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In `F33f`_`[control engineering`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Control_engineering]`_`f, a `!single-input and single-output`! (`!SISO`!) system is a simple single-`F33f`_`[variable`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Variable_(computer_science)]`_`f `F33f`_`[control system`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Control_system]`_`f with one input and one output. In radio, it is the use of only one `F33f`_`[antenna`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Antenna_(radio)]`_`f both in the `F33f`_`[transmitter`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Transmitter]`_`f and `F33f`_`[receiver`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Receiver_(radio)]`_`f.

>>Contents

• `F0af`_`[Details`#details]`_`f

• `F0af`_`[See also`#see-also]`_`f

• `F0af`_`[References`#references]`_`f

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>>Details

SISO systems are typically less complex than `F33f`_`[multiple-input multiple-output`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Multiple-input_multiple-output_system]`_`f (MIMO) systems. Usually, it is also easier to make an order of magnitude or trending predictions "on the fly" or "back of the envelope". MIMO systems have too many interactions for most of us to trace through them quickly, thoroughly, and effectively in our heads.

Frequency domain techniques for analysis and controller design dominate SISO control system theory. `F33f`_`[Bode plot`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Bode_plot]`_`f, `F33f`_`[Nyquist stability criterion`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Nyquist_stability_criterion]`_`f, `F33f`_`[Nichols plot`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Nichols_plot]`_`f, and `F33f`_`[root locus`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Root_locus]`_`f are the usual tools for SISO system analysis. Controllers can be designed through the `F33f`_`[polynomial`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Polynomial]`_`f design, root locus design methods to name just two of the more popular. Often SISO controllers will be PI, PID, or lead-lag.

>>See also

• `F33f`_`[Control theory`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Control_theory]`_`f

>>References

• `:citerefpartington2004`a`F33f`_`[Partington, Jonathan R.`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Jonathan_Partington]`_`f (2004). `*Linear Operators and Linear Systems: An Analytical Approach to Control Theory`*. `F33f`_`[Cambridge University Press`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Cambridge_University_Press]`_`f. p. 75. `F33f`_`[ISBN`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=ISBN_(identifier)]`_`f 0-521-54619-2.

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