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There is something about your attenuator that I don't understand, maybe its for some reason.
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The attenuator sections look fine to me? The resistor values all look to be close to the classic values for 2, 3, 5, 10 and 20dB sections. I can't see how or why anyone would do it differently unless you went to T sections rather than Pi.
At work we have always used 300R for the shunt resistors in a 3dB pad and I think this is common practice to allow 300R resistors to be used here. But 270R is also used here. Note that there is a decimal point typo in the table because the series resistor should be 248R and not 24.8R for a 20dB attenuator.
For ultra wideband operation (up into the GHz region) the frequency response of a 20dB attenuator can be improved if it is made up from arranging 120R (or 124R) 0805 package SMD resistors in series or parallel. It's possible to make a precision 20dB attenuator by selecting/grading 5% 120R and 124R resistors on a DMM and it should work well up into the GHz region. 0805 SMD resistors with a value in the 82R to 150R region will behave very well over a huge bandwidth. Often you will see commercial attenuators where the designer has tried to use parallel or series resistor combinations to improve the bandwidth in a similar way.
At work I still use an old 'company' DOS program to design Pi or T attenuators. It dates back to the 1980s but it works really well. I can remember the values for the classic attenuators but this program is still very useful for custom values or for different input or output impedances.