An ultra-wideband frequency selective surface (FSS) absorber with high angular stability and polarization independency applied in microwave band is proposed. The absorber is composed of three identical Teflon layers and dual FSS layers with distinct patterns. The miniaturized FSSs with unique patterns demonstrate advantages of facile manipulation of the impedance and multiple resonances in an ultrawide frequency range. The use of identical dielectric substrate greatly reduces the complexity in the absorber design, compared with the conventional way that requires variable dielectric constants for a multilayer structure. Experimental results reveal that more than 90% absorption rate in the frequency range of 2.79 – 20.62 GHz for normal incidence is achieved. The absorption rate can still retain more than 80% in the range of 4.41 – 20.93 GHz for both TE and TM polarizations with the incidence of 60° .

A distinctive frequency selective surface (FSS) to effectively enhance the electromagnetic shielding performance of high-speed electronic systems while preserving good mechanical ventilation is proposed in this article. The FSS consists of periodic segmented circular patterns in two-dimensional view and hollow vent holes in spatial, which exhibits a wide 2 GHz stopband at the interested frequency of 28 GHz. The new design also demonstrates stability to wave oblique incidence and polarization. The FSS shielding panel is prototyped and measured for validation. A satisfactory agreement between simulation and physical experiment is achieved.

Microwave devices based on high-power magnetrons are currently used widely and there is a strong demand for phase-controlled magnetrons. In this work, the performance of a 20-kW S-band continuous-wave magnetron with varied anode voltage ripple is studied. The anode voltage ripple is introduced to an equivalent model of the magnetron to evaluate the system's performance theoretically. The effects of the anode voltage ripple and the injection parameters on the magnetron's output are thus analyzed numerically. Furthermore, experiments are performed while the anode voltage ripple is varied from 4.2% to 0.6% using a shunt capacitance-adjustable ripple filter module. A nearly tripled locking bandwidth is observed under a constant injection ratio at 0.1 with decreasing ripple. The ripple-suppressed system pulls its sideband energy to the locking frequency and thus achieves a spectral intensity increment of 0.9 dB, phase noise reduction of 13 dB at an offset of 100 kHz, and phase jitter convergence from ±1.8° to ±x0.9°. The experimental features validate the results obtained from the theoretical analyses. The results of this investigation also provide guidance for future industrial applications of phase-locked magnetron arrays.

This letter presents a novel broadband single-lossy-single-lossless-layer frequency selective rasorber (FSR) with high passband selectivity, facilitated by an enhanced equivalent circuit model (ECM). Leveraging the ECM method for an FSR by substituting typical LC resonant circuits with mixed series-parallel LCL resonant circuits for both the lossy and lossless FSSs, significantly enhances the passband selectivity. The intentionally introduced inductance in the lossy FSS sharpens the passband roll-off, while in the lossless FSS creates an additional transmission zero, further improving selectivity. Simulations reveal a -3 dB passband of 10.04 GHz to 10.56 GHz, with a minimum insertion loss of 0.48 dB at 10.28 GHz. The proposed FSR achieves a 139.4% fractional bandwidth, spanning from 3.61 GHz to 20.22 GHz, and maintains stable performance for both TE and TM polarizations across a wide incidence up to 55°. The agreement between simulation and measurement confirms the practical application potential of the FSR design.

In this paper, a random forest regression (RFR) is proposed to reconstruct the statistical characteristics of electric fields in perforated enclosures. The power balance method and a diffusion equation–based model have been applied to the analysis of such problems; however, they are unable to account for the statistical nonisotropy problem. To solve it, RFR is used to predict the variances of six basic electric fields, the real and imaginary parts of the three rectangular electric field components, in perforated enclosures under external excitation. Using the predicted variances, the probability density function to represent each basic electric field can be generated as they are assumed to obey normal distribution with zero mean value. Then the statistical characteristics of other electric fields can be calculated by an analytical method and Monte Carlo method. Using the proposed method relies on RFR, the overall statistical characteristics of electric fields in perforated enclosures with the electric dimensions less than ten times the wavelength can be accurately reconstructed. Using the predicted statistics, the practical electromagnetic compatibility problem, such as global shielding effectiveness of a perforated enclosure, can be evaluated in seconds.