Wide bandwidth traveling wave maser employing magnetic stagger tuning

Abstract

This paper presents experimental work which shows that magnetic stagger tuning provides an efficient means for trading excess gain for bandwidth in traveling wave masers. A high gain traveling wave maser (20 dB/in. at 4·2°K) has been developed at 4000 mc and operated with a transverse field superconducting magnet as a wide-band amplifier system. The maser, which employs meander-line slowing and iron-doped rutile as the active material is operated with various sections of the paramagnetic crystal resonating at different frequencies. This is made possible by placing the maser in a superconducting magnet which generates a field profile that can be varied in steps along its length of the maser. A 4·0 in. iron-doped rutile crystal, which produces 78 dB peak electronic gain over a 12 mc instantaneous band, can be made to yield 33 dB of gain and 66 mc of bandwidth by stagger tuning. In addition to presenting experimental data which is in good agreement with the simple theory of magnetic stagger tuning, this paper describes for the first time the performance of a traveling wave maser which is magnetically stagger-tuned in a small compact superconducting magnet. This work is significant from a system standpoint since an electronically, variable gain-bandwidth microwave amplifier has been developed. Furthermore, both these devices can be operated in a closed-cycle helium refrigerator.