Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Gain enhancement methods for printed circuit antennas

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

We report a facile design of an ultra-thin broadband metamaterial absorber (MA) for C-band applications by utilizing a single layer of a metal-dielectric-metal structure of FR-4 substrate. The absorption performances are characterized using a numerical method. The proposed MA exhibits the broadband absorption response over the entire C-band spectrum range from 4.0 GHz to 8.0 GHz with absorptivity above 90% and the high absorptivity is remained over 80% for a large incident angle up to 40° under both transverse electric (TE) and transverse magnetic (TM) polarizations over the band. The origin of absorption mechanism is explained by the electric and surface current distributions, which is also supported by the retrieved constitutive electromagnetic parameters, significantly affected by magnetic resonance. In addition, compared with the previous reports, the proposed MA presents a greater practical feasibility in term of low-profile and wide incident angle insensitivity, suggesting that the proposed absorber is a promising candidate for C-band applications.

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Facile design of an ultra-thin broadband metamaterial absorber for C-band applications.

We report a numerical study on the design of a broadband metamaterial absorber (MMA) with a single layer of metal–dielectric–metal based on an FR-4 substrate for X-band applications. The MMA structure consists of a periodic array of a split circle ring and lumped resistors coupled within split segments. The MMA structure achieves a broadband absorption response in the frequency range of 7.8–12.6 GHz with an absorptivity of above 90% under normal incidence for all polarization angles. The absorptivity remains above 70% in the frequency range of 6.8–11.8 GHz at wide incident angles from 0° to 30° for both transverse electric and transverse magnetic polarizations. The physical mechanism of the absorber is explained by the electric and the surface current distributions that, in turn, are significantly affected by magnetic resonance.

Numerical study of a broadband metamaterial absorber using a single split circle ring and lumped resistors for X-band applications

Abstract In this paper, a new Wilkinson Power Divider ‎‎(WPD) using open and short stubs is proposed. ‎Open and short stubs are utilized instead of 1/4 wave transmission lines in initial ‎structure to achieve harmonics suppression. The proposed WPD is designed for ‎operational frequency of 0.9 GHz and creates 3 transmission ‎zeros at 1.8 GHz, 2.7 GHz and 3.6 GHz, for suppressing second, third and fourth harmonics. The proposed WPD has been fabricated and the ‎measurement results are in good accordance with simulation results. The designed ‎WPD has a 22 % fractional bandwidth with 0.1 dB insertion loss.‎

Wilkinson Power Divider with Band-pass Filtering Response and Harmonics Suppression Using Open and Short Stubs

This article presents the design of an ultra-wideband monopole antenna with a gain enhanced performance using a novel double split ring metasurface reflector. A circular patch configuration is used here as the radiating element for the simplicity and reliability of such structures. The antenna radiates well beyond the ulta wideband (UWB) frequencies but the performance enhancement using double split ring Metasurface reflector is within UWB frequency. The periodic array of dual split ring patches with varying split angles placed in a columnar arrangement is responsible for the metasurface structure to reflect effectively in phase-agreement over a broadband without affecting the impedance bandwidth of the principal radiator. With such a low profile setup (gap between antenna and reflector is in the order of at the lowest operating frequency of the antenna) the wideband gain-enhanced characteristic makes the design versatile enough for numerous practical applications. A high increment in the antenna gain performance (nearly 5.5 dB) is recorded over the UWB frequency range. Experimental results are found to be in good agreement with the simulations. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1296–1300, 2017

An ultra-wideband monopole antenna with a gain enhanced performance using a novel split-ring meta-surface reflector

In this article, a broadband metamaterial microwave absorber on a low-cost FR-4 Epoxy substrate is proposed. The unit cell of the absorber consists of a staircase shape metallic patch placed on the...

Broadband metamaterial absorber on a single-layer ultrathin substrate

In this paper hairpin unit based compact quarter wavelength line is proposed in order to miniaturize the Wilkinson power divider (WPD) and hybrid branch line coupler (HBLC). The proposed line consists of two series lines and a hairpin unit (HPU) in between them. The proposed line provides significant size reduction due to high slow-wave factor. The electrical lengths and impedances of the HPU are adjusted to produce two transmission zeros (TZs) above the operating frequency. These TZs are tuned to get good selectivity as well as suppress the harmonics. The proposed line is further utilized to design a compact WPD and HBLC operating at 1.5 GHz. The dimensions of those are 0.06λg × 0.184λg and 0.06λg × 0.25λg, respectively, where λg is the guided wavelength. A significant size reduction of 55% and 70% are obtained for WPD and HBLC, respectively, as compared to reference one at 1.5 GHz. The proposed designs (WPD and HBLC) are analyzed, fabricated and tested.

Design of Compact Wilkinson Power Divider and Branch Line Coupler Using Hairpin Based Line

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Design of Miniaturized 10dB Wideband Branch Line Coupler Using Dual and T-Shape Transmission Lines

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.

Mukesh Kumar

Papers

An ultra-wideband monopole antenna with a gain enhanced performance using a novel split-ring meta-surface reflector

Broadband metamaterial absorber on a single-layer ultrathin substrate

Design of Compact Wilkinson Power Divider and Branch Line Coupler Using Hairpin Based Line

Design of Miniaturized 10dB Wideband Branch Line Coupler Using Dual and T-Shape Transmission Lines

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