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In this article, a novel design of compact frequency-selective rasorber exhibiting absorption–transmission–absorption characteristics and having high passband selectivity has been proposed. A square-loop resonator with mounted lossy elements serves as the elemental broadband absorber from 4 to 12 GHz. The transmission frequency at 8.4 GHz is realized by printing a Minkowski fractal-shaped resonator with a high-Q factor on the resistive layer, which provides a transmission pole at the frequency corresponding to the passband of a double-cross-slot-shaped bandpass layer. The functioning of the proposed frequency-selective rasorbers (FSR) is explained by a corresponding equivalent circuit model. The proposed FSR exhibits higher selectivity at the passband, thus making it a suitable candidate for shielding the narrowband radiating system. Measurements performed on the fabricated prototype of a 17 × 17 unit cell array provides experimental validation. Further, a low radar cross-section antenna is realized by integrating a patch antenna with the proposed FSR, which achieves an average out-of-band monostatic radar cross-section (RCS) reduction of 11.92 and 5.04 dB in the lower (4–7.5 GHz) and upper (9.2–10.8 GHz) absorption bands, respectively, while maintaining the other antenna parameters. Furthermore, the bistatic total RCS reduction of 77% and 60% are achieved in the lower and upper frequency bands, respectively. [ABSTRACT FROM AUTHOR]

The received signal of the electronic equipment often depends on its surrounding multidimensional dynamic electromagnetic environment (MDEE) featured with large airspace, high field strength and wide frequency band. This brings great challenges to predict the electromagnetic compatibility (EMC) of the electronic equipment dynamically. As an extension to the conventional equivalent construction (EC) process for the static single-source electromagnetic environment, based on the response of an antenna port, a novel EC method for the dynamical multi-source heterogeneous electromagnetic environment is proposed in this article. By applying this EC method to a radar system under a practical dynamic working scene, an innovative electromagnetic sensitivity threshold test method is carried out in the laboratory. The experimental results show that the theoretically predicted value is in good agreement with the measurement, where the error is less than 1dB. With the methods proposed in this article, the dynamic analysis and prediction of EMC in MDEE can be carried out with the consideration of the characteristics of the electronic equipment, so that the electromagnetic environment adaptability of the electronic equipment can be readily improved. [ABSTRACT FROM AUTHOR]

Phase switched screen (PSS) has been proposed for more than two decades for its applications on radar cloaking. However, the PSSs in most publications need a thickness of one-quarter wavelength to realize perfect cloaking at the operating frequency of the incident radar-detecting wave, which seems too thick for engineering. In this article, a new design of the dual-band artificial magnetic conductor (AMC) is proposed in which the electromagnetic band gaps are shifted among two bands by adjusting the biasing current on the four p-i-n diodes. By controlling the states of the diodes between on and off, the in-phase reflection frequency of the AMC can switch from 2.5 to 5.3 GHz. Based on the AMC structure above, a potential dual-band PSS is realized through different switching schemes and, therefore, achieves good stealth effects during the two bands above. [ABSTRACT FROM AUTHOR]

Potential radar absorbing material (RAM) for suppressing electromagnetic (EM) wave over a range of oblique angles of incidence are needed in many applications. In this article, an attempt is being made to build cost-effective and efficient RAM using the EM characterization of microwave heat-treated (MHT) electronic waste followed by an EM mixing model-assisted analytical approach. The robust and facile top-down fabrication technique is employed for the development of heterogeneous composites, which are further subjected to microwave heat treatment at distinct power wattages. The magneto-dielectric spectrographic analysis of samples is carried out in the range of 8.2 to 12.4 GHz. The Debye parameters are optimized and succeeded to obey EM property of the synthesized samples. Jaya's algorithm is adopted for the optimal design of single and dual-layer RAMs at normal and oblique angle incidence based on the constitutive EM parameters under certain restrictive conditions. The embraced MHT method prompts an improvement in microstructure coherency that further increases absorption bandwidth (BW). As a result, a 2.1 mm thick single layer RAM achieves a minimum reflection coefficient (RC) of −17.1 dB at 10.3 GHz with a 100% BW below −10 dB threshold. The groundbreaking findings are obtained by performing a three-fold study of dual-layer RAMs, culminating a minimum RC of −47.8 dB at 11.8 GHz with a layer thickness of 1.8 mm. This article shows that the microwave heat-treated composites have enormous potential in the development of lightweight and broadband RAMs for stealth applications. [ABSTRACT FROM AUTHOR]

