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Publication Number: 393764 Rule Parts:  Publication Date: 04/12/2007
Keyword: UWB Compliance Measurements

First Category: Administrative Requirements
Second Category: Measurement Procedures

Question:   1: What constitutes the bandwidth of a UWB emission?
2: How is the UWB emission bandwidth determined? 
3: What portion of the UWB emission spectrum is required to be within the authorized frequency bands? Is it adequate for just the center frequency to be within the authorized band?
4: Can a device be certified under the UWB rules if its emission bandwidth resides outside of the authorized frequency bands when all of its emissions are below the prescribed limits? 
5: What other subtleties should be considered when determining the bandwidth of a UWB device emission spectrum?
6: How are the emissions limits to be applied in determining compliance of a UWB device?
7: Is any specialized test equipment necessary for performing UWB compliance measurements?
8: What compliance information should be included with the application for certification?
9: What type of measurement antenna should be used for performing radiated emissions measurements on UWB devices when assessing compliance to the UWB rules?
10: Is there a provision for operating wireless tank level gauges under the UWB rules?



Answer:   UWB Compliance Measurements Answers to FAQs :
1: The bandwidth of a UWB emission is defined by the points on the emission spectrum where the amplitude is 10 dB below the maximum emission amplitude (i.e., the -10 dB points). In cases where the measured emission spectrum contains multiple (more than two) -10 dB points, the outermost points define the bandwidth (i.e., the widest bandwidth is assumed).
2: The bandwidth of a UWB emission must be determined from a radiated measurement with the device using the antenna with which it is designed to operate (i.e., the antenna frequency characteristics may define the radiated bandwidth of a UWB device and is thus considered an integral part of the system). It is recommended that this measurement be performed using the spectrum analyzer peak detector with a resolution bandwidth of 1 MHz or greater and the maximum-hold function. The device under test should be measured for maximum bandwidth by varying the antenna height between 1 to 4 meters, varying antenna polarization between horizontal and vertical and rotating the device 360 several times.
3: For a UWB emission spectrum, the entire fundamental bandwidth (that portion of the spectrum between the outermost -10 dB points) must be contained within the authorized frequency band. For example, the emissions spectrum from a ground penetrating radar (GPR) applying for authorization under Section 15.509 must have its fundamental bandwidth located below 960 MHz.
4: It is presumed that this question refers to a scenario whereby the frequencies associated with the maximum emission and the -10 dB points are located within a frequency band that is outside of those bands authorized for UWB operation (e.g., 960-3100 MHz), but are less than the applicable emissions limit. Under these conditions, the requirement that the -10 dB bandwidth be fully contained within the authorized frequency bands is not realized and thus the device can not be authorized.
5: When measuring the bandwidth of a UWB device using a radiated test set-up, it is imperative that appropriate adjustments be made to the measured amplitude levels to account for the frequency-dependent components of the measurement system (e.g., antenna gain or factor, pre-amplifier gain, cable loss, etc). Since UWB emissions can have bandwidths several GHz wide, these frequency-dependent characteristics can vary dramatically over the fundamental emission.
6: In each rule section pertaining to specific UWB applications, a table is included listing the emission limit applicable in each frequency band. The device under test must comply with all applicable limits accounting for all specified frequency bands. For example, an application for authorization of a device under Section 15.509 (low frequency imaging device) must demonstrate compliance not only to the emission limits provided for the 960-1610 MHz band, but also to those limits specified for both the 1610-1990 MHz and the above 1990 MHz band.
7: A spectrum analyzer with a quasi-peak detector is required for measuring UWB emissions below 960 MHz to verify compliance with the emissions limits in that portion of the spectrum. An analyzer with a true RMS detector is recommended, but not required, for measuring UWB emissions above 960 MHz. An alternative is provided in procedure (3) contained in Appendix F of the UWB First Report and Order (ET Docket No.98-153) for performing the emissions measurements with an analyzer that does not include an RMS detector. Also, a low-noise preamplifier is required to measure emissions to the levels necessary to determine compliance with the limits specified in the frequency band 960 to 1610 MHz for some UWB applications (e.g., indoor UWB devices authorized under Section 15.517). If the radiated measurements are not conducted in an anechoic chamber, then the use of this pre-amplifier may also require that a pre-select filter be inserted ahead of the pre-amplifier to prevent saturation from strong ambient RF signals.
8: At a minimum, the following information is required for processing a UWB application for certification:  The UWB application category (e.g., imaging device, indoor system, handheld device, etc.) and the applicable rule section - The lower and upper -10 dB frequencies (fL and fH, respectively) and the frequency of the maximum observed emission level (fM) - A description of the procedure used to determine the UWB bandwidth - The maximum radiated emissions (including narrowband emissions) and the associated frequencies observed in each frequency band identified in the applicable emission limits tables - In the event that no emissions are observed in the above frequency bands, report the measurement systems minimum sensitivity (noise floor) in these bands (i.e., show that the measurement system was capable of detecting emissions down to the level dictated by the applicable emissions limit). - A complete description of the measurement system, including antenna, pre-amplifier, etc. This should include information such as antenna gain/factor, preamplifier noise figure and gain, particularly at each frequency for which a data point is provided (peak emission frequency, -10 dB points, etc.) - Calibration information for the measurement system at each frequency for which a data point is reported. - If applicable, report all digital circuitry emissions exceeding the applicable UWB limits and provide a complete description of the process used to justify invoking the exception stated in Section 15.521(c) - A description of the technique used to determine RMS average emission levels - A description of the test site used, specifying whether the measurements were performed in a test chamber, outdoor test site, with or without a ground screen, and any other pertinent information. - Where applicable, indicate the presence of required labels and/or a manual disable switch - Describe the pulse characteristics (PRF, pulse width, etc.). Is the pulse pseudo random (dithered) or periodic? An oscilloscope plot would be helpful. - Supporting photographs depicting the measurement system set-up and the device under test.
9: Two measurement antennas will likely be necessary for performing these tests. A log-periodic antenna is recommended for performing the necessary radiated measurements below 960 MHz, although other types of measurement antennas (e.g., biconical) can be used. For the radiated measurements above 960 MHz, a broadband horn antenna or a broadband log periodic antenna may be used. When using a horn antenna to measure emissions from a device that is not placed on a turntable (e.g., a ground penetrating radar placed near the ground to replicate actual operating conditions), the antenna should be pointed in the direction of the radiating head. This is consistent with ANSI C63.4 Section 8.3.1.2, which states that the antenna must be kept within the cone of radiation and pointed at the area of the device under test
10: Section 15.517(a)(4) authorizes the use of tank level gauges as indoor UWB devices only if they are used within metal or underground storage tanks, and the emissions are directed downward.

 



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