S.V.K. Shastry

Reflectivity level of RF shielded anechoic chamber

The reflectivity level of an RF shielded rectangular chamber with a non-uniform absorber lining has been investigated using the geometrical optics approach. The excitation antennas considered are the Hertzian dipole, a halfwave dipole and a pyramidal horn. A simple model is employed for the reflectivity of the absorber lining for normal incidence.

Computer aided analysis of ESD effects in dual gate MOSFET VHF amplifier

The authors present a computer-aided analysis model for the prediction of the response of a dual gate MOSFET VHF amplifier to electrostatic discharge (ESD) induced transient electromagnetic (EM) fields. With the help of the frequency spectrum of ESD generated electric field, the frequency-dependent y-parameter set for the device, and the antenna parameters, the model predicts the time-domain response for a given tuned frequency and bandwidth of the VHF amplifier. It appears that the amplifier responds at its tuned frequency during the steep rising edge of the electric field. The amplitude of response decreases sharply with increase in distance from the ESD source.<<ETX>>

Surface charge monitor payload of GSAT-2 spacecraft

The design, development, and the on-orbit performance of the surface charge monitor payload of GSAT-2 spacecraft have been briefly outlined in this paper. The payload, comprising four detector electronics heads and a central electronics module, has been operating continuously from May 14, 2003 to August 14, 2003.On-orbit data from the surface charge monitor payload of GSAT-2 spacecraft has been briefly summarized in this paper. The payload, comprising four detector electronics heads and a central electronics module, has been operating continuously since May 14, 2003, except when switched OFF during the period from August 14, 2003 to September 12, 2003. The data correlated well with the GOES-10/12 data on Geomagnetic activity.

Lumped Element Model for Spacecraft Surface Charging Studies

The external surfaces of a spacecraft exposed to Earths magnetospheric plasma can build up differential voltages which can result in an electrostatic discharge (ESD). This discharge may induce transient electromagnetic interference (EMI) in the electronics circuitry and may give rise to switching anomalies or system failure under certain environmental conditions. This paper outlines the development of Lumped Element Model (LEM) of a spacecraft for surface charging studies. A numerical solution procedure using method of moments and triangular patch modelling to determine the capacitance of conducting objects in free space has been developed. Differential equations of spacecraft charging have been derived and the surface charging of INSAT-2E spacecraft has been simulated. The results obtained for INSAT-2E using LEM concept are compared with those obtained using the NASA Charging Analysis Program (NASCAP) for a similar satellite. Using LEM of a conducting plate located in free space, and with the help of circuit simulation software, the transient structural current due to a blow-off discharge is predicted. Power supply lines, command and control lines, lines connected to antenna probes, switches and thence to microwave devices can pick up ESD transients. Hence ESD immunity should be built into microwave subsystem as well. Techniques of hardening microwave subsystem against on-board ESD have also been outlined.

Development of circuit model for spacecraft charging studies

The external surfaces of a spacecraft exposed to Earths magnetospheric plasma can build up differential voltages which can result in an electrostatic discharge (ESD). This discharge may induce transient electromagnetic interference (EMI) in the electronics circuitry and may give rise to switching anomalies or system failure under certain environmental conditions. This paper outlines the development of circuit model of a spacecraft for surface charging studies by assuming Maxwellian distribution function to represent the plasma particles in space. Analytical expressions for charging and discharging current sources of the geosynchronous Earth orbit (GEO) plasma have been obtained. A numerical solution procedure using method of moments and triangular patch modelling to determine the capacitance of conducting objects in free space has been developed. Differential equations of spacecraft charging have been derived and the surface charging of INSAT-2E spacecraft has been simulated.

Issues and concerns in using composites for spacecraft structures

Several problem areas that are associated with the use of composites in spacecraft structures have been highlighted. In particular, the problem of controlling static-charge build-up on composites has been analyzed in some detail.

Electromagnetic coupling and radiation analysis of lossy multiconductor lines in high speed switching circuits

The effect of line losses on crosstalk and radiation in a multiconductor microstrip transmission line system, has been investigated using the modal theory in the frequency domain. The fast Fourier transform (FFT) has been employed to determine the time domain response of the lines to signals from high speed switching circuits. The crosstalk reducing effect of a lossy shield line has also been studied using this technique. The frequency domain expression for the line currents has been used along with the asymptotic form of dyadic Greens function for a grounded dielectric slab, to determine the frequency spectrum and the waveform of the radiated field.

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.

Simulation of the response of external ESD protection circuits for CMOS ICs

CMOS ICs are highly susceptible to electrostatic discharge (ESD) induced voltage/current stresses. The IC manufacturer provides an on-chip protection circuit for improving the ESD susceptibility threshold of CMOS devices. However, device failures continue to occur due to electrical overstress (EOS) or due to ESD. For example, the CD4050B device has a built in immunity level of 2 kV for the human body model (HBM) ESD waveform. Hence the EOS/ESD failures noticed in these devices may be either due to a HBM-ESD stress level which is higher than 2 kV or due to other types of work practice/area related ESD stress waveform. Thus, there appears to be a need for providing external ESD protection circuits such that the device performance is not affected adversely. This paper gives an account of studies made using SPICE and MC4 circuit simulation software, to determine the effectiveness of some of the HBM-ESD external protection circuits.

Shielding of electromagnetic fields of current sources by spherical enclosures

Expressions for the shielding effectiveness of a conductive spherical enclosure excited by a Hertzian dipole have been derived using the dyadic Greens function technique. This technique has the advantage that the fields inside or outside the enclosure due to arbitrary current distribution may be found by employing the same set of dyadic Greens functions. The shielding effectiveness for plane wave incidence has been determined by considering the limiting case of the current source external to the spherical shell. Computed values of shielding effectiveness deduced in this manner have been compared with those obtained by the numerical evaluation of the expressions derived by earlier authors. The theory presented here may be useful to EMC (electromagnetic compatibility) engineers who must consider electromagnetic coupling from current sources in the vicinity of shielding enclosures.<<ETX>>