Optimal Design: Confining the Spurious Ripples of Coupled Line Microstrip Bandpass Filter for WiMax Links

R. A. SOOMRO, F. A. UMRANI, M. R. ANJUM, B. S. CHOWDHRY, I. A. LASHARI

Abstract


The development of advanced meta-materials and new fabrication techniques has revealed the new dimensions of Microstrip structures. Microstrip filters designed with meta-materials offer several merits of being smaller in size, low cost and good performance. However, bearing these merits, such structures also suffer in efficiency due to the ghost of spurious passbands emerged at harmonics of the centre frequency. Furthermore, heterogeneous dielectric material encircled with conductors generates undesired odd-even spurious passbands during propagation. The variation in propagation speeds between odd and even modes results in unwanted ripples in the microstrip coupled lines. These needless spurious bands are generally hurtful in microwave filters especially for wireless applications such asWiMAX.In this regard, the proposed work focuses on the investigation of new microstrip parallel coupled structure to control the insertion and return losses in the passband of bandpass filter (BPF) for WiMAX applications. The concern of adjusting the ripple levels of filter is attained by properly tuning the resonator elements and selection of Aluminum oxide (Al2O3) as substrate materials. The utilization of Alumina as substrate material reduces the dissimilarity in propagation velocity of the odd and even modes in microstrip coupling structures. After tuning the resonator elements significant outcomes have been observed in terms of return losses (S11) reaching the extent of >10dB to persuade the requirements of WiMAX band of 5.792GHz. The proposed work presents the optimal simulation model with AWR Microwave Office platform to evade the presence of spurious modes and complementing the bandwidth and ripple levels of the filter.

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