Circuit analog absorbers

We finally note that an array with a groundplane and resistive loads actually belongs to a simple form of circuit analog absorbers. This relationship was pointed out in reference 54 and is also discussed in a different context in Section 6.12.1.4. 

Certainly, we have produced a loaded groundplane impedance Zi+ that does not go through zero over a considerable frequency range. However, we have in effect merely produced an absorber, or more precisely a circuit analog absorber. For an in-depth discussion about this type, see Chapter 9 in reference 102. 

One paper in particular was investigating a combination of circuit analog and Jaumann absorbers. It was the result of a computer optimization process apparently without any consideration of physics. In less than 10 minutes 1 spotted the first fundamental and disastrous design flaw The interelement spacings were larger than a full wavelength For the author such an observation is an extremely emotional affair. It simply means that grating lobes are present in some bistatic... 

With analogy to electric circuits, a transfer function of the antenna can be calculated and the response of the antenna to an incoming wave obtained. The output signal is usually expressed as antenna cross-section. It is defined as the ratio between the total energy absorbed by the antenna and the incident spectral density function of the incident wave. In the case of Nautilus antenna (2300 kg, 3 x 0.6 m) the cross-section is of the order of 10 25m2 Hz. 

Radiant energy incident on a partition with holes partly escapes the partition and is partly absorbed by and reflected from the partition. Accordingly, the analogous electrical circuit, including the energy that escapes the partition, may be constructed as shown in Fig. 9.25. 

---