We present a new technique for designing low-profile planar microwave lenses. The proposed lenses consist of numerous miniature spatial phase shifters distributed over a planar surface. The topology of each spatial phase shifter (SPS) is based on the design of a class of bandpass frequency selective surfaces composed entirely of sub-wavelength, non-resonant periodic structures. A procedure for designing the proposed lenses and their constituting spatial phase shifters is also presented in the paper. This design procedure is applied to two different planar lenses operating at X-band. Each lens is a low-profile structure with an overall thickness of 0.08λ0 and uses sub-wavelength SPSs with dimensions of 0.2λ0 × 0.2λ0, where λ0 is the free-space wavelength at 10 GHz. These prototypes are fabricated and experimentally characterized using a free-space measurement system and the results are reported in the paper. The fabricated prototypes demonstrate relatively wide bandwidths of approximately 20%. Furthermore, the lenses demonstrate stable responses when illuminated under oblique angles of incidence. This feature is of practical importance if these lenses are to be used in beam-scanning antenna applications.

Wideband Planar Microwave Lenses Using Sub-Wavelength Spatial Phase Shifters

Aim of this paper is to compare and prove implementation of normal multiplication and Vedic multiplication (using Urdhva Tiryakbhyam Sutra) on digital hardware requires same number of multiplication and addition operations.It makes difference only for mental calculations. Few VHDL codes has been developed for this. All multipliers has been tested for 16X16 multiplications for comparison. Test vectors has been given through a text file. Implementation has been done for the Xilinx FPGA device, Virtex XCV 300 -6PQ240. Various multiplier implementations such as Array multiplier, Multiplier Macro, Vedic multiplier with full partitioning, Vedic multiplier using 4 bit macro, multiplier using 4 bit macro, fully Recursive Vedic multiplier, Vedic multiplier using 8 bit macro have been tested and compared for optimum area and speed.

Conventional versus Vedic Mathematical Method for Hardware Implementation of a Multiplier

Major advances in millimeter-wave antennas have been made in recent years, in particular in two areas. A new class of leaky-wave antennas based on open millimeter waveguides has been proposed and investigated, and substantial progress has been achieved in integrated antennas where active and passive circuits, possibly in monolithic form, are combined with the radiating elements in one compact unit. Interesting developments have taken place also in a third group of millimeter-wave antennas, that of microstrip antennas and printed circuit antennas in general. An attempt is made to summarize these developments. >

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Millimeter wave antennas

Operators are currently considering the deployment of small cells to complement their macrocellular networks and increase their coverage and capacity. However, in order to roll-out a large number of small cells and allow anytime, anywhere wireless broadband connectivity through wireless technologies, operators must still face the challenge of backhauling the traffic from the small cells to the core network in a cost-effective manner. In this paper, backhaul challenges for small cell base stations (BSs) are discussed, and potential wired and wireless solutions together with their benefits and drawbacks are presented. The use of large scale antennas systems and free-space optics is also discussed. Moreover, a wireless backhaul planning tool targeted at finding the most cost-effective backhaul solution using a mixture of wireless technologies is presented. Simulation results confirm that the optimum backhaul solution is a combination of various options, which can overcome inherent scenario constraints while providing a cost-effective performance.

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Small cell backhaul: challenges and prospective solutions

Nanocrystalline undoped and Cr-doped PbS thin films were prepared on glass substrates by a simple chemical bath deposition method. The X-ray diffraction analyses of the films showed their polycrystalline nature with cubic structure and preferential growth along the (111) orientation. Cr incorporation decreases the average PbS crystallite size from 59.97 to 37.59 nm, whereas the strain and dislocation density showed an increasing trend. The atomic ratio of doping for Cr is about 0.63, 1.75, and 4.70% according to energy-dispersive X-ray (EDX) spectroscopy. Morphological analysis showed that the average sizes of nanoclusters decreased from 73 to 41 nm as the Cr concentration increased. The optical band gap values are increased with increasing Cr doping. The photoelectrochemical (PEC) behaviors and the stability of the Cr doped PbS photoelectrodes were studied in 0.3 M Na2SO3 electrolyte solution. Also, the incident photon-to-current efficiency and applied bias photon-to-current efficiency are calculated and showed optimized values of 13.5% and 1.44% at 0.68 V and 390 nm. Moreover, the optimized electrode shows high chemical stability and a long lifetime. Finally, the effect of temperature on the PEC behaviors is evaluated and the different thermodynamic parameters are calculated.

