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Re: First PCB pictures of the V2
Hey Pablo and Hey Larry,
It¡¯s really cool that you two have an eye on our conversation ? And thanks for your opinions! I wish you both a Happy New Year~ Hey Gabriel, Thanks for giving me your development data! It¡¯s always exciting to see someone else¡¯s design style. ? As a common advice (to everyone ?): If you want to filter your power supply, I highly recommend to not use those standard 100nF Caps! Yes, it looks like everyone is using them (and unfortunately those still get recommended in the datasheets). But at a RF-view they far from optimum. The purpose of those Caps is to filter noise thus acting like a pass through at low frequency (DC) and shorting higher frequencies to GND as much as possible. At most frequencies these Caps are above their self-resonance frequency (SRF). That¡¯s why you should use a SMD ceramic capacitor with as many internal layers as possible at your desired size to lower parasitics like ESR and ESL, for example, a 4u7 at 0402 or 10u at 0603. In plain theory they are not recommended at high frequencies due to their SRF. But if you measure them with a precise VNA you¡¯ll find out that due to the internal layer stacking the parasitic inductance (ESL) is very low as many layers connected in parallel. Therefore, the capacitors impedance (even as it acts as an inductor) stays quite low at higher frequencies (several GHz) and obtain a very neat noise filter characteristic! Oh, and please put those bypass caps as near as possible to the desired IC supply pin. In fact, not all ICs need to have the bypass cap directly next to their power supply pin, but for some especially RF-ICs this is essential! 1) Absolutely! This SMA connector style you are using has a really bad performance at higher frequencies. It¡¯s not just the stub giving you a parasitic inductivity also the discontinuity inside the bended connector affects the port match (at least if you don¡¯t want to pay some extra to have a perfectly matched bending)¡ But unfortunately, it¡¯s the only connector type you can use as you need to maintain a really (really!) good mechanical resilience and a long bulkhead. (But just between the two of us: most of the high end VNAs do not even reach a 20dB return loss at their ports either¡) Concerning the RF input cap: Your DGS seems to be fine (just by looking at it). Am I right assuming the Cap can endure 6.3V (max 10V?) 2) Yeah, I already thought this might be the reason why. As JLC is not able to put those IC on the PCB you need to do it on your own. But even so you should put critical passive components at the same side as the ICs. (e.g. some bypass caps or this 50Ohm E-Cal match!) ? It nearly adds no extra time to the population process RF-switches: That¡¯s why those Infineon switches produce a negative voltage level internally~ Please check them out as you can also use them easily up to several GHz, which might come handy in further versions/designs ;D 3) Don¡¯t you think the cut out might be a bit too much? :¡¯D And I had a look again at JLC¡¯s part library. The 68Ohm 0402 is available now: So maybe you can change the size and get rid of the DGS. As you want to use only ¡®standard¡¯ components those 50Ohms resistors have typically a bad impedance behaviour at higher frequencies due to their high parasitic inductance¡ At least for the E-cal and reference 50Ohm match you should think about replacing those single resistors with 2x100 Ohm resistors parallel +DGS. (At high end application they even try to force their 50Ohm reference to be a good match by adding attenuators in front of it, as those internal used SMD resistors are most of the time not as good as the external calibration match is ?) And once more: I highly recommend to put at least the E-cal match resistor directly next to the switch pad, as this would improve your internal calibration and add a bit more stability to your system! 4) Oh yeah, the reference match¡! I truly remember the same experience meanwhile I developed my directional module ?. To obtain a good performance at (very) high frequency it is necessary to mirror the signal pathway. Not only due to the not ideal match but also due to the uncertainties within the trace (and if you want to refer the internal match to the external calibration load /DUT also due to the mismatch given by the DC-Block). But I do admit that inside your frequency range the given mismatches/discontinuities shouldn¡¯t be to high and may just appear at higher frequencies (>2 GHz), thus the gain and phase shift might be not affecting the system so much. 5) If you catch the wrong balun type, the yield can be awful! ? That¡¯s the reason why so many devices out there need to be tuned before they get delivered to the costumer¡ As you can not afford this in this application a stable balun with a good yield is the rise and fall of your whole application. Give those TC1-1-13M+ a try. As far as I know from my and others designs they should obtain a fairly good performance! I also did a simulation with your resistor values. But instead of a 50Ohm and 0.3pF I used 2 times 50Ohm to balance the baluns and adjusted the tuning R&C! Look how good it turned out ? 6) If you use ferrites for debugging please be careful at 1GHz and above, as ferrites permeability is decreased significantly, and they start to act dielectric. 7) Having U301 switched to port 2 there is also a signal at the trace to U2 reduced by U301s isolation value. The datasheet gives an isolation between 15 to 20dB at 3GHz (with perfect termination!). The signal then gets reflected at U2 and propagates trough U301 back to your mixer with a total attenuation of roughly 25 to 30dB, whereas signals which got coupled into the trace between U301 and U2 are only attenuated by 15dB! If you want to, I would suggest to change U2 into an low noise amplifier. For example BGA2800, as this LNA just needs 3 caps to be up and running. It is also pretty cheap and concerning your application you can surely run this amplifier up to 4GHz! ? The amplifier can be used exactly the same way as the switch by turning it on and off. The isolation between U301 and U1 is better than 20dB when turned off. In addition, it would amplify your couplers output signal, hence improving your SNR. This comes in handy as your LO signal from mixer is just 27dB damped (Isolation between RF-IN and LO Port) and interferes with your S11-signal. Furthermore, thanks to LNA¡¯s output match with better 20dB, the mixers does not see any bad impedance match coming from the baluns! 8) To add some stability to your system it would be good, if you would add some DC-Block Caps between mixer and BB-Amplifier (like those 10u 0603) depending on your lowest IF frequency. Hopefully this helps you to solve your problems soon~ I wish you all the best! ? -Melanie |
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Re: Bi-Quad Antenna 430 MHz is this a good one?
#calibration
Its on cardboard. One side is white the other is black, from ikea.
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Re: Bi-Quad Antenna 430 MHz is this a good one?
#calibration
On 1/2/20 10:38 AM, ersoz@... wrote:
my question is this a useable antenna or is there something wrong? ???? Looks fine to me, but - what is the antenna on?? Is that laying on a table top?? Mounted on a piece of cardboard or foamboard?? White painted metal reflector? Can't tell from the pics.? Might have to build one myself.? Thanks. |
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Re: errors of "error" models
#102: The Complete "Demystification" of the "VNA Measurements" Kind - Farewell
Hello, Well, we arrived at last at The End of a rather long Road. The VNA gives to The Common User the Value: (g - o)*(l - s) - - - - - - - - - =: CR (g - s)*(l - o) so that the Common User has just one equation in four Variables: (G - O)*(L - S) - - - - - - - - - - - = CR (G - S)*(L - O) from which he could compute the G if he would know the 3 values S, L, O. * Now, stop reading, please, and think a little about it * - Who of us knows these 3 Values ? We don't. So, for each triple of (S, L, O) values we think, believe, accept, or whatever else we like to be consider as "true", this equation produces a * d i f f e r e n t * value of G. That's all. Farewell, Sincerely, gin&pez@arg :102# |
Mel
@blackmagic
Jim Allyn - N7JA
gin&pez@arg