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)

/pdf/capacitive-circuit-method-for-fast-and-efficient-design-of-2slqpdlohd.pdf

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

A microstrip line fed rectangular patch antenna with slots in the patch radiator is designed to realise triple resonant frequencies with satisfactory impedance matching (|
 S
 11
|≤-10 dB) at 3.36, 5.96, and 9.09 GHz. Current distribution analysis is presented to provide an insight to the mechanism of triple resonance generation. A triple-band artificial magnetic conductor (AMC) is designed and analysed based on resonance phenomenon of stepped impedance resonators. The resonant frequencies of the AMC coincide with the antenna. A rectangular split-ring slot is embedded in the metallic ground of the antenna. The designed AMC is placed beneath the antenna maintaining an air gap between the structures. The slot in the ground plane enables the surface waves to interact with the AMC. The proposed arrangement enhances the gain from 1.38 to 3.77 dBi at 3.36 GHz, 3.22 to 6.29 dBi at 5.96 GHz, and 7.58 to 11.16 dBi at 9.09 GHz. The proposed structure exhibits good radiation patterns with low cross-polarisation and high front to back ratio at all the three resonant frequencies. A prototype of the proposed structure is fabricated and the measured results are in good agreement with the simulated results.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-map.2017.0815

Gain enhancement of triple-band patch antenna by using triple-band artificial magnetic conductor

Application of metamaterials for performance enhancement of planar antennas: A review

Radio frequency identification (RFID) is a rapidly developing technology, and RFID sensors have become important components in many common technology applications. The passive ultra-high frequency (UHF) tags used in RFID sensors have a higher data transfer rate and longer read range and usually come in unique small and portable application designs. However, these tags suffer from significant frequency interference when mounted on metallic materials or placed near liquid surfaces. This paper presents the recent advancements made in passive UHF-RFID tag designs proposed to resolve the interference problems. We focus on those designs that are intended to improve antenna read range as well as scalability designs for miniaturized applications.

/pdf/recent-advances-in-passive-uhf-rfid-tag-antenna-design-for-3e5xdluphf.pdf

Recent Advances in Passive UHF-RFID Tag Antenna Design for Improved Read Range in Product Packaging Applications: A Comprehensive Review

In this paper, a novel planar active artificial magnetic conductor (AAMC) frequency-reconfigurable antenna printed on an FR4 substrate is proposed. Its AAMC metal pattern in a unit cell consists of a compound-five-ring nesting (CFRN) structure. It is loaded with only one varactor diode connected to the ground plane by a metallic via. In comparison to the conventional single-circle-ring AMC, the dimension of the CFRN-AMC has been reduced by about 44% along with a lower reflection loss. The frequency-reconfigurable antenna is constructed by placing a triangle-shaped dipole antenna operating at 1.8 GHz over the proposed active CFRN-AMC ground plane consisted with 5×5 periodic unit cells. The prototype of the CFRN-AMC-backed antenna was fabricated and measured. The measured results agree well with the simulated data. It is found that by tuning the capacitance applied on the CFRN-AMC from 2.2 to 0.5 pF, the frequency band of the AMC-based antenna has been varied in the range of 1.51 through 2.12 GHz along with the highest radiation gain of 5.37 dBi at 1.74 GHz. This gain is about 3.16 dB higher than that of the antenna without using the AMC. In addition, the presented CFRN-AMC-based antenna remains a very low profile, since the separation distance between the antenna and the AMC plane is only 2 mm or 0.012λ, where the λ denotes the wavelength at 1.8 GHz in free space.

/pdf/design-of-a-low-profile-frequency-reconfigurable-and-high-3qf7wvfbo6.pdf

Design of a Low-Profile, Frequency- Reconfigurable, and High Gain Antenna Using a Varactor-Loaded AMC Ground

A microstrip line fed pentagonal printed ultra wideband (UWB) monopole antenna with partial ground plane having triple notches is proposed. The realized antenna has an operating bandwidth (VSWR ≤ 2) ranging from 3.1 GHz and continuing beyond 12 GHz. A novel mushroom-shaped slotted electromagnetic bandgap (EBG) inspired structure is used near the feedline to introduce triple notches at CBRS (3.5–3.7) GHz, WLAN (5.15–5.725) GHz and X-band downlink satellite communication (7.25–7.75) GHz frequencies. The band notch characteristics are demonstrated with current distribution and impedance analysis. Further, the proposed structure has stable radiation patterns, gain and group delay in the UWB range except the notch frequencies. Finally, a prototype of the proposed antenna is fabricated and measured results are in good agreement with the simulated results.

Design and analysis of triple notch ultrawideband antenna using single slotted electromagnetic bandgap inspired structure

/pdf/design-of-triple-band-slot-patch-antenna-with-improved-gain-33xh7naseb.pdf

Design of Triple Band Slot-Patch Antenna with Improved Gain Using Triple Band Artificial Magnetic Conductor

[1] Indian mesosphere-stratosphere-troposphere (MST) radar is located at Gadanki (13.5°N, 79.2°E) in a tropical zone of India. In this region the background atmospheric parameters such as atmospheric winds, temperature, and humidity show a distinct change from monsoon to winter season. For example, the monsoon season is dominated by tropical easterly jet winds in the upper troposphere (i.e., 14–17 km), and the winter season is dominated by westerly winds with peak value at about 12–14 km. The basic wind patterns in the two seasons differ significantly, and this is expected to give rise to differences in the characteristics of atmospheric turbulence parameters in the two seasons. In this paper, various atmospheric turbulence parameters such as eddy dissipation rate (ɛ), eddy diffusivity (Kh), and horizontal scale length (l0 and LB) are obtained for the first time for the monsoon and winter seasons by using the available data sets from MST radar. An attempt is made to understand and explain the seasonal variability of these turbulence parameters in terms of the observed changes in the background atmospheric conditions.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009RS004256

Characteristics of atmospheric turbulence in terms of background atmospheric parameters inferred using MST radar at Gadanki (13.5°N, 79.2°E)

A novel design of a compact penta-band frequency selective surface (FSS) is presented in this letter. The FSS unit cell consists of five metallic structures, two at the top surface and three at the bottom surface of the dielectric, which provide five stopbands in PCS, WiFi, CBRS, lower WLAN, and X -band downlink satellite communication frequency ranges. The mechanisms of stop-band generations are elaborated with current distribution patterns and equivalent circuit modeling. The structure is polarization-insensitive and shows a stable response under oblique incidence up to ±54°. The FSS unit cell is compact with dimensions 0.1 λ × 0.1 λ , where λ signifies the free-space wavelength corresponding to the lowest resonant frequency. A prototype of the proposed FSS is fabricated, and the measured results are in accord with the simulated results.

Anumoy Ghosh

Papers

Gain enhancement of triple-band patch antenna by using triple-band artificial magnetic conductor

Design and analysis of triple notch ultrawideband antenna using single slotted electromagnetic bandgap inspired structure

Design of Triple Band Slot-Patch Antenna with Improved Gain Using Triple Band Artificial Magnetic Conductor

Characteristics of atmospheric turbulence in terms of background atmospheric parameters inferred using MST radar at Gadanki (13.5°N, 79.2°E)

Design and Analysis of a Compact Penta-Band Polarization-Insensitive Bandstop Frequency Selective Surface