Iet Microwaves Antennas & Propagation最新文献

The authors investigate electromagnetic scattering by a circular strip with impedance boundary conditions in detail. The excitation is obtained by the H-polarised line source and the impedance boundary condition with different impedance values on each surface of the circular strip is imposed. Electromagnetic scattering from circular strips is formulated employing an integral equation approach including the orthogonal polynomials while expressing the current densities on inner and outer surfaces. To consider the edge condition, the current density on the scatterer is expressed in terms of Gegenbauer polynomials with the weighting function. Unlike the previous studies, the authors investigate the behaviour of the EM field regarding the location of the cylinder source, the size of the aperture and the different impedance values. The convergence of the proposed approach, which is one of the analytical–numerical methods, is investigated for different impedance values; considering the results, resonators with impedance surfaces of certain complex values and certain locations of the cylinder source perform better than the known PEC and PMC resonators for some specific resonance cases. An effective analytical–numerical approach is proposed for such geometry with the impedance boundary condition. An extensive analysis and comparison with other methods are provided. The limit cases of the impedance boundary condition (Dirichlet and Neumann boundary conditions) are validated.

In this study, a compact wideband circularly polarised Multiple Input Multiple Output (MIMO) antenna with the two parasitic elements is proposed. The printed monopole antenna for wideband circular polarisation proposed in authors' previous study is used as an antenna element. One-sided substrate reflector is installed at the back side of the antenna, positioned 0.2λ₀ away, to improve the gain. The circularly polarised radiation, deteriorated by the influence of mutual coupling of two antenna elements and reflector, is improved by deploying two parasitic elements on the bottom layer of the antenna's substrate. The antenna's size is 0.99λ₀ × 0.32λ₀ and the reflector's size is 1.41λ₀ × 0.82λ₀ (λ₀ is the free-space wavelength at lowest operating frequency). The measured bandwidth of 10 dB impedance with a 3 dB axial ratio is 33.49% from 3.53 to 4.95 GHz, which can be utilised for sub-6 GHz 5G applications. The simulated and experimental results are compared to validate the antenna characteristics.

A novel Frequency and Polarisation Selective Surface (FPSS) is proposed, which separates two adjacent bands with a narrow transition zone by the staggered separation scheme and is suitable for atmospheric remote sensing. The traditional FSS is transparent in a particular frequency band for both the TE and TM polarisations, while it is opaque in another band for both orthogonal polarisations. The FPSS is introduced in a new splitting scheme that operates above 300 GHz. The channel 420–430 GHz of the TE polarisation and the channel 360–400 GHz of the TM polarisation transmit in the FPSS. In contrast, the band 360–400 GHz of the TE polarisation and the channel 420–430 GHz of the TM polarisation are reflected. The water vapour and the oxygen profiles are detected by the 380 GHz band and the 425 GHz band, respectively. The insertion loss is lower than 1 dB, and the reflection band rejection is superior to 10 dB in the experiment, which determine the sensitivities of the bright temperature by 1.5 (RMS K). The scattered wave of the FPSS is calculated through the far field pattern, the maximum of which is about 5%. The side effect of the scattered wave is able to be ignored in the optical path.

Propagation models are essential for the prediction of received signal strength and the planning of wireless systems in a given environment. The vector parabolic equation (VPE) method has been widely applied to the modelling of radio wave propagation in tunnels. However, carrying out simulations for large-scale environments is still computationally expensive. A convolutional neural network (CNN)-based propagation model, which can provide high-fidelity received signal strength prediction based on results from low-cost VPE simulations, is proposed. A thorough study of the generalisability, including both interpolation and extrapolation capabilities, of the proposed CNN model is conducted. It is found that the proposed model can achieve significant computational savings while maintaining acceptable accuracy, and its performance is validated in both simulations and actual tunnel cases.

This paper presents a differential complementary metal oxide semiconductor inductor-capacitor voltage controlled oscillator (LC-VCO). The VCO is adopted from the gate-to-source capacitor feedback Colpitts VCO which has the advantage of large value of negative conductance. Due to the large negative conductance, the VCO has a more reliable startup oscillation at the lower currents. The main characteristics of the VCO such as negative conductance, oscillation frequency and phase noise are discussed and analysed. The value of parameters in this circuit have been determined using Non-dominated Sorting Genetic Algorithm (NSGA-II) to have the optimum performance. The designed VCO oscillates at 2.76 GHz under a supply voltage of 1.4 V. Power dissipation of the proposed VCO is 873 μW which is significantly lower than that of some other VCOs. The post-layout simulation results of the proposed VCO are presented and compared with the performance of some other VCOs.

