International Journal of RF and Microwave Computer-Aided Engineering最新文献

A multifunctional frequency-selective rasorber (MFSR) with passband stealth performance by using PIN diodes is investigated, which is made up of two reconfigurable components (a lossy layer and transmissive polarization converter surface (lossless layer)). The proposed MFSR shows transmission in-band and absorption out-band at working state, but the transparent window is closed to achieve full-band stealth at nonworking state. Besides, the equivalent circuit model (ECM) is constructed to annotate the operating principle of the designed MFSR. The MFSR indicates a wide cross-polarized transmission window from 3.71 to 4.38 GHz between two absorption bands at working, meanwhile a broadband copolarized reflection band (S₁₁ < −10 dB) is accomplished in 1.78–5.50 GHz. At nonworking, an ultra-wideband stealth band is realized in 1.81–7.0 GHz when the absorptivity is over 80%, which has a 117.8% fractional bandwidth (FBW). In addition, the MFSR has a stable oblique incident characteristic (up to 25°). Finally, the sample of the MFSR is manufactured and experimented to demonstrate the availability of this design.

In this article, distance and frequency-dependent indoor wireless channel characterization and modeling are presented in C, X, and Ku bands at the line of sight (LOS) and nonline of sight (nLOS) scenarios. Complex frequency responses of the indoor radio channel are measured using the frequency-domain approach. The terminal and measurement setup dependencies of the propagation channel are deconvoluted using closed-form expressions devised from a two-port network model approach of the antenna transreceiver system. Subsequently, terminal independent frequency-domain channel transfer functions (CTFs) and time-domain channel impulse responses (CIRs) are derived for accurate statistical analysis of large- and small-scale fading parameters of the propagation channel. A distance-dependent statistical pathloss model is proposed. Successively, a frequency domain channel model using the fifth-order autoregressive process is proposed. Subsequently, the existence of the multiple clusters in the environment is analyzed by the poles of the transfer functions of the model. Models are validated in both time and frequency domains by comparing the computer-simulated synthetic model data with the empirical channel responses. The measurement data and the model data are seen to be in good agreement.

This paper proposes a 10 × 10 MIMO multiband broadband planar antenna for tablets or laptops. The designed antennas cover a large number of the popular sub-6-GHz application bands, such as 0.617–0.96, 2.1–2.7, 3.5–4.5, and 6.1–7.2 GHz for public safety communications, radio systems, Bluetooth, Wi-Fi, and satellite communications. The proposed antenna is designed with grounded branches, which can generate a wide bandwidth and cover most of the sub-6-GHz application band by coupling between branches of different lengths and antennas. MIMO antennas have been measured to have an envelope correlation coefficient of less than 0.7 and have met the standards set by international organizations for human radiation absorption simulations. The proposed antenna validates the unique 10 × 10 MIMO antenna structure and feasibility. Multiple operable frequency bands are realized, and the radiation effect of the antenna on the human body is analyzed if it complies with international market standards. The proposed antenna design is well suited for multiband and broadband requirements.

A novel low-loss tunable filter using its own coupled lines is proposed in the paper. The filter is based on a substrate-integrated suspended line (SISL) structure with two inner layers, fabricated on a low-cost FR4 substrate. The suspension line and the cavity are completely covered by copper. In the novel structure, the coupled line can be tuned and has a variable coupling coefficient. The performance of the dual-band filter can be flexibly tuned by using the coupled lines. The passband widths can be tuned independently with the range from 0.31 to 0.92 GHz. The center frequencies of the passbands can also be tuned independently, with the tuning range of 1.1 GHz. A low insertion loss of less than 0.54 dB is shown in the proposed filter. The proposed filter shows potential application in future tunable microwave circuit.

This article presents an ultrathin chiral metasurface which can exhibit multiband asymmetric absorption as well as symmetric transmission in a specific frequency band outside the absorption regions. Unlike most electromagnetic metasurface absorbers, the proposed structure does not have a continuous conducting sheet at the bottom which also allows it to act as a bandpass spatial filter. The metasurface has a substrate thickness of only λ_high/62.5 and λ_low/34 at the highest and lowest operational free-space wavelengths, respectively. The transmission band is centered at 5.5 GHz, and the asymmetric absorption bands are centered at 3, 3.33, and 4.5 GHz, respectively. The operational bands can be tuned as per user requirements. The metasurface has an angular stability of 45° for both TE and TM incidence. It can be used for radar cross-section (RCS) reduction, electromagnetic shielding, and as a spatial bandpass filter.

This article presents a resistor-loaded wideband absorber using a tightly coupled dipole structure. The conversional inherit wide bandwidth tightly coupled dipole which was used as an antenna is adopted as a unit cell. The port of the dipole is loaded with resistors to dissipate the microwave energy. The design principles of the absorber are given. An equivalent circuit model composed of an RLC resonant circuit is proposed to analyze the performance of the absorber. To demonstrate, a 288 mm × 288 mm absorber ranging from 1.96 to 8.08 GHz is fabricated and measured. The measured results agree well with the simulated ones which show that the absorber can work from 2 to 8.18 GHz with an absorption rate of more than 90%. Moreover, the proposed absorber is also insensitive to the polarization angle of the incident wave. When the incident angle changes from 0° to 45°, the absorption rate is nearly unchanged over the operating band.

