IMPLEMENTATION OF 10DB ASYMMETRIC DIRECTIONAL COUPLER WITH HIGH DIRECTIVITY

摘要

Directional couplers play a vital role in most of RF communications, acting as power divider and combiner. A 10 dB - Planar directional coupler with high directivity, isolation, coupling efficiency with compact integration in RP devices is proposed. The proposed couplers are designed for 2.45 GHz frequency to serve for WLAN applications. By increasing bandwidth, high directivity can be obtained in 10 dB- directional coupler. This is achieved by creating slots and bends in directional couplers. Coupling factor is an important parameter in directional coupler which is improved by equalization of odd mode and even mode phase velocities as per numerical approaches. Thereby more capacitance effect is introduced that in turn increases the velocity. The performance of the planar directional coupler is affected by the excitation of surface waves due to microstrip discontinuities that causes crosstalk, coupling and attenuation in multilayer microstrip circuit. The proposed design greatly reduces the effect of surface waves by placing slots into the substrate surface. A parametric study is done for choosing an appropriate distance of placing slots at various positions. The results of the parametric study is also provided for the verification. Meander line structure is introduced in directional coupler for improved capacitance and inductance effect. Simulation is done using EM simulator. The key design parameters such as reflection coefficient, transmission coefficient, isolation, coupling factor, bandwidth, VSWR, directivity defines the performance of the coupler. Through the simulation the return loss for the proposed coupler is obtained as -33.06 dB. An impedance bandwidth of 28.5% can be achieved at the resonance frequencies., VSWR obtained through simulation as 1. Experimental model is also fabricated for the proposed design. The designed and the measured results show greater agreements.