Freedom from Feedback

As a theoretical rule of thumb, a good decoupling requires a distance of 5 to 10 λ. ¹⁾ In practive, in most cases a distance of 3 λ is sufficient.

λ = v/f with v∼3×10⁸ m/s.

At 2.1 GHz (e.g. UMTS) the formula returns 300'000'000/2'100'000'000 = 300/2100 = 0.14m.

Three λ will then be 0.42m i.e. 42cm.

For GSM-R Deutsche Bahn requires a decoupling of up to -60 dBm. According to a simulation of one of our antenna supplier a distanec of 350 cm is sufficant to fulfill this requirements

Source: entkopplung_gsm-r_-_v02.pdf