Hybrid analog/digital precoding is a promising technology that reduces the hardware complexity and power consumption of large-scale millimeter wave (mmWave) multiple-input multipleoutput (MIMO) communication systems. Most prior work has focused on hybrid precoding for narrowband mmWave systems. MmWave systems, however, will likely act on wideband channels with frequency selectivity. Therefore, this paper presents an effective OFDM-based hybrid precoding algorithm (named as W-LS-IR algorithm) for wideband mmWave systems. Firstly, the initial phases of the analog precoding matrix are randomly generated, and the digital precoding matrix is initialized via the least squares (LS) method. Then, the column of the analog precoding matrix is derived from the dominant left singular vector of a residual matrix, and the corresponding row of the digital precoding matrix is updated using the LS method. Through the iterations of the aforementioned stage, the hybrid precoding matrix will approach a stable solution finally. Compared with related works, the proposed algorithm can improve the spectral efficiency of wideband mmWave MIMO communication systems. Simulation results are presented to confirm the efficiency of the proposed algorithm.
This piece of work replicates on the antenna array thinning exploring the benefits of known Fourier Analysis. In this communication Fourier transform is applied to the synthesis of periodic arrays for minimizing the Peak Side Lobe (PSL) level and thereby enhancing the directivity. Furthermore, the concept of Fill Factor(degree of thinning) i.e, reduction in the number of active elements is experimented for the above said objective. The proposed methodology is workedout on periodic linear and planar arrays. Numerical study and simulation results are composed with array thinning designs from literature. The analysis demonstrates the superiority of the illustrated Fourier technique.
In this paper, an ultrathin egg-shaped microbubble was proposed and analyzed for pressure sensing firstly, which was fabricated by utilizing an improved pressure-assisted arc discharge technique. By tailoring the arc parameters and the position of glass tube during the fabrication process, the thinnest wall of the fabricated microbubble could reach 873 nm. Such an ultrathin film structure is very suitable for pressure sensing. Especially, as only a commercial fusion splitter and pressure pump were utilized to achieve such functions, the fabrication cost was very cheap. The fiber Fabry-Perot (FP) interference technique was used to analyze its pressure sensitivity by filling the inner wall of the microbubble with different air pressures. The experiment results depicted that the end face of microbubble expands with the increase of the filling pressure. The pressure sensitivity of such an egg-shaped microbubble could reach up to 14.3 pm/kPa in terms of interference spectrum shift, while the maximum cavity deformation sensitivity of the microbubble vs. pressure could reach up to 0.334 nm/kPa in terms of cavity length change. Besides, the maximum sensitivity vs. temperature was only 27.83 pm/˚C. Results of this study could be good reference for developing new pressure sensors with low cost, high sensitivity and good anti-temperature interference abilities.
Space-time adaptive processing (STAP) for airborne radar employs training samples to estimate clutter covariance matrix (CCM). However, the target-like signals contained in the training samples severely corrupt the accuracy of the CCM. This paper proposes a novel non-homogeneous STAP algorithm for target-like signal elimination based on reduced-dimension sparse reconstruction (RDSR) to overcome this issue. The proposed algorithm exploits the high-resolution angle-Doppler spectrum obtained by RDSR to estimate and eliminate target-like signals. Theoretical analysis and simulation results show that the proposed algorithm effectively suppresses clutter and improves the performance of STAP in non-homogeneous environments.
A main defect of far-field (FF) measurement techniques is long measurement time, which often leads to the problem of inefficient use of measurement facilities that is a strong limiting factor in many measurements. To solve this problem, in this study, we propose a technique to accelerate the antenna measurement that is achieved by sparse test results in the FF measurement system. In the data processing part of the measurement, the concept of the quadrature analog-to-information conversion (QAIC), which make the approach both efficient and easy to implement in existing FF measurement facilities, is discussed. Simulations are provided to show this low-speed uniform sampling approach. The proposed strategy is then applied to measure the pattern of a standard rectangular horn antenna in an anechoic chamber. The experimental results demonstrate that our technique can reduce the measuring time by at least 34.4% while guaranteeing the measurement accuracy. These results demonstrate the potentials of the method.
In this paper, a stub-loaded penta-mode resonator (PMR) with its analysis, characterization and applications for bandpass filter (BPF) is presented. Even-/odd-mode analysis method is employed to analyze the PMR which exhibits five transmission poles (TPs) and three inherent transmission zeros (TZs). By changing the dimension parameters of the resonator, TPs and TZs can be flexibly controlled, and wideband/dual-wideband/tri-band BPF has been designed successfully utilizing the same configuration. For validation, all these three filters are fabricated and measured, and the measured results are in good agreement with the simulated ones.
