I am reading this article (https://arxiv.org/ftp/arxiv/papers/1901/1901.02069.pdf) where I have come across this sentence: "we first designed a
parallel coupled Chebyshev bandpass filter as shown in Fig.2a, whose substrate was gallium arsenide material, dielectric constant was 12.9, conductor was made of gold, the resonator was made of half-wavelength resonator with open circuit at both ends, and the input-output coupling was made of tap line." It is at the end of page 3.
English it not my first language, and I am not sure what "tap line" is in this context. According to the "Modern Electronics Dictionary" book (http://160592857366.free.fr/joe/ebooks/Electronics%20and%20Electrical%20Engineering%20Collection/GRAF,%20R.%20F.%20(1999).%20Modern%20Dictionary%20of%20Electronics%20(7th%20ed.)/Modern_Dictionary_of_Electronics_7E.pdf): Tap — 1. A fixed electrical connection to a specified
position on the element of a potentiometer, transformer,
etc. 2. A branch. Applied to conductors, such as a battery
tap, and to miscellaneous general use. 3. A connection of
the terminal end of one conductor to another conductor
at some point along its run; the process of making such
a connection. Also, a connection or connection point
brought out of a winding, as in a transformer, at some
point between the ends of the winding, for controlling
output ratios. 4. Connection on the phone line that lets a third party listen to what is being said in a telephone
conversation.
Best Answer
+1 for linking to the source, and saying whereabouts in it to find the relevant passage.
This is the filter they are referring to -
Part of the problem is that English is not the authors' first language. There is not a transmission line type called 'tap line'.
An impedance match is made to the filter by running the line to a 'tap point' on the resonator. A connection to a point on a resonator is often called a tap point or tapping point, because the intention is to move it to adjust the impedance match. As the tap point approaches the centre, the terminal impedance the filter presents to the outside world falls, and at the end of the resonator it is maximum. It needs to be adjusted so that the outside world's impedance (likely 50 ohms) loads the resonator down to the correct Q for the filter design.
They make this distinction because there are other ways of getting an impedance match into a filter. One way is to run another line parallel to the last resonator, and adjust the coupling by adjusting the spacing. Another way is to use a small series capacitance, either a discrete or printed component, to a point on the resonator. Each of these matching methods has its own contribution to the frequency response of the complete filter.
You'll see from the diagram that this is not simply a tap point to the resonator, but a short length of line parallel to it, with a connection to a tap point at the end. There may be technical design reasons for going for a compound matching configuration like this. However, I have used this method for the more prosaic reason that if the tap point is too high up, it's easy to cut the connection, trim off the excess, and solder a short wire between the resonator and the track lower down, to tune the filter by hand.