Distributed-element circuit: Difference between revisions

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{{Short description|Electrical circuits composed of lengths of transmission lines or other distributed components}}

[[File:LNB circuit.jpg|thumb|upright=1.5|alt=Satellite-TV block-converter circuit board|A [[low-noise block converter]] with distributed elements. The circuitry on the right is [[lumped element]]s. The distributed-element circuitry is centre and left of centre, and is constructed in [[microstrip]].]]

'''Distributed-element circuits''' are [[electrical circuitscircuit]]s composed of lengths of [[transmission line]]s or other distributed components. These circuits perform the same functions as conventional circuits composed of [[Passivity (engineering)|passive]] components, such as [[capacitor]]s, [[inductor]]s, and [[transformer]]s. They are used mostly at [[microwave]] frequencies, where conventional components are difficult (or impossible) to implement.

Conventional circuits consist of individual components manufactured separately then connected together with a conducting medium. Distributed-element circuits are built by forming the medium itself into specific patterns. A major advantage of distributed-element circuits is that they can be produced cheaply as a [[printed circuit board]] for consumer products, such as [[satellite television]]. They are also made in [[coaxial cable|coaxial]] and [[waveguide (electromagnetism)|waveguide]] formats for applications such as [[radar]], [[satellite communication]], and [[microwave link]]s.

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=== Coaxial ===

[[File:Koaxrichtkoppler.jpg|thumb|alt=Photograph|A collection of coaxial [[directional coupler]]s. One has the cover removed, showing its internal structure.]]

[[Coaxial cable|Coaxial line]], a centre conductor surrounded by an insulated shielding conductor, is widely used for interconnecting units of microwave equipment and for longer-distance transmissions. Although coaxial distributed-element devices were commonly manufactured during the second half of the 20th century, they have been replaced in many applications by planar forms due to cost and size considerations. Air-[[dielectric]] coaxial line is used for low-loss and high-power applications. Distributed-element circuits in other media still commonly transition to [[coaxial connector]]s at the circuit [[Port (circuit theory)|ports]] for intrconnectioninterconnection purposes.<ref>{{multiref|Natarajan, pp. 11–12|}}</ref>

=== Planar ===

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=== Waveguide ===

{{main|waveguideWaveguide (electromagnetism)}}

[[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 ===

{{main|dielectricDielectric resonator}}

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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{{see also|Fractal antenna}}

[[file:Hilbert resonator.svg|thumb|upright|alt=diagram|Three-iteration Hilbert fractal resonator in microstrip<ref>Janković ''et al.'', p. 197</ref>]]

The use of [[fractal]]-like curves as a circuit component is an emerging field in distributed-element circuits.<ref>Ramadan ''et al.'', p. 237</ref> Fractals have been used to make resonators for filters and antennae. One of the benefits of using fractals is their space-filling property, making them smaller than other designs.<ref>Janković ''et al.'', p. 191</ref> Other advantages include the ability to produce [[wide-band]] and [[Multi-band device|multi-band]] designs, good in-band performance, and good [[out-of-band]] rejection.<ref>Janković ''et al.'', pp. 191–192</ref> In practice, a true fractal cannot be made because at each [[Iterated function system|fractal iteration]] the manufacturing tolerances become tighter and are eventually greater than the construction method can achieve. However, after a small number of iterations, the performance is close to that of a true fractal. These may be called ''pre-fractals'' or ''finite-order fractals'' where it is necessary to distinguish from a true fractal.<ref>Janković ''et al.'', p. 196</ref>

Fractals that have been used as a circuit component include the [[Koch snowflake]], [[Minkowski island]], [[Sierpiński curve]], [[Hilbert curve]], and [[Peano curve]].<ref>Janković ''et al.'', p. 196</ref> The first three are closed curves, suitable for patch antennae. The latter two are open curves with terminations on opposite sides of the fractal. This makes them suitable for use where a connection in [[cascade connection|cascade]] is required.<ref>Janković ''et al.'', p. 196</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)|attenuatorsattenuator]]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, Aa card of microwave absorbent material can be inserted into the waveguide.<ref>Hilty, pp. 426–427</ref>

== Circuit blocks ==

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=== Filters and impedance matching ===

{{main|Distributed-element filter}}

[[File:Microstrip Hairpin Filter And Low Pass Stub Filter.jpg|thumb|alt=See caption|upright=1.3|Microstrip [[band-pass]] hairpin filter ''(left)'', followed by a [[low-pass]] stub filter]]

Filters are a large percentage of circuits constructed with distributed elements. A wide range of structures are used for constructing them, including stubs, coupled lines and cascaded lines. Variations include interdigital filters, combline filters and hairpin filters. More-recent developments include [[fractal]] filters.<ref>Cohen, p. 220</ref> Many filters are constructed in conjunction with [[dielectric resonator]]s.<ref>{{multiref| Hong & Lancaster, pp. 109, 235|Makimoto & Yamashita, p. 2}}</ref>

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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- coupled branch line couplers are more suitable for high-coupling power dividers.<ref>Ishii, p. 226</ref>

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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==== 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 (2004), 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&nbsp;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)|attenuatorsattenuator]]s, [[phase shifter]]s, and [[antenna array]] [[antenna feed|feed]] networks.<ref>{{multiref|Chang & Hsieh, p. 227|Maloratsky (2004), p. 117}}</ref>

=== Circulators ===

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== Bibliography ==

* Ahn, Hee-Ran, ''Asymmetric Passive Components in Microwave Integrated Circuits'', John Wiley & Sons, 2006 {{ISBN|0470036958}}.

