The antenna consists of about 1500 slotted waveguide pairs, and each of them has a T/R 
module attached to its rear. All modules are connected to an RF-feeding network, power lines 
and control circuits. Furthermore, directional couplers for calibration of each transmit /receive path 
which rely on a separate feeding network are included. 
4 - SCANSAR MODE 
The pixel size of 10 m x 10 m and four-looks limits the swath width to the values given 
in Fig. 5. An increased swath width can be achieved by using SCANSAR operation instead of 
the normal strip-mapping mode. In SCANSAR operation the length of the synthetic aperture is 
divided, for instance, in 3 shorter apertures. Accordingly, the pixel size will be approximately 3 
times larger, assuming the chirp bandwidth is only 1/3 of the one used for standard strip mapping 
mode. Fig. 8 shows the achievable increase of swath width and S/N improvements due to the large 
pixel size in reference to S/N = 10 dB assumed in strip mapping mode. Fig. 9 shows the small 
variations of radiometric resolution due to the good S/N. 
Such an active phased array system has overall losses which are about 10 dB lower (in SAR 
operation) than those of the conventional passive antenna systems used in X-SAR and ERS-1. The 
expected values for the analysed system are quoted in Table 1. 
one-way loss [dB] 
two-way loss [dB] 
antenna & waveguides 
0.5 
1.0 
integration over antenna main lobe 
0.9 
1.8 
receiver noise figure 
2.5 
atmosphere 
0.2 
0.4 
quantisation and processing 
2.0 
sum 
7.7 
Table 1: Estimation of system losses. 
These values are also based on industrial studies which are continuing. Achieved results for backseat - 
tered energy Eire discussed in the next section. 
5 - AVERAGE TRANSMIT POWER FOR SIGNAL TO NOISE RATIO OF 
lOdB 
For computations of the minimum required transmit power, the following assumptions have 
been used: 
• Empirical equations for the average backscatter coefficient [2] 
• Gain adaptation (Fig. 3) and band width adaptation (Fig. 1).