In this paper, we consider the design of the BFN for wideband steered arrays providing the advanced beam features considered above.
To attain a wideband (beam-squint free) steering, the BFN is designed by exploiting the TTD principle , and the phase shifter approach must be avoided.
Indeed, optics allows to naturally implement the TTD principle, thus realizing ultra-wide band beam-squint free phased arrays with high interference immunity, low size and weight BFN's.
It is modular, since different TTDU's can be easily grouped together, on the one hand to build control units of larger and larger arrays, and, on the other hand, to improve the driving performances of the BFN for a fixed array dimension.
Taking all the above into account, a novel Nolen matrix based modified topology was utilized in order to design the architecture of the BFNs presented herein.
BFN provides an array with appropriate amplitude and phase excitations, whereas each BFN input port corresponds to a discrete radiated beam in space.
The basic building block of most spaceflight heritage passive switched BFNs is the ferrite Y-toroid switch.
The two BFNs are configured to serve, respectively, the East and West families of hopping spot beams.
The building blocks of passive variable BFNs are ferrite variable power dividers (VPD), phase/amplitude control modules (PAC) and phase shifters.
For this reason, as well as their lower level of insertion loss, VPDs are generally preferred over PACs in variable BFNs for transmit applications.
Since the four beams are independently formed by four separate sets of active elements and beam-forming networks (BFN), there is no intermodulation (IM) phenomenon for this four-beam phased-array antenna.
In addition, a complex and expensive BFN is required to provide the needed control, power and phasing distribution for all of those elements.