Utilizing Nonuniform Coupled Transmission Lines to Compact Microstrip Circuits Such as Edge-Coupled Bandpass Filters

Abstract

Abstract-In this paper, we propose a method to reduce the length of the narrowband microstrip Uniform Coupled Transmission Lines (UCTLs), which has a general application to compact microstrip circuits. In this method, we use Nonuniform Coupled Transmission Lines (NCTLs) instead of UCTLs. To synthesize the desired NCTLs, their normalized width and gap are expanded as two truncated Fourier series. Then, the optimal values of the coefficients of the series are obtained through an optimization approach. The usefulness of the proposed method is verified using some examples. Also, an edgedcoupled bandpass filter is compacted using the proposed method and then is fabricated and measured.

Analysis of a nonuniform guiding structure by the adaptive finite‐difference and singular value decomposition methods

“…The microstrip lines with nonuniform profiles are used in microwave circuits as resonators and filters. In [24], a low-pass filter is designed using the nonuniform microstrip line with parameters of ε r = 3.5, H = 768 μm, and l = 10 cm. Two filter ports are terminated with 50 Ω F I G U R E 3 Comparison between the proposed method and the exact solution of V and I of a single uniform TL (A)jVj(v), (B)jIj (mA), (C) ∠V (rad), (D) ∠I (rad)…”