Browse Prior Art Database

Compact Variable Delay Line

IP.com Disclosure Number: IPCOM000045727D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 35K

Publishing Venue

IBM

Related People

Davidson, A: AUTHOR [+3]

Abstract

This article relates generally to delay lines for electrical signals and more particularly to mechanically variable delay lines wherein the delay line itself is a coplanar waveguide.

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Compact Variable Delay Line

This article relates generally to delay lines for electrical signals and more particularly to mechanically variable delay lines wherein the delay line itself is a coplanar waveguide.

The components of the variable delay line system 1 are shown schematically in Fig. 1. A stepping motor 2 or other mechanical drive mechanism is coupled by means of a gear drive 3 to a rotating shaft 4. A disk 5, which generates the delay, is turned by shaft 4 to vary the electrical length of a transmission line which has been formed on disk 5. Electrical signals are coupled to disk 5 via input coaxial cable 6 and coupled from disk 5 via output coaxial cable 7.

Disk 5 and the delay transmission line on disk 5 are shown in detail in Fig. 2. Disk 5 is made of a high dielectric constant material so as to get as much delay per unit length as possible consistent with low electrical losses. Either quartz or sapphire may be used. A uniform nickel-plated, copper film is deposited on disk
5. A coplanar waveguide structure is formed in the copper by photolithography, providing a signal lead 10 isolated from ground conductors 11 by a pair of etched moats 12. One end of the coplanar waveguide is at the center of disk 5, where it makes either a fixed or sliding contact 13 to coaxial input transmission line 6. The other end of the coplanar waveguide is terminated in a 50-ohm matching resistor 14 so as to minimize reflections from that end. A unique feature of this variable delay generator is that the delay can be made periodic without having to reverse any motors or gears.

A sliding contact 15 is positioned near the edge of disk 5 where it makes a connection to the coplanar waveguide. It is clear from the diagram that as disk 5 is rotated, the length of coplanar waveguide between the two contacts 13, 15 varies.

Special care must be taken with the sliding contacts 13, 15 so that excessive wear is avoided. It would be desirable for the contacts to withstand 100,000 full rotations of disk 5 with no intermittent or other failures.

One embodiment that should satisfy the reliability requirement involves using brass contacts and nickel plating on the copper coplanar waveguide. In this way, the soft brass accrues most...