Iet Microwaves Antennas & Propagation最新文献

A miniaturised integrated passive device (IPD) balun design with low insertion loss and balanced amplitude and phase is proposed for Wi-Fi/Bluetooth applications. In this design, a novel topology based on the modified T-type filter structure is introduced to offset the parasitic and coupling effects that cause poor balance in IPD design. The proposed balun design is fabricated on a GaAs substrate. The measured insertion loss is lower than 0.9 dB and the measured return loss is >16 dB in the frequency range of 2.2–2.9 GHz. The measured results of amplitude and phase show rather minor imbalances, which are lower than ±0.67 dB and ±1.8° respectively. The fabricated device size is 0.9 mm × 0.6 mm only.

In the design of antenna arrays which require fast and robust flat-top beam synthesis, computationally efficient methods are preferred. This feature is usually met by analytical techniques or simple optimisation procedures. On the other hand, in the flat-top beam synthesis, a common requirement is the ability to control beamwidth or sidelobe level. However, this can result in a high dynamic range ratio (DRR) of array's excitation coefficients. In this paper, a straightforward method for the design of symmetrical flat-top arrays with controllable sidelobe level or DRR is proposed. The method is based on quadratic and cubic transforms of Gaussian excitations. In addition, the method utilises zero coefficients whose positions are used to control the DRR, including the ability to achieve its minimum. Compared to other flat-top arrays with analytically shaped beams, the proposed arrays have lower DRRs for the same sidelobe level.

A 0.45-V low-power wideband image-rejection low-noise amplifier (LNA) using Taiwan Semiconductor Manufacturing Company (TSMC) 0.18-μm CMOS process has been proposed. The supply voltage, power consumption and chip area of the proposed LNA can be reduced using forward body biasing, folded cascode topology and a feedback capacitor. Moreover, a wideband gain-enhancement-and-image-rejection (WGEIR) circuit including a variable resonant LC tank and a common-gate amplifier has been developed. The inductance of the variable resonant LC tank can enlarge the gain of the proposed LNA. The capacitance of the variable resonant LC tank can achieve the image rejection. Using the WGEIR circuit, gain enhancement and wideband image rejection can be achieved simultaneously. The variable inductors and capacitors are developed for suppressing wideband image signals and good image rejection ratio (IRR). The combination of the variable inductors and capacitors can achieve eight image-reject frequencies under three control voltages. The proposed LNA shows the measured results including a 10-dB power gain, a 3-dB noise figure (NF) and a −11-dBm input third-order intercept point (IIP₃) at 2.4 GHz, respectively. The measured IRR ranges from 18 to 23 dBc around 3.6–4.5 GHz, which is 900-MHz image-reject bandwidth. The measured proposed LNA using the mentioned techniques consumes 0.8-mW power.

A 3D metal-only waveguide-based phoenix cell for reflectarray is presented. The proposed cell consists of two concentric square waveguides and a metallic block in the centre, which offers two operation modes. The first mode uses its cross section to tune reflection phase while the second mode varies the heights of two waveguides to manipulate reflection phase. The principle of the two different modes is analysed in detail. A metal-only reflectarray antenna at 20 GHz is designed based on the first mode of the phoenix cell. It is fabricated using selective laser melting 3D printing technology. A good agreement between simulations and measurements is achieved. The measured gain at 19.75 GHz is 30.25 dBi with an aperture efficiency of 51.17% respectively. Also, the measured 1-dB gain bandwidth is 15% (19–22 GHz). A dual band metal-only reflectarray operating at 20 and 25 GHz is designed based on the second mode of the phoenix cell. The two metal-only reflectarray antennas fully demonstrate the capabilities of the proposed 3D metal-only phoenix cell.

The inconsistent polarised directions and the radiation pattern transformation of the elements need to be considered in the analysis and simulation of large circularly polarised conformal arrays. Without relying on full-wave simulations of the full array, a polarisation phase compensation and a pattern transformation method are proposed to solve these problems. When the position and orientation of the conformal array elements are known, the polarisation phase compensation method can provide a solution to keep the initial phase direction of each circularly polarised antenna element consistent in the global coordinate system. Then, a pattern transformation method is proposed to obtain the radiation pattern of each antenna in the global coordinate system. In this method, the local antenna polarised radiation patterns with amplitude and phase information are expressed in the global coordinate system through the mutual conversion relationship between the local and global coordinate systems. These methods can provide a guidance for array design and performance simulation, especially theoretically applicable to the arbitrary conformal arrays.

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.