About a few basic common sense of transmission line

Recently, a few issues of cable join respect are concerned in often the friend enquires aerial is made, I want to talk about a few the individual's experience here. Actually, oneself feel of these problems put forward, basically lack the concept of long term, short line to cause. Introduce two special transmission line segment above all: 4 wavelengh of １ ／ 2 wavelengh of transmission line and １ ／ transmission line, see figure below.

／ of a paragraph of １ is in the graph 4 wavelengh transmission line, for example our commonly used 75 Ω and cable of coaxial of 50 Ω radio frequency, choose certain length, the 4 wavelengh of １ ／ that can become some frequency to nod transmission line. This paragraph of transmission line has one very main character on corresponding frequency dot: When A carries short circuit, b carries impedance to show infinity; When B carries short circuit, a carries impedance to show infinity. Manage together, when open a way of one aspect of the matter, impedance of other one aspect of the matter is shown infinitesimal.

This one character also applies to the parallel transmission line that place laying a plan shows likewise, for example some earlier transmission line of year of commonly used 300 Ω balance.

This kind of character of 4 wavelengh line can be １ ／ sometimes we bring huge go to the lavatory, half Zhen Zitian line that pursues as follows used this one character.

Different picture is on commonly used by two metals or metallic canal forms half brace up child aerial, this kind of antenna unlike amount to Zhen Zitian line has 0 potential to nod what can secure in all to use in that way, the method that uses right plan institute to show can solve a problem well. The 4 wavelengh of １ ／ that the structure inside dotted line can regard lower end short circuit transmission line, upright impedance shows infinity on, as it happens is usable will regard as secure half brace up child the structure that prop up.

Then, the structure that pursues below understood very easily also.

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