Miniaturization Of Microstrip Band-pass Filter And The Plane Magic T-structure Design And Analysis

With the rapid development of the modern technology, high-speed, multi-band and large-capacity are the main interests of wireless communication technology. High-performance, miniaturization and multi-band filters are the key points in modern microwave and millimeter circuits. As we know, the four port magic-T structure is easy to achieve in-phase/out-of-phase power distribution and plays an important role in the microwave technology. The planar magic-T structures based on SIW (Substrate-integrated waveguide) and DSPSL (Double-sided parallel-strip line), are very convenient to overcome the drawbacks of the conventional waveguide magic-T structure, such as 3-D structure, narrower frequency bandwidth; and have important applications in microwave integrated and miniature circuits.A new crossed open stub structure is proposed in this work. Based on the conventional 1/4 or 1/2 wavelength broadband bandpass filter, two tri-band filters with sharp roll-off skirt selectivity can be realized by changing the locations of the transmission zeros created by the crossed open stubs. A new E-plane SIW power divider is proposed to replace the conventional T/Y-j unction SIW power divider, the new planar SIW magic-T using the power transmission from slotline to SIW, has nearly 50% size reduction compared with the former structures, and the fractional bandwidth for the magic-T structure is about 18%. Another multi-layer planar DSPSL magic-T structure based on the E-plane DSPSL power divider and conventional slotline magic-T circuit, is also proposed using the same analysis method with the planar SIW magic-T. Due to the intrinsic equal power dividing characteristic of the E-plane DSPSL structure, some redundant quarter/half wavelength transmission lines are not required, and the fractional bandwidth of the magic-T is over 40%, due to the broadband coupling between the slotline and DSPSL structure. Most of all, further size reduction has been achieved for the magic-T, while the magic-T structure almost keeps broadband transmission characteristic as the conventional slotline magic-T structures; all the structures designed in this work are expected to find potential applications in microwave multi-band communication systems and planar microwave integrate circuits.