A simple, fast and efficient method for designing wideband radar absorbers is proposed. The idea is to modify the circuit analog absorber method without perturbing the bandwidth. This is done by utilizing the asymptotic behavior of such an absorber at low frequency and replacing the band-stop resonating frequency selective surfaces with low-pass capacitive ones, which can be synthesized by square patches. It is shown that higher frequencies are not influenced by these modifications. A thin wideband capacitive circuit absorber (CCA) is presented with 28% reduction of thickness and 57% increase of bandwidth in comparison to the Salisbury screen. It is also explained why some optimized metamaterial designs fail to compete with the CCA method. For high permittivity layers, it is shown that the CCA is a better solution than the Jaumann absorber and improvements both in thickness and bandwidth are possible. A three layered ultra wideband (4-24 GHz) CCA is presented with total thickness of 15.1 mm. Finally, a design capable of handling oblique angles of incidence for both polarizations and fulfilling different mechanical, thermal and fabrication constraints is given. The absorption band covers the entire C, X and Ku radar bands (4-18 GHz), showing significant improvement compared to the published circuit analog absorbers. (Less)

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Capacitive Circuit Method for Fast and Efficient Design of Wideband Radar Absorbers

A review of Mesosphere–Stratosphere–Troposphere (MST) radar developments and studies, circa 1997–2008

A new generation of high-resolution (1 km) forecast models promises to revolutionize the prediction of hazardous weather such as windstorms, flash floods, and poor air quality. To realize this promise, a dense observing network, focusing on the lower few kilometers of the atmosphere, is required to verify these new forecast models with the ultimate goal of assimilating the data. At present there are insufficient systematic observations of the vertical profiles of water vapor, temperature, wind, and aerosols; a major constraint is the absence of funding to install new networks. A recent research program financed by the European Union, tasked with addressing this lack of observations, demonstrated that the assimilation of observations from an existing wind profiler network reduces forecast errors, provided that the individual instruments are strategically located and properly maintained. Additionally, it identified three further existing European networks of instruments that are currently underexplo...

Exploiting Existing Ground-Based Remote Sensing Networks to Improve High-Resolution Weather Forecasts

This letter focuses on the modification of a unit cell of a metamaterial absorber to decrease its operational frequency. By decreasing the operational frequency, we can increase capability of the absorber for practical applications and decrease sensitivity of the structure response to the curvature. The structure has been implemented by the array of the unit cell on the FR4 substrate in the front of a conductive plate. Both the simulated and experimental results indicate the structure provides 20% decrease in the minimum operation frequency with respect to the reference structure. Also, the operating frequency range of the structure with absorptivity more than 90% is 1.35–3.5 GHz, i.e., 88% fractional bandwidth. The structure has appropriate response under oblique incident angle from 0° to 40°.

A Metamaterial Absorber With a New Compact Unit Cell

Energy harvesting (EH) or scavenging is recognized as harvesting energy from ambient energy sources in the surrounding environment. This paper reports a literature review on radio frequency (RF) EH using different metasurface/metamaterial structures based on split-ring resonators (SRRs), electric inductive–capacitive (ELC) resonators, square-patch unit cells, square-ring unit cells, etc. The essential parameters in rectifying antenna (rectenna) design are included, such as receiving antenna efficiency, conversion efficiency, dimensions, supporting substrate properties, frequency band, and overall performance, etc. It is noted that rectenna design using conventional antennas such as microstrip antennas, monopole antennas, slot antennas, dielectric resonator antennas, etc. suffers from low power conversion efficiency with larger size. To overcome the above-mentioned constraints and enhance the conversion efficiency with smaller size, metasurface/metamaterial structures are used as EH collectors. An introduction to EH is discussed, followed by an overview of energy sources in the ambient environment. Several hypothetical and experimental studies on metasurface-based EH systems are summarized.

