The objective of adaptive beam-forming algorithm is to increase SINR(Signal to Interference Ratio) or SJR(Signal to Jamming Ratio) of the received signal. Null pattern synthesis to the direction of interference or jamming signal by using a spatial separation characteristic between the user signal and the unwanted signal in the various propagation environments can be performed by using adaptive beam-forming algorithm.
A phased array antenna system for the adaptive beam-forming is classified by either a single-port phased array antenna system or a multi-port phased array antenna system.
The problem with most adaptive beam-forming imposed on the multi-port phased array antenna system is that it needs a receiver at each element in order to get the amplitude and phase of the signals to form the covariance matrix. The receivers are usually expensive and require regular calibration.
Another approach to adaptive beam-forming is to minimize the total output power of the array in the single-port phased array antenna system. Since the total output power consists of both the desired and interference signals, some constraints are needed to insure that only the interference signals are nulled and the main beam of the desired signal is little influenced.
This paper describes the study of the optimization of the adaptive beam-forming algorithm to adaptively correspond to a signal that changes in real time on a single-port phased array antenna system. Optimization algorithm based on the theory of evolution was mainly used for the null pattern synthesis in a single-port phased array antenna system but it may cause the symptoms to go into an infinite loop because it operates based on a random process. Therefore, the cost function does not converge constantly in real time environment of time varying situation in which the interference signal power level and the direction of incidence change.
In this study, an adaptive nulling algorithm for solving a variety of problems in a single-port phased array antenna system is proposed. The proposed adaptive algorithm does not require a priori knowledge of the incoming signal direction and this algorithm can maintain a continuous and stable SJR without any prior information on the incident direction of the jamming signals or interference signals in time-varying situation in which the interference signal power level and the direction of incidence change. This algorithm is the combination of the PSO(Particle Swarm Optimization) algorithm and the gradient-based perturbation algorithm, which shows stable nulling performance adaptively even on the moving jammer environment where the incident direction and the power level of the interference signal change with time.
Additionally, in this study a new technique and cost function which can classify the jamming signal and target signal from the spectral distribution of received signal in order to minimize the main beam distortion of target signal and to form nulls in the direction of the jamming signal in array antennas of single-port system is proposed. The proposed cost function is applied to the proposed algorithm which has the fast convergence and stable nulling performance.