This paper presents some theoretical and experimental analyses of the rotating-magnet based mechanical antenna (RMBMA), a promising portable transmitting antenna for ELF-ULF (3-3000 Hz) wireless communication. Based on the Amperian current model, a theoretical model is developed to analyze the electromagnetic fields generated by RMBMA. A prototype is manufactured and measured, and the measurements coincide well with the calculations based on the established theoretical model. The results reveal that this new technique can create a constant channel condition in complex propagation environment, and an RMBMA with a small size can produce an AC magnetic field of 1 pT at hundreds of meters across lossy media, such as soil and sea water.
This paper presents a dual-band Multi-Input Multi-Output (MIMO) antenna design with acceptable isolation and compact size for wireless applications. The proposed antenna operates at two frequencies (2.75 GHz-5.3 GHz) and consists of two symmetrical monopoles with a T-shaped junction that is added on the upper layer of the substrate and used to connect the two monopoles and the ground plane. The T-shaped junction is added to enhance the isolation between the two antennas. Different forms of slots have been etched on the ground plane to adapt the frequency bands to the desired frequencies. The simulations and measurement are used to examine the performance of the antenna in terms of S parameters, radiation patterns and the envelope of correlation coefficient. The results show that the MIMO antenna has two resonance frequencies (2.75 GHz and 5.3 GHz), is suitable for WLAN applications and comes with a mutual coupling that is less than 12 dB. As a result, an envelope correlation coefficient lower than 0.001 and a diversity gain higher than 9.98 dB are obtained, which means that the antenna has a remarkable diversity gain at operating bands.
In this paper, design and development of a novel electromagnetics band gap cell is presented. The EBG cell is designed aiming its use at relatively low frequencies. It is designed as a uni-planar structure to simplify the fabrication processes. It consists of multiple parallel combinations of L and C. These components are realized using planar microwave integrated circuit technology. The components L & C are designed as a meander-line inductor and inter-digital capacitors, respectively. The cell is perfectly symmetrical along x and y-axes to have uniform performance along two orthogonal directions. It is evaluated for its S-parameters and reflection phase. Simulated and measured results are presented for frequency range of 0.885 GHz to 3.1 GHz.
In this article, a negative index metamaterial (NIM) superstrate is designed and cooperated with the filtenna to produce miniaturize communication front end for gain enhancement without any substantial increase in the profile of the whole structure. A finite array Double H Split Ring (DHSR) of 11x9 unit cells has been designed on a dielectric substrate to form the NIM metamaterial superstrate. The proposed superstrates and filtenna have an overall dimension of 0.67λox0.54λox1.19λo at 10.16 GHz with 10.6 dB total broadside gain in simulation and 9.8 dB in measurement at 10.22 GHz (λo = 30 mm). This miniaturized communication front end which consists of a filter, an antenna and a gain enhancer affords smaller size with the overall volume of 0.43λo3 in the context of using metamaterial superstrate for gain enhancement reported in the earlier literatures.
This paper proposes a composite right/left-handed cylindrical waveguide. Negative permeability is realized by the cutoff TM01-mode in a hollow waveguide, and negative permittivity is realized by the cutoff dominant TE-mode in a sector waveguide with a ridge. Usefulness of the proposed cylindrical waveguide is verified from the numerical computations of both the dispersion diagrams and the transmission characteristics of the structure with finite-number unit cells. Finally, measurement of the fabricated waveguides is performed for the experimental verification.
In this paper, a novel multi-physics parametric modeling approach using artificial neural networks (ANNs) for microwave passive components is proposed. In the proposed approach, the ANN is used to learn the nonlinear relationships between electromagnetic (EM) behaviors and multi-physics design variables. The trained model can accurately represent the EM responses of the passive components with respect to the multi-physics input parameters. Therefore, the proposed model can provide accurate and fast prediction of EM responses using low computational cost and little time for multi-physics design. The advantage of the proposed model is demonstrated by two microwave examples: the proposed model can save about 98% computational cost compared with the EM model, and the CPU time of the proposed model is less than 0.1 s while that of the EM model needs many minutes.
In this paper, we propose a simulation model of electromagnetic waves propagation in media with different kinds of dispersions. This model exploits the dependence of the polarization current density and the voltage electric in the context of the Transmission Line Matrix method with the Symmetrical Condensed Node (SCN-TLM) and novel voltage sources. By solving Maxwell's and polarization current density equations, the proposed model, named JE-TLM, gives a full solution of Maxwell's equations and polarization terms which describe the Lorentz linear dispersion, nonlinear instantaneous Kerr and retarded Raman effects. The scattering matrix characterizing the SCN with the new voltage sources is provided, and the numerical results are compared with those of the literature or with the theoretical ones.
