FREQUENCY / PHASE EFFECTS OF ANTENNAS
[attachment=16066]

The radiation patterns of the antennas presented in the previous section are for antenna geometries most commonly
used. The antenna should be viewed as a matching network that takes the power from a transmission line (50 ohm, for
example), and matches it to the free space "impedance" of 377 ohms. The most critical parameter is the change of VSWR
with frequency. The pattern usually does not vary much from acceptable to the start of unacceptable VSWRs (> 2:1). For
a given physical antenna geometric size, the actual radiation pattern varies with frequency.


LINEAR PHASED ARRAY
The linear phased array with equal spaced elements is easiest to analyze and forms the basis for most array designs.
Figure 3 schematically illustrates a corporate feed linear array with element spacing d.


ROTMAN BOOTLACE LENS
Another method of feeding an array of
elements is to use a lens such as the Rotman
(rhymes with rotten) Bootlace type shown in
Figure 5. The lens consists of a parallel plate region
(nowadays microstrip or stripline construction) and
cables of specified length connecting the array of
elements to the parallel plate region. The geometry
of the lens and the cable lengths are designed so that
all ray paths traced from a beam port on the right
side to its associated wavefront on the left array port
side, are equal