| Summary: | 碩士 === 國立高雄第一科技大學 === 電子工程研究所 === 104 === This paper presents the design of dual-band crossover, the circuit structure is composed of two conventional branch-line couplers. In the proposed design, we make all quarter-wavelength asymmetric spur lines improved by asymmetric coupled lines being equivalent to the circuit consisted of a branch line merging parallel open stub. According to the theory, the relative function of the asymmetric spur lines and equivalent circuit can be derived. Furthermore, the symmetric spur lines can be transformed to asymmetric spur lines in appropriate condition and obtain the relative function. Then, we can implement the design of dual-band crossover achieved the criteria by the steps of theory.
Two different frequency ratio examples selected in common frequencies were designed to verify the theory. The first circuit operating at 2 GHz/1 GHz, the result of the measurement in lower band is S_11=-33.2 dB、S_21=-27.6 dB、S_31=-41.9 dB、S_41=-0.62 dB, bandwidth of 200 MHz, in upper band is S_11=-32.1 dB、S_21=-47 dB、S_31= -28.1 dB 、S_41=-0.72 dB and bandwidth of 200 MHz. The second circuit operating at 2.4 GHz/1.8 GHz, the result of the measurement in lower band is〖 S〗_11=-29.7 dB、S_21=-21.15 dB、S_31=-13.1 dB、S_41=-0.51 dB, bandwidth of 300 MHz, in upper band is S_11=-19 dB、S_21=-36 dB、S_31=-24.3 dB、S_41=-0.78 dB and bandwidth of 400 MHz. As the results, the performance of two cases achieve to specification. The asymmetric spur lines structure can improve the conventional circuit being unable to be fabricated because of the Open-circuit stub impedance is too large when the frequency ratio is lower. Asymmetric spur lines will be use diversification in the future.
|
|---|