This article presents a wideband circularly polarised (CP) antenna array using a miniaturised double box branch-line coupler. This was achieved by creating a slow wave structure by introducing open-circuit stubs on the inside arms of the branch-line coupler. The 2 × 2 antenna array is made of four CP slot radiating elements excited through 1 × 4 feeding network. Moreover, sequentially rotation method is used to increase the axial-ratio (AR) bandwidth of the array. The CP slot radiating element is fed by coplanar waveguide. The feedline of the horn-shaped radiator includes a circular matching stub. Ground connected asymmetric T-shaped stub, a pair of grounded L-shaped square strips, and single strip line are shown to induce CP and enhance the antenna's 3 dB impedance bandwidth and AR performance. The antenna constituting the array has impedance bandwidth of 2.45 GHz from 4.8 to 7.25 GHz that corresponds to a fractional bandwidth of 40%, and its 3 dB AR extends between 4.8 and 6.25 GHz. Compared to a conventional double-box branch-line coupler the size of the proposed coupler is reduced by 35% by increasing the capacitance of the coupler's arms. This also is shown to increase the impedance bandwidth of the coupler. A 2 × 2 array was fabricated, and its performance verified. Measured results confirm the proposed antenna array exhibits CP covering the bands of WiMAX IEEE 802.16, C-band and ITU-R F386.9. The measured 3 dB AR bandwidth of the antenna array extend from 3 to 7.3 GHz and its impedance bandwidth extends from 3.2 to 9.0 GHz. The antenna array radiates with a peak gain of 11.5 dBic.

The authors proposed an ultrawideband (UWB) dual-polarised tightly coupled dipole array (TCDA). A split X-shaped resistive frequency selective surface (FSS) is utilised, which can get more admirable impedance matching. The proposed antenna can achieve active voltage standing wave ratio (VSWR) below 2.9 when scanning up to ±75° and ±60° in the E and H planes from 2 to 18 GHz, respectively. Furthermore, two rectangular patches served as directors are designed, which can provide stronger forward radiation to reduce the loss of resistive FSS for radiation efficiency. As a result, the average radiation efficiency is above 84% and the lowest radiation efficiency is 70%. Moreover, the overall antenna profile is 15 mm (0.1λ at the largest working wavelength). To validate the design method, a 16 × 16 array prototype is fabricated and measured. Good agreement is achieved between the simulations and measurements.

Millimetre-wave (mmWave) frequencies play a vital role in fifth-generation (5G) wireless systems and beyond due to the vast available bandwidth of several GHz. This paper presents channel characteristics and their channel models for mmWave based on extensive channel measurements at 26 and 38 GHz conducted in 5G scenarios, such as the rooftop, the high-speed railway, and the Industrial Internet of Things scenarios. The channel sounder receiver (Rx) uses an omnidirectional or phased array antenna to meet the requirements of channel measurement, such as recording absolute delay and obtaining 3-dimensional angular information. We use the classical close-in model and floating-intercept model to model path loss. Meanwhile, channel statistics in the delay domain are derived from the measured power delay profiles. Note that the different scenarios are measured with the same channel sounder, making the measurement results of different scenarios comparable. It is shown that the shadow fading parameter σ is 0.7 dB as fewer large scatterers exist in the rooftop scenario. Moreover, due to the significant dependence of delay spread on the geometric relationship between the transmitter (Tx), Rx, and surrounding environment, the statistical data in the delay domain varies significantly in different scenarios. The channel characteristics and models will guide future air-interface, beamforming, and transceiver designs for 5G and beyond.

Antennas using the active frequency selective surface (AFSS) can achieve fast beam-scanning ability at a low cost. In this study, a switched beam antenna with a high gain and 360° coverage in the horizontal plane is proposed. Twelve columns of AFSS form a cylindrical cavity and are transmissive or reflective to the incident electromagnetic waves under the control of PIN diodes. Benefiting from a coaxial continuous transverse stub array placed at the cavity centre and using 4 units to generate a high gain omnidirectional radiation, the proposed antenna can realise a highly directive switched beam. An antenna prototype is designed, fabricated and measured. Results show that it achieves a |S₁₁| < −10 dB bandwidth of 12.9% and is able to sweep its beam around the azimuth plane with a high gain up to 13.6 dBi at 5.8 GHz working frequency.

In this article, the authors propose a super wide band CPW-fed fractal monopole antenna suitable for phased array antennas with a shaped beam radiation pattern, operating in the frequency ranges below and above 1 GHz at the same time. The antenna has an octagonal radiator with fractals of the same shape added to its edges and sides. Also, the symmetrical elliptical ground planes have reduced the antenna size and, consequently, the mutual coupling in the antenna array. Despite the super-wide frequency range, the antenna's radiation pattern is relatively steady in the E-plane, and the negligible ripple on the radiation pattern makes it suitable for shaped beam radiation patterns in phased array design. The single-element antenna with an overall size of 0.24λ × 0.38λ at 500 MHz is printed on an FR-4 substrate. The outcomes of the simulation and measurement are well agreed in the frequency band of [500 MHz to 5.5 GHz] with an impedance bandwidth (|S11|< −10dB) of 166.67% and VSWR< 2. Also, the fidelity factor of the antenna is studied to investigate the SWB performance.