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

Microwave ablation (MWA) is based on the energy absorbed by biological tissue through microwave emission, which raises the temperature of the tumor to perform the treatment. MWA has the advantage of causing minimal bleeding and treating deep tumors. In this study, MWA for various slot design situations in a microwave coaxial antenna (MCA) was simulated through numerical analysis. For the slot design, the number of slots and the distance between slots were determined by the analysis parameters. A tumor developed inside the liver tissue was implemented, and the temperature distribution of the tumor and surrounding liver tissue was calculated for all cases selected for numerical analysis. The Helmholtz electromagnetic equation was used to calculate the electromagnetic field inside the tissue, and the modified Pennes bioheat equation was used to calculate the temperature change in the tissue due to the emitted microwave. Treatment effects were quantitatively analyzed for each slot design condition through an apoptotic variable based on the calculated temperature distribution. Lastly, conditions that produce optimal treatment effects were derived depending on the number of slots. The analysis showed that as the distance between the slots increased from 0.5 to 3.5 mm, the optimal treatment effect was obtained when the number of slots was 4, 3, 3, and 2, respectively, and the microwave input power at that time was 3.0, 2.8, 2.6, and 3.0 W, respectively. This is expected to allow for more rigorous and more therapeutically effective MWA.

In China, high-speed trains have become a major means of transportation for the masses. When the passengers wearing pacemakers travel on high-speed trains, electromagnetic environment in the carriage where the GSM-R voice and data antennae are located should be concerned. In this work, a real-size carriage monopole antennae simulating voice and data antennae as high-frequency radiation sources and wearing pacemaker passenger’ models were established to study the electromagnetic exposure of the passenger at different conditions. The results showed that when the passenger faced the voice antenna, he suffered much greater electromagnetic radiation than when his back in turned from it. The electric field strength, average SAR, and temperature rise of the heart when facing the antenna were 27.3 V/m, 0.0102 W/kg, and 0.0016°C, respectively. Meanwhile, the temperature rise of the pacemaker was 0.001°C. We also obtained the values of electromagnetic dose for the whole body. All data were below the limits of the ICNIRP guidelines. These results indicate that the electromagnetic fields generated by the GSM-R voice and data antennae do not harm the health of passengers wearing pacemaker.

This paper proposes and analyzes a 2 × 2 multi-input multioutput antenna based on an open-loop resonator structure and an inverted L structure. The top layer of the antenna uses symmetric inverted hook-shaped and inverted L branches and is connected to the bottom layer of the dual-feed port and the ground plane using the VIAs, respectively. The open-loop resonator structure at the bottom of the antenna and the top layer of the branched circuit are resonated to provide wide-bandwidth and dual-frequency characteristics. The substrate uses FR4 with an area of 40 × 30 × 0.8 mm³. Although the two antenna feed ports are very close to each other, using via to connect the defective bottom ground structure and the top inverted L-shaped branch, the isolation still achieves an excellent performance of 15 dB. The antenna has multiband application characteristics, and the bands include 2.29–5.51, 6.14–10.26, 2.29–5.33, 5.19–6.64, and 6.78–10.16 GHz. In pattern and MIMO transmission efficiency measurement, the peak radiation efficiency is 89%, the peak gain is 8.5 dBi, and the ECC is less than 0.034. In the transmission efficiency measurement mode using 64-QAM, watching the error vector magnitude at 2.56 and 5.11 GHz, the demodulation effect is very good, and the respective throughput results are 100% and 79.2%. The broadband characteristics of the antenna have a variety of applications, and it is simulated at the specific absorption rate, which meets the standards set by the Federal Communications Commission and is very suitable for use in wearable devices. The antenna can be applied to the X-band, n77, n79, Sub-6 GHz, WiMax, DSRC, WiFi 6, WiFi 6E, WiFi 7, C-V2X, and C-band.

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.