P.V.N. Murthy

Electromagnetic field to unshielded wire coupling model

The problem of determining the currents induced in termination networks at the ends of a transmission line by an incident electromagnetic field is quite important in determining the electromagnetic compatibility of electronic systems. The coupling of EM field to unshielded wire over a ground plane has been analysed for vertically and horizontally polarised incident E fields. Experimental results are given for the vertically polarised case. It has been shown that the coupled voltage can be reduced either by reducing the height of the wire over the ground plane or by using a terminating capacitance.

EMI modelling and analysis of power switching circuit

This paper deals with the modeling and estimation of differential mode conducted emissions from a DC/DC Converter (buck converter) which operates at 295 kHz. Typical Buck converter is modeled as ac equivalent circuit and simulations are carried out. Fixed resistive load impedance is considered for the simulation and conducted emissions are simulated in frequency range of 10 kHz to 1MHz. Practical Conducted emissions tests are carried out and these results are compared with simulation results.

NASA ISRO Synthetic Aperture RADAR (NISAR) spacecraft magnetic field studies

The objective of this study is to optimize the location of the magnetometer in the presence of the magnetic torquers on the NASA ISRO Synthetic Aperture RADAR (NISAR) Spacecraft which involves identifying the locations of minimum magnetic field areas due to magnetic torquers. The modelling and simulation are carried out with the help of Computer Simulation Technology (CST) software. Magneto static solver is used to find out the Magnetic field at various places inside/outside of spacecraft.

Noise coupled to unshielded wire due to computed transient electromagnetic fields generated by ESD events in spacecraft

Spacecraft when placed in plasma, spacecraft charging occurs which results in ESD discharge. This paper focuses on ESD fields radiated in spacecraft level and the noise coupled to a nearby wire when it is exposed to these radiated fields. A dipole model is considered to predict the transient radiated fields. The ESD current data is experimentally obtained in order to obtain the noise coupled to nearby wire. Furthermore, telegraphers equations have been employed to compute the induced current and voltage. Additionally, the fields radiated and noise coupled to the wire under various conditions are computed and plotted.

Charging analysis of GSAT-17 patch antenna

GSAT-17 spacecraft is one of the most complicated and technologically advanced Satellites being built by Indian Space Research Organisation (ISRO). The payload configuration of GSAT-17 spacecraft is 24 channels In Normal C-Band Transponders, 12 channels in Upper Ext. C-Band Transponders, 2 Channels in Lower Extended C transponders, 2 Channels each in MSS and DRT/SAR. For Lower Ext-C band, 0.75m × 0.77m Tx./Rx. patch array (8×4) antenna is designed for both uplink and downlink signals. This antenna is mounted on EV top of the satellite and provides coverage to southern Indian peninsula and Antarctica. This poses a charging threat, if not properly grounded, due to GEO spacecraft charging. Hence a good grounding scheme is necessary for ESD compliance. A study was taken up to assess the surface and internal charging effects on the antenna and proper grounding scheme was worked out to mitigate this problem.

Automation of low frequency conducted susceptibility (CS01) test

Conducted and radiated mode EMI/EMC tests are carried out at subsystem level to establish Electromagnetic compatibility in spacecraft. EMI/EMC test requirements of ISRO spacecraft subsystems are derived from MIL-STD 461C and the procedure given in MIL-STD 462. Low frequency conducted susceptibility test (CS01) is automated to perform the test accurately from 30Hz to 50kHz. The power line impedance of subsystem is also computed as a part of automation. This automation is done by controlling the instrument with GIPB interface and visual basic is used as the programming language.

Study on EMI/ESD effects of Electric Propulsion System on spacecraft systems and mitigation techniques

A study has been made to determine the probable EMI and ESD effects of Electric Propulsion System (EPS) on Spacecraft performance to generate and implement mitigation techniques to overcome these effects. Detailed literature survey has been made on the tests carried out by other space agencies on EPS in Anechoic Chamber along with Vacuum chamber and spacecraft charging related aspects of EPS. The EMI/EMC tests results of Rusiian Keledish thruster SPT-50, planned to be used on-board GSAT-9 satellite, with ISAC made Power Processing Unit (PPU-10) have been compiled. This paper consolidates the literature available on satellites that have flown in the past with Electric Propulsion Systems. Based on these experiences and EMC measurements conducted mitigation techniques, precautionary measures and the areas requiring in depth study for future ISRO satellites are presented.