Jovian hectometric radio emission (HOM: 300--3000 kHz) has a number of persistent structural features associated with it as observed by the Voyager 1, Voyager 2, Ulysses, and Galileo spacecraft for specific jovigraphic latitudes (-4¿ to +7.1¿) and local times (0.3 to 10.5 hours). Most notable are the presence of HOM emission between 270¿ and 120¿ central meridian longitude (CML) and the region of reduced emission intensity (a gap) between 120¿ and 270¿. We displayed the Ulysses and Galileo data using time-frequency occurrence probability spectrograms and show that the observed HOM emission features are nearly identical to those observed by the Voyager spacecraft. This implies that the HOM structure is long-lived and fixed in its longitudinal position within the Jovian magnetosphere. HOM structure depends on small changes in the observer's jovigraphic latitude, so the different jovigraphic latitudes of the spacecraft were used to probe the HOM beam structure. From this analysis we found that the CML width of the main HOM gap is directly correlated to the latitude of the spacecraft. We conclude that the latitudinal thickness of the HOM beam is about 12¿, extending from -5¿ to +7¿ magnetic latitude. ¿ 1998 American Geophysical Union