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An innovative measurement methodology is developed and successfully implemented for a spot beam antenna and payload characterization of high-throughput satellites (HTSs) in a compact antenna test facility (CATF). With the developed measurement methodology, total measurement time and measurement setup duration are reduced by more than 70% with respect to conventional measurement techniques. The proposed methodology is successfully implemented in multiple spacecraft (SC) of the Indian Space Research Organisation (ISRO).

Compact antenna test ranges are used for fast and accurate measurement of satellite antennas and payloads. The measured performance of compact range feed dictates the quality of Quiet zone at CATF. A Dual Linear Q/V-Band feed compliant to standard compact range feed specifications was designed. The designed feed will be used for RF characterization of advance communication payload. In this paper, design aspects and simulated results of proposed feed are discussed.

The measurement of static and dynamic unbalance of satellite is carried out on vertical dynamic balancing machine (VDBM) [1]. The Velocity pickup is a transducer in VDBM, which measures the dynamic...

An innovative test methodology is proposed and implemented successfully for characterization of advanced high capacity multi-beam satellite's payloads at Compact Antenna Test Facility (CATF). Payload characterization in CATF is a mandatory test as it provides end-to-end performance of payload in radiated mode, simulating on-orbit conditions. Usually quantitative measurement of each payload parameter for each transponder is performed at the location, where In-orbit-test (IOT) is planned. To achieve this satellite is moved using CATF DUT Positioner such that geographical IOT location is aligned to Nominal Plane wave Axis of CATF. This method is commonly used for antennas having single coverage area/footprint. In case of multiple beam spacecrafts, characterization of all beams may not be possible at a single location due to sharp roll-off of the beams (away from location). Hence, characterization is required to be carried out at each beams peak location. The proposed method is validated by means of measurement example and implemented successfully for characterization of multi-beam spacecrafts.

Compact antenna test ranges are used for fast, precise and real time measurement of antenna and payload parameters. ISRO has established a Compact range at Bangalore and has a rich experience of characterizing more than 33 satellites and 200 subsystem level antennas over wide frequency range from 1–40 GHz. The standard set of compact range feeds comprises 7 dual linear polarized and 2 single linear polarized feeds in the range of 1–40 GHz. In case of satellites with payloads in lower C, Nor C and Upper ext. C-band, 3 compact range feeds should be used for performing payload characterization which consumes considerable test set up time. In this view, an ultra-wide C-band (65% Bandwidth) is designed covering the above mentioned frequency bands. In this paper, design methodology and simulation results of the proposed feed are presented.

A Spacecraft-Charging Effects Protection Plan is implemented to evaluate the impact of spacecraft-charging-related effects on a spacecraft. The plan involves defining the properties of the natural space plasma to which the spacecraft will be exposed, developing design guidelines with the purpose of reducing or eliminating the effects attributed to spacecraft charging, and performing computer analyses to model the charging level of the spacecraft and determine how spacecraft charging can adversely affect the spacecraft. The analysis is carried out using NASCAP (NASA’s Spacecraft Surface Charging Program). Calculation of absolute potential buildup is carried out and differential potential buildup is derived. Due to the differential voltage developed on different material surfaces of spacecraft in differently illuminated conditions, electrostatic discharge can occur. This ESD can cause arcing, flashover discharge, the coupling of ESD onto the desired signal and punch through of surface. On the basis of the analysis, design recommendations are made to address spacecraft-charging issues that arise.

Compact Antenna Test Facility (CATF) facility is extensively used for evaluating the antenna pattern and payload performance for all communication satellites in the integrated condition. Operating frequency range of the CATF is from 1-40 GHz. Standard feeds are available in CATF, which will cater testing in the frequency range from 1–40 GHz. Facility can also be used as standard far-field range (By-passing the reflectors and in direct Line Of Sight: LOS) for limited characterization of antennas in the frequency range less than 1GHz. With an increase in the application of UHF frequency usage in the spacecraft sphere, it is required to extend feed capability in the lower operating frequency range of facility. In view of this, it was proposed to design and develop an UWB antenna operating in the frequency band from 200 MHz - 1 GHz so that facility measurement capabilities can be extended. In this paper, design aspects of antenna, feeding network, fabrication, pattern and gain measurement procedure are discussed. Comparison of simulated & measured pattern and gain values shows good match between them.

An innovative design of Ultra Wide-band (over 55% fractional bandwidth) and Low X-pol (Axial Ratio (AR) ≤1dB) helical antenna is presented in this paper. Presented design is generic in nature and can be implemented in any frequency band. We have demonstrated the same in S-band (2.1-3.7 GHz) to meet our internal application. The effect of spacing between turns, number of turns and pitch angle of helical conductor over axial ratio is investigated and presented here. Peripheral feeding technique is used in the design and the off-axis AR within ±100 from the bore sight is ≤ 1 dB over the band. An ultra wide band impedance match between helical conductor and 50 ohm coaxial feed line is achieved by introducing a matching section in between. The matching section presented here is novel, since it is an integral part of the helical conductor section and thus made out of same conductor wire. A minimum of −10dB input reflection coefficient (S11) over the desired band 2.1 GHz to 3.7 GHz is achieved. Further, near band center (2.9 GHz) demonstrated S11 is better than -30 dB using this method. Details of design, modeling in CST (Computer Simulation Technique), and fabrication of the antenna along with the comparison of simulated and measured parameters are presented. An excellent match is observed between simulated and measured results.

