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a. Constant Amplitude Excitation b. Cosine Amplitude Excitation Figure 12: Array Factor versus Element Amplitude Variation (note logarithmic amplitude scale) Microstrip antenna arrays will be further explored within the electromagnetic simulations of the following sections. In many instances, the element spacing for most applications is approximately half-wavelength (l 0 /2) in air. Although somewhat higher gain may be attained, using element spacing beyond half-wavelength produces high sidelobe levels, particularly near ±90° off boresight. Therefore, in the simulations to follow, element spacing in the plane of the antenna will be approximately half-wavelength. LINEAR MICROSTRIP ARRAY ANTENNAS Figure 13 illustrates the configuration of a parallel feed – alternately referred to as corporate feed – linear array composed of four, in-line elements. Each element of the linear array is fed from the output of a power divider which facilitates excitation of either equal or unequal power to each element. The power distribution to the elements of an array, as previously indicated, is commonly referred to as amplitude taper and is utilized to reduce sidelobe levels. Unequal amplitude taper is accompanied by main beamwidth extension and reduced gain with respect to uniform, or equal, power distribution to each element. The excitation to each element of the array may also be varied in phase. Progressive differential phase excitation is employed to steer the main beam off- boresight, and is a unique and attractive feature for large phased array radar applications as an alternative to inertial (mechanical) platforms. A four element linear array has been constructed using the single element, 5.80 GHz microstrip antenna previously described and analyzed. The data from EM analysis of the four element array is summarized in Table VI below. 0 30 60 90 120 150 180 15 - 10 - 5 - 0 5 10 15 ß = 0° Elevation Angle ( q) Array Factor Amplitude 0 30 60 90 120 150 180 15 - 10 - 5 - 0 5 10 15 ß = 0° Elevation Angle ( q) Array Factor Amplitude Figure 13: Four-Element Linear Array Microstrip Antenna Design 16 www.cadence.com/go/awr

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