"no fixed pattern" is a correct and usable phrase in written English.
You can typically use it to describe the lack of a uniform or consistent structure for something, such as a timeline or process. For example, you might say, "This project has no fixed pattern, so we need to be prepared for anything!".
The hopak has no fixed pattern of steps.
In the capitalist countries, on the other hand, no fixed pattern of industrial health service has emerged.
However, it is evident that there is no fixed pattern of sharing the available bandwidth between one or more flows.
There was no fixed pattern suggested for dose titration.
Typically, a linear variation in Λ would cause no fixed pattern of behaviour in the satellite intensities.
Although generally used, the term "gait" may be, however, misleading as, in insects, there are no fixed patterns with instable transitions as found in walk, trot, and gallop of horses, for example (see Graham 1972, Fig. 7).
As is almost inevitably the case when sensitive social issues are exposed to international debate, battle lines were drawn between conservative countries, largely Islamic or Roman Catholic, and more secular nations, though there was no fixed geographical pattern.
As Ross (2009) maintains, no one, not even those in traditional professions, can any longer expect a fixed pattern of employment in the course of their lifetime.
These signals followed a fixed pattern: beeps come randomly, but are invariably followed by boops a short (and fixed) period of time later.
The wheel revolving in a fixed pattern is itself a symbol of routine sameness.
In the total average of a 10,000-images dataset, for example, the contrast of a fixed-pattern background image increases 10,000-fold since this small but fixed pattern adds up coherently.