Study on the interactions between electromagnetic fields and biological tissue at high frequency band is an important aspect in the area of wireless communications. The use of millimeterwave frequency band for fifth Generation (5G) devises involves new challenges in terms of Radio Frequency Electromagnetic Field Exposure (RF-EMF) limits and compliance assessment since the basic restrictions for limiting human exposure change from the Specific Absorption Rate (SAR) to the power density. The Electromagnetic Field Exposure to the human head has been studied based on power density by means of numerical simulation for the frequency band of 10 GHz. Study on radio frequency energy absorption has been done based on radiation from a printed monopole antenna at frequency of 10 GHz, transmitting directly towards the human head tissue model. Human head model is constructed from magnetic resonance images with frequency dependent tissue electrical properties. It is shown that at millimeter wave frequency, i.e. 10 GHz, with realistic source (20 mW) and head-source separation distance (10 mm), the amount of power density is in the range of regulatory limits and requirements on EMF exposure. The obtained results might provide valuable information for the design of 5G handheld devices and EMF compliance assessment.
A novel array-antenna decoupling surface (ADS) for mutual coupling reduction in microstrip patch antenna is proposed in this paper. The proposed ADS is composed of a group of primary reflector patches and a pair of rectangular and T-shaped secondary reflector patches. Through generating the reflected waves with equal magnitude but out of phase of the coupling waves, the isolation of the antenna elements could be significantly improved by the novel proposed ADS. Then, for verification, a two-element microstrip antenna array covered by the proposed ADS with an edge-to-edge separation of 0.11λ0 (λ0 is the wavelength of the operating frequency in free space) was designed and fabricated. As expected, the experimental results have demonstrated that an additional 40.4 dB isolation enhancement at the resonant frequency was achieved by the proposed ADS. Moreover, a much wider bandwidth of the isolation was also obtained than that of return loss of 10 dB. In addition, a gain improvement of 0.95 dB was achieved at 2.45 GHz by utilizing the novel ADS. Thus, the decoupling structure can be applied to multiple-input multiple-output (MIMO) systems for its simple structure and high isolation providing.
Surface impedance of thin graphite films with metallic properties is evaluated by a waveguide technique based on measuring reflection and transmission coefficients of thin film membranes at operating frequencies in rectangular waveguides. One- and two-layer membranes of finite thickness, completely filling the waveguide cross-section, are investigated. Formulas allowing analytical estimates of surface impedances for nonmagnetic films made of amorphous carbon are derived. Simulation results for graphite films at frequencies from 5 to 10 GHz are analyzed.
A dual-port reader antenna based on magnetic coupling in near-field (NF) and linear polarization in far-field (FF) is proposed for UHF RFID multiservice applications. The prototype consists of four straight dipoles fed by double-side parallel stripline structure with two feed ports. The proposed antenna can operate at different modes by feeding each corresponding port. In NF mode, a strong and uniform magnetic field can be generated over the interrogation zone. In FF mode, a linearly polarized performance can be obtained. The antenna prototype is printed onto a piece of FR4 substrate with an overall size of 180 × 180 × 1.6 mm3. The measured tests on reading range are carried out, and the results exhibit 100% reading rate for near-field tags within 100 mm and reading distance of far-field tags is 120 cm. Both simulated and measured results show good capability for near- and far-field applications.
A dual-polarized broadband single-layer reflectarray antenna based on square spiral element is presented in this paper. Two designs with similar square spiral structures but different construction processes and transition patterns are investigated and compared. The comparison results show that the design utilizing the sweeping method of varying the length of the first stub of one-arm square spiral is more suitable for the building the reflectarray. Several 441-element reflectarray antennas fed by horn with different offset angles are also simulated and compared to show the broadband characteristic. A reflectarray with offset angle of 15 degrees is then fabricated and tested. The measured results show good radiation performances, and the 1-dB gain bandwidth of 34.7% is obtained. The measured gain is 27.1 dB at the center frequency of 15 GHz, which is equivalent to 45.6% aperture effifficiency.
This paper presents a novel Y shaped fractal defected ground structure (FDGS) for the mutual coupling (MC) reduction between coplanar closely spaced microstrip antennas. The proposed FDGS has band-gap characteristic, which induces the current distribution on the antenna patch. This will contribute to achieving 25 dB MC reduction. When realizing the MC reduction, the antenna efficiency is increased. Moreover, the envelope correlation of the MIMO system is decreased, which helps to increase the MIMO system capacity.
This paper presents an extension and update of a theoretical procedure developed by the authors for the determination of the electromagnetic waves scattering at interfaces between dielectric waveguides in cascade. The theoretical core of the problem is based on the generalized scattering matrix concept, together with the generalized telegraphist equations formulism and the modal matching technique. The new version includes the following updates: a) possibility of using any material as waveguide cover, b) inclusion of alternating microchannels with optical waveguides, and c) possibility of analyzing periodic structures of segmented optical waveguides for sensing applications. The spectral results obtained for modulus and phase of the reflection and transmission coefficients have shown the potentiality of the new proposal in the scientific topics of photonic crystals, refractive index sensors and optical biosensors.