quadrature hybrid couplers are useful in communications systems and measurement applications. Many 3-dB, 90-deg. hybrid directional couplers have been developed for narrowband use but, with growing interest in ultrawideband (UWB) communications, a proposed 90-deg. quadrature hybrid coupler has been designed for use from 1 to 10 GHz. It was realized in broadside stripline technology, with the coupled regions connected by means of a tandem structure. The coupler was modeled and simulated using commercial computer- aided-engineering (CAE ) simulation programs, such as the Advanced Design System (ADS) from Agilent Technologies (www.agilent.com) and the High Frequency Structure Simulator (HFSS) from Ansoft (www.ansoft.com), with simulations showing close agreement with measurements. A prototype yielded amplitude unbalance of ±1.5 dB, phase unbalance of 90 ±7 deg., and isolation and return loss of better than 14 dB from 1 to 10 GHz.

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