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A Comprehensive Review of Metasurface Structures Suitable for RF Energy Harvesting

A compact ultra‐thin ultra‐wideband microwave metamaterial absorber

Atmospheric winds in the troposphere have been observed routinely for many years with wind profiling (VHF and UHF) radars using the Doppler beam swinging (DBS) technique. Accuracy of wind estimates using wind profiling radars with different beam configurations has its limitations due to both the system of observation and atmospheric conditions. This paper presents a quantitative analysis and evaluation of horizontal wind estimation in different beam configurations up to an altitude of 18 km using the mesosphere–stratosphere–troposphere (MST) radar located in Gadanki, India. Horizontal wind velocities are derived in three different ways using two-, three-, and four-beam configurations. To know the performance of each configuration, radar-derived winds have been compared with the winds obtained by simultaneous GPS sonde balloon measurements, which are considered to be a standard reference by default. Results show that horizontal winds measured using three different beam configurations are comparabl...

Evaluation of DBS Wind Measurement Technique in Different Beam Configurations for a VHF Wind Profiler

A multifrequency phased-array Doppler sodar system has been installed recently at the National Atmospheric Research Laboratory (NARL) for the continuous observation of the lower atmosphere from near ground to the atmospheric boundary layer (ABL). The NARL sodar, developed in technical collaboration with the Society for Applied Microwave Electronics Engineering and Research (SAMEER), was built using piezoceramic tweeters, which are capable of generating 100-W acoustic power. In favorable atmospheric conditions, the sodar gives wind profiles up to 1 km. The performance evaluation is one of the most important aspects for quality assurance of sodar operations. This paper presents the first results of experimental observations of the NARL sodar system and its scientific validation. The NARL sodar has been validated using the simultaneous observation of another sodar system (Scintec model MFAS64). Various physical parameters of the atmosphere are derived using the results obtained from both of the syst...

First Results of Experimental Tests of the Newly Developed NARL Phased-Array Doppler Sodar

This article reports an ultra-thin, compact metamaterial absorber with wideband absorption at microwave frequencies. The proposed structure contains circular and rectangular split rings, and has thickness of 0.049λ0 with respect to the center frequency of the bandwidth. This structure provides wideband absorption of 3.84 GHz from 12.80 GHz to 16.64 GHz with 90% absorptivity and absorption peaks are observed at 13.2 GHz and 16.5 GHz. The full width half maximum of the structure is 5.48 GHz from 12.09 GHz to 17 57 GHz. The absorption mechanism and polarization behavior of the structure have to be studied. The proposed metamaterial absorber is sensitive to polarization but wideband absorption is attained only for specific normal and oblique angles of incidence, with reduced absorptivity. The structure has been fabricated, and the measured results match well with the simulation responses. The advantage of the proposed absorber is its wideband absorption with compact (8 mm × 8 mm size), ultra-thin (1 mm thick substrate) structure compared to that of the other existing microwave metamaterial absorbers.

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An Ultra-thin Compact Wideband Metamaterial Absorber

Real time weather monitoring in aircraft is gaining its importance in emerging IoT applications Here a compact microstrip rectangular patch antenna with different slots have been proposed The slots are introduced to reduce the resonating frequency and to obtain miniaturization of antenna Here a microstrip patch antenna is developed with resonating frequency in the range of S band Slots of various shapes are introduced to shift the resonating frequency range to L band By this we achieve reduction in size of antenna The antenna uses inset feeding techniques and substrate used is FR4 epoxy Microstrip patch antenna is simulated by HFSS software

I. Srinivasa Rao

Papers

A compact ultra‐thin ultra‐wideband microwave metamaterial absorber

Evaluation of DBS Wind Measurement Technique in Different Beam Configurations for a VHF Wind Profiler

First Results of Experimental Tests of the Newly Developed NARL Phased-Array Doppler Sodar

An Ultra-thin Compact Wideband Metamaterial Absorber

A compact antenna for IoT applications