### I. Introduction

### II. Baseline Determination in Bistatic SAR

*B*, the altitude of the satellites is

*H*, and the look angle at the transmitter is represented as

*θ*

_{L}. Notably, the transmission/reception satellites were synchronized and operated in simultaneous transmission mode. Notably, for a given pulse repetition frequency (PRF), the bistatic SAR in Fig. 1 bears the blind look angle at which the return signals travel along path

*r*

_{T}+

*r*

_{R}to reach the satellite during transmission.

*B*. The other is the common plane specular echo reflected by the Earth’s surface between the two satellite trajectories along path length 2

*r*

_{s}.

*H*= 500 km and

*B*= 200 km. The red stripes represent the blind look angle, while the blue and green stripes are the footprints of the direct signal and the common plane specular echo, respectively. The direct signal and the specular echo disturb the sensing of return signals from the observation area. Therefore, for a fixed PRF, swath widths are limited only to the look angles that do not correspond to the blind angles and are not disturbed by the direct signal and specular echo. As shown in Fig. 2, for a PRF of 14,400 Hz, the observable area for the bistatic SAR is quite narrow for

*B*= 200 km. Furthermore, the frequency of the PRF range is slightly higher than expected. This may be attributed to the antenna used in the simulation in this study, which was manufactured by the authors in their own laboratory, with dimensions of 1.5 m width and length in a parabola configuration [15]. Notably, the PRF should be high enough to be high enough to avoid ambiguity.

*H*, this study took recourse to forbidden arrival times, expressed as Eqs. (1)–(3), where

*T*is the pulse repetition interval (PRI) of the transmitted signal and

*l*,

*m*, and

*n*are the integers including zero.

*t*

_{D}(

*l*) and

*t*

_{E}(

*m*) are the forbidden arrival times resulting from the direct signal and the specular echo, respectively, while

*t*

_{B}(

*n*) is the forbidden time for transmission. If three forbidden arrival times occur at the same time, the forbidden look angle can be minimized.

*t*

_{D}=

*t*

_{E}can be easily estimated. However, the

*t*

_{B}might not always coincide with the other two since it is quantized by the PRI. For instance, in Fig. 2, it can be observed that for B = 200 km, the

*t*

_{D}coincides with

*t*

_{E}at PRF = 14,300 Hz, but

*t*

_{B}has different values. Fig. 3(a) displays the arrival times when the baseline changes for PRF = 14,300 Hz. The

*t*

_{D}(blue) and

*t*

_{E}(green) are coincident for

*B*= 175 km and 200 km, but the

*t*

_{B}does not coincide for both baselines. Therefore, to find the accurate PRF and baseline at which three arrival times coincide simultaneously, repeated calculations are necessary. As the PRF changed, the baselines satisfying

*t*

_{D}=

*t*

_{E}were first identified, and then their coincidence with

*t*

_{B}was checked. After conducting iterations of the above process, the proper PRF and baseline at which the three signals arrived simultaneously were identified. For PRF = 14,400 Hz, Fig. 3(b) shows that

*t*

_{D}=

*t*

_{E}for

*B*= 182 km and 208 km, but the arrival times of the three signals collapse into the same instance only for

*B*= 208 km.

### III. Bistatic SAR System Performance Evaluation

### 1. Ambiguity-to-Signal Ratio

*G*

_{t}(

*θ*)/

*G*

_{r}(

*θ*); , the transmission/reception slant range

*r*

_{T}/

*r*

_{R}, the bistatic angle

*β*, the aspect angle

*ψ*, and the angle at which the ambiguity signal occurs in the range direction angle

*θ*

_{A}. In particular, bistatic RASR can be expressed as in [13, 16]. Notably, when receiving the

*n*-th signal, the ambiguity ratio can be calculated using the ratio of the

*n-*th received signal to the other signals.

##### (4)

*G*

_{t}/

*G*

_{r}), the bistatic angle (

*β*), the aspect angle (

*ψ*), and the transmit/receive slant range (

*r*

_{T}/

*r*

_{R}) caused by the separation of the transceiver. When the PRF reached 14,400 Hz, the baseline with the maximum swath width was assumed to be 208 km. It was also assumed that the two satellites maintained the same speed at an altitude of 500 km, as well as the same baseline and fly parallel, and that both were operating in stripmap mode.

*θ*

_{AZ}is the azimuth angle.

### 2. Resolution

*θ*

_{i}) and cos(

*β*/2)cos (

*ψ*) terms also increased, as a result of which improvements in the ground range resolution performances of both monostatic and bistatic SAR were observed.

*L*

_{T}being the size of the transmission satellite antenna.

*r*

_{T}is larger than

*r*

_{R}, which means that the bistatic azimuth resolution performs better than its counterpart. It is further observed that as the incidence angle increases,

*r*

_{T}becomes longer and the azimuth resolution value becomes lower.

*P*

_{t}is the transmission power,

*G*

_{T}is the transmission antenna gain,

*G*

_{R}is the reception antenna gain,

*λ*is the wavelength,

*k*the Boltzmann constant,

*V*

_{s}is the satellite speed,

*τ*is the pulse width,

*T*

_{0}is the thermal noise,

*NF*is the constant noise,

*BW*is the transmission bandwidth, and

*L*

_{t}is the system’s total loss.