# Performance Analysis of Amplitude Comparison Monopulse Direction-of-Arrival Estimation
## 1 Introduction  
Radar can be largely divided into search and tracking radar depending on function. Search radar is used to locate targets within a relatively wide space, and the target information acquired is the distance, azimuth and elevation of the target. In contrast, tracking radar can continuously radiate a very sharp pencil-beam towards an object providing precise spatial position information, such as target distance, azimuth and elevation. Monopulse radar is a representative tracking radar. Most modern radar seekers use the monopulse technique. Monopulse is algorithm of estimating the angular location of a target by receiving a signal from a target by multiple antennas and comparing amplitude and phase. There are several ways to measure angle information, and the most commonly used method is the amplitude comparison monopulse method, which compares the amplitude of the received signal. The classical monopulse technique [1; 2; 3; 4; 5; 6] is no longer useful, because the monopulse beams are distorted due to several causes, which may lead to angle errors. The previous papers [7; 8; 9] addressed the performance improvement of monopulse radars by reducing the angular error of targets obtained through the monopulse algorithm. In [7], the authorsconsider the problem of detecting and estimating the angle information of a radar target that is obtained by a number of antennas. The amplitude of the signal received by a number of antennas is assumed to depend on the angle information of the target, but the time-of-arrival (TOA) of the signal is assumed to be the same at all of the antennas. The generalised likelihood ratio test is used to express the detection and parameter-estimation method for the radar receiver. In Gaussian noise environment, accuracy formulas for the angle estimates, valid for high signal-to-noise ratios, are used to compare the performance of an optimum four beam monopulse system. In [8], it is shown how to permit successful communication and signal direction-of-arrival (DOA) tracking in the presence of a large number of sidelobe interferers and a small number of main-beam interferers. The author suggested to use an adaptive angle estimator, which would make its DOA estimate based on the received signal pulse and on the previously observed covariance statistics of the noises present at the four beam outputs. In [9], the theory of adaptive arrays to the angular measurement problem has been addressed. The maximum likelihood theory of angular measurement guides to adaptive sum and difference monopulse beams. An algorithm for estimating DOA, based on the outputs of adaptively distorted sum and difference monopulse beams, is shown to perform well in the presence of sidelobe and/or main beam interference. Simulation of an array in external noise has shown that the estimator provides good angular accuracy in both sidelobe interference and main beam interference environments. In [10], the authors derived explicit expressions of a particular angle as a function of the phase imbalance in the monopulse radar receiver channels. The amplitude-based angle (ABA) processor is analysed and it is shown both analytically and by computer simulations that its performance in the presence of glint is superior to that of the conventional or exact processor. The effect of amplitude-phase non-consistency on the monopulse system has been studied in [11]. Also, it deals with the problem of resolution of multiple targets and presents a novel close-form for resolving two target angles [11]. The sum-difference patterns of a digital beamforming-based asymmetric monopulse have been used for angle estimation [12]. The slope of the monopulse curve is used for studying the effect of the amplitude-phase mismatch on the estimation performance. In [13], the performance of the monopulse receivers in the secondary surveillance radar (SSR) with regard to the internal sources of error is considered. Their general performances in a Gaussian noise environment are discussed.