pulse width is line delay
The pulse width is the line delay. This is the only military approved way to generate pulses. They disallow one shots. The usual way is to use a lumped element LC delay line, but for your short pulses a regular line is better.
The RF switches are to switch in different lengths of line for different pulse widths. Some logic families have programmable delays in ps range increments.
A detailed view of how the XOR-delay line single shot works is as follows. In steady state, the line to one input of the XOR and the output of the delay line to the other XOR input have the same logic level which makes the XOR output low.
When the input line changes state, one input to the XOR changes state immediately while the change in logic level at the input of the delay line starts traveling down the line. Before it reaches the end and the other input of the XOR, the inputs to the XOR are different and the output goes high. After the chagnge of logic level gets to the output of the delay line and the other input of the XOR both inputs to the XOR are at the same logic level and its output returns to zero. Therefore, the XOR output pulse width is equal to th delay line time delay.
If you want only high transition triggering, you supress the low going triggering by putting a AND gate at the output of the XOR and feed the input line to it as well. That way a low going input line will block the XOR output.
The first oscillator I described was only to trigger the one shot if you wanted a periodic pulse stream like from a lab instrument pulse generator.
The pulse width can be varied by changing the delay through the delay line. The line can be a series of transmission lines that are switched in and out and can also include the silicon variable delay IC for very fine tuning. The transmission lines are in a binary sequence of delays so that they can be switched in tandem or bypassed with a DPDT switch to form about (2^N) different equally incremented delays from N lines.