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"A New Patent Drafting Strategy"
In recent years, the U.S. Court of Appeals for the Federal Circuit and the Supreme Court of this country has issued a number of opinions that benefit the would-be copyists by limiting a patentee's ability to enforce his or her patent rights through the use of "the doctrine of equivalents." The doctrine of equivalents (DOE) is used by a patentee when a competitor's product is not literally the same, but nonetheless, is "close enough" that it infringes because it is equivalent. This is an extremely valuable tool in a patentee's arsenal against competitors because it is rare that a competitor’s product is literally described in a patentee's issued patent. It is substantially more frequent that the competitor has "tweaked" its product such that it is not literally the same from a technical perspective, but nevertheless, it performs and is equivalent to the invention described (claimed) in an issued patent.

A patentee loses its right to use the DOE to ensnare an infringer when, during communication with the United States Patent and Trademark Office (patent prosecution), a patent attorney must amend (or merely argue) a claim limitation to get the patent issued in light of what is previously known (prior art). This cutting off of the DOE is termed "prosecution history estoppel" (PHE).

Here are a couple simple examples relating to a car to illustrate the dramatic effect PHE has on limiting a patentee's rights.
Example 1
A patent attorney drafts and files an application with the following original claim:

Claim 1. A car comprising: a body; a suspension; and a gasoline engine.

Assume the patent issues without amendment. In this circumstance a patentee would be able to successfully sue a would-be copyist for literal patent infringement for producing a car with a gasoline engine (assuming the car also had a body and suspension). In addition, because there was no amendment to the claim during prosecution, no PHE would apply. Thus, the patentee would also be able to successfully sue under the DOE a competitor that produced a car with a diesel or alcohol powered engine - assuming that diesel and alcohol engines are equivalent to gasoline engines. The end result is that the patentee would have broad patent protection because the DOE was available to expand the claim beyond its literal scope.
Example 2
Now take the example of a patent attorney who drafts an even broader original claim by removing the limitation that the engine is gasoline powered:

Claim 1. A car comprising: a body; a suspension; and an engine.

On its face, this is a broader claim because it literally covers every potential type of engine. However, now let us assume that it is generally known that there are various types engines available to be used in cars and that the Patent and Trademark Office (PTO) rejects the claim because the engine limitation is too broad. In response to the office action, the patent attorney amends Claim 1 to include the gasoline limitation. The claim is allowed and the patent issues with the following claim:

Claim 1. A car comprising: a body; a suspension; and a gasoline engine.

This is the same claim as in the patent in Example 1, but because of the amendment during prosecution, PHE now applies. The patentee would still be able to successfully sue under literal infringement the competitors that produce a car with a gasoline engine. However, more importantly, because the claim was amended, PHE would cutoff the patentee's ability to successfully sue under the DOE competitors that produce cars with diesel or alcohol powered engines.

Thus, the application that was originally drafted with a broader claim, has been dramatically narrowed because of the amendment and resulting PHE.

Just a few years ago, Example 2 was the accepted strategy for drafting a patent application. The strategy was essentially to draft the claims as broadly as possible and then fight it out with the Patent Office and eventually narrow the claims through amendments during prosecution until the claims were sufficiently narrow for the examiner to accept them. This was a good strategy because there were no ramifications, i.e. no PHE. However, recent case law dictates that any narrowing amendment made to a claim element for purposes of patentability completely bars any resort to the DOE with respect to the amended limitation. In response to these decisions, the old drafting strategy was dead, or at least it should be. At The Patent Office, it is.

Example 1 illustrates the new patent strategy utilized by The Patent Office. The strategy is to draft patent applications that seek protection only as broad as the applicant is rightfully allowed. This requires a patent attorney to conduct a more thorough search of the prior art before drafting the application. This new strategy effectively reduces the amount and nature of the amendments to the claims during prosecution. This preserves a patentee's ability to utilize the DOE to broaden its claims to ensnare or ward off would-be infringers.

It cannot be stressed enough how important it is for a patent attorney to recognize and adapt to these new precedents. Failure to do so leaves a would-be patentee with a patent that is far too narrow to be truly effective. The Patent Office is experienced in drafting applications utilizing this new strategy and has formulated additional drafting techniques that help swing the pendulum back in the patentee's favor.

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