Distributed-element circuit: Difference between revisions

Revision as of 04:01, 24 October 2019

Revision as of 05:21, 24 October 2019

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=== Fractals ===

{{see also|Fractal antenna}}

[[fileFile: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]] 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>

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=== Filters and impedance matching ===

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>

{{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>

As with lumped-element filters, the more elements used, the closer the filter comes to an [[brickwall filter|ideal response]]; the structure can become quite complex.<ref>Harrell, p. 150</ref> For simple, narrow-band requirements, a single resonator may suffice (such as a stub or [[spurline filter]]).<ref>Awang, p. 296</ref>

Impedance matching for narrow-band applications is frequently achieved with a single matching stub. However, for wide-band applications the impedance-matching network assumes a filter-like design. The designer prescribes a required frequency response, and designs a filter with that response. The only difference from a standard filter design is that the filter's source and load impedances differ.<ref>Bahl (2009), p. 149</ref>

=== Power dividers, combiners and directional couplers ===