# Analysis of a Bistatic Ground-Based Synthetic Aperture Radar System and Indoor Experiments
## 4 Discussion  
The bistatic GB-SAR configuration is beneficial for the study of bi-directional scattering properties of targets, which provides better performance in target identification and classification. However, the image quality of a bistatic GB-SAR configuration would be less than that in the monostatic one due to the following four major reasons.  
Firstly, the degradation of range resolution at an extremely near range occurs due to the inherent bistatic geometry as shown in Equation (3). However, this effect would be negligible for most of the usable range for airborne, satellite, or GB-SAR operations where \(B/r\) is negligible.  
Secondly, the reduction in coherent integration length and thus azimuth resolution occurs with increasing baseline \(B\), as shown in Equation (8) and in Figures 5-7. One can use squint operation of Tx and Rx so that antenna footprints overlaps completely with each other.  
Thirdly, the returned power would be reduced especially for strong uni-directional backscattering targets such as trihedral corner reflectors. Most natural targets are bi-directional scatterers, and such bistatic operation will be advantageous to assess the scattering property of natural targets. Manufactured targets may have well-known scattering properties and such bistatic SAR configurations would be helpful for target identification and reconnaissance purposes.  
Lastly, a complex geometry of bistatic configuration may be a hurdle for the use of approximation in the frequency-domain SAR focusing algorithms as shown in Equation  
Figure 6: Bistatic GB-SAR focused image by (**a**) RDA and (**b**) BPA for \(B=0.5\) m.  
Figure 7: Bistatic GB-SAR focused image by (**a**) RDA and (**b**) BPA for \(B=1\) m.  
(16). More sophisticated SAR focusing algorithms should be developed for bistatic SAR operations onboard airborne or satellite configurations for faster SAR processing. In any case, BPA, which is slow but accurate, would be a good reference for the evaluation of the other frequency-domain focusing algorithms.  
In this experiment, we used a Ku-band system to achieve high resolution in a conventional lecture room--a large bandwidth with small antenna aperture. The results show that such an experiment can be done cost-effectively with no high-end facilities such as an anechoic chamber.  
The purpose of this experiment was to simulate the case of a satellite mission where Tx is followed by an Rx (or vice versa) with no specific target distance or squint operation. Although the indoor experimental setup allows relatively small _B/r_ of 0.5\(\sim\)0.01, it can detect the bi-directional scattering effect of targets. This is just one case study of many bistatic SAR configurations. The GB-SAR system is versatile to use various frequencies and bandwidths as far as the antenna characteristics are supported. Other bistatic modes can also be applicable such as the bistatic SAR with larger _B/r_, one with squint operation, one-stationary-and-one-moving antenna mode, and one with arbitrary antenna positions. The system can also be extendable to multistatic modes by adding microwave switches. More sophisticated bistatic cases will be reported separately in the near future.