Iet Microwaves Antennas & Propagation最新文献

In this paper, we propose a Double Pulse-based Dual Coprime Frequency Diverse Array Multiple Input Multiple Output (DCFDA-MIMO) radar for enhanced target parameter estimation, including range, angle, and Doppler. The proposed model employs an unstructured approach for parameter estimation using the recently developed DCFDA-MIMO radar, which has garnered significant attention due to its superior target resolution compared to traditional Frequency Diverse Array MIMO (FDA-MIMO) radar. Because most conventional designs rely on a structured approach using a single pulse, conventional FDA-MIMO radar suffers from increased computational complexity due to multiple signal classification (MUSIC) and strong coupling between range and angle parameters. To address these challenges, we introduce an efficient, low-complexity method that effectively reduces range-angle coupling and improves target parameter estimation. Unlike existing techniques, the proposed approach uses the Double Pulse method, transmitting the first pulse without frequency increments to estimate the angle. In contrast, the second pulse incorporates suitable frequency increments to estimate range and Doppler separately by incorporating the estimated angle information. Monte Carlo simulations validate that the proposed DCFDA-MIMO-based Double Pulse method significantly improves target parameter estimation in terms of signal-to-noise ratio (SNR), signal-to-interference-and-noise ratio (SINR), and Cramér–Rao lower bound (CRLB) compared to existing array structures.

The presented paper addresses the divergence issue of Nicholson–Ross–Weir (NRW) algorithm encountered during the electrical characterisation of half-wavelength or thicker low-loss dielectric materials. To overcome this limitation, an S₂₁-parameter-based extraction method is proposed for determining the complex permittivity of low-loss dielectrics in rectangular waveguide and free-space measurement environments at GHz frequencies. The iterative Newton method, supported by an initial guess, is employed for permittivity extraction. Explicitly formulated equations suitable for broadband iterative computations are presented. Measurements on a variety of low-loss dielectric material specimens in both rectangular waveguide and free-space measurement environments in X-band are demonstrated to ascertain the accuracy and stability of extraction procedure. Root-Mean-Square-Error (RMSE) calculations across the frequency band, along with comparisons to other reported extraction techniques are presented to demonstrate accuracy improvements. Furthermore, the uncertainties associated with the extracted complex permittivity in different measurement environments are analysed and discussed.

A wideband high-efficiency compact all-metal folded transmitarray antenna (CAMFTA) with integrated planar feed is proposed in this paper. It consists of a transmission metasurface (TMS) with the function of reflecting y-polarised wave, as well as transmitting x-polarised wave and twisting its polarisation by 90°, a linear polarisation conversion reflection metasurface (RMS), and a planar slotted patch as the feed. All these components are made of metal, making the entire structure relatively cheap to manufacture and resistant to stringent environments. Particularly, in addition to the low-profile nature of the folded structure, the metal-only planar feed is co-designed and integrated with RMS, resulting in a further reduced profile and a compact configuration. In order to validate the superiority of the design, a CAMFTA is simulated, implemented and measured at X-band. The results of experiments demonstrate a high degree of correlation with simulations, with peak aperture efficiency of 29% and 3 dB gain bandwidth of 13%, respectively. To the best of the authors' knowledge, this is the first CAMFTA reported in the literature, and it offers a number of advantages, making it very suitable for high-gain applications where a compact, low-cost, low-profile configuration with steady performance is required.

Beampattern of a frequency diverse array (FDA) is a function of time, range and angle. The shape of this beampattern is dependent on the frequency offsets (FO) that are applied to each element. These FO are sampled from a window function whose parameters are optimised to yield minimum peak side lobe level (PSLL) and half-power beamwidth (HPBW). Time-variance is usually ignored because it can be removed by signal processing at the receiver. However, the travelling beam is still time-variant. This work shows that, in a time-variant beampattern, the optimum PSLL of these window functions degrade while HPBW is unaffected. A window function that is based on a sum of three Sinc functions (s-Sinc) is proposed for FO optimisation. The superiority of this window is established by comparing the optimum PSLL and HPBW in a time-invariant scenario. Later, time-variance is introduced, and s-Sinc function is used to minimise time-variant PSLL and HPBW. Results show that a beampattern with low time-variant PSLL and HPBW can be synthesised compared to their time-invariant counterparts.

A reflectionless filter is designed based on the dual-circuit theory. Two types of reflection-less filters are presented for this methodology. The proposed configuration consists of two dual branches. Two dual-bandpass filters are used in two branches of the structure, which are connected using Wilkinson-like power dividers. Out-of-phase reflected signals from each of the two branches are delivered to a resistor, resulting in a reflectionless port. A coupled line bandpass filter is fabricated and measured to verify the presented configuration and design equations. There is a good agreement between theory and measurement.

