHz and fast roll-off characteristics is presented. The overall element thickness of the proposed FSS is λ/56, which is smaller than previously proposed miniaturized structures. The comparison between all patch layers with the proposed structure which is not an all patch layers is explicated in detail with its convoluting effects. The validity of this design procedure is verified with an equivalent circuit model, and a sample is fabricated and measurement done using a WR 90 waveguide setting for experimental verification.
Recently, magnetic-resonance-based electrical properties tomography, by which the electrical properties (EPs), namely conductivity and permittivity, of biological tissues are reconstructed, has been an active area of study. We previously proposed an explicit reconstruction method based on the Dbar equation and its explicit solution given by the generalized Cauchy formula. In this method, as in some other conventional methods, the values of EPs on the boundary of the region of interest must be specified by the Dirichlet boundary condition of the partial differential equation. However, it is difficult to know the precise values in practical situations. In this paper, we propose a novel method that reconstructs EPs without the prior information of boundary EP values by deriving a new representation formula of the solution of the Dbar equation with the complex-derivative boundary condition. Numerical simulations and phantom experiments show that the proposed method can reconstruct EPs without knowledge of the boundary EP values. Therefore, the proposed method greatly enhances the applicability of the current EPT methods to practical situations.