tailieunhanh - Giai đoạn mảng anten P6

Fixed beam arrays are usually either linear arrays or assemblies of linear arrays to make a planar array. Thus the linear array is a basic building block. When the array elements are in series along a transmission line, the array is termed “series.” Similarly, when the elements are in parallel with a feed line or network, the array is termed “shunt.” A further division of series feeds is into resonant or standing wave feeds, and travelling wave feeds. Shunt feeds are generally of corporate type, or distributed. Each of these types is discussed below. . | 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 SIX Array Feeds Fixed beam arrays are usually either linear arrays or assemblies of linear arrays to make a planar array. Thus the linear array is a basic building block. When the array elements are in series along a transmission line the array is termed series. Similarly when the elements are in parallel with a feed line or network the array is termed shunt. A further division of series feeds is into resonant or standing wave feeds and travelling wave feeds. Shunt feeds are generally of corporate type or distributed. Each of these types is discussed below. SERIES FEEDS Waveguide slots lend themselves to series feeding as they are spaced along the transmission feed line waveguide . This is independent of whether the slot equivalent circuit is series or shunt see Chapter 5. Dipoles are usually more suited to shunt feeds. Microstrip patches can be fed in series by microstrip lines connecting adjacent patches but these arrays offer much less control over the array excitation. Since most series-fed arrays use waveguide slots these are emphasized both for resonant and for travelling wave arrays. Figure shows an experimental single waveguide array with longitudinal slots. Resonant Arrays Impedance and Bandwidth. The most common resonant array is a waveguide with slots at half guide wavelength spacings with the guide ends shorted and with power coupled in or out along the guide. The end shorts allow standing waves to exist and the Ag 2 spacing allows all slot radiators to be in phase. Such a waveguide array is called stick planar arrays are made up of closely packed sticks. Ideally the sum of slot conductances should equal unity and the sum of slot susceptances should equal zero for shunt slots. The obvious limitation of resonant feeds is that they are resonant at only one frequency Over a bandwidth the slot .