When compressive sensing was employed to solve electromagnetic scattering problems over wide incident angles, the selection of sparse transform strongly affects the efficiency of the CS algorithm. Different sparse transforms will require different numbers of measurement. Thus, constructing a highly efficient sparse transform is the most important work for the CS-based electromagnetic scattering computing. Based on the linear relation between current and excitation vectors over wide incident angles, we adopt the excitation matrix as sparse transform directly to obtain a suitable sparse representation of the induced currents. The feasibility and basic principle of the algorithm are elaborated in detail, and the performance of the proposed sparse transform is validated in numerical results.
This paper presents a heart-shaped planar monopole antenna for ultra-wideband (UWB) applications. To increase the impedance bandwidth of the antenna and achieve UWB coverage, we use a heart-shaped radiating patch fed by a microstrip line and an elliptical curved ground plane. Based on this structure, by etching an annular slot loaded with a capacitor in the heart-shaped radiating patch, a planar band-notched UWB antenna can also be obtained. Specifically, to demonstrate the potential application of the proposed structure, a UWB antenna design with a reconfigurable notched band is presented by using a varactor to replace the capacitor. Commercial software ANSYS HFSS is used to analyze and design this antenna. Measured results of the fabricated antenna show good agreement with simulated ones.
This paper proposes a compact and miniaturized branch-line coupler using a crossing bond wire structured slow-wave branch line (CBWSWB). The proposed coupler achieves a size reduction of 82% compared with a conventional implementation. Measured S11, S21, S31 and S41 of the proposed coupler are better than -24, -3.7, -3.7 and -28 dB at 3 GHz, respectively. Furthermore, the phase difference between through and coupling ports of the coupler is within 1°.
In this paper a CPW-fed annular slot antenna is miniaturized with enhanced impedance bandwidth using a reactive impedance surface (RIS) substrate. Such meta-surface (RIS) is realized by patterning 3×3 array of circular elements over an inexpensive FR-4 substrate which is backed by a circular metallic plane. Due to the compensation of electric and magnetic energy stored by antenna and RIS substrate respectively, the antenna resonance frequency is shifted by 53.6% compared with a simple slot antenna. By the inclusion of such reactive surface, input impedance of the antenna is reduced, and a remarkable improvement in impedance bandwidth from 11.66% to 64.26% is also noticed. Therefore, both miniaturization and bandwidth enhancement are achieved simultaneously with the present loading technique. The directivity of the RIS loaded antenna is increased further by loading a concentric metallic ring over the RIS loaded structure at a height above the RIS plane. The Ring & RIS loaded structure is fabricated for measurement purpose. A good agreement is obtained between the simulated and measured results for both RIS loaded and Ring & RIS loaded configurations. The ring loading over the RIS antenna provides improvement in directivity about 5 dB. The peak gain and bandwidth are measured as -1.03 dBi and 58.62%, respectively.
A triple-band planar electromagnetic band-gap (EBG) structure used for gain enhancement and wideband radar cross section reduction (RCSR) of antenna is presented in this paper. Three band-gaps of an EBG structure are realized by introducing two pla-nar spiral inductances on a planar EBG structure. An equivalent model of EBG is given to further understand the formation of three band-gaps. The proposed EBG is placed around antenna units and arrays to calculate the affection of the RCS and the gain. Due to the band-gaps of the EBG structure, RCS of antennas is reduced, and the gain of antennas is enhanced. Results show that the RCS is reduced as much as 20 dB from 9 GHz to 21 GHz, and both of bandwidth and gain of antennas can be slightly enhanced. Two antenna units operating at 8.6 GHz are fabricated and measured to verify the correctness of simulation. Measured and simulated results are in good agreement.
A compact circularly polarized antenna using a wide L-shaped slot and a microstrip feedline is proposed. The measured results demonstrate that the antenna has an axial ratio (AR) < 3 dB bandwidth ranging from 5-8.5 GHz and an S11 < -10 dB bandwidth ranging from 4-8.6 GHz. The antenna is very simple, composed of an L-slot and a microstrip feedline placed beneath and to the edge of the L-slot. The size of the antenna is 20 x 20 mm2 which is attractive for compact wireless devices that operate in C-band. The antenna has very low cost and does not require: a large size, truncated corners, reflecting surfaces, complex feeding structure, and via connections, which increase fabrication cost and design complexity.
