From the above discussion I think Nora wants to use a log detector to monitor signals over 0.9 to 2.2 GHz, and is not sure how to couple a suitable antenna to a MMIC with a differential input.
From MMIC data sheet I can understand that the 1:1 balun transformer is needed if a well matched response is expected over the wide bandwidth. If Nora wants to use the log detector with an antenna as an accurate instrument, she will need to get a commercial wideband antenna like a logarithmic one which is matched to 50 Ohms, to guarantee system flat response over the full band.
If Nora needs a signal indicator only, then any monopole whip or wire antenna, approximately quarter-wavelength long at band center will work. Log detectors like ADL5513 have a dynamic range > 60 dB, so signal levels from ~+10 dBm down to -50 dBm can be indicated. I have used AD8313 for the same purpose, with a monopole antenna; I can detect signals down to -50 dBm, and even point direction to their source by that simple monopole.