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A metasurface-based polarization converter for ultrawideband radar cross-section (RCS) reduction of planar and conformal surfaces is presented in this paper. Initially, a polarization converter is designed which consists of a modified concentric double (MCD) square ring resonator-based unit cell along with an air gap in between the substrate and the ground plane. This air gap enhances the polarization conversion bandwidth (PCBW) of the converter. An ultrawide PCBW ranging from 6.3 -20.5 GHz (106%) is obtained with a high polarization conversion ratio (PCR) of 0.9 for normal incident EM waves. The conversion efficiency is also found to be stable for oblique incidences over the aforementioned band with a PCR of above 0.8 upto ±35 • angles of incidence. Later on, a checkerboard configuration of the polarization conversion metasurface (PCMS) array and its mirror array is applied on a planar as well as on a cylindrical conformal surface for reducing the radar cross section (RCS). It is observed that a consistent 10 -dB co-polarized monostatic RCS reduction is achieved with the planar PCMS surface over an ultrawideband (5.5 -20.5 GHz). Even with the cylindrical surface, nearly 10 dB RCS reduction is obtained upto central angles of 60 • over a wideband. Both the structures are simulated and measured after fabrication, and a reasonably good agreement is obtained between them.INDEX TERMS Artificial magnetic conductor (AMC), conformal checkerboard surface, polarization converter (PC), radar cross section (RCS), ultrawideband.

Articles you may be interested inGaInNAs double-barrier quantum well infrared photodetector with the photodetection at 1.24 μ m Appl. Phys. Lett. 91, 051102 (2007); 10.1063/1.2767185GaInNAs/GaAs quantum wells grown by molecular-beam epitaxy emitting above 1.5 μm Appl.High-resolution x-ray diffraction ͑HRXRD͒ and photoluminescence ͑PL͒ have been used to study the diffusion of atoms in 8-nm Ga 0.628 In 0.372 N 0.015 As 0.985 / GaAs quantum well, with and without dielectric encapsulants. These samples were repeatedly annealed in the temperature range of 680-800°C over times of up to 16 000 s. HRXRD simulations, by using dynamic scattering theory and Fick's diffusion model with a constant diffusion coefficient, demonstrate that the diffusion lengths are shorter than 2 nm under the annealing conditions studied. In this range of diffusion lengths, the transition energy E e1−Hh1 , numerically calculated from the Schrödinger equation using a potential derived from the diffusion equation, increases linearly as the square of the diffusion length. The steady-state PL blueshifts, after a fast initial blueshift due to the rearrangement of local nitrogen bonding configurations N-Ga m In 4−m ͑0 ഛ m ഛ 4͒, otherwise known as short-range order, as a function of annealing time are well fitted by using the linear function. The values of ⌬E SRO and diffusion coefficients obtained are 18-28 meV and 3.0ϫ 10 −20 -3.5ϫ 10 −18 cm 2 / s, respectively. The activation energy characterized from the diffusion coefficients at different temperatures is 3.25 eV and is not affected by the dielectric encapsulates.

Self-aligned ZnO nanorods (NRs) were grown on n-Si(100) substrate by RF sputtering techniques. The NRs are uniformly grown on 2-inch wafer along [0001] direction. Single-crystalline wurtzite structure of ZnO NRs was confirmed by X-ray diffraction. The average diameter, height, and density of NRs are found 48 nm, 750 nm, and 1.26 × 1010 cm−2, respectively. The current-voltages (I-V) characteristics of ZnO NRs/Si heterojunction (HJ) were studied in the temperature range of 120–300 K and it shows a rectifying behavior. Barrier height (ϕB) and ideality factor (η) were estimated from thermionic emission model and found to be highly temperature dependent in nature. Richardson constant (A*) was evaluated using Richardson plot of ln(Io/T2) versus q/kT plot by linear fitting in two temperature range 120–180 K and 210–300 K. Large deviation in Richardson constant from its theoretical value of n-Si indicates the presence of barrier inhomogeneities at HJ. Double Gaussian distribution of barrier height with thermionic equation gives mean barrier heights of 0.55 ± 0.01 eV and 0.86 ± 0.02 eV for two different temperature regions 120–180 K and 210–300 K, respectively. Modified Richardson plot provided two values of Richardson constant for two temperature regions. However, for higher temperature range (210–300 K), the calculated value of Richardson constant ∼123 A cm−2 K−2 was close to the ideal Richardson constant for n-Si.

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A silicon Mach-Zehnder modulator with a low-loss phase shifter formed by restricted-depth doping is fabricated and characterized. The phase shifter has a PN junction at the bottom of the rib waveguide, whereas the top of the rib is un-doped. Device simulations confirm that the phase-shifter loss is reduced by 26−28% with an increased phase-shifter length to keep a π phase shift with the same bias condition in comparison with a conventional PN junction through the whole depth. An optical loss as low as 1.6 dB has been achieved in the fabricated phase shifter with a 6-mm length. The Mach-Zehnder modulator with the phase shifter has a fiber-to-fiber loss of 9 dB. 10-Gbps non-return-to-zero on-off keying with extinction ratio of 11 dB is demonstrated under push-pull operation with a 6 V pp driving voltage on each arm.

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Abstract-The work presents a simple and novel design approach to extend the bandwidth of existing Dielectric Material Based Microwave Absorber (DMBMA). The design comprises planar square patches of DMBMA placed periodically on a metalbacked FR4 sheet. For demonstration purpose, the DMBMA is synthesized by adding conducting carbon fillers in polyurethane matrix, and its electromagnetic parameters are measured in X-band. A single reflection null is observed in DMBMA owing to λ/4 resonance. In comparison, the bandwidth of 8 GHz (10-18 GHz) is achieved for −10 dB reflection for square patch based DMBMA. The thickness of proposed absorber is 2.75 mm. An additional resonant mode is observed due to capacitive coupling between the square patches. The enhanced bandwidth is attributed to the overlapping of λ/4 resonance and induced coupling mode. A good agreement between the simulated and measured data is observed.