You must write a detailed post on both the RISATs,
so I can plagiarise it for my article
RISAT program was approved in 2003 and the main role of the satellite was civilian applications while the secondary role was military applications.Hence it was decided that the satellite will be using an indigenous C-band SAR. The target launch was in 2007,but was significantly delayed because of the complex technologies involved in it and these problems were accompanied by the fact that these kind of technologies were developed 1st time inhouse. Then in 2008, 26/11 happened and this pushed the need for a dedicated ,all weather high resolution satellite. Hence it was decided to use an Israeli X-band SAR based on Israeli TecSAR-1 radar satellite which was launched by PSLV.
Israeli TecSAR-1
Thus RISAT-2 was developed in a short span of time using an Israeli X-band SAR and was launched in 2009.
RISAT-2 launched in 2009
Later RISAT-1 was launched in April 2012.
RISAT-1
Later ISRO divided RISAT series into 2 types called RISAT-1 series using a C-band SAR for civilian applications and RISAT-2 using X-band SAR for military applications.Thus RISAT-1 & 2 series of satellites were developed for civilian and dedicated military applications.Again RISAT-2 series was divided into 2 types called RISAT-2A series using an indigenous AESA based X-band SAR and RISAT-2B series using a Radial Rib antenna based X-band SAR similar to that of TecSAR-1 & old RISAT-2. Hence I suspect that RISAT-2A series uses indigenous X-band SAR while RISAT-2B uses an Israeli X-band SAR( Israeli origin is my assumption)
Thus there a 3 types of RISATs .
RISAT-1 series using a C-band SAR for civilian applications . satellites in this series are RISAT-1,1A,1B .
RISAT-2B series using an X-band SAR (probably Israeli radar) with Radial Rib antenna for dedicated military applications . Satellites in this series are RISAT-2B, RISAT-2BR1 & RISAT-2BR2.
RISAT-2BR1 with Radial Rib antenna similar to TecSAR-1 & old RISAT-2.
RISAT-2A series using an Indigenous AESA based X-band SAR for military applications. 25cm resolution.
RISAT-2A using Indigenous AESA based X-band SAR.