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.

This paper brings out the technique employed to mitigate the spurious noise seen riding on the telemetry parameter signals from subsystems, in particular Wheel Drive Electronics (WDE). WDEs are used for speed control of Reaction Wheels (RW). Four numbers of Reaction Wheels are mounted in tetrahedral configuration in the spacecraft. The combined vector of all the wheels obtained by varying wheel speeds is used to orient the spacecraft in orbit. The wheel speed and motor current parameters of these actuators are very critical signals as these are used to determine health of the Reaction Wheels thereby determining the pointing accuracy of the spacecraft platform. On these signals, spurious noise was observed to be riding during wheel operations. These noise signals were spike-like and minimum amplitude of 0.5 V. The process to locate the source of these noise signals and their mitigation is presented in this paper.

This paper presents the investigation on the effectiveness of the various shield termination methods to be adopted in spacecrafts. The emission characteristics of various shield termination methods such as such as pigtail, halo technique, EMI back shell, and overall shielding was studied. Experiment was performed in the anechoic chamber to analyze the radiated emissions in the frequency range of 20 kHz to 50 MHz. It was demonstrated that, the shielding effectiveness of the halo technique is 10 dB better than the pigtail method. The EMI back shell and overall shielding based termination methods provides the effectiveness 35 dB better than the pigtail method.

The objective of this analysis is to derive radiation susceptibility levels for subsystems in the NASA ISRO Synthetic Aperture RADAR (NISAR) Spacecraft at Sband SAR payload frequency. This involves finding electromagnetic field distribution at various subsystem locations. The analysis was carried using Computer Simulation Technology (CST) microwave studio software. In Microwave studio Time Domain Solver with Finite Integration Technique (FIT) is used to find out the Electric field distribution at various panels of the 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, telegrapher's 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.

ASTROSAT is a scientific mission aimed at providing space based multi-wavelength observatory in the frontier areas of astronomy. It carries scientific instruments sensitive over a wide spectrum of wavelengths covering Visible, Ultra Violet, Soft X-rays and Hard X-rays over an energy band of 2–100keV. It accommodates five payloads to perform the task. Scanning Sky monitor (SSM) is one of the payloads designed to measure the soft X-rays over a band of 2–10keV for transient events. Electrical integration of SSM payload poses huge challenges in the form of design and implementation of electrical distribution system for rotating mechanism, grounding of electronics packages on Carbon Fibre Reinforced Plastic (CFRP) platform, problems faced during the testing in dis-assembled mode and measures taken to overcome the same. This paper discusses the above mentioned aspects from the perspective of electrical integration and testing.

Resourcesat-2A is an imaging remote sensing satellite carrying three payloads namely Linear Self Scanning Sensor-4(LISS-4), Linear Self Scanning Sensor-3 (LISS-3) and Advanced Wide Field Sensor (AWiFS). LISS-4 is a high resolution multi-band camera. The Payload Electronics (PLE) and Baseband Data Handling System (BDH) handle multiple clocks and high bit rate data. BDH is accommodated on main platform and payload is mounted on a rotating deck which is assembled with payload platform. The electrical environment has an effect on the performance of LISS-4. The performance of the payload is assessed by Mean of digital number (DN) and Standard Deviation (SD). LISS-4 has been tested separately in autonomous mode test and with satellite systems in Integrated Spacecraft Test (IST). Increase in mean and SD was observed in IST. As a corrective action, grounding of PLE was improved and the signal lines were separated from power lines. This action improved the performance and specifications have been met. The results are presented in this paper.

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.

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.

CARTOSAT-2 series is an advanced Cartographic satellite carrying four high resolution earth imaging payloads: PAN, MX EVM1 and EVM2. During satellite integration and testing phase, a set of tele-commands pertaining to power system not responded. It was attributed to E-field noise coupling from the adjacent harness. This noise was generated by switching of solar array strings and then getting coupled to power control package. This paper describes the problem, analysis and the corrective action to reduce the coupled noise.

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.

This paper presents a computation of the absolute free space capacitance and electrostatic body potential of a spacecraft using moment method with triangular patch modeling. Expressions are derived numerically and the moment integral is evaluated. The capacitance of a square plate is computed to validate the approach. Finally, the free space capacitance of a typical spacecraft is computed for various configurations and body potential is evaluated. The derived expressions are simple and suitable for developing the charging analysis tool. As this approach is more general, it can be easily applied to any practical spacecraft configuration.

Space applications demand power converters of high reliability, fault tolerance, high power to volume and weight ratios. Weinberg converter is one such topology having these features built in. This topology can also be called as, coupled inductor fed push-pull converter. It provides continuous current at its output , which reduces the requirement of filter bank capacitors at the output stage. In this research article, isolated Weinberg converter working principle is explained with large signal and state space analysis. Also building of working breadboard model and its test results are dealt. The paper brings out the inherent fault tolerant feature of the Weinberg converter.