This paper proposes a method for estimating the excitation of array antennas by backward-transforming phaseless field data into the very near-field. The very near-fields are reconstructed at the antenna aperture using the Tikhonov source current reconstruction method (SRM). Two field amplitudes in different planes recover very near-field data from phaseless fields. The excitation estimation technique relies on the localised nature of very near-field currents around the antenna. Through spatial filtering of the reconstructed equivalent currents, the current distribution of each individual element is isolated. The excitation of each array element is then determined by analysing its current distribution over a separate surface mesh. Excitation estimations of two different array antennas with measurement and simulation results have been carried out to validate the proposed method. The relative amplitude errors of the excitation estimation with simulation data are 7.5% and 3.9% for using equivalent electric and magnetic current, respectively. In the measurement scenario, which includes the errors of manufacturing and testing, the maximum relative amplitude error is about 12% and the maximum phase recovery deviation is about ±9°.

A double-layer wideband circularly polarised (CP) metasurface (MTS) antenna is proposed. The MTS consists of a 4 × 4 L-shaped patch array. The modal behaviours of the proposed MTS are investigated using the characteristic mode theory. Two characteristic modes with orthogonal current distributions are selected as the operational modes. Furthermore, an aperture-coupled feeding structure is employed to excite the two orthogonal modes with a 90° phase difference, enabling CP radiation. It can also excite the MTS to generate multiple resonances and axial ratio (AR) minimum points, which collectively yield an acceptable bandwidth for both impedance and AR. Finally, an antenna prototype is designed to validate the simulated results. The measured results show that the MTS antenna offers a −10 dB impedance bandwidth (IBW) of 34.9% (4.25–6.05 GHz), a 3 dB AR bandwidth (ARBW) of 13.2% (5.3–6.05 GHz) and a maximum gain of 7.3 dBic.

This paper presents a new approach to designing transmission line (TL) and power divider/combiner (PDC) using an oversized air-filled substrate-integrated waveguide (OS-AFSIW). Our approach enhances the average power handling capability and reduces the loss. By strategically increasing the width of proposed TL, we achieve improved power handling capability. However, this approach can introduce higher-order modes, which can be detrimental. Therefore, this paper focus on designing a balanced delta port magic-T PDC configuration within the OS-AFSIW that exclusively supports the fundamental TE₁₀ mode and effectively suppresses the unwanted higher-order modes. This paper conducted a thorough analysis of the proposed PDC's average power handling capability, resulting in excellent agreement between fabricated and simulated results. The OS-AFSIW PDC was implemented on an FR4 and low-profile Rogers RO4003 laminate with a thickness of 32 mil, resulting in a compact design with a footprint of 144.63 × 58.4 mm². The fabricated PDC exhibits outstanding performance characterised by input and output return losses exceeding 10 dB, good isolation across the entire Ku-band (offering a fractional bandwidth of 28.57%), and significantly reduced loss compared to conventional air-filled structures. Notably, at 15 GHz, our design demonstrates impressive improvements of approximately 35% in the loss and 17% in the Average Power Handling Capability (APHC), which is a significant advantage for practical applications.

This paper addresses the problem of surface wave confinement and the suppression of undesired transverse electric (TE) mode propagation inside the grounded dielectric slab when excited by the transverse magnetic (TM) slot launcher. As a solution, we propose a surface waveguide (SWG) design based on self-complementary Bowtie metasurfaces. Leveraging the concepts of TE soft and TM hard bandwidth operations, the SWG effectively confines TM surface waves while suppressing unwanted TE modes. We present an analytical model capable of calculating the Bowtie metasurface's reflection coefficient for oblique-incidence excitation. Additionally, a simple yet efficient electromotive force (EMF) algorithm is introduced for analysing the reflection phase for oblique-incidence excitation across a range of wavenumbers and frequencies. We use the proposed EMF model to calculate the TE soft and TM hard bandwidth operations of the Bowtie metasurface. We present a uniplanar, compact and wideband slot launcher to excite directed and well-trapped TM mode inside the SWG. We fabricated a novel Rotman lens based on the Bowtie SWG and slot launcher to further support our methodology. The SWG lens exhibits a $��\pm �$ 56° scanning range, similar to that of its microstrip lens counterpart while offering the potential for reconfigurability and suitability in millimetre-wave applications.

At present, researchers often focus on various aspects such as the meteorological conditions along the long-wave propagation path and the conductive characteristics of the Earth's surface, and analyse the long-wave ground wave propagation delay one by one. If a unified analysis and modelling can be carried out for the long-wave propagation delay affected by multiple factors, it will significantly improve its prediction efficiency and engineering implementation efficiency. Firstly, this paper conducts analysis from the time domain and the frequency domain, and discovers its obvious periodic time-varying characteristics. Based on this, a quadratic polynomial model with periodic terms is constructed and used as the first prediction model. Next, in order to improve the accuracy and make full use of historical data, the new predicted values are inserted into the sequence of measured values to construct a quadratic polynomial long-wave prediction model based on the sliding window and with periodic terms (Model 2). Finally, these two models are used to make predictions for different durations on the 7-day delay data. The actual measurements show that in the short term, the accuracies of the two models are equivalent, and when the prediction duration increases, the advantages of Model Two become more apparent.