Future naval radio frequency emitters, particularly radars, will produce shipboard operational electromagnetic environments greater than what are produced today. Presently, hazards of electromagnetic radiation to ordnance and electromagnetic susceptibility certification test methods cannot meet the higher power level requirements and primarily employ deterministic test methods. The purpose of this study is to introduce and experimentally validate an electromagnetic probability-of-effect assessment tool which statistically assesses the magnitude of a system/subsystem's hardness or safety margin to upset/failure under any level of threat. The generalized extreme value and generalized log-logistic distributions are leveraged for enclosure maximum field and device threshold distributions, respectively, and the hardness margin, from structural reliability analysis, is applied for probability-of-effect prediction. [ABSTRACT FROM AUTHOR]

This paper provides qualitative and quantitative values for the received interference power at the antenna ports of automotive radars as well as the probability of their occurrence for actual and future, not yet measurable traffic scenarios on main roads. The influence of the environment, the road traffic behavior, and the radar penetration rate for a defined antenna configuration can be observed. The basis for the analyses are ray-tracing based simulations in order to achieve adequate predictions for the received power levels due to multipaths. The results show that for a radar penetration rate of 100%, the difference between the strongest overall incoherent received interference power level and the level that is received in 90% of the time is up to 7 dB, dependent on the antenna placement and the environment. [ABSTRACT FROM PUBLISHER]

A frequency-modulated continuous wave (FMCW) radar is used to sounding wireless channel. An intermediate frequency signal of the FMCW radar can be treated simultaneously as a frequency-domain signal as well as a time-domain signal when the modulation time is sufficiently long. This distinctive compatibility enables the FMCW radar system to measure the normalized impulse response for the power delay profile and Rician K-factor by using an oscilloscope. This theory is fully demonstrated and experiments are performed in the reverberation chamber for the small-scale fading environments of Rayleigh and Rician conditions, and all measurements are verified by using the oscilloscope. [ABSTRACT FROM AUTHOR]

The measurement of a radar chirp waveform is critical to assessing its spectral compliance. The Fourier transform for a linear frequency-modulated chirp is a sequence of frequency-domain impulse functions. Because a spectrum analyzer measures the waveform with a finite-bandwidth intermediate-frequency (IF) filter, the bandwidth of this filter is critical to the power level and shape of the reported spectrum. Measurement results are presented that show the effects of resolution bandwidth and frequency sampling interval on the measured spectrum and its reported shape. The objective of the measurement is to align the shape of the measured spectrum with the true shape of the signal spectrum. This paper demonstrates an approach for choosing resolution bandwidth and frequency sampling interval settings using the example of a linear frequency-modulation (FM) chirp waveform. [ABSTRACT FROM AUTHOR]

Accurate measurements of fast flowing outlet glaciers in Greenland and Antarctica are of vital importance to improve ice-sheet models that predict the ice-sheets’ contribution to sea-level rise over the next century. Radars with high sensitivity and advanced processing capabilities are required to sound ice in fast-flowing glaciers. We developed the multichannel coherent radar depth sounder/imager (MCoRDS/I) for ice thickness measurements and 3-D imaging of bedrock over important areas of Greenland and Antarctica. Radio frequency interference (RFI) degrades the sensitivity of the MCoRDS/I system, thus affecting the quality of the data collected. Data from the 2010 Greenland field season exhibited a degraded signal-to-noise ratio (SNR), requiring extensive RFI analysis, investigation, and mitigation for the MCoRDS/I system. Measurements were taken in an electromagnetic interference (EMI) chamber on individual sections of the MCoRDS/I system to isolate the sources of RFI. Then, RFI mitigation techniques were implemented for the offending sections and EMI chamber measurements verified the integrity of the solution prior to the 2011 Greenland deployment. Recorded data from the 2011 Greenland field season also verified that the RFI mitigation resulted in more than 20 dB improvement in the SNR compared to the 2010 Greenland data. The reduction of EMI emissions has also been beneficial to data collection in subsequent deployments. [ABSTRACT FROM PUBLISHER]

