Required accuracy in manufacturing process of three‐wire transmission line used in inductive radio system for detecting linear motor vehicle position

The three-wire transmission lines consisting of square-wave-formed line conductors has a structure in which any two of the three line conductors iterate narrow and wide sections at a specified interval along the longitudinal direction. Among those sections, the narrow section has the following problem. If line conductors deviate even a little from their normal positions due to the inaccuracies in the manufacturing process, relatively large unbalances will be produced in the mutual impedances and admittances between them. This leads to the crosstalk between the positive and negative phase sequence components of the signal and consequently to the detection error in the position of the vehicle. We considered the case where the manufacturing inaccuracies distribute at random or uniformly along the longitudinal direction. A quantitative analysis is made for the problem arriving at a guide for the manufacturing accuracy of the transmission line, which is required to ensure the desired accuracy of position detection. It is desirable in the narrow section that the two conductors maintain a distance above a certain value. It is also desirable that the radius of the line conductor be as small as possible, as long as the transmission loss of the line is within the tolerable value. Compared with the transmission line consisting of helically wound conductors, which we have already reported, there will still be a more strict requirement on the manufacturing accuracy on the transmission line consisting of square-wave-formed conductors.