A 4 Gc/s travelling-wave tube for microwave radio links

The type W7/3G is a new 4Gc/s travelling-wave tube for the output stage of microwave radio links, developed as a result of extensive experience with an earlier tube. The electron gun uses a partially-shielded cathode to give a convergent beam, and it has been found that this gives better performance than a completely shielded electron gun. At the same time the absence of magnetic shielding inside the tube gives a simple construction and makes it easy to set up. The construction and the features necessary to obtain satisfactory performance in high-quality microwave links are described. The tube operates at 3kV 40mA, and gives an output of more than 5 watts for 10mW input in the frequency range 3.6¿4.2Gc/s. Other performance details of the tube are given. The operating voltage permits a simple construction and requires a relatively low magnetic field of about 400 gauss. Furthermore it has simplified the design of a periodic permanent-magnet circuit in which reproducible operation and easy setting-up of tubes has been obtained. This periodic focusing circuit is fully described.