in "Lessons in Electric Circuits", VOL III, ChPT 14, all the possible configurations of standing wave for a certain transmission line are shown. For instance, this is the case of a transmission line left open at the ends:
According to the operating frequency and the transmission line characteristics, there may be:
My question is: do these different configurations of standing waves exist simultaneusly (i.e. the total voltage and current waveforms are their superposition) or does each of them exclude each other?
From the author's analysis, it looks like there is only one of these configurations, at a certain frequency. But I've seen many similar situations in which there is a superposition of standing waves. For instance, I'm thinking at the analogy with a rectangular waveguide:
In this situation there are not V and I, but only E and H fields, but the situation is similar: the metallic surfaces of the shell's lateral wall set the condition $$E = 0$$ (as well as I = 0 or V = 0 are set respectively by the open circuit or the short circuit at the end of a transmission line), which may determine the standing waves shown in figure.
For this structure, I've always been told that all these modes exist simultaneously: when a source is put inside the waveguide, it excites all propagation modes, some of which are above cut-off (and will propagate) and some other which are below cut-off (and will be attenuated). So, according to the operating frequence, multiple standing waves may exist.
Is there a similar situation, with cut-off standing waves frequencies, for transmission lines?