Dual band planar hybrid coupler with enhanced bandwidth using particle swarm optimization technique

This paper presents the design procedure, and implementation of a dual band planar quadrature hybrid with enhanced bandwidth. The topology of the circuit is a dual stage quadrature hybrid, which provides much larger flexibility to allocate the desired operating frequencies and necessary bandwidth than other previously published configurations. In this paper, small dual frequency transformers in two sections are used to modify conventional broad band hybrid coupler for having arbitrary dual band operation frequencies. This performance of the proposed coupler is verified by using commercial simulators and measurements. To this aim, by merging compilers and full-wave simulators, particle swarm optimization is used to achieve proper values to have desired goals. Finally, a dual stage quadrature hybrid for dual band (2.4 and 5.8GHz) wireless local area network systems has been fabricated, aimed to cover the bands corresponding to the standards IEEE802.11n. The measured results validate good dual band performance at 2.4/5.8GHz with enhanced bandwidths up to 12.5% and 25%, for the lower and upper bandwidth, respectively which satisfies the bandwidth requirement for the this standard.