BFN can be classified into following categories of characteristics:
1. Radiation modes: directional, omnidirectional or both switched directional and omnidirectional;
2. Different systems: transmitting, receiving or both switched transmitting and receiving;
3. Single-beam or multi-beam radiation pattern;
4. Percentage bandwidth: narrowband (15 %), moderate band (15% - 25%), and wideband (over 25%);
5. Passive or active;
6. Single layer or multilayer PCB;
7. Different transmission lines;
8. Switched or non-switched circuit;
9. With or without phase shifter(s);
10. With or without crossovers;
11. Configuration of elements: distributed elements, lumped elements or combination of distributed and lumped elements.
The main requirements and characteristics of BFN: frequency range, bandwidth, input/output impedances, matching, isolation between terminals, insertion loss, phase and amplitude imbalance, number of beams, switching time, maximum power, size, environmental stability, cost. Fig.1 illustrates the design flow of a printed BFN. The definition of the system level specification is the first step in the design flow. This involves both the system level requirements which are applied directly to a BFN, and the derived requirements which depend on system requirements. BFN specifications include electrical, cost, size and other requirements. RF specification also includes margin for manufacturing tolerances, environmental conditions, and performance degradation over system’s life. For all requirements, a designer has to choose consecutive integer values of weighting coefficients ki corresponding to each parameter (step 2 of design flow), from k = 1 for the most important parameter. The maximum value of k can be less than or equal to the number of parameters, depending on whether some parameters are considered to have the same importance or not. Selection of a BFN prototype (step 3 of design flow) must take into account the corresponding weighting coefficients.