ACLR - Adjacent Channel Leakage Ratio
Measuring ACLR (Adjacent Channel Leakage Ratio) is one of the most important tasks in the development of base stations for WCDMA. The requirement on subsystem and component level is often much tougher than on the system level. When testing for instance a D/A converter, or other components in the transmitter chain such as amplifiers and mixers, not even the performance of the worlds best spectrum analyzer, the R&S FSU, has always been accurate enough to reveal the performance of the device under test.
With the latest firmware update the R&S FSU Spectrum Analyzer offers important new functions. The noise correction algorithm corrects for inherent noise in the ACP measurement function and thus enhances the dynamic range for ACP measurements. In the case of WCDMA with 3.84 MHz channel width in an offset of 5 MHz, the FSU now achieves a dynamic range better than 84 dB, an improvement of 7 dB. Already delivered units will also benefit from this enhancement. Upgrade the firmware to release 1.41 and reach the new level of performance!
Why are these high Adjacent Channel Leakage Ratio (ACLR) values needed with Signal Generators?
For WCDMA base stations, the 3G specifications demand an ACLR performance of 45 dB in the adjacent channel. The manufacturers of base stations add some headroom so that their products have an ACLR of around 50 dB. The modules inside the base station, and the components inside the modules, each need to have a 10 dB better ACLR, to fulfil the specifications.
That means the ACLR of amplifiers must be in the range of 60 dB to 70 dB.
If the Adjacent Channel Leakage Ratio ACLR of the signal generator were in the same range, the additional error of the ACLR measurement would be about 3 dB.
This is why the ACLR of a signal generator has to be one order higher than that of the components to be tested.
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