Processing All Things Federal Circuit
October 23, 2023 - Last Week in the Federal Circuit

Recently in the Federal Circuit: More on Indefiniteness in IPRs


Means-plus-function claim elements can be a sticky wicket during an inter partes review, to borrow a phrase from the cricket lovers out there. These are claim elements drafted under 35 U.S.C. § 112(f) (or its predecessor paragraph 6) that recite an element of a combination as a means for performing a specified function. Normally, elements like that are construed to cover the structure disclosed in a patent’s specification corresponding to the claim-recited function. But things get messy when the specification arguably lacks corresponding structure. In district court, that would be a basis for indefiniteness. But the Board in IPRs has consistently declined to hold claims unpatentable for indefiniteness, limiting its review to prior-art unpatentability issues. The Board and the Federal Circuit thus have grappled with what to do in an IPR with potentially indefinite claims reciting mean-plus-function elements. One recent case took another stab at the problem.

Case of the (recent-ish) week: Sisvel Int’l S.A. v. Sierra Wireless, Inc., 22-1493 (October 6, 2023)

Panel: Chief Judge Moore and Judges Clevenger and Chen, with Judge Chen writing the opinion

You should read this case if: you have a matter regarding inter partes review of a patent with a means-plus-function claim element.

Sierra Wireless petitioned the Board to review a patent related to methods of channel coding when transmitting data in radio systems. The Board construed the limitation “means for detecting” as a mean-plus-function limitation. But the Board concluded that the scope of claims with this limitation could not be determined because the specification failed to disclose corresponding structure for the claimed means. The Board thus declined to evaluate whether claims with this limitation were patentable over the prior art.

The Federal Circuit vacated and remanded the Board’s decision on the “means for detecting” limitation. The Court expounded on earlier precedent, distinguishing two types of indefiniteness challenges to claims with mean-plus-function elements in the computer arts. For the first type, the specification discloses no algorithm corresponding to the claimed means at all. In that scenario, the knowledge of a skilled artisan is generally not relevant to determining whether the specification discloses adequate corresponding structure. For the second type of challenge, the specification discloses an algorithm but the parties dispute its adequacy.

The Federal Circuit explained that this case involves the second type of challenge because the parties disputed whether the specification’s references to named software protocols were sufficient to disclose an algorithm. But the Board had wrongly treated the case as presenting the first type of challenge. It refused to consider expert testimony about the adequacy of the specification’s disclosures because it concluded the references to known protocols were not algorithms. The Federal Circuit held this was error: “[i]f there is some disclosure of structure in the specification for performing the claimed function, the question of whether the specification discloses sufficient structure must be viewed in light of the knowledge of a skilled artisan”; “for a means-plus-function limitation where the corresponding structure is an algorithm, the specification need not disclose all the details of the algorithm to satisfy the definiteness requirement of § 112 ¶ 2 so long as what is disclosed would be sufficiently definite to a skilled artisan.”

The Court instructed the Board on remand to analyze the expert testimony on the adequacy of the specification’s disclosures. It also explained that if the Board were still to determine that the specification lacks a sufficiently disclosed algorithm, it should then determine whether that made it impossible to resolve the prior-art challenge. Barring such impossibility, the Board must resolve the prior-art challenge on the merits despite potential indefiniteness.