Modelling, Design and Construction Of A Multipurpose Anechoic Chamber

Chung, Boon Kuan (2003) Modelling, Design and Construction Of A Multipurpose Anechoic Chamber. PhD thesis, Multimedia University.

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Abstract

A multipurpose anechoic chamber that operates over a very wide frequency range from 30 MHz through 18 GHz has been designed and constructed at the Faculty of Engineering of Multimedia University. An innovative design technique has been developed, giving rise to the construction of an asymmetrical-shaped anechoic chamber which fulfils the different requirements for various measurement needs using lower cost materials. The facility can be used for EMC tests, antenna measurements, monostatic and bistatic RCS measurements, RF transceiver testing, calibration of scatterometer, and other electromagnetic research experiments. It is suitable for both industrial use and basic research. Abeam-tracing technique has been used to develop a model for calculation of wave propagation in the anechoic chamber. The major advantage of beam-tracing over ray-tracing is the path loss information for multiple receiver locations can be determined simultaneously as opposed to running a ray tracing simulation for each receiver location one at a time. As a result, the computing time is greatly reduced. The computer program simulates an impulse transmitted from a dipole antenna and propagating in all directions in the form of polygon-shaped beams. The possible paths for the beams to reach the receivers are recorded. Instead of calculating the field strengths for a large number of discrete frequency points, the received impulses resulting from various multipath propagation are combined to give a time-domain impulse response. A Fast Fourier Transform (FFT) is performed to obtain the desired electric field in frequency domain for frequency range 30-1000 MHz. The asymmetrical chamber geometry has been optimised, taking into account the limited physical space, to achieve the extremely wide operating frequency range with low cost absorbing material. Combination of pyramid and wedge-shaped RF absorbers is used for lining of the chamber walls and ceiling to exploit the advantages of the different absorber shapes. The modelling method has been used to predict the site attenuation prior to the chamber construction. Ease of construction and ease of lining the absorber material on the chamber surfaces are preserved in the design. Constructability of the design allows for all seams to be properly welded. Reasonably high shielding effectiveness has been achieved. Space efficiency of the design allows for two additional screened rooms to be constructed next to the anechoic chamber: one is used as the control room to house the test and measurement equipment; and other is used for conducting certain RF measurements. The low-frequency applications of the anechoic chamber are for EMC test. The required site validation criterion of EN50147-2 and ANSI c63.4 for radiated emission measurements is met for frequencies 30-1000 MHz. The field uniformity requirements of EN61000-4-3 standard are also achieved. Thus the anechoic chamber can be used to perform radiated RF immunity test on electronic products. The quietness of the anechoic chamber is adequate for antenna measurements. Field probe measurements have been made across the quiet zone in the vertical and horizontal transverse directions, for both vertical and horizontal polarisations. The peak-to-peak interference amplitudes are less than 0.3 dB for frequencies from 3 GHz to 18 GHz. Reflectivity level as low as 53 dB has been achieved at 6GHz. The measurement facility is also suitable for accurate polarimetric measurements of both monostatic and bistatic RCS. The smallest RCS that can be reliably measured is as low as -70 dBsm for monostatic case and -80 dBsm for bistatic case. Time-gating technique is applied to improve the measurement accuracy. The scattering from 3-inch and 6-inch spheres can be accurately measured in both magnitude and phase for all four polarisation combinations. The project involves securing the financial resources, determining the required specifications, designing the chamber structure, procuring various components and instrumentation, planning the logistical arrangements(contract,shipping, insurance, haulage, time to delivery, storage space), supervising the construction process, and evaluating the anechoic chamber according to the specific performance criteria. The necessary features such as access doors, ventilation , lighting, electrical power supply, power -line filters, connection panels, cables, pneumatic air supply, turntable, and motorised antenna mast are included in the design. In this project , to reduce cost, several components of the facility have been designed and fabricated which include the knife-edge shield doors, waveguide lighting units, connection panels, low-profile non-metallic turntable, adaptive antenna elevation mechanism , and horizontal scanning mechanism. The experience gained throughout the project has given the author a through understanding of the theories, design considerations and construction of a microwave anechoic chamber.

Item Type: Thesis (PhD)
Subjects: L Education > LB Theory and practice of education > LB2300 Higher Education
Divisions: Faculty of Engineering (FOE)
Depositing User: Mr Shaharom Nizam Mohamed
Date Deposited: 03 Dec 2009 07:40
Last Modified: 04 Dec 2009 11:16
URI: http://shdl.mmu.edu.my/id/eprint/44

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