* Albanese, V J; Peyser, W P, [https://ieeexplore.ieee.org/document/1125207/ "An analysis of a broad-band coaxial hybrid ring"], ''IRE Transactions on Microwave Theory and Techniques'', vol. 6, iss. 4, pp.&nbsp;369–373, October 1958.

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* Craig, Edwin C, ''Electronics via Waveform Analysis'', Springer, 2012 {{ISBN|1461243386}}.

* Doumanis, Efstratios; Goussetis, George; Kosmopoulos, Savvas, ''Filter Design for Satellite Communications: Helical Resonator Technology'', Artech House, 2015 {{ISBN|160807756X}}.

* DuHamell, R; Isbell, D, [https://doi.org/10.1109/IRECON.1957.1150566 "Broadband logarithmically periodic antenna structures"], ''1958 IRE International Convention Record'', New York, 1957, pp. &nbsp;119–128.

* Edwards, Terry C; Steer, Michael B, ''Foundations of Microstrip Circuit Design'', John Wiley & Sons, 2016 {{ISBN|1118936191}}.

* Fagen, M D; Millman, S, ''A History of Engineering and Science in the Bell System: Volume 5: Communications Sciences (1925–1980)'', AT&T Bell Laboratories, 1984 {{ISBN|0932764061}}.

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* Garg, Ramesh; Bahl, Inder; Bozzi, Maurizio, ''Microstrip Lines and Slotlines'', Artech House, 2013 {{ISBN|1608075354}}.

* Ghione, Giovanni; Pirola, Marco, ''Microwave Electronics'', Cambridge University Press, 2017 {{ISBN|1107170273}}.

* Grieg, D D; Englemann, H F, [https://doi.org/10.1109/JRPROC.1952.274144 "Microstrip&nbsp;– aMicrostrip—a new transmission technique for the kilomegacycle range"], ''Proceedings of the IRE'', vol. 40, iss. 12, pp.&nbsp;1644–1650, December 1952.

* Gupta, S K, ''Electro Magnetic Field Theory'', Krishna Prakashan Media, 2010 {{ISBN|8187224754}}.

* Harrel, Bobby, ''The Cable Television Technical Handbook'', Artech House, 1985 {{ISBN|0890061572}}.

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* Helszajn, J, ''Ridge Waveguides and Passive Microwave Components'', IET, 2000 {{ISBN|0852967942}}.

* Henderson, Bert; Camargo, Edmar, ''Microwave Mixer Technology and Applications'', Artech House, 2013 {{ISBN|1608074897}}.

* Hilty, Kurt, "Attenuation measurement", pp. &nbsp;422–439 in, Dyer, Stephen A (ed), ''Wiley Survey of Instrumentation and Measurement'', John Wiley & Sons, 2004 {{ISBN|0471221651}}.

* Hong, Jia-Shen G; Lancaster, M J, ''Microstrip Filters for RF/Microwave Applications'', John Wiley & Sons, 2004 {{ISBN|0471464201}}.

* Hunter, Ian, ''Theory and Design of Microwave Filters'', IET, 2001 {{ISBN|0852967772}}.

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* Janković, Nikolina; Zemlyakov, Kiril; Geschke, Riana Helena; Vendik, Irina; Crnojević-Bengin, Vesna, "Fractal-based multi-band microstrip filters", ch. 6 in, Crnojević-Bengin, Vesna (ed), ''Advances in Multi-Band Microstrip Filters'', Cambridge University Press, 2015 {{ISBN|1107081971}}.

* Johnson, Robert A, ''Mechanical Filters in Electronics'', John Wiley & Sons Australia, 1983 {{ISBN|0471089192}}.

* Johnson, Robert A; Börner, Manfred; Konno, Masashi, [https://doi.org/10.1109/T-SU.1971.29611 "Mechanical filters&nbsp;– afilters—a review of progress"], ''IEEE Transactions on Sonics and Ultrasonics'', vol. 18, iss. 3, pp.&nbsp;155–170, July 1971.

* Kumar, Narendra; Grebennikov, Andrei, ''Distributed Power Amplifiers for RF and Microwave Communications'', Artech House, 2015 {{ISBN|1608078329}}.

* Lacomme, Philippe; Marchais, Jean-Claude; Hardange, Jean-Philippe; Normant, Eric, ''Air and Spaceborne Radar Systems'', William Andrew, 2001 {{ISBN|0815516134}}.

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{{featured article}}

[[Category:Distributed element circuits| ]]

[[Category:Radio electronics]]