Why would it matter if the loop transfer function had high amplification of radio waves if nothing else could respond to such high frequency inputs?
An important topic of robust control is to design controllers that make the closed-loop system more robust to disturbances and to sensor noise. Thus, we seek to reduce the maximum value of the load sensitivity transfer function PS = P/(1+PC) and the noise sensitivity transfer function CS = C/(1+PC). Of course there may be instances when we want to amplify certain inputs at a particular range of frequencies. In this case we want the open loop transfer function to have high amplification in that frequency range. The point is to attenuate undesirable effects cause by exogenous inputs and for L to have high gain at certain frequencies if this gives a desirable outcome (i.e., we want L to have high gain up to a certain frequency for good reference signal tracking). --Soto 22:14, 26 November 2007 (PST)