A low-profile antenna is proposed in this letter for realizing dual polarizations with omnidirectional radiation patterns. Vertical polarization is obtained by a modified annular ring slot antenna, and horizontal polarization is obtained by a modified printed arc dipole array. By combining the ground plane of the ring slot antenna and the dipole array on the same layer, the profile of the antenna is reduced to minimum extent. The proposed prototype has a low profile of 0.024λ0 (λ0 is the free-space wavelength at 2.4 GHz). To verify the design, the proposed antenna is fabricated and measured. Measured reflection coefficients, isolation, and radiation patterns results agree well with the simulated data. The common band of vertical and horizontal polarizations makes the proposed antenna satisfy the WLAN diversity systems with omnidirectional characteristic.
For the difficulty of calculating and measuring coupling electromagnetic quantity of complex multi-cavities, a microwave chaotic double cavity model is designed, and a new method is put forward to analyze the coupling effect of the double cavities. The new method combines Random Coupling Model (RCM) and network cascade theory and can successfully predict the Probability Density Function (PDF) of the induced voltage at target point of the double cavity compared with other methods. Experiment is added to verify the effectiveness of the new method in this paper. In addition, the new method provides a new approach to analyze and predict the coupling electromagnetic quantity of the complex double cavities in practical engineering.
A compact wideband quarter mode substrate integrated waveguide (QMSIW) band-pass filter with wide stopband performance is presented in this paper. Compared with conventional SIW cavity, the QMSIW cavity occupies only one fourth of the size. A meandered H-shaped slot is etched on the cavity to change the current direction for size reduction. In order to prove the validity, a compact fourth-order band-pass filter with wide stopband is fabricated on a single-layer Rogers RT/Duroid 5880 substrate. The measured in-band insertion loss is only 1.02 dB including the loss caused by two connectors, and the stopband attenuation in the frequency band from 4.02 GHz to 12.63 GHz is better than 25 dB. The whole size of the filter is only 20.6×26.8×0.254 mm3.
A new radiation pattern reconfigurable antenna is designed and fabricated. The antenna is able to radiate in four orthogonal directions in the azimuth plane and sweep the whole azimuth. The radiation pattern reconfigurability is obtained using the passband and stopband characteristics of EBG surfaces which are used to form EBG panels to surround the feeding dipole centered in the structure. Switching between passband and stopband is implemented using active elements in the structure.
A simple and novel WLAN antenna and a kind of neutralization line, which introduces a certain amount of signal to cancel out the unwanted mutual coupling between two antennas, are designed in this paper. The WLAN antenna working at 2.45 GHz and 5.8 GHz frequency bands is designed, fabricated and measured. The simulated and measured results show that the isolation between the two decoupled antennas can be improved to above 20 dB in both frequencies after decoupling. The lumped match network occupies less space for antennas and gains a good matching performance in the operating frequencies.
A compact fully integrated wideband six-port device composed of a suspended stripline Wilkinson power divider and three bias stripline of 3-dB quadrature directional couplers is presented. In order to integrate the six-port circuit, a multilayer circuit structure has been adopted by the via hole interconnection at the output port of the divider. The 3-dB quadrature directional coupler is composed of two 8.34-dB quadrature directional couplers by series connection. In this way, the six-port circuit structure is simplified and reduced. A multisection impedance match structure has been adopted in the suspended stripline Wilkinson power divider to achieve ultra-wide frequency band. In the experiment, The fully integrated six-port device has obtained good measurement result. It is superior to other present six-port networks in microwave performance with the same dimension.
A novel balanced filter circuit with wideband common mode suppression using coupled lines is proposed in this paper. A wideband filter with half open stubs is used to realize two transmission zeros for the differential mode passband. The common mode can be suppressed over 15 dB from 0 GHz to 3f0 (f0 is the center frequency of the passband) with insertion loss greater than 15 dB over the upper stopband. A balanced filter with 3-dB fractional bandwidths of 38% is designed and fabricated. Good agreement can be observed between measured results and theoretical expectations.
In this paper, we provide full-wave numerical results concerning the effective magnetic permeability of the rod-shaped ferrites which is useful in the calculation of the inductance or the efficiency of rod antennas. This study concerns the circular cross-section ferrites with a centered winding fitting the diameter of the rod. A careful attention is taken to the simulation model, and obtained results are in better agreement with the measured coils than existing solution published earlier.
