Evaluation Engineering - December 2008 - (Page 45)

Figure 1. Example of a Highly Directional Open Boundary Quad-Ridged Horn Antenna as these developments mature. ANSI ASC C63 ® membership represents industry, regulatory bodies, military, universities, and consultants located in the United States, so a wide range of users impacted by ANSI standards has direct input. With the global economy driving the market, there is an increasing need to harmonize the various antenna calibration standards where appropriate. Work began over a decade ago speciﬁcally to bring the Standard Site Method (SSM) of ANSI C63.5 into the European standard CISPR 16 as the method of antenna calibration to be used. However, parts of the standard did not meet the view of the CISPR working group then assigned this task. In the SSM method, the antenna factor was derived at a particular antenna height above the ground plane. There also was discussion on the accuracy and uncertainty of such antenna calibrations that still is being argued, namely what ANSI C63.5 provides vs. what the other proposed calibrations require. Of course, the needs of the user must be better deﬁned in the accuracy and uncertainty of the calibrations. For example, is it absolutely necessary to have an antenna calibration that has the lowest uncertainty if the other techniques have uncertainties slightly larger? Near Free-Space Antenna Factor (NFSAF) Antennas calibrated under NFSAF over a conducting ground plane are specified with horizontal polarization, R=10 m, h 1 =2m, and h 2 =1 to 4 m. Under this geometry, antenna factors are minimally affected by the test environment. This is what you have been getting with your antenna calibration for years, and it should match up with previous calibration data. The calibration is performed on a high-quality antenna test site deﬁned in both ASC C63.5-2006 and CISPR Pub 16-1-5 (2003). Free-Space Antenna Factor (FSAF) Ideally, FSAF is an environment having no reﬂections or couplings to the antennas. It is not very realistic. In the case of biconical antennas, to get the FSAF using ANSI C63.52006, a correction factor is applied to the actual calibration that produced the NFSAF. The FSAF shall be used for product testing and site validation measurements in conjunction with the geometry-specific correction factors (GSCF). In the case of broadband horn antennas that are highly directional (Figure 1), there is an option for the FSAFs. These are measured using a technique where the antenna does not see signal reflections or the reflections are so small they have little or no effect on the calibration. GSCF GSCFs are provided by the standard or measured for each frequency at a speciﬁc geometry. These correction factors are for a pair of antennas for test-site validation and are not geometry-speciﬁc antenna factors. SSM The SSM is the most commonly used method for antenna calibration over a conducting ground plane and highlighted in ANSI C63.5. Usually three pairs of measurements are needed which involve three antennas. Continued on page 46 levear AV Measurement Instruments Suitable for Car AV Equipment NEW AV Multitester VP-7670T Compact tester combining Audio analyzer, Video analyzer, and AM/FM Signal generator. www.kikusuiamerica.com Common Terms Here is a listing of the most common terms related to antenna calibration: www. ev alua t ion e n gin e e rin g.com Visit www.rsleads.com/812ee-007 http://www.rsleads.com/812ee-007 http://www.evaluationengineering.com http://www.rsleads.com/812ee-007

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Evaluation Engineering - December 2008 Contents Editorial Product Briefing Test Software C-V Measurements Nanoelectronics Test Product Guide Company Guide Machine Vision EMC Test Index of Advertisers

Evaluation Engineering - December 2008

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