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Vol . 8 No. 1 February 2000

Measurement Capabilities

DRDO is a pioneer in India to set up a wide range of antenna measurement facilities. These include:

Indoor Near-Field Facilities

Planar Near-Field Measurement (PNFM) Facility

Cylindrical Near-Field Measurement (CNFM) Facility

Automated Planar Near-Field Measurement (APNFM) Facility

Spherical Near-Field Measurement (SNFM) Facility

Outdoor Antenna Test Range

Indoor Near-Field Facilities

Planar Near-Field Measurement (PNFM) Facility

Salient Features

Microwave anechoic chamber

Planar scanner covering a large area

Inhouse developed software packages for near-field data acquisition, transformation and results presentation.

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The anechoic chamber designed and developed indigenously is of size 7 m x 7 m x 5.4 m, lined with pyramidal type microwave absorbers of various sizes on all sides. It has specially designed airconditioning setup. A CCTV facility is installed to monitor the activities inside the chamber during the measurement. The chamber is provided with suitable bay lights to get a clear view. A control room adjacent to the chamber houses the RF equipment, CCTV monitors, system computers, and programmable logic control (PLC) with motor drives.

The scanning area of the planar scanner in X and Y directions is 2.5 m x 2.5 m. The scanner is controlled by a PLC system and is interfaced with a platform to operate either on DOS or WINDOWS. All the axes are provided with software, hardware limit switches and kill switches. The software for near-field data acquisition and near-field to far-field transformation is developed inhouse and is available in both DOS and WINDOWS. All the requisite settings are done through menu-driven, userfriendly software. The output data can be presented in rectangular, 3D and contour plot formats. The frequency range of operation extends from 1 GHzto 18GHz.

Cylindrical Near-Field Measurement (CNFM) Facility

Salient Features

Microwave anechoic chamber

Angular positioner and a planar scanner covering a large area

Inhouse developed software packages for near-field data acquisition, transformation and results presentation

The CNFM facility has been indigenously developed using the PNFM chamber facility. In this setup, the AUT is mounted on an angular positioner which offers 360 rotation in horizontal plane. The probe antenna is mounted on a two-axes planar positioner in which the horizontal axis is used for aligning the probe and the vertical axis is used for data acquisition. Both the positioners are controlled by an IBM compatible, DOS-based 80386 PC. The angular positioner controller unit is interfaced with PC through a synchro-to-digital converter card and a multipurpose analog-digital card. The PC also communicates with HP83620A RF microwave source and an SA 1783 microwave receiver. The communication is achieved through an IEEE 488 Bus (GPIB). The facility has been successfully operated from C-band to Ku-band. The facility is iDEALly suitable for measurement of linear arrays and arrays with wide angular raDIATion pattern in one plane.

Automated Planar Near-Field Measurement (APNFM) Facility

Salient Features

Microwave anechoic chamber

Planar scanner covering a large area

Inhouse developed software packages for near-field data acquisition? transformation and results presentation

Microwave measurement and analysis setup

The anechoic chamber designed and developed indigenously is of size 18 m x 12m x 10 m, Automated planar near-field antenna test rangelined with pyramidal type microwave absorbers of various sizes on all sides. The absorbers are arranged in a graded fashion for a quite zone level better than -40 dB. The floor is hARDEned so that tracked vehicles can be driven inside for measurements on vehicle mounted antennas. It has all other features as in case of PNFM facility.

The scanning area of the planar scanner in X, Y, and Z directions is 10 m x 6.5 m x 1 m, respectively. The peak/rms positioning accuracy achievable is 300/100 microns. The scanner is controlled by a PLC system and is interfaced with a platform to operate either on DOS or WINDOWS. The X-axis motion is by rack and pinion and that of Y and Z axes is by lead screw. The feedback is through linear scale in X-axis and by rotary encoders in Y and Z-axes. All the axes are provided with software, hardware limit switches and kill switches.

The software for near-field data acquisition and near-field to far-field transformation is developed inhouse and is available in both DOS and WINDOWS. All the requisite settings are done through menudriven, user-friendly software. The output data can be presented in rectangular, 3D and contour plot formats. The antenna sizes up to 7 m wide x 4 m high can be measured. The frequency range of operation extends from 1 GHz to 18 GHz.

Spherical Near-Field Measurement (SNFM) Facility

This full-fledged automated SNFM facility makes use of SA Model 2022A antenna analyser system which is programmed to perform a variety of antenna measurements. A key feature is the capability of performing measurements in the near-field of AUT as well as direct far-field of moderate size antenna. The facility makes use of HP1000 computer for data acquisition, transformation and analysis. This enables the user to compute the near/far-fields in all directions. The facility mainly consists of a microwave anechoic chamber and a control room.

The microwave anechoic chamber is shielded. All six interior surfaces of the chamber are lined with pyramidal-shaped absorbing materials to create a quiet zone of 3 m diameter sphere. The chamber is of ~z. The reflectivity is better than

18 m x 8 m x 6.5 m, and is capable of measurements from 1~8~z. The reflectivity is better than -50 dB and the RF shielding is better than 100 dB. The anechoic chamber houses an optical alignment system and a source tower with orthomode probe. The maximum diameter of AUT is 150 wavelengths and the accuracy of computation is -60 dB. The positional accuracy of the antenna positioner is 0.02 deg Az, 0.03 deg roll.

The measurement accuracy of the SNFM facility is + 0.5 dB in gain, + 1 dB at 30 dB in side lobe level, + 0.1 deg in beamwidth and + 0.1 deg in null location. The measurement time for a 1.2 m reflector at C-band is typically 4 hr and the data transformation time is 3.5 hr.

Outdoor Antenna Test Range

The outdoor antenna test range (ATS) is located in a remote place with 1.6 km separation between the transmitter and receiver. The transmitting antenna is a parabolic reflector with adjustable height. The synthesised source is 2180 SA of 100 mW CW power output. The testing antenna is mounted at the receiver side on a 3-axes positioner at an altitude of 21 m from ground, whose capacity is 1 tonne. The 3-axes positioner can hold a planar antenna more than 3 m high and 7 m long. The elevation can rotate from +45 to 90, the top azimuth has 360 continuous rotation, and the bottom azimuth has +240 rotation. The receiving end consists of a 1783 SA phase and amplitude receiver and a 1580 SA pattern recorder. The sensitivity of the receiver is -100 dBm.