Comparative analysis of lumped and distributed reflective shunt attenuators

In many applications, selection of a reflective variable attenuator is based upon performance requirements such as dynamic range, bandwidth and switching speed. This paper presents an analysis of lumped and distributed reflective shunt attenuators and compares their respective performance in terms of dynamic range and bandwidth. The variable attenuators are explored as a function of the number of shunt elements and element resistances. It is shown that the attenuation from a lumped attenuator increases by about 6dB for every doubling of the number of shunt elements, while the attenuation more than doubles in dB in the case of a distributed attenuator. For both cases, the attenuation improves by about 6dB when the element resistances are halved. In addition, an approximate equation that is useful for hand calculations is provided for the distributed attenuator.