Ghanshyam Singh

Measurement of Dielectric Constant and Loss Factor of the Dielectric Material at Microwave Frequencies

A new technique to evaluate the dielectric constant and loss factor of a homogeneous dielectric material using rectangular shaped perturb cavity has been developed. The values of S-parameters are measured experimentally by placing the sample in the center of the cavity resonator. Sample under test is fabricated in the form of a cylinder. The real and imaginary part of the permittivity can be then calculated from the shift in the resonance frequency and Q-factor. The results of a Teflon sample are also tabulated.

Opportunistic Spectrum Sensing by Employing Matched Filter in Cognitive Radio Network

The sophistication possible in a software defined radio has now reached a level where each radio can conceivably perform many beneficial tasks that help the user and network. It can also minimize the spectral congestion. If a radio could use favourable frequencies and choose waveforms that would minimize and avoid interference with existing radio communication systems, it would be an ideal software defined radio or in general sense cognitive radio which has all the properties of software defined radio along with the property of artificial intelligence. The presented paper is underpinning on the spectrum sensing, which is performed by implementing matched filter and is supported along with the simulation results.

A Dual-Mode Input Voltage Modulation Control Scheme for Voltage Multiplier Based X-Ray Power Supply

A dual-mode input voltage modulation (IVM) control scheme for a three-phase zero current switching series resonant (SR) inverter-fed three-phase voltage-multiplier based X-ray power supply is proposed to achieve a quick rise of output voltage. In this control scheme, a quasi-resonant control circuit is connected at the lower arm of the three-phase inverter to control the effective input voltage across the inverter by raising or lowering the voltage level at the lower arm of the inverter. At the startup of the power supply, the quasi-resonant control circuit shorts the lower arm of the three-phase SR inverter to ground, causing the inverter to see maximum voltage and the output voltage to rise with maximum speed toward the target voltage. As the output voltage reaches 90% of the target voltage, the effective input voltage across the inverter is reduced to a value that corresponds to the target output voltage by raising the voltage level at the lower arm of the inverter. As a result, the rise rate of the output voltage slows down and overshoot is prevented. Experimental results based on the scaled-down laboratory prototype are presented to verify the effectiveness of the proposed dual-mode IVM control scheme.

Design of Single PIN Shorted Three-Dielectric-Layered Substrates Rectangular Patch Microstrip Antenna for Communication Systems

In this paper, we have simulated a single-pin-shorted microstrip line fed three-dielectric-layer (with different permittivity and thickness) rectangular patch microstrip antenna for all those communication systems whose limited antenna size is premium. Low permittivity hard foam has been used as one substrate to achieve wide bandwidth. The simulation of this proposed antenna has been performed by using CST Microwave Studio, which is a commercially available electromagnetic simulator based on the finite difference time domain technique.

A Novel Digital Beamformer with Low Angle Resolution for Vehicle Tracking Radar

In this paper we propose a digital beamformer utilizing the radar integrator method of detection. In the receive mode the digitized radar returns weights are allocate on the such a way that the first pulse reflect a SUM pattern and the subsequent three pulses reflect DIFFERENCE pattern. The pulses on DIFFERENCE pattern are added to each other and the net signal subtracted from signal received in SUM pattern. This results in very narrow beam which shows narrow spatial resolution. The schematic is presented and the results are shown.

Analysis of a tapered vane loaded broad-band gyro-TWT

The wide-band low-gain feature of a tapered smooth wall gyro-traveling wave tube (gyro-TWT) was combined with the low beam energy, low magnetic field, and high gain, though narrow band, feature of a vane loaded nontapered gyro-TWT, to propose a distributed, tapered vane loaded gyro-TWT for both high gains and wide bandwidths. The device was analyzed for the tapering of any one of the three parameters - the waveguide radius, the vane depth, and the vane angle keeping the remaining two as constant. The magnetic field was also synchronously tapered. The optimum taper and vane parameters were predicted for a large gain and bandwidth.

Throughput maximization with reduced data loss rate in cognitive radio network

In this paper, we have investigated a technique to eliminate the sensing-throughput trade-off of the conventional method in the cognitive radio network. First, we have discussed the sensing—throughput trade-off caused by the conventional method in the cognitive radio network and then proposes a frame structure for eliminating such an issue which is presented in the conventional approach. However, the proposed method has a drawback, which is solved by the enhancement in the frame structure. We have numerically simulated and compared the throughput of cognitive users for both (conventional and propose) methods. The frame structure enhancement technique decreases the probability of frame collision between the primary and secondary users (SUs) and reduces the data rate loss.

A SIMPLE SYNTHESIS TECHNIQUE OF SINGLE- SQUARE-LOOP FREQUENCY SELECTIVE SURFACE

In this manuscript, a simple synthesis method of single square loop frequency selective surface (SSLFSS) is discussed, which may flnd the suitable application in the fast analysis and fabrication of the frequency-selective surface. The presented technique is used to design SSLFSS at 3GHz, 15GHz, 22GHz and 26GHz. At every frequency of interest, the analytical result is very close to the required result. Moreover, a way to control the re∞ection at any frequency is discussed, which may flnd an application in controlling the re∞ection level at any frequency. However, we have proposed two simple, cheaper and lightweight structures at 3GHz and 22GHz for the application in various satellite communications. The proposed process has been extended to the analysis of bandpass structure and desired results have been achieved, which indicates the utility of the method of synthesis of both the bandpass and bandstop structures.

Analysis of an azimuthally periodic vane-loaded cylindrical waveguide for a gyro-travelling-wave tube

A cylindrical waveguide, provided with wedge-shaped metal vanes projecting radially inward from the wall of the guide, excited in the transverse electric (TE) mode, was analysed. The analysis was carried out considering the angular harmonics generated by the angular positioning of the vanes. A set of equations was generated in the Fourier amplitudes of field constants. The condition for nontrivial solutions for the field constants gave the dispersion relation of the structure. From the expression of power flow down the structure, its interaction impedance was also estimated. The shape of the dispersion characteristics and the value of the cutoff frequency as well as the interaction impedance characteristics of the waveguide were found to depend on the vane parameters their number as well as their radial and angular dimensions. The optimum vane parameters were obtained corresponding to the minimum variation of the slope of the ω-β dispersion plot, such parameters being useful from the standpoint of the ban...

Numerical Computation of Resonant Frequency of Gap Coupled Circular Microstrip Antennas

In this paper the numerical computation of resonant frequency of gap coupled circular microstrip antennas using the concept of cavity model has been presented. The resonant frequency of the gap-coupled circular patches is computed and the mode number is also evaluated. The computed results are compared with published results. The previously published results are based on experimentation and do not present a clear mathematical model for the same structure. An extensive comparison with Method-of-moments based software (IE3D) is also done. The accuracy of prediction is reasonably good.