https://pubs.rsc.org/en/content/articlepdf/2020/RA/C9RA11042A

The structure and photoelectrochemical activity of Cr-doped PbS thin films grown by chemical bath deposition

Influence of precursor molar concentration on the structural, morphological, optical and electrical properties of PbS thin films deposited by spray pyrolysis technique using perfume atomizer

Optical and magnetic properties of PbS thin films doped with Fe2+ ions

One of the major challenge for practical Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM)system is the accurate channel estimation which is very essential to guarantee the system performance. In this paper, the Subspace Pursuit (SP), Orthogonal Matching Pursuit (OMP) and Compressed Sampling Matching Pursuit(CoSaMP) techniques combined with Minimum Mean Square Error(MMSE) and Least Mean Square(LMS)tools are used to estimate the channel coefficients for MIMO-OFDM system. These algorithms are used for the channel estimation in MIMO-OFDM system to develop the joint sparsity of the MIMO channel. Simulation results shows that SP, OMP and CoSaMP techniques combined with MMSE and LMS tools provides significant reduction in Normalized Mean Square Error (NMSE) vs Signal to Noise Ratio (SNR) when compared to SP, OMP and CoSaMP technique with Least Square (LS) tool and also the conventional channel estimation methods such as LS, MMSE and LMS. Moreover CoSaMP combined with LMS tool performs better than SP and OMP techniques with LMS tool with less computational time complexity.

Sparse channel estimation for MIMO-OFDM systems using compressed sensing

An analysis of multiple scattering of electromagnetic (EM) waves by two loss-free dielectric spheres with radii greater than a wavelength and located in the bear field of a source of radiation is presented. The incident field is expressed in terms of spherical vector wave functions (SVWF). Translational and rotational addition theorems are employed to express the SVWF of the incident field in the coordinate system associated with the dielectric scatterer. Numerical computations are performed for obtaining the amplitude and phase patterns of fields multiply scattered by two loss-free dielectric spheres, whose centers are located on the boresight axis and in the nearfield of an open-ended circular cylindrical waveguide excited in its dominant mode. Numerically computed results show good agreement with measured results obtained from a systematic experimental study on forward scatter performed in the X -band.

Multiple scattering of EM waves by dielectric spheres located in the near field of a source of radiation

This paper reports the deposition and characterisation of spray-deposited ternary PbZnS thin films. PbZnS thin films were prepared with different concentrations of zinc (0, 1, 2, 3 and 4 wt-%). XRD studies reveal the polycrystalline nature of the films. The doped films exhibit face-centred cubic structure with a strong (2 0 0) preferential orientation similar to that of the undoped film. Lead sulphide (PbS) unit cell volume contracts with Zn doping. Transparency increases with Zn doping and optical band gap values of the PbZnS films coated with Zn concentration greater than 1 wt-% exhibit a blue shift which may be attributed to Moss–Burstein effect. Electrical studies reveal that all the films have resistivity in the order of 10−1 ohm-cm. The obtained results infer that Zn doping enhances the optical and electrical properties of pure PbS making the doped films suitable for optoelectronic applications.

S. Ravishankar

Papers

Influence of precursor molar concentration on the structural, morphological, optical and electrical properties of PbS thin films deposited by spray pyrolysis technique using perfume atomizer

Optical and magnetic properties of PbS thin films doped with Fe2+ ions

Sparse channel estimation for MIMO-OFDM systems using compressed sensing

Multiple scattering of EM waves by dielectric spheres located in the near field of a source of radiation

Studies on ternary PbZnS films suited for optoelectronic applications