To jam an active radar signal you must overwhelm the returns from the jamming targets active radar with your own transmissions. There are weapons systems that a

To jam an active radar signal you must overwhelm the returns from the jamming targets active radar with your own transmissions. There are weapons systems that are designed to home in on these emissions and use them for targeting e.g. HARM. With the advent of networked multispectral frequency hopping radars you would have to have a tremendous power source to jam radar in any geographically significant area and then those power sources become large juicy targets. So it is not usually a long term solution to jam modern radar but you can gain a temporary tactical advantage.