Schottky diodes for X-band mixer (HSMS-8202, BAT15-04R, etc.)
From what i know:
Most popular is HSMS-8202 (marking "2R", 2 in series)
Sometimes it is BAT15-04R (marking "4R", 2 in series)
Recently i found unknown 2-series schottky diode in small package with marking "S11s" (maybe it is Infineon BAT diodes, but i did not found datasheet. Although marking is very similar to BAT15-04W: "S8s"). If somebody familiar with schottky diodes can be used at this frequency please share you knowledge.
Any of the mentioned Schottky diodes are good at X-band.
The secret of a good mixer is in the design (open any satellite Ku-band LNB and see how it is done_), and a good LO input power , >10 dBm for a typical balanced mixer.
In balanced mixers, at the RF port the diodes are "in parallel", o RF port impedance is close to 50 Ohms. LO port sees the diodes "in series", so LO port impedance is >150 Ohms. IF matching is also lose to 50 Ohms. All above is good for wideband mixers with a stable LO frequency.
While ago I did replace in a microwave down-converter mixer an HSMS-8202 with BAT-15.
After that replacement the mixer needs more LO power and the conversion loss was higher. Everything went normal when I found for replacement the original HSMS-8202.
I am not familiar with BAT15 specifications, so I cannot compare them with HSMS series.
I used HSMS diodes in detectors and mixers and they were good.
\Replacing original diodes by other type is often bringing a bit poorer performance, the poorer the higher the frequency.