Practical_Antenna_Handbook_0071639586

508 P a r t V I : A n t e n n a s f o r O t h e r F r e q u e n c i e s
Interferometer Antennas
The resolution of an antenna is a function of its dimensions relative to the wavelength
l of the received signal. Better resolution can be achieved by increasing the size of the
antenna, but that is not always the best solution and beyond a certain point is totally
impractical. Figure 22.8 shows a summation interferometer array. Two antennas, each with
aperture a, are spaced S wavelengths apart. The radiation pattern is a fringe pattern
(Fig. 22.9), consisting of a series of maxima and minima. The resolution angle f to the
first null is
S a
f = +
57.3
(22.6)
The interferometer can be improved by adding antennas to the array. Professional
radio astronomers use very long or wide baseline antennas. With modern communications
it is possible to link radio telescopes on different continents to make the widest or
longest possible terrestrial baseline.
Figure 22.8 Interferometer array.