Impedance Matching for Helical Antenna
Hope that I am not oversimplifying your problem.

I am not fully versed on this antenna, but to me, an impedance of 140Ohms seemed a little off for anything that I have laid out for 1.7GHz. (Pardon my ignorance for your analysis, but just in case.)  There are some impedance transformers for 1.7 GHz in Minicircuits, but I have the sense that those frequencies are prohibitively high for them. Depending on your output power, an LC impedance matching network or a microstrip matching network would work better. You might consult to Pozar for textbook examples. For broadband applications, I have used Richard Li's book for intuitive broadband matching tricks, there might be some use in checking that book also.