This study presents a novel microstrip diplexer with a joint T-shaped resonator. The T-shaped resonator has an extremely small frequency ratio using microstrip with practical line width. Additionally, the T-shaped resonator can be used as a frequency selective signal splitter, making it feasible to design a diplexer for a system with two extremely close bands. The diplexer using a joint T-shaped resonator does not require combining circuits and matching networks. A diplexer used in the UMTS-WCDMA system is designed and measured. The proposed diplexer has high isolation and wide stopband in addition to satisfying the passband requirement. A satisfactory agreement between the simulated results and the measured results validate the proposed configuration.
This paper presents general design formulas for a dual-band impedance transformer with an inherent and selectable transmission zero. The inherent transmission zero can block unwanted signal or interference and improve the overall circuit performance by suppressing spurious response and enhancing selectivity. The considered load has unequal complex impedances at two uncorrelated frequencies. The proposed transformer consists of three sections of transmission lines and two shunt stubs. The parameters of each transmission line and stub are obtained using the derived analytical formulas without any time-consuming try-and-error procedure or numerical solution. The proposed design formulas reduce the need to use a transmission line with extremely high or low impedance. Two impedance transformers are designed and fabricated. Good agreement between numerical and measured results validates the proposed design formulas.
This work presents a four-channel multiplexer that uses joint T-shaped resonators. The multiplexer contains four second-order bandpass filters that are combined by two joint T-shaped resonators. The joint T-shaped resonators are also inherently the resonant elements and frequency selective signal splitter. Therefore, the proposed multiplexer has compact size because of fewer resonators and no matching/combining circuit.The T-shaped resonator also makes the presented structure suitable for multiplexers having very close bands. The multiplexer is then modified to obtain a switchable FDD diplexer which is an important device in dual-band wireless communication system. The mechanism of band switching is discussed. Only two diodes are required to control the switching between the two FDD bands. Good agreement between the simulated and measured responses validates the proposed structure.Index Terms-Bandpass filter (BPF