PROJECTS HANDLED

  I have worked in the following areas during the years 1993 - 2000.

                              1. Analysis and design of microwave antennas.

Tools used are as follows.

(a)     Method of Moments (MoM)

(b)     Spectral domain technique

(c)     Finite Difference method (FDM)

(d)     Time domain – Finite Difference method (TD-FDM)  

2. Antenna measurements and diagnostics

These are carried out in

(a)     Planar Near-Field Measurement (PNFM) facility.

(b)     Cylindrical Near-Field Measurement (CNFM) facility.

(c)     Far-field antenna test range.

3.  Radar systems.

 Involving the following.

(a)     Airborne radar system analysis and design.

(b)     Signal processor development on ADSPs.

 Project-1 :  Array antenna for multi-mode radar

The antenna for multi-mode radar is a planar circular slotted waveguide array employing broadwall offset radiating slots, and is required to give –30dB peak sidelobe level in both the principal planes.

I have carried out the analysis and design of the radiating slots using Method of Moments (MoM). The analysis includes broadwall slots radiating into (a) free space and (b) dielectric cover. The method is based on Galerkin’s approach with entire domain sinusoidal basis functions and takes into account the waveguide geometry and frequency. The theoretical results are in good agreement with experimental results. I have carried out the analysis, and developed a software for design of resonant array of radiating slots using equivalent circuit approach. The antenna has been designed and fabricated. The measured electrical parameters have met the required specifications.

In this connection, I have been awarded DRDO Establishment Republic day award in 1994.

Copyright has been obtained for this software entitled ‘Characterisation of Broadwall Radiating Slots- Dielectric Cover’ (L-15290/96). For the case of slots radiating into free space, copyright has been obtained for this analysis software entitled ‘Characterisation of Broadwall Radiating Slots’ (L-14429/95).

Project-2 : Helicopter based airborne radar

I am a member of the team involved in the design and development of radar for Advanced Light-weight Helicopter.

I carried out a detailed study of the radar performance and designed various modes of operation to meet the Naval requirements. These modes are bifurcated into Surface Surveillance modes and Air Surveillance modes. The design involves selection of various radar parameters such as PRF, pulse width, pulse compression ratio, etc. Also, I made an in-depth study of the signal processing chain from Platform motion compensation, Moving Target Detection, FFT processing, CFAR, etc. and simulated in MATLAB environment for optimising the detection performance of the radar.

Presently, I am leading a 3 member team and developing the signal processor for the radar using ADSP’s. These programmable DSPs are based on Super Harvard Architecture (SHARC). The issues such as data management, timing analysis, SHARC coding are being carried out.

Project-3 : Microstrip based missile fuse antenna

I designed a microstrip based planar antenna for missile proximity fuse. This multi-layer antenna consists of 7 x 1 strip dipole radiating elements, that are fed electromagnetically through a strip line based feeder. A 1 : 7 stripline based corporate power divider feeds the antenna, the design of which has been carried out using LIBRA. The constraints placed on the design are severe not only from the electrical point of view, but also from the available physical space. The design successfully catered for all these parameters, and the antenna has been fabricated and tested, and found to meet all the specifications.

Project-4 : FD-TD software development

I have developed Finite Difference – Time Domain (FD-TD) software for analysing planar structures like Coplanar Waveguides (CPW), and the metallic waveguide structures. The method uses standard Yee’s grid for discritising the geometry of the object, with suitable absorbing boundary conditions for confining the computational volume. The software mainly uses a Gaussian excitation pulse, and leap-frog time stepping is carried out till the response of the structure decays to a negligible value. The scattering parameters of the structure are then computed by using the Fourier transformed time domain response.

This software has been successfully used to compute the characteristic line impedance of the CPWs, and to characterise the rectangular waveguide discontinuities.

Project-5 :  Slotted antenna for Airborne Surveillance radar

The Airborne Surveillance radar antenna is an S-band planar elliptical nonresonant array of 6.2m x 1.2m dimensions, which has been successfully designed and developed indigenously. This is the India’s first antenna exhibiting peak sidelobe levels less than -40dB.

I have carried out the design of the radiating broadwall slots and developed a nonresonant array design methodology. This novel design uses the individual slot characterisation data, which has been obtained accurately using MoM, and integrates with the array design procedure. The array has been successfully tested in an open test range and is found to give better than –40dB peak sidelobe level over a bandwidth of 350MHz. These results demonstrated the accuracy and the capabilities of the design.

Towards my contributions in the design and development of antenna, I have been awarded DRDO Establishment Republic day award in 1995 and 1998.

Project-6 :  Ground based surveillance radar array antenna

This array antenna employed narrow wall radiating slots, unlike the broadwall slots used in earlier projects. The ground based radar antenna is a linear narrow wall slot, nonresonant array of 2m in length.

The analysis of narrow wall slot is complicated as the slot projects into the broadwalls, across the 90⁰ corners. I have developed a novel Hybrid method for the analysis of this geometry, which includes the corner diffraction effects, finite wall thickness and coupling of various slot portions.  I formulated a coupled magnetic field integral equation, which is solved by moment method using entire domain sinusoidal basis functions. The MoM matrix elements are computed using finite difference method (FDM) coupled with Measured Equation of Invariance (MEI). Also, I carried out measurements on narrow wall slots using HP8510B vector network analyser and good agreement is found between theory and experiment.

This analysis has been used, successfully, in the design and development of narrow wall slot linear array for ground based surveillance radar. This array antenna is required to have high frequency bandwidth, along with main beam very close to boresight. To meet these critical requirements, I developed a nonresonant array design methodology based on earlier mentioned Hybrid approach leading to a successful completion of the design and development. The experimental results of the array have met all the specifications.

This work on the narrow wall slots formed the core of my Ph.D. thesis.

Project-7 :  Design and establishment of Cylindrical Near-Field

Measurement (CNFM) facility.

I am a member of the team that carried out the design, development and establishment of CNFM facility at DRDO, Bangalore. This facility is used for indoor antenna measurements in the near-field.

My specific tasks are development of software for carrying out the cylindrical near-field to far-field transformation. The transformation procedure involves the measurement of the tangential components of the electric field on the measurement cylinder. The cylindrical modal coefficients are extracted from the measured data using Hankel functions of second kind, and the far-field is obtained through these coefficients. The effect of probe on the test antenna pattern is also considered.

The alignment of the antenna under test is very critical in case of CNFM. I have carried out a detailed study on the effects of alignment errors on the radiation pattern, and brought out the tolerance levels and alignment procedure for measurements.

For this work I have been awarded DRDO Establishment Republic day award in 1994.

Project-8 :  Antenna diagnostics using Planar Near-field

Measurement (PNFM) facility.   

Locating the defective portions or defective radiating elements play a crucial role in the diagnosis of antenna aperture distributions. Towards this, I have developed an analysis for ‘inverse transformation’. This transformation calculates the aperture amplitude and phase distributions from the measured near-field data over a planar surface infront of the antenna under test. This algorithm uses FFT and is computationally efficient. It has been successfully used for isolating the defective elements of the ground based phased array antenna and the airborne slotted waveguide radar antennas. The resolution of the algorithm is so fine that it can distinguishably identify and compute the complex aperture distributions of two successive radiating elements that are separated by half a wavelength.