The WR28 Circulator, which is specified over 35.5-36.0 GHz can also be offered as an isolator by the addition of a TRAK termination. The device was design for Space applications and has been supplied as a qualified FM.

WR28 Circulator
Parameter Value Measure
Operating Frequency 35.5 to 36.0 GHz
Operating Temperature -20 to +80 C
Insertion Loss 0.10 dB max.
Return Loss 23.0 dB min.
Isolation 23.0 dB min.
Forward/Reverse Power 1 W CW

Note that each flange on the WR28 Circulator has through holes which does mean that the device are a little larger than the standard 19.05mm (across the opposing ports) although alternative version with any combination of standard and non standard flange arrangement can be provided. The following is a typical room temperature plot at 10dBm input power.
WR28_36 GHz