DTF? remove it? what do you mean? its part of the test.
Habib,
have you got a DTF with dummy load at the end of the feeder? try also DTF with the load at the end of the last tail. if its alright, then there is the problem with the antenna.. but you are in the range of 900MHz, so acceptable VSWR is limit is 1.4 = 15.6dB on Return-Loss. on the DTF acceptable limit is 1.05 along your cable from the origin to the end.