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This paper presents a novel and improved design of signal combiners for highly efficient outphasing power amplifiers. Additional shunt reactances for an output power back off efficiency peaking, as they are required for the standard Chireix combiners, are eliminated. The circuits are based on two transmission lines with different line lengths and allow compact implementations. Analytical design equations are derived and formulas describing the operation of the new combiners are presented. Several design examples are given for combiners equivalent to the standard Chireix and to new circuits and compared with respect to their physical implementation. Design trade offs are discussed.