khouly said:i think the frequency of operation is a factoe also
then u have to use transmission line matching network insted of lumped element matching network
also check the self resonsnce frequency of the capacitors and inductors u use
Ruritania said:Thank you all for the reply.
The following is something I forgot to mention last time:
1. The operating freq. of the receiver is 433.92MHz, which is in the ISM band.
2. The procedure I performed the measurement:
(1). I first designed a PCB board with metal runners as short as I can (I assumed that the freq. is not so high, so I used short metal runners to neglect the transmission line effect).
(2). I then solder a capacitor as large as 1u to block the DC at both input port and output port, respectively. and then the SMA connector.
(3). With power on, I measured the S11 and S22 (Surely I did it after having calibrated the VNA).
(4). By using @DS, I calculated and designed the matching network for both input and output. The simulated S11 and S22 were both less than -20dB.
(5). Then I soldered the LCs with the values obtained from step 4, with the DC blocking capacitor removed.
(6). Then I repeated step 3. But the result were really bad, it was almost the same with no matching network at all, say, above -1dB.
(In addition, the capacitors and inductors I used are all from Murata.)
Thanks again for your attention, I wish I could get more suggestions.
sorry i have one question how do i know the circuit is oscillation on the Spectrumvfone said:One reason that your simulation is different from the measurement, is because probably you didn’t take in consideration the parasitics.
Usually when the curve goes out of the Smith chart means that your circuit is unstable at some frequencies. Check for oscillations with a Spectrum Analyzer, using a wide span.
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