The graph shows the two faults marked with XXI and XXII again. The triangle marker 1 has left and rights a nice gap to cover the 6 dB bandwidth. It is already more than 250 MHz, and to cover GSM 850 plus GSM 900 we need 136 MHz only. Even the gap at GSM 850/900 for 9.5 dB return loss is big. The gap for GSM 1800 is big enough as well. The drawback is that the marker 2 is outside the gap. The interesting to know is what will happen if we load the Touchtone/SP1 file to Atyune and start the tuning. Is it possible to tune the antenna II on GSM dual band or even GSM quad band by matching circuit? Is the antenna able to cover GSM quad band plus UMTS 2100? The answer I will save for a further chapter. Nevertheless, everybody has the freedom to download the Touchtone/SP1 file and to play with. For some reasons the antenna shows a third resonance at 2500 MHz range.
The upper text is out of the IoT M2M Cookbook here. If you are interested in a copy of the book please do not hesitate to drop an email to harald.naumann (at) gsm-modem.de .
Remark: My first low budget VNA had a to noisy output. The Smith Chart diagram contained to many loops and at UMTS 2100 and LTE 2700 the noise made the diagram close to unusable. I replaced it to a profesional VNA listed here.