Promising preliminary results are presented for an isolator in finline structure using hexaferrite thick film. The nonreciprocal properties of this structure were measured in the frequency range 44-50 GHz. The experimental results exhibited an isolation in excess of 30 dB between 47.7 and 49 GHz. At 48.5 GHz the forward-to-backward ratio was greater than 20. It is suggested that such structures would be suitable for higher frequencies.