Regarding Jamming, following the Bruneval Raid the Germans instituted Aktion Wismar. This required that German radar be frequency agile. Seetakt was already partly Wismar compliant by 1942, however. This was because the British began jamming Calias B stations being used for directing blind fire against coastal shipping in early 1941. The German response was to make Seetakt frequency agile.Thorsten Wahl wrote: On the other hand the opponents were developing electronic counter measures
-reduce radar retroreflection
Wuerzburg (the primary AA directing radar) however, never did become very frequency agile and was more vulnerable to noise jamming tactics such as Carpet.
Freya wasn't as vulnerable to noise jamming as the Germans allowed the British to think it was. The Germans let the British think that their jamming was working well against Freya so that they would not develop more effective jamming techniques.
Freya and Seetakt encoded the sent pulses and their receivers responded mainly to echoes that contained the encoding. The British at first used frequency modulation noise jamming and this was actually more effective against the GEMA radar designs, but they dropped this and went to amplitude modulation noise jamming, which was ironically less effective.
Window was the most effective means of dealing with both Wuerzburg and Seetakt (especially Wuerzburg with conical scan), at least until Wuerzburg developed MTI. Window wasn't used much at sea though, but had there been a real need, MTI could have been added to Seetakt fairly easly.
The Germans developed a jamming technique that jammed the lobing or scanning frequency. This was why Type 274 couldn't spot the the fall of shot. The tranmitted beam wasn't scanned or lobe switched, so that the scanning frequency would remain hidden from the enemy. It therefore couldn't detect splashes falling outside of the very narrow beam of less than 1*. Seetakt also used Lobe On Receive Only from 1940 onward as well. USN FC radars such as MK8 and Mk13 were very vulnerable to this type of counter measure.
The Germans were the leaders in development of reduced radar cross section by experimenting with Stealth aircraft ideas and stealth U-boat conning towers and so forth. Of course reducing the radar cross section of large WWII warships isn't practical even now.