With the increasing use of millimeter-wave radar in automobiles, mutual interference between vehicle-mounted millimeter-wave radar systems is becoming increasingly serious. Mutual interference between vehicle-mounted millimeter-wave radars significantly reduces the accuracy of target parameter estimation and the reliability of target detection. In view of this, this study proposes an interference suppression method that combines the Variational Mode Decomposition (VMD) algorithm and Variation Index Constant False Alarm Rate (VI-CFAR). First, the method performs adaptive decomposition of the intermediate frequency (IF) signals of an interfered vehicle-mounted millimeter-wave radar by VMD in order to obtain several different intrinsic modal functions (IMFs). Then, the relevant IMFs containing target information are identified based on the spectrograms of each IMF, followed by signal reconstruction of the relevant IMFs using VI-CFAR. Finally, the relevant IMFs are superimposed to complete the signal reconstruction. In the case of simultaneous interference by several different interference radars, the results of simulation experiments show that the method can improve the Signal-to-Interference Ratio (SIR) of the target and increase the detection of the interfered target to a greater extent than the Adaptive Noise Cancellation (ANC), Empirical Modal Decomposition (EMD), and Iterative Zeroing methods. According to the SIR results of the simulation experiments, it can be seen that under the static interference of several slightly weak interference sources, the SIR of each target is improved by 8.1, 8.1, 5.8, and 7.9 dB, respectively, after suppressing the interference by the method, whereas in the dynamic cases of simultaneous interference of several strong interference sources and detection of several weak targets, the SIR of each target is improved by 4.6, 2.2, 7.9, and 6.8 dB, respectively. Therefore, the method has some performance advantages.

Antenna systems with more complicated geometries have been created as a result of evolving technology and rising performance standards in the industry. The geometric complexity of modern antennas makes it difficult for circuit theory tools or parametric studies to produce adequate findings, making it difficult for designers to create the designs they want. Even though full-wave electromagnetic (EM) modeling tools are widely utilized today, they are computationally expensive for local optimization alone. In order to speed up the stages of the simulation-based design of high-performance systems, many strategies have been devised to solve and/or minimize this challenge. Thanks to their adaptability, affordable computing costs, and widespread usage, surrogate-based models have grown to be a well-known branch. Herein, an innovative knowledge-based methodology for building a coplanar waveguide (CPW)-fed antenna using surrogate models is presented. In this work, a knowledge-based methodology using surrogate modeling is applied as an advanced approach that combines domain-specific knowledge with surrogate models to optimize the performance of a microwave antenna in a computationally efficient manner. For this aim, firstly, a 3D-EM simulator is deployed to generate a dataset for a deep learning-based surrogate model. When compared to the conventional optimization approach using direct deployment of EM simulators which is around 47.2 h, the proposed surrogate model approach has an average cost reduction of over 50% which corresponds to a total computational time of 24.3 h. The collected results are compared to performance metrics for prototype antenna designs as well as simulated outcomes from EM simulators and counterpart works from the literature.

A sixteen-port circularly polarized (CP) ultrawideband (UWB) multiple-input−multiple-output (MIMO) belt antenna is designed and developed for wireless body area network (WBAN) applications. The proposed antenna comprises sixteen modified octagon-like ring antenna elements with a common ground. These antenna elements are designed on leather material and can be worn as a belt. Each antenna element contains a microstrip line feed and a modified octagon-like open-ended ring radiator to generate circular polarization. The belt antenna provides an impedance bandwidth (S₁₁ ≤ −10 dB) of 3.08–11 GHz (112.5%) and a 3 dB axial ratio bandwidth (ARBW) of 4.7–7.07 GHz (40.27%). The envelope correlation coefficient (ECC) amongst the resonating elements is <0.003. Additionally, the bending analysis and specific absorption rate (SAR) of the presented antenna are examined. The overall size of the belt antenna is 30 mm × 574 mm × 1 mm. The designed belt antenna is suitable for WBAN applications due to its leather material, good on-body performance, and nearly identical simulated and experimental results.

In this article, an improved nonlinear model for gallium nitride high-electron-mobility transistors (GaN HEMTs) is proposed. Aiming at the problem of insufficient accuracy of the nonlinear DC model caused by the self-heating effect and trap effect in the traditional model, this thesis uses the Softplus function to improve the traditional nonlinear DC model and establishes a nonlinear DC model including the self-heating effect, which is verified by the three GaN HEMT devices of different sizes. The MSE of I_ds is less than 2.44 × 10⁻⁶. The traditional empirical basis model needs to calculate the partial derivative of the current expression with respect to V_ds, which is tedious and complicated. The proposed model can be directly used to fit the G_m. The verification results show that the MSE of the G_m is less than 1.07 × 10⁻⁴, which proves the effectiveness of the equation.