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=== Distributed resistance ===
Resistive elements are generally not useful in a distributed element circuit. However, distributed resistors may be used in [[attenuator]]s and line [[electrical termination|terminations]]. In planar media they can be implemented as a meandering line of high-resistance material, or as a deposited patch of [[thin-film]] or [[thick-film]] material.<ref>{{multiref|Maloratsky (2012), p. 69|Hilty, p. 425|Bahl (2014), p. 214}}</ref> In waveguide, A card of microwave absorbent material can be inserted into the waveguide.<ref>Hilty, p. 426–427</ref>
== Circuit blocks ==
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=== Power dividers, combiners and directional couplers ===
{{main|Power dividers and directional couplers}}
[[File:Microstrip Sawtooth Directional Coupler.jpg|thumb|upright|alt=Sawtooth coupler on a circuit board|Microstrip sawtooth directional coupler, a variant of the coupled-lines directional coupler<ref>Maloratsky (2009), p. 160</ref>]]
A directional coupler is a four-port device which couples power flowing in one direction from one path to another. Two of the ports are the input and output ports of the main line. A portion of the power entering the input port is coupled to a third port, known as the ''coupled port''. None of the power entering the input port is coupled to the fourth port, usually known as the ''isolated port''. For power flowing in the reverse direction and entering the output port, a reciprocal situation occurs; some power is coupled to the isolated port, but none is coupled to the coupled port.<ref>Sisodia & Raghuvansh, p. 70</ref>
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==== Hybrids ====
[[File:Ratracecoupler-arithmetics.svg|thumb|upright|alt=Drawing of a four-port ring|Hybrid ring, used to produce sum and difference signals]]
A directional coupler which splits power equally between the output and coupled ports (a {{nowrap|3 [[decibel|dB]]}} coupler) is called a ''hybrid''.<ref>Maloratsky (2009), p. 117</ref> Although "hybrid" originally referred to a [[hybrid transformer]] (a lumped device used in telephones), it now has a broader meaning. A widely-used distributed element hybrid which does not use coupled lines is the ''hybrid ring'' or [[rat-race coupler]]. Each of its four ports is connected to a ring of transmission line at a different point. Waves travel in opposite directions around the ring, setting up [[standing wave]]s. At some points on the ring, destructive [[wave interference|interference]] results in a null; no power will leave a port set at that point. At other points, constructive interference maximises the power transferred.<ref>Chang & Hsieh, pp. 197–198</ref>
Another use for a hybrid coupler is to produce the sum and difference of two signals. In the illustration, two input signals are fed into the ports marked 1 and 2. The sum of the two signals appears at the port marked Σ, and the difference at the port marked Δ.<ref>Ghione & Pirola, pp. 172–173</ref> In addition to their uses as couplers and power dividers, directional couplers can be used in [[balanced mixer]]s, [[frequency discriminator]]s, [[Attenuator (electronics)|attenuator]]s, [[phase shifter]]s, and [[antenna array]] [[antenna feed|feed]] networks.<ref>{{multiref|Chang & Hsieh, p. 227|Maloratsky (2009), p. 117}}</ref>
=== Circulators ===
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\end{pmatrix}</math>
for an ideal three-port circulator, showing that circulators are non-reciprocal by definition. It follows that it is impossible to build a circulator from standard passive components (lumped or distributed). The presence of a ferrite, or some other non-reciprocal material or system, is essential for the device to work.<ref>Maloratsky (2009), pp. 285–286</ref>
== Active components ==
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