Hi,
I'm Dr. David Kirkby, the director of Kirkby Microwave.
Since a few people asked, I can confirm that the attenuator supplied in the SMA kits
http://www.kirkbymicrowave.co.uk/support/Kits/85033/is measured with an Agilent 85052B 3.5 mm cal kit,
not the SMA kit supplied. There are 5 measurements made on the SMA attenuator:
- S11
- S21
- S12 (in theory the same as S21)
- S22
- Reflection coefficient at the male port, with the female port unterminated
S11 and S22 measurements can't be expected to be very accurate at low frequencies, as the return loss of the attenuator is very good. A high return loss means a high measurement uncertainty. As the frequency rises, so the return loss of the attenuator deteriorates, and the S11 and S22 measurements are more meaningful. But the S21 measurement is useful at all frequencies.
The measurement of a reflection coefficient at the male port with the female port unterminated gives a return loss that will be met in many practical circumstances.
On the N kits
http://www.kirkbymicrowave.co.uk/sales/85054/we also measure the reflection coefficient at the female port, with the male port unterminated. But we don't do that on the SMA kits as the nut on the male SMA wobbles around, changing the capacitance to the inner conductor. Since such a measurement is potentially unstable, we don't do it.
There's no doubt the attenuator is not a perfect test of a VNA, but it has in the past highlighted problems when people have entered the coefficients incorrectly.
There's a review of our kit on Amazon UK by Dr. Robert Watson at Bath University. He describes how he used airlines, and a Beatty Standard and compared the kit with various other kits. See
https://www.amazon.co.uk/Kirkby-Microwave-85033-calibration-verification/dp/B01BAWR70M/ref=sr_1_1?ie=UTF8&qid=1467301985&sr=8-1&keywords=85033+sma+calibration+kit/I have no connection with Robert Watson, other than he bought a couple of kits, and another UK university bought one when they were collaborating with him. I never studied at Bath University, and have never met him, but he has agreed if anyone has any questions, he may be contacted. You can find his details on the Bath University website.
As for the comments by someone about the DC resistance of the loads, we are less concerned about their DC resistance than their RF performance. The loads are tested to have a return loss of at least 32 dB from 50 MHz to 7 GHz in a standard kit. (They are usually much better). We have an HP 3457A 6.5 digit multimeter (currently at Keysight for calibration), so could easily measure the DC resistance using 4-wire Kelvin connections. However, I feel that's irrelevant, as it does not indicate the RF performance at all, because the real part of the resistance is
not independent of frequency. You will never see a specification for the DC resistance (other than 50 or 75 ohms) in any cal kit from Agilent. Of course, if the DC resistance is well away from 50 ohms, the return loss at low frequencies would be poor, and we would reject the load, irrespective of what its performance is like at microwave frequencies.
On some loads, the return loss at 50 MHz (the lowest frequency we measure) will be worst than at 7 GHz. Whilst this is the exception, rather than the rule, it does indicate that the DC resistance is not so important.
We do now provide measured S-parameters on the opens, shorts and loads so if one has a VNA that allows the S-parameters to be imported, that data could be used.
Someone asked why when they loaded the floppy disk into an 8753, it indicated a maximum frequency of 3 GHz. That is because we find it quicker to create the files on our 8753ES, which is a 3 GHz unit. The actual coefficients are valid to 7 GHz, and a 6 GHz 8753 will calibrate up to 6 GHz. I have never seen one, but there's some information in one of the data sheets from Agilent that suggest there were versions of the 8753 up to 8.5 GHz. I guess these were "specials". If you did have such a unit, a standard SMA kit would not calibrate it beyond 7 GHz.
We can do SMA kits up to 12 GHz now, but they are more expensive, as very few loads have suitable performance at 12 GHz.
I strongly suggest if anyone does have any queries about how to use our kits, it is better to ask us, than ask on a forum like this. I see people asking if the SMA_M_M file is the right one to use in a particular circumstance.
Oh, and one more thing. The Agilent N9912A FieldFox is a very poor VNA. If you ask Agilent, they will tell you it is only designed for basic measurement. It can not even measure the phase of S21 - only the magnitude. When I first played with an N9912A I thought there was a fault on it, as the dynamic range is only about 50 dB. I'm told that is normal. The N9912A really is a brain-dead instrument.
Dr. David Kirkby,
Kirkby Microwave.