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=== Waveguide ===
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[[File:Waveguide-post-filter.JPG|thumb|alt=Rectangular waveguide filter with five tuning screws|A [[waveguide filter]]]]
Many distributed-element designs can be directly implemented in waveguide. However, there is an additional complication with waveguides in that multiple [[waveguide mode|modes]] are possible. These sometimes exist simultaneously, and this situation has no analogy in conducting lines. Waveguides have the advantages of lower loss and higher quality [[resonator]]s over conducting lines, but their relative expense and bulk means that microstrip is often preferred. Waveguide mostly finds uses in high-end products, such as high-power military radars and the upper microwave bands (where planar formats are too lossy). Waveguide becomes bulkier with lower frequency, which militates against its use on the lower bands.<ref>Ghione & Pirola, p. 18</ref>
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=== Dielectric resonator ===
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A dielectric resonator is a piece of dielectric material exposed to electromagnetic waves. It is most often in the form of a cylinder or thick disc. Although cavity resonators can be filled with dielectric, the essential difference is that in cavity resonators the electromagnetic field is entirely contained within the cavity walls. A dielectric resonator has some field in the surrounding space. This can lead to undesirable coupling with other components. The major advantage of dielectric resonators is that they are considerably smaller than the equivalent air-filled cavity.<ref>Penn & Alford, pp. 524–530</ref>
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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 (electronics)|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,
== Circuit blocks ==
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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>
A power divider is often constructed as a directional coupler, with the isolated port permanently terminated in a matched load (making it effectively a three-port device). There is no essential difference between the two devices. The term ''directional coupler'' is usually used when the coupling factor (the proportion of power reaching the coupled port) is low, and ''power divider'' when the coupling factor is high. A power combiner is simply a power splitter used in reverse. In distributed-element implementations using coupled lines, indirectly coupled lines are more suitable for low-coupling directional couplers; directly
Distributed-element designs rely on an element length of one-quarter wavelength (or some other length); this will hold true at only one frequency. Simple designs, therefore, have a limited [[Bandwidth (signal processing)|bandwidth]] over which they will work successfully. Like impedance matching networks, a wide-band design requires multiple sections and the design begins to resemble a filter.<ref>Bhat & Khoul, pp. 622–627</ref>
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