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Slotted lines are used for microwave measurements and consist of a movable probe inserted into a slot in a transmission line. They are used in conjunction with a microwave power source and usually, in keeping with their low-cost application, a low cost Schottky diode detector and VSWR meter rather than an expensive microwave power meter. Slotted lines can measure standing waves, wavelength, and, with some calculation or plotting on Smith charts, a number of other parameters including reflection coefficient and electrical impedance. A precision variable attenuator is often incorporated in the test setup to improve accuracy. This is used to make level measurements, while the detector and VSWR meter are retained only to mark a reference point for the attenuator to be set to, thus eliminating entirely the detector and meter measurement errors. The parameter most commonly measured by a slotted line is SWR. This serves as a measure of the accuracy of the impedance match to the item under test. This is especially important for transmitter antennas and their feed lines; reflected power is wasted and can damage high-power transmitters. Slotted lines are no longer widely used, but can still be found in budget applications. Their main drawback is that they are labour-intensive to use and require calculation, tables, or plotting to make use of the results. They need to be made with mechanical precision and the probe and its detector need to be adjusted with care, but they can give very accurate results. ==Description== The slotted line is one of the basic instruments used in radio frequency test and measurement at microwave frequencies. It consists of a precision transmission line, usually co-axial but waveguide implementations are also used, with a movable insulated probe inserted into a longitudinal slot cut into the line. In a co-axial slotted line, the slot is cut into the outer conductor of the line. The probe is inserted past the outer conductor, but not so far that it touches the inner conductor. In a rectangular waveguide, the slot is usually cut along the centre of the broad wall of the waveguide. Circular waveguide slotted lines are also possible.〔Multiple sources: 〕 Slotted lines are relatively cheap〔Thomas H. Lee even describes a microstrip slotted line for use up to that he claims can be made for less than $10. He calls this a " cost reduction" over the price of a network analyser. That is, its cost is 10,000 times less than an analyser costing $100,000 (Lee, pages xv, 268-271).〕 and can perform many of the measurements done by more expensive equipment such as network analysers. However, slotted line measurement techniques are more labour-intensive and often do not directly output the desired parameter; some calculation or plotting is frequently required. In particular, they can only carry out a measurement at one spot frequency at a time so producing a plot of a parameter versus frequency is very time consuming. This is to be compared to modern instruments like network and spectrum analysers which are intrinsically frequency swept and produce a plot instantly. Slotted lines have now largely been superseded, but are still found where capital costs are an issue. Their remaining uses are mostly in the millimetre band, where modern test apparatus is either prohibitively expensive or not available at all, and with academic laboratories and hobbyists. They are also useful as a teaching aid as the user is more directly exposed to basic line phenomena than with more sophisticated instruments.〔Multiple sources: 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Slotted line」の詳細全文を読む スポンサード リンク
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