tailieunhanh - Giai đoạn mảng anten P2

Basic Array Characteristics This chapter is concerned with basic characteristics of linear and planar arrays, primarily with uniform excitation. The theory of, and procedures for, the design of array distributions to produce narrow-beam, low-sidelobe patterns, or shaped beams, are covered in detail in Chapter 3. Impedance effects due to mutual coupling are treated in Chapter 7. | Phased Array Antennas. Robert C. Hansen Copyright 1998 by John Wiley Sons Inc. ISBNs 0-471-53076-X Hardback 0-471-22421-9 Electronic CHAPTER TWO Basic Array Characteristics This chapter is concerned with basic characteristics of linear and planar arrays primarily with uniform excitation. The theory of and procedures for the design of array distributions to produce narrow-beam low-sidelobe patterns or shaped beams are covered in detail in Chapter 3. Impedance effects due to mutual coupling are treated in Chapter 7. Covered here are such parameters as pattern beamwidth bandwidth sidelobes grating lobes quantization lobes and directivity. UNIFORMLY EXCITED LINEAR ARRAYS Patterns In general the excitation of an array consists of an amplitude and a phase at each element. This discrete distribution is often called an aperture distribution where the discrete array is the aperture. The far-field radiation pattern is just the discreet Fourier transform of the array excitation. The array pattern is the product of the isolated element pattern and the isotropic array factor this is the forced excitation problem. To achieve this the element drives are individually adjusted so that the excitation of each element is exactly as desired. More common is the free excitation situation where the element drives are all fixed and the element excitations are those allowed by the scan impedance. The latter is discussed in detail in Chapter 7. Here the concern will be only with the forced excitation array where the excitations are constant in amplitude but may have a scan phase. A common notation in the antenna literature is used here where X is wavelength d is element spacing k 2n k and the angular variable is w. The latter is u sin 0 sin 0Q where 0Q is the scan angle. Uniform equal spacing is assumed in this chapter unequally spaced arrays are discussed in Chapter 3. Although it is simpler to have a coordinate system axis in the center of a linear array complications ensue for .