Rajveer S. Yaduvanshi

Bio: Rajveer S. Yaduvanshi is an academic researcher from Ambedkar Institute of Advanced Communication Technologies and Research. The author has contributed to research in topics: Dielectric resonator antenna & Antenna (radio). The author has an hindex of 11, co-authored 73 publications receiving 408 citations.

Wide Band Circularly Polarized Dielectric Resonator Antenna With Stair-Shaped Slot Excitation

Abstract: A singly-fed wideband circularly polarized dielectric resonator antenna is proposed in this communication. Antenna structure contains a rectangular and two half split cylindrical dielectric resonators. Multiple orthogonal modes are excited in the antenna structure when excitation is applied through a stair-shaped slot. Measured results show that antenna provides wider 3-dB axial ratio and impedance bandwidths of 41.01% and 49.67%, respectively. Proposed antenna can be utilized in C-band applications.

Inverted-Sigmoid Shaped Multiband Dielectric Resonator Antenna With Dual-Band Circular Polarization

Abstract: A multiband dielectric resonator (DR) antenna is proposed with dual-band circularly polarized (CP) response. This antenna consists of an inverted-sigmoid shaped DR. A metallic strip is applied at the surface of the DR to achieve the circular polarization. The fundamental and higher order hybrid modes are excited in the antenna structure because of the specific geometry. The antenna with dual-band CP response provides the measured 3 dB axial ratio (AR) bandwidth of 19.98% in the lower band and 3.07% in the upper band. The upper band 3 dB AR response can be tuned in different 10 dB impedance passbands of the antenna by changing the location and width of the metallic strip. Antenna response can also be tuned to obtain the triple band CP operation.

On the Navier-Stokes equations

Abstract: A criterion is given for the convergence of numerical solutions of the Navier-Stokes equations in two dimensions under steady conditions. The criterion applies to all cases, of steady viscous flow in two dimensions and shows that if the local ' mesh Reynolds number ', based on the size of the mesh used in the solution, exceeds a certain fixed value, the numerical solution will not converge.

Free space experimental scattering database continuation : experimental set-up and measurement precision : Testing inversion algorithms against experimental data: Inhomogeneous targets

Abstract: In the present paper, the experimental set-up of Institut Fresnel used to measure the scattered fields of different elongated objects is precisely described. Since the special issue on 'Testing inversion algorithms against experimental data', the modifications of this system, outlined here, have mostly been done to improve the synchronization of the apparatuses and the precision of our measurements. Due to a large number of requests from the inverse problem community, it has been decided to add new measurements to the Institut Fresnel's database. All the new targets presented here are two-dimensional inhomogeneous ones. They are made of different dielectrics or are mixing metal and dielectric parts. Both TE and TM polarizations are measured for each target, from 2 to 10 GHz and even 18 GHz for the most complex target. In the first part of this paper the set-up is described precisely. The second part is devoted to the presentation of the targets. Finally, some TE and TM comparisons of measurements and direct problem simulations are shown to accredit our experimental method and to give an idea of the accuracy of these measurements.

Millimeter wave beamforming for wireless backhaul and access in small cell networks and practical approaches in software-defined radio

Abstract: Mobile data traffic will continue its tremendous growth in some markets, and has already resulted in an apparent radio spectrum scarcity. There is a strong need for more efficient methods to use spectrum resources, leading to extensive research on increasing spectrum reusability on flexible radio platforms. This study solves this problem in two sub topics, millimeter wave communication on wireless backhaul for spectrum reusability, and flexible prototyping radio platform using software-defined radio (SDR). Wireless backhaul has received significant attention as a key technology affecting the development of future wireless cellular networks because it helps to easily deploy many small size cells, an essential part of a high capacity system. Millimeter wave is considered a possible candidate for cost-effective wireless backhaul. In the outdoor deployment using a millimeter wave, beamforming methods are key techniques to establish wireless links in the 60 GHz to 80 GHz to overcome pathloss constraints (i.e., rainfall effect and oxygen absorption). The millimeter wave communication system cannot directly access the channel knowledge. To overcome this, a beamforming method based on codebook search is considered. The millimeter wave communication cannot access channel knowledge, therefore alternatively a beamforming method based on a codebook search is considered. In the first part, we propose an efficient beam alignment technique using adaptive subspace sampling and hierarchical beam codebooks. A wind sway analysis is presented to establish a notion of beam coherence time. This highlights a previously unexplored tradeoff between array size and wind-induced movement. Generally, it is not possible to use larger arrays without risking a performance loss from wind-induced beam misalignment. The performance of the proposed alignment technique is analyzed and compared with other search and alignment methods. Results show significant performance improvement with reduced search time. In the second part of this study, SDR is discussed as an approach toward flexible wireless communication systems. Most layers of SDR are implemented by software. Therefore, only a software change is needed to transform the type of radio system. The translation of the signal processing into software performed by a regular computer opens up a huge number of possibilities at a reasonable price and effort. SDR systems are widely used to build prototypes, saving time and money. In this project, a robust wireless communication system in high interference environment was developed. For the physical layer (PHY) of the system, we implemented a channel sub-bandding method that utilizes frequency division multiplexing to avoid interference. Then, to overcome a further interfered channel, Direct Spread Spectrum System (DSSS) was considered and implemented. These prototyped testbeds were evaluated for system performance in the interference environment.

A Low-Profile Wideband Circularly Polarized Crossed-Dipole Antenna With Wide Axial-Ratio and Gain Beamwidths

Abstract: A low-profile wideband circularly polarized (CP) crossed-dipole antenna that has both wide axial-ratio beamwidth (ARBW) and half-power beamwidth (HPBW) is presented in this paper. The crossed dipoles are composed of four trapezoidal patch arms, and they are fed by a pair of vacant-quarter printed rings to generate CP radiation. Four identical parasitic elements that consist of a horizontal triangle patch and a vertical metallic plate are symmetrically intervened between the crossed dipoles and the ground plane. It has been found that the parasitic elements can effectively decrease the antenna profile, increase the operating bandwidth, and simultaneously enhance the ARBW as well as the HPBW. A prototype was fabricated and measured to verify the design. The measured results show that the prototype has a low profile of $0.1\lambda _{0}$ , a −10 dB impedance bandwidth of 78.3% and a 3 dB AR bandwidth of 63.4%. Moreover, a 3 dB ARBW of more than 120° and an HPBW of more than 110° are achieved simultaneously within a wide passband of 50.7%.

A Low-Profile Wideband Circularly Polarized Crossed-Dipole Antenna

Abstract: A low-profile crossed dipole antenna with wide bandwidth is investigated in this letter. The double-sided printing crossed dipoles consisting of four-stepped rectangular patches are fed by a pair of vacant-quarter printed rings, generating circularly polarized radiation. Two adjacent axial-ratio (AR) passbands with AR < 3 dB are generated due to the stepped rectangular patches, and they are merged together by adding an additional dielectric slab above the ground plane, resulting in a very wide AR bandwidth. Also, an irregular ground plane is used for the antenna, which can desirably enhance the boresight gain without involving high-profile cavity. To verify the feasibility of the proposed design, a prototype operating at C-band has been fabricated and measured. Reasonable agreement between the simulated and measured results is obtained. The prototype has a low profile of 0.13 λ0 (in terms of the center frequency of passband), a 10-dB impedance bandwidth of 66.9%, a 3-dB AR bandwidth of 55.1%, and an average gain of approximately 10.4 dBic within passband.