Design of asymmetrical coupled line interdigital filter for long term evaluation (LTE)-26 band

Filters are key components in RF transmitter and receiver sections. The purpose of this paper is to design a asymmetrical coupled line inter digital filter for Long Term Evaluation (LTE) band 26, having uplink from 814MHz to 849MHz. Design principle of proposed filter is based on even and odd mode coupling nature of asymmetric microstrip coupled lines. Dimensions of the filter play an important role in RF front end design. The asymmetrical coupled line inter-digital design reduces the dimension as compared to other filter designs, such as microstrip coupled line filter. This approach also reduces the cost of fabrication due occupation of smaller footprint as compare to coupled line bandpass filter. This asymmetrical coupled line inter digital bandpass filter provided good stop band attenuation which is about -20dB at ± 20MHz of cutoff frequency. The proposed filter is implemented using FR-4 substrate having ϵ
_r
= 4.4 height =1.6 mm. The obtained results of simulation show insertion loss of 2dB (S
₂₁
= -2dB), return loss of 15 dB (S
₁₁
= -15 dB) and ripple of 0.1dB. The filter shows good response for passband frequencies.