The effect of mutual coupling on the performance of adaptive antennas has been a topic of considerable interest for the last three decades. The general conclusion of the work reported in the open literature is that mutual coupling degrades the performance of adaptive antennas. We have carried out an in-depth study of the effects of mutual coupling on the performance of adaptive antennas. Our studies show that this conclusion is not entirely correct. Yes, one does need the in-situ array manifold to obtain the fi xed response in the desired signal direction. Otherwise, adaptive weights can also suppress the desired signal. Note that for adaptive antennas based on minimizing the mean squared error between the array output and a locally generated reference signal, this is not an issue. However, mutual coupling between antenna elements hardly affects the nulling performance of adaptive antennas. In fact, in a given size aperture, as the number of antenna elements is increased, one obtains better nulling performance, irrespective of the increased mutual coupling between antenna elements. Also, as expected, for strong wideband interfering signals, one should carry out space-time adaptive processing (STAP).A daptive-antenna array systems constitute a multidisci pline technology area that has spanned a number of dec ades in the engineering and scientifi c community, due to advances in electromagnetics and signal processing [1][2][3][4][5][6][7][8]. Adaptive arrays consist of antenna elements that sense the signal environment, and a real-time signal processor that automatically optimizes a user-defi ned metric, such as signal-to-noise ratio (SNR), by combining the weighted output of each element (or channel). Adaptive antennas thus can provide real-time adaptive nulling and beamforming. They have appli cations in radar, navigation, RF communication systems, seismic analysis, and sonar [8].The origins of adaptive nulling can be found in the 1960s, when a sidelobe canceller was developed to aid in radar applications [9], and the least-mean-square (LMS) error algorithm was established based on the steepest-descent method [10]. Both of these contributions enabled automatic interference suppression without knowledge of the interferers. Therefore, a weak desired signal can be extracted from a environment with strong interferers [11]. Experimental verifi cation of adaptive nulling was given in [12,13]. Over the decades, the research expanded to provide improvement in convergence, tracking, robustness, power consumption, and versatility of the signal-processing algorithms [2,6,14,15]. In addition, research in adaptive array applications was extended in the areas of radar [16,17] and varying communications systems, such as spread spectrum, TDMA, CDMA, TOA, and indoor radio [18][19][20][21][22][23][24][25]. A third major area of research for adaptive arrays is the effect of the antenna array design itself on its performance in the adaptive mode [26][27][28][29][30][31][32][33][34][35][36][37]. The element pattern [26,27,31], distrib...
An adaptive antenna for handheld GPS receivers is presented. The antenna has a small aperture, small volume, and is lightweight. The antenna uses four spiral elements to provide broadband satellite coverage and can also be used in conjunction with a space‐time adaptive processor (STAP) for interference suppression. The antenna with integrated feed is easy to fabricate as well. The performance of a simulated and experimental antenna is compared and found to be in agreement. Finally, the nulling performance of the antenna is examined for a few simple interference scenarios.
An adaptive antenna for handheld GPS receivers is presented. The antenna has a small aperture, small volume, and is lightweight. The antenna uses four spiral elements to provide broadband satellite coverage and can also be used in conjunction with a space-time adaptive processor (STAP) for interference suppression. The antenna with integrated feed is easy to fabricate as well. The performance of a simulated and experimental antenna is compared and found to be in agreement. Finally, the nulling performance of the antenna is examined for a few simple interference scenarios. ANTENNA DESIGNAn adaptive antenna for a handheld GPS receiver needs to possess a number of electrical and physical characteristics. The first electrical characteristic is three-dimensional interference suppression. To provide this, the antenna needs to have at least three elements. The second electrical characteristic is satellite signal reception. For this, the antenna needs to have a broad right-hand NAVIGATION:
Recently, there has been increased interest in GPS navigation for spinning cylindrical platforms (60-160 mm diameter). As expected, a single antenna element does not provide spherical coverage which is needed for continuous satellite tracking. To provide the desired coverage, one can use antenna diversity with multiple antenna elements. Previously, different antenna diversity techniques were compared, and it was shown that the maximum gain method (i.e., choosing the element with the highest gain) provides the spherical coverage. However, it is a challenge to implement this method because of the unknown time-varying platform attitude. In this paper, a novel tracking algorithm is derived that implements the maximum gain method by modifying the receiver itself. Example results are shown for the delay lock loop (DLL) and demonstrate that the proposed approach is able to provide continuous satellite tracking as the platform rotates and eliminate the need for knowledge of the timevarying platform attitude.
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