Two axis direction finding antenna system using difference-sum patterns in x-band
Shaikh, Sarmad Ahmed (2015) Two axis direction finding antenna system using difference-sum patterns in x-band. [Thesis]
This thesis work proposes the direction finding antenna system in two axis (θ,∅) in x-band (8 to 12 GHz) using difference (Δ) and sum (Σ) patterns of received signal. Direction finding system is constructed using microstrip patch antennas array and 180º hybrid rat race ring coupler which generates Δ and Σ of two received RF signals. Individually, both coupler circuit and antenna elements are optimized in terms of feed location and size using ADS electromagnetic simulation software. In this work, 10 GHz frequency of operation is chosen. Initially, direction of arrival (DOA) is obtained in one axis (θ) using the patterns of Δ and Σ ports of antenna array of two elements. Using the equations of Δ and Σ of two input signals, radiation patterns at different θ values have been observed in simulation and compared with measured pattern values of constructed circuit. By taking the ratio of Δ to Σ patterns, DOA has been estimated of designed circuit. Later, another DOA circuit in other direction (∅) is constructed and DOA has been estimated. By taking the 3D patterns of each circuit in anechoic chamber, both of these circuits are simulated and measured for performance; and from -40 to +40 degrees DOA has been observed with rms error of less than 5 degree in both axis with phi angle from 0 to 180 degrees. Another circuit which combines all these four antennas into one system also has been simulated. At 10 GHz operating frequency, experimental results using material RT Duroid 5880 (εr =2.2, thickness = 1.575mm) show that satisfactory performance can be achieved with proposed setup.
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