Based on second-order cone programming, we present a new superdirective beamforming method with interferences and noise suppression for small aperture HF receive arrays. In the novel method, low side lobe level (SLL) and nulls are not only used to suppress interferences and noise, but also play an important part in overcoming the low array efficiency brought by superdirective beamforming. According to the actual condition, the new method can present a good tradeoff between directive gain, array efficiency, SLL, nulls and robustness against array uncertainty. Compared with the existing methods, it is more effective in suppressing interference and noise. The superiority and validity of the proposed method can be illustrated by numerical results.
One varactor-tunable High Impedance Surface (HIS) is proposed and used in design of an active metamaterial absorber. The proposed HIS structure is based on mushroom-type HIS, in which varactors are introduced to adjust the effective capacitance and tune the resonance frequency. The primary ground plane is etched as the bias network for these loaded varactors, and another ultra-thin grounded sheet is attached to the bottom. In addition, the absorbing characteristics are introduced for dielectric loss to construct an active metamaterial absorber. Numerical simulations show that a wide tuning range can be achieved by adjusting the varactor capacitance, and effective absorption is realized at different states. Two identical absorbers, which are loaded with fixed-value chap capacitors of different capacitances, are fabricated and measured using a waveguide measurement setup. Excellent agreement between the simulated and measured results is demonstrated.
This paper presents a simple method of tuning the AMC band of a high-impedance surface. The tunability is obtained with only two varactor diodes and a simple biasnetwork. The proposed structure, when used as a ground plane for a microstrip antenna, splits the resonance frequencies on the two sides of a reference antenna frequency. The resonance split is analyzed by employing cavity model and transmission line model of the patch antenna. Considerable tuning range is obtained in both the split bands. The simulated, measured and calculated results are found to be in good agreement.
The uniform asymmetrical microstrip parallel coupled line is used to design the multi-section unequal Wilkinson power divider with high dividing ratio. The main objective of the paper is to increase the trace widths in order to facilitate the construction of the power divider with the conventional photolithography method. The separated microstrip lines in the conventional Wilkinson power divider are replaced with the uniform asymmetrical parallel coupled lines. An even-odd mode analysis is used to calculate characteristic impedances and then the per-unit-length capacitance and inductance parameter matrix are used to calculate the physical dimension of the power divider. To clarify the advantages of this method, two three-section Wilkinson power divider with an unequal power-division ratio of 1:2.5 are designed and fabricated and measured, one in the proposed configuration and the other in the conventional configuration. The simulation and the measurement results show that not only the specified design goals are achieved, but also all the microstrip traces can be easily implemented in the proposed power divider.
This paper proposes an amplify-and-forward (AF) distributed relay network consisting of a one-source-one-destination pair and two-level N relays. Optimal relay amplifying matrices (or vectors) at the relays in the first and second levels are determined based on the minimum mean square error (MMSE) criterion. Power is globally, locally, and aggregately constrained at the relays in the first and second levels, independently or separately. With the derived optimal relay amplifying matrices, bit error rate (BER), mean square error (MSE) behavior, and the achievable rate are investigated. It is also proven that minimizing the MSE is equal to maximizing the signal-to-noise ratio (SNR) in a three-hop AF wireless relay network.
This paper proposes a novel scheme for a multi-way communication where users combine bi-directional multi-pair messages exchange with multi-directional multi-pair exchange. Particularly, we focus on the system where multiple users have multiple antennas exchange both private and common messages with each other. In this scheme, we can use simple zero forcing combined with successive network code decoding enables all user to decipher the encryption message from the relay despite the fact that they all have different self-information which they use as a key.
In this paper, a novel ultra-wideband (UWB) bandpass filter (BPF) based on multiple-mode resonator (MMR) is presented. The structure of the proposed MMR constructed by a modified triple-mode stepped-impedance resonator (SIR) loaded with a T-shape stub. This stub loaded resonator can generate two more resonate modes and two transmission zeros (TZs) simultaneously. Five resonate modes of the proposed MMR are roughly allocated in the UWB pass band, as well as two TZs at the lower and upper cut-off frequencies of the passband, leading to sharp roll-off. Using aperture-backed interdigital-coupled lines for feeding, passband is realized, first harmonic resonate mode (sixth mode) suppressed by first TZ of the interdigital-coupled lines, and upper stopband extended. Resonant modes and TZs are discussed together. Finally, the proposed filter is fabricated and measured, and predicted results verified in measurement.