A single-layer partially reflective surface (PRS) structure is presented to design single-feed Fabry-Perot resonator antennas (FPRA) with a large gain bandwidth and compact size. The design of the PRS structure applied in this antenna is based on the theory of tightly coupled antenna arrays. Owing to strong mutual coupling between the overlapped patches, the proposed antenna obtains a wider bandwidth and more compact size. Experimental results show that the antenna obtains a 32% 3-dB gain bandwidth from 8.8 GHz to 12.2 GHz, with a peak gain of 13.5 dBi. Moreover, the relative impendence bandwidth is 40.9% for the voltage standing wave ratio (VSWR) less than 2 from 8.45 GHz to 12.8 GHz.
A novel capacitive loaded U-slot defected ground structure (DGS) is presented in this letter to provide narrowband rejection property. The principles for the selective rejection and the strategies for size-reduction and external Q-factor improvement are detailed based on transmission line equivalent model and the lumped parallel RLC model developed from transmission line model at resonance frequency. The design concept is well validated by the design and measurement of an exemplary high Q BSF.
The effects of exposure to the electromagnetic field from base stations have received considerable attention. Currently, researches have shown that the exposure level from a base station varies with time due to the traffic. The traffic for mobile communications has a temporal and spatial correlation. In this paper, we develop an approach to study the variation law of exposure to the base stations and analyze the correlation of exposure in time and in space. We use a spectrum analyzer to measure the transmission power of the base stations at the different periods of a day. We obtain the analytical expressions for representing the variation of exposure with time using Genetic Algorithm. The self correlation of exposure to a single base station in time series and the cross correlation of exposure to base stations in the same area are both discussed. We find that the self correlation coefficients of exposure to a single base station are more than 0.9 in two hours and more than 0.5 in eleven hours. Particularly, the spatial correlation of exposure is slightly stronger than the time correlation and the cross correlation coefficients are up to 0.99.
In this paper, a new analysis method of broadcast beamforming for a massive MIMO antenna array, targeting at the fifth generation mobile communication, is introduced. In order to solve the problem of narrow broadcast beam coverage, the element phase of massive MIMO antenna array is optimized using a method, which combines both numerical electromagnetic analysis method and global optimization algorithm. The analysis results show that the optimal value of 3 dB broadcast beam width for 64 elements in the horizontal plane is 36 degree, which is 0.55 times of that of the 4G base station. In addition, the optimal value of gain loss increases to about 13 dB compared with the gain of the antenna fed with equal amplitude and in phase. So it is also necessary to take the system link budget of the broadcast channel into consideration. The proposed analysis method and design solution can provide reference for the research of the next generation mobile communication.
A compact coplanar waveguide fed multiband antenna is proposed and investigated. The proposed antenna consists of a rectangular radiating patch and dual meander strips with a defected ground plane. The size of the fabricated prototype is 28.3 × 24 × 1.59 mm3. The proposed antenna radiates at three different resonant modes, which cover 2.29-2.63 GHz, 3.26-3.96 GHz, and 4.97-6.10 GHz. The proposed antenna can be used for TD-LTE 2300/2500 (2.305-2.4 GHz), WLAN (2.4-2.4835 GHz and 5.15-5.875 GHz) and WiMAX (2.3-2.4 GHz and 3.3-3.7 GHz) applications. The proposed antenna exhibits an omnidirectional radiation pattern in the H-plane and a dipole-like radiation pattern in the E-plane. The measured peak gains are 2.64/4.48/6.08 dBi at the 2.4/3.5/5.5 GHz operating frequency bands, respectively.
This letter presents a high gain slot antenna for K-band non-contact measurement systems. The proposed antenna consists of a slot antenna on a grooved metal structure with a single frequency selective surface. In addition to a high-gain characteristic, a reduced size is strongly required for easy embedding. These features are the main objectives of this antenna design. To achieve these two objectives, an optimization procedure, based on a global algorithm, is used. Both simulation and optimization are carried out by means a full-wave electromagnetic simulation tool. Eventually, to validate the proposed design, a prototype of the antenna has been manufactured and tested. More than 15 dB of gain is measured over the operating frequency range, while optimal gain can reach 17 dB at frequency 25.5 GHz. These characteristics make this antenna very suitable for non-contact measurement i.e. radar systems.
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