A Slow-Wave Rat-Race Coupler Using Substrate Integrated Suspended Line Technology

This paper presents a slow-wave rat-race coupler using substrate integrated suspended line (SISL) technology. Double-sided interconnected strip line (DSISL) is utilized to further reduce the loss of the suspended line circuit. Using the DSISL concept, a slow-wave structure based on modified meander line configuration is proposed. Formed by simple circuit topology with only three parameters of one unit cell, the characteristic impedance and slow-wave factor of the proposed slow-wave DSISL can be controlled separately. Utilizing the proposed slow-wave DSISL, a rat-race coupler at 1.5 GHz has been designed and fabricated by standard printed circuit board process. A 90.5% size reduction is achieved, and the fractional bandwidth is 26.5%. Benefiting from SISL technology, the proposed slow-wave rat-race coupler is self-packaged and has advantages of low cost and light weight.