Conventional field strength sensors use different detection methods, each having advantages and disadvantages. Modern signals in, for instance, wireless communication systems and radars use very complex modulation. Other signals, such as the ones often measured in reverberation chambers with mode stirring, are fast-varying with high dynamic range. Conventional probes struggle to give reliable measurement data in these situations, while the more expensive solutions based on optical-electric conversion and heterodyne receiver, are so costly that often only one component of the field is measured. The impact of conventional field strength probes when measuring (complex) modulated signals is discussed. Furthermore, this paper describes the design, fabrication, and characterization of fast, broadband, three-axis, and high-dynamic range probes. They have been designed for mapping the fast-changing electric field strength in complex electromagnetic environments such as reverberation chambers under mode-stirring operation. [ABSTRACT FROM PUBLISHER]

In this paper, we derive a double inequality that permits one to obtain a lower and an upper limit for the value of the impulse bandwidth of a measuring receiver. The limits are the reciprocal of the integral of the relative envelope of the impulse response (lower limit) and the integral of the relative frequency response (upper limit) of the intermediate frequency (IF) filter. Since the limits are relative quantities, their evaluation does not require the use of a calibrated generator, the only significant sources of error being receiver's vertical scale nonlinearity and noise proximity. Here, the deviation between the impulse bandwidth and its limits is quantified for practical IF filter configurations. The dominant contributions to measurement uncertainty are identified and suggestions for reducing their magnitude are also offered. [ABSTRACT FROM PUBLISHER]

In all applications of the gigahertz transverse electro- magnetic (GTEM) cell, there is an interplay between the equipment under test (EUT) and the cell reflecting metal walls, as represented by images of the EUT. Moreover, owing to the multiple reflections within the cell and to its tapering structure, the phenomenon of illumination and reillumination of the EUT can hardly be avoided. These problems, known as reactive effects of the cell, are investigated in this paper. A simple new approach for an efficient investigation of the interactions between the EUT and the cell is provided. Closed-form expressions for the reflection coefficient, the relative deviation in field, and the relative error in the induced current caused by the reactive effect of the cell are derived. Each of these expressions encompasses both the mutual influence of the EUT's radar cross section (RCS) and the reactive effects of the cell. It is shown that depending on the frequency-dependent phase factor e!, strong and weak test conditions may occur since the overall incident field will exhibit maxima and minima. Hence, evidence showing that the total incident field impinging on the EUT generally deviates from the primary excited TEM field is provided. Moreover, the relative deviation in the field and the relative error in the induced current are quantified. Finally, the frequency dependence of the well-known one-third-rule of thumb is demonstrated. [ABSTRACT FROM AUTHOR]

This paper examines the probability that any millimeter-wave radar systems will interfere mutually by considering spatial, temporal, and operational frequency-related overlaps. It examines the nature and magnitude of the interference under different conditions and for different sensor types before concluding that in an overlapping frequency band, the probability that interference will occur is high. It goes on to demonstrate that, though there are some forms of interference that can be identified and controlled, there are others which are impossible to isolate, resulting in degraded target detection performance and tracking. [ABSTRACT FROM AUTHOR]

Wideband and ultrawideband (UWB) technologies have achieved: notable progress in recent years, aided immeasurably by improvements in solid-state manufacturing, computers, and digitizers. As a result, wideband systems that were difficult or impossible to implement ten years ago are now being built for an increasingly wide variety of applications including transient radar, concealed object detection, mine clearing, pipeline inspections, archeology, geology, electronic effects testing, and communication. In this paper, we discuss current wideband source technology around the world as well as laboratory and test facilities. We also will briefly touch on frequency limitations of anechoic chambers, design of transmission line simulators, frequency regulation requirements for outdoor ranges, and personnel exposure limits. [ABSTRACT FROM AUTHOR]