Once more you will detect the typical faults marked with XXI and XXII. The bandwidth for the lower GSM bands is very small and the triangle marker 1 for the middle of the GSM 900 band is on the right side of the gap. There is a need for a matching circuit for sure. For the higher GSM bands up the UMTS 2100 the antenna looks good. If it will be used for GSM 1800 or GSM 1900 only, then a return loss of 9.5 dB can maybe archived in the final design. For some reasons this antenna shows a resonance at 2400 MHz range as well.