A dual polarised active phased array antenna with low cross polarisation for a polarimetric airborne SAR

In the Netherlands, a polarimetric c-band aircraft SAR (synthetic aperture radar) is under development. The project is called PHARUS, an acronym for phased array SAR. This instrument will serve remote sensing applications. The antenna system will contain 48 modules (expandable to 96). A module is composed of a transmit/receive (T/R) module, a microstrip patch antenna and both are connected via a ratrace or hybrid ring. The antenna shall have an azimuth scan range of +/-20° and an elevation scan range of +/-15°. With a centre frequency of 5.3 GHz ( = 56 mm) this results in an element spacing of 41 and 44 mm. These are also the cross-section dimensions of the module. The cross-polarization of the microstrip patch antenna is reduced by feeding the two probes of the patch simultaneously. The ratrace, which is used as a splitter, has also other useful properties. A monitoring channel is implemented for the internal calibration of the antenna system