In this paper, empirical relations for the evaluation of both the resonant frequency fr and the quality factor Q for the dominant TM010 mode of a circular substrate integrated waveguide (SIW) cavity resonator are proposed and validated. These formulas are based on well established analytical expressions valid for the case of circular metallic cavity resonator, in which an equivalent radius Req, empirically derived, is employed. Their effectiveness is demonstrated by comparing the empirical predictions with the full wave results.
A passive millimeter-wave imager BHU-2D-U has been developed by Beihang University. This imager is designed for detecting concealed weapons on human body. It is a subsequent model of BHU-2D, which is also developed by the same group. In this paper, the improvements of BHU-2D-U over BHU-2D are introduced. Firstly, BHU-2D-U is used for whole body scan, which is different from BHU-2D. Thus, the field of view (FOV) of the new imager is enlarged and a new antenna array type is adopted. Secondly, the enlarged FOV requires smaller antenna spacing and compact receiver arrays. In order to reduce the volume of the receivers, I/Q demodulators operating in double side band mode are adopted because it does not need the image-reject filter, which is usually a bulky one. Thirdly, the quantity of the correlators increases because the number of receiving elements is doubled. To cope with the increase of the correlator quantity, a multiplexing technique is used in the FPGA internal layout of the correlator array unit. After a brief introduction, the system design and configuration is illustrated in detail. Finally, imaging experiments on a person with concealed weapon are conducted, by which the design and image reconstruction algorithms are verified. To conclude, initial results of BHU-2D-U have proved that the improvements are effective.
An omnidirectional dual-polarized slot antenna with high port isolation for 2.4-GHz wireless local area network (WLAN) applications is proposed in this paper. The omnidirectional radiation patterns of the vertical polarization (VP) and horizontal polarization (HP) are achieved by individually cutting two orthogonal slots onto the metal walls of a cuboid antenna. The overall volume of the compact antenna is only 60 × 10 × 10 mm3 (0.488λ0 × 0.081λ0 × 0.081λ0 ). A prototype of the designed antenna is manufactured and tested. Both simulated and measured results show that the -10 dB impedance bandwidths of dual polarizations cover the desired band of 2.4-2.484 GHz and the port isolation, in the operating frequency, is less than -35 dB. Stable measured gains are greater than 2.75 and 1.35 dBi for the VP and HP, respectively.
Constrained Least Mean Square (CLMS) algorithm is used to adapt the antenna array weights. CLMS in its simple form fails to capture the Signal of Interest (SOI) if there is an error in the Direction of Arrival (DOA) estimation. Moreover, it will consider the SOI as an interferer and create null in the desired DOA. The large gain will be towards the detected wrong direction. Derivative constraints and Bayesian beamformer are two techniques used to overcome such a problem. Derivative constraints destroy a lot of Degrees of Freedom (DOF). Bayesian beamformer destroys only one DOF but vulnerable to binning error. The proposed algorithm overcomes the problem of binning error in the Bayesian beamformer with only one extra DOF.
A new planar inverted-F antenna with a very large bandwidth starting from 817 MHz to 11.5 GHz (VSWR < 3) is proposed as an alternative for high performance mobile phones intended to cover the major part of the mobile phone frequencies worldwide as well as the ultra-wideband (UWB) frequency range. A prototype of the antenna was constructed and the reflection coefficient and radiation patterns were measured to demonstrate an adequate radiation performance. The antenna dimensions of 4 x 2.5 x 0.5 cm3 are compatible with the requirements imposed by the most recent commercially available smartphones. Besides, the easy construction without a matching network or a complicated geometry is an additional feature that can be reflected in low fabrication cost.
This paper describes the design, modeling and optimization of an efficient ISM band dual patch rectenna capable of achieving more than 80% RF-to-DC conversion efficiency at low/medium power densities. The circuit is based on a full-wave rectifier, designed and optimized at 2.45 GHz with ADS software and the FDTD algorithm. The performances of the rectenna have been accurately predicted using the full-wave 3D-FDTD method extended to lumped linear and non-linear elements. It exhibits 73% (<VDC = 1.1 V for RL= 1.2 kΩ) measured efficiency at a low power density of 14 μW/cm2 and 84% (VDC = 1.94 V) at 43 μW/cm2. The differences between the experimental and FDTD simulated efficiencies are less than 3%. The proposed circuit is particularly suitable for low/medium power recycling and power remote supply of wireless sensors, sensor nodes and actuators.
Compact symmetrical four-ports differential bandpass filters with good common-mode suppressions are proposed in this work. The presented filters are designed based on half-wavelength coupled resonators with compact size, good filtering responses for differential-mode, and wide common-mode suppression range. To further improve the common-mode performances within the differential-mode passband, T-shaped resonators are loaded at the center of the structure. It is noted that, the size of filter does not become larger with loaded T-shaped resonators. Both these two filters are centered at 1.8 GHz for Global System Mobile Communication (GSM) with 7.8% fractional bandwidth. For differential-mode, the insertion is less than -1.2 dB in the 3-dB passband and the matching is better than -20 dB. Good stopband characteristics are also obtained with more than -20 dB out-of-band attenuation from dc to 1.6 GHz in the lower stopband and from 2.0 to 4.8 GHz in the upper stopband. For common-mode, better than -15 dB suppression is achieved within dc to 6.2 GHz and with the help of the loaded T-shaped resonators, the rejection in the differential-mode passband is improved to be more than -40 dB. Theory analysis, simulation, and measurement show good agreement with each other.
An inverted micro-strip line (IML) is proposed at microwave and millimeter wave frequencies. This IML on high resistivity silicon (HRS) is studied from 10 to 100 GHz and presents an attenuation lower than 0.08 dB/mm on the whole frequency band. A parametric study, in order to minimize the attenuation and the dispersion of the inverted line in the 10-100 GHz bandwidth, is performed using numerical full wave calculations with HFSS (High Frequency Structural Simulator) tool. A complementary study is added: a large variety of characteristic impedances (for instance, from 38 Ω to 87 Ω at 60 GHz) is performed, the change of propagation modes is observed and the qualification and quantification of the losses allows minimizing them. A comparison with a line of the same length and width without ground plane, the Planar Goubau Line (PGL) is reported in the 10-100 GHz band and a first measure of the PGL is performed, in the 55-67 GHz band, presenting the same propagation mode as the IML at 60 GHz. The measured attenuation of 0.064 dB/mm in the 55-67 GHz obtained for the PGL promises a comparable value for the IML in the measured band.
A robust direct data domain least squares (D3LS) beamforming algorithm that is capable of reducing the sidelobe level of the beam pattern is presented. By exploiting the sparsity of the desired beam pattern, the proposed method can enhance the performance with its lower sidelobe level and deeper null for interference while the robustness against steering vector mismatch is increased when a proper regularization parameter is selected. Simulation results demonstrate the effectiveness of the proposed method.
Based on a construction of concentric deformed annular slots with a stepped microstrip feed line, two designs of dual-band dual-sense circularly polarized slot antenna are proposed in this paper. Compared with the first antenna, the second design possesses the merits of simple structure by devising a twin-slot with less adjusted parameters to achieve the same satisfactory output responses. The results from simulations and measurements demonstrate that both of the antennas have good quality of impedance matching and dual-sense circular polarization at 1.6 GHz and 2.5 GHz.
Measurements of mm-wave excitation spectra of high-order whispering gallery modes in free-space cylindrical disk resonators as functions of resonator thickness have been made. Resonators in the form of tight stacks of thin dielectric disks excited via dielectric waveguides have been used in the experiment. Experimental conditions for the excitation of thin-disk resonators have been found. A simple approach for the modeling of resonator spectra and recovery of dielectric parameters has been proposed.
In this paper, 60 GHz millimeter-wave indoor propagation characteristics are simulated and analyzed using the method of SBR/IM (shooting and bounding ray tracing/ image). And the simulated and measured results agree well, so the correctness of the method has been validated. Some propagation parameters are obtained in the simulation, such as the indoor reception power distribution, distribution of phase angle of received power, root mean square (RMS) delay spread, direction of arrival, RMS angular spread, Doppler shift, etc. The analysis of the above results provides the foundation for the indoor coverage of millimeter-wave communication system.
Failure mode characterization was applied to coplanar transmission lines by utilizing 0.5-10-GHz S-parameter measurements and post-calculated TDR (Time-Domain-Reflectometry) analysis. Coplanar waveguide transmission lines were inkjet-printed on 1.0-mm-thick flexible plastic RF substrates. Inductive, resistive, and capacitive types of failures-as the main failure modes caused by manufacturing, bending, or thermal cycling stresses-were investigated. The inkjet-printed CPW (Co-Planar Waveguide) lines were damaged by inductive shorts due to mechanical hits or resistive and capacitive failures due to bending of the substrate. By using the TDR method the type and physical location of the failure can be determined.