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GTEM CABLE EMISSION STUDIES MEASUREMENT TECHNOLOGY LIMITED JUNE 29 TH 2010 Dr. Zaid Muhi-Eldeen Al-Daher Dr. Angela Nothofer Prof. Christos Christopoulos

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GTEM User Group Meeting - MTL Luton Presentation Outline Repeatability Issues Correlation Algorithm EUT (Antenna Gain) Simulation & Measurements Results

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GTEM User Group Meeting - MTL Luton Repeatability Issues: Input Reflections – S11 Return loss due to reflections at the cells input port Losses include: mismatches and discontinuities, path losses, current and RF termination characteristics Reflection losses should be better than -20dB Peaks occur at every λ/2 away from the characteristic frequency Termination cross over Increasing reflections

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GTEM User Group Meeting - MTL Luton Repeatability Issues: Field Factor (Normalization) – GG Cell Up to 5dB errors

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GTEM User Group Meeting - MTL Luton Repeatability Issues: Field Factor (Normalization) – NPL Cell Up to 4.5dB errors

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GTEM User Group Meeting - MTL Luton Repeatability Issues: Field Factor (Normalization) – Both Cells Difference in performance behaviour. Different in induced field strengths – size factor. Difference in e0y mean values (10dB in this example) must be normalised further.

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GTEM User Group Meeting - MTL Luton Repeatability Issues: Field Factor – Both Cells Common Normalization Common characteristic frequency More ripples

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GTEM User Group Meeting - MTL Luton Repeatability Precautions Cables, wires, bundles, devices under test must be all positioned within the testing volume of the GTEM cell. The primary y-component of the electrical must be measured rather than calculated. Data must be normalised to a common value of e0y. Normalisation with respect to the input power if possible.

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GTEM User Group Meeting - MTL Luton Bundles

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GTEM User Group Meeting - MTL Luton Repeatability Measurements (Different wire lengths) Coil In-Line Twisted Inverse Twisted

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GTEM User Group Meeting - MTL Luton Correlation Algorithm Total radiated power algorithm is based on a multi-dipole model positioned over a perfect conducting ground plane. Assumptions: 1- Any EUT may be represented by a set-up of three orthogonal dipoles 2- Dipoles are electrically short w.r.t wavelength. E.g. at 1GHz max dimension must not exceed 30cm 3- Designed for frequency range of 300 to 1000MHz. 4 - Any radiation elements must not have a gain greater than a dipole 5- The maximum power can be depicted from any direction

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GTEM User Group Meeting - MTL Luton Gains Using Antenna Theory By treating wires and bundles as potential radiating elements, studying their gains across the frequency range becomes vital. Strong directivities and high gains will invalidate the GTEM correlation algorithm. Measuring gains and antenna patterns in a GTEM cell is different to that of an anechoic chamber since there isn't really a transmitting antenna. By measuring the received power relative to that applied at the apex, and by accounting for any path and power losses, the gain produced by the EUT along with its cables can be determined as follows:

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GTEM User Group Meeting - MTL Luton Gains Using Antenna Thoery A factor that compensates towards the different field strengths inside the GTEM cell.

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GTEM User Group Meeting - MTL Luton Gains – CST Simulations – Max values in 3D

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GTEM User Group Meeting - MTL Luton Gains – CST Simulations – Radiation Patterns

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GTEM User Group Meeting - MTL Luton Gains – CST Simulations – Radiation Patterns

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GTEM User Group Meeting - MTL Luton Gains – CST Simulations – Radiation Patterns

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GTEM User Group Meeting - MTL Luton Gains – CST Simulations – Radiation Patterns

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GTEM User Group Meeting - MTL Luton Gains – Measurements Signal Generator Spectrum Analyser

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GTEM User Group Meeting - MTL Luton Gains – Measurements – Single Direction

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GTEM User Group Meeting - MTL Luton Cable/Wire Bundles & The Correlation Algorithm – Problems The problem of consistency in cable positioning and bundling while using the three-position correlation algorithm for emission testing in GTEM cells seems to be unavoidable in achieving sustainable repeatable results for the following reasons: Cables cannot be simply held in one position without being rotated around the EUTs axis. By rotating the cables around the EUT main axis, the shape and length of cables will change. Accordingly, the emission levels observed could incorrectly differ considerably at different orthogonal positions. In order to minimize repeatability errors cable movements must kept to a minimum.

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GTEM User Group Meeting - MTL Luton Cable/Wire Bundles & The Correlation Algorithm – Problems By averaging the received powers of the three orthogonal positions, emission levels could be well underestimated. Equipments with cables fail to meet the assumptions of the three-position correlation algorithm particularly at frequencies above 0.8GHz.

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GTEM User Group Meeting - MTL Luton Cable/Wire Bundles & The Correlation Algorithm – Solution Going with the viewpoint of maximizing emissions according to the standard recommendations; an alternative correlation algorithm could be arranged as follows: Instead of rotating the EUT and its cables in three orthogonal positions, doing a measurement in the direction of maximum emissions could be sufficient. This however will require a +/-180º azimuth scan inside the GTEM which could be conducted manually without the need of turntable, in steps of 30º as it is unlikely the EUT along with its cables will have a higher radiation pattern beamwidth than 30º. In this way, the movement of cables will be kept minimum and their effects will be low across azimuth measurements.

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GTEM User Group Meeting - MTL Luton Azimuth Measurements Errors up to 10dB

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GTEM User Group Meeting - MTL Luton Azimuth Measurements Errors up to 6dB

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GTEM User Group Meeting - MTL Luton Thank You

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