The typical faults marked with XXI and XXII in the other graphs are not visible on first view. If you have a closer look you can detect the peak at 1500 MHz range. The bandwidth of this antenna covers all the four GSM bands, UMTS 2100 and even the 2400 MHz band for Wi-Fi, Bluetooth and ZigBee as well. Even for a VSWR of 1.5 (return loss 13.98 dB) the bandwidth can be archived. If this antenna will tell a VSWR of 1.5 in average, then this will be the truth.
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: The MiniVNA 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.