This paper presents typical design, realization and space qualification tests of waveguide-iris filter used for space applications. Along with electrical specifications (including corona and multipaction) of the filter, various aspects of space requirements such as feasibility of fabrication, compatibility to work under free space environment, ability to work throughout the mission life without failures etc., are discussed. Measured and simulated filter characteristics show good agreement and is flown successfully.

Compact high power diplexer has been designed for Mars Orbiter Mission (MOM) spacecraft of Indian Space Research Organization (ISRO), launched in November-2013. This is realized using waveguide combline filter structures with an additional objective of multipaction-free operation. Used in S-band TT&C transponder that handles continuous RF power of 200W in telemetry path besides an isolation of >145dB to telecommand path. Diplexer design, realization and test results are presented. Mission performance of on-board diplexer is normal.

The MARS Orbiter Mission (MOM) spacecraft carries on-board sensitive receiver and high gain antenna system to cater to the requirement of inter-planetary and deep space communication. This paper describes, among others, the stringent EMC requirements for MOM spacecraft, summary of EMC analysis carried out, modification on subsystem level EMI/EMC test limit and EMI/ESD mitigation techniques followed to achieve EMC compliance of MOM Spacecraft.

This paper elaborates implementation of new and advanced concepts such as Modular Power System and bus bar scheme for power distribution in ISRO's high power communication satellite. The advantages of using Modular Power System vs. conventional power packages, details of new design and realization of Modular Power System are discussed. New mechanical housings realized for high power communication satellite are described. Usage of bus bar for power distribution has many advantages (as compared to wired harness) such as, reduced power distribution loss, higher current carrying capability, improved EMC performance, better thermal management and scope for mass reduction.

An S-band, compact, high power filter, for use in the Mars Orbiter Mission (MOM) of Indian Space Research Organization (ISRO), has been designed and tested for multipaction. The telemetry, tracking, and commanding (TT&C) transponder of MOM is required to handle continuous RF power of 200 W in the telemetry path besides simultaneously maintaining an isolation of greater than 145 dBc to its sensitive telecommand path. This is accomplished with the help of a complex diplexer, requiring high power, high rejection transmit path filter, and a low power receive path filter. To reduce the complexity in the multipaction-free design and testing, the transmit path filter of the diplexer is split into a low rejection filter integral to the diplexer and an external high rejection filter. This paper highlights the design and space qualification phases of this high rejection filter. Multipaction test results with 6 dB margin are also presented. Major concerns of this filter design are isolation, insertion loss, and multipaction. Mission performance of the on-board filter is normal.

Presented in this paper is an overview of passive intermodulation (PIM) in microwave space systems. Application of some of the PIM analysis and prediction techniques to the Indian national communication satellite, INSAT-2E, has been discussed in some detail. PIM control measures and PIM testing techniques that are proposed to be adopted in the design of the communication payload have been briefly summarized.

The external surfaces of a spacecraft exposed to Earth's 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 cir...

Communication experiments using normal lab setup, which includes more hardware and less software raises the cost of the total system. The method proposed here provides a new approach through which all the analog and digital experiments can be performed using a single hardware-USRP (Universal Software Radio Peripheral) and software-GNU Radio Companion (GRC). Initially, networking setup is formulated using SDR technology. Later on, one of the analog communication experiments is demonstrated in real time using the GNU Radio Companion, RTL-SDR and USRP. The entire communication system is less expensive as the system uses a single reprogrammable hardware and most of the focus of the system deals with the software part.

Smoothing and differencing is one of the major important and necessary step in the field of signal processing, image processing and also in the field on analytical chemistry. The search for an efficient image smoothing and edge detection method is a challenging task in image processing sector. Savitzky Golay Filters are one among the widely used filters for analytical chemistry. Even though they have exceptional features, they are rarely used in the field of image processing. The designed filter is applied for image smoothing and a mathematical model based on partial derivatives is proposed to extract the edges in images. The smoothing technique of SG filter offers an extremely simple aid in extracting the edge information. An approach using SG filter which can be applied in preserving edge information is one of the major tasks involved in the classification process in the domain of Optical Character Recognition. The paper is focused on designing the Savitzky Golay filter by using the concepts of linear algebra. The main objective of the paper is to portray a clear cut idea about Savitzky Golay filter and to study the design of Savitsky Golay filters based on the concepts of Linear Algebra.

This paper is an attempt to reveal the untapped immense power of the GNU Radio - an open source software, in control and monitoring systems, both real time applications and class-room demonstrations. GNU Radio has already gained wide acceptance and glory in communication and signal processing. As a novel attempt to bring the controlling capability of GNU Radio to limelight, an experiment for temperature control, out of its innumerable applications, and the possibility of a revolution by this free open source software is predicted and explained through this paper. This paper describes the hardware and software requirements for the temperature control experiment with SBHS (Single Board Heater System) using GNU Radio and describes the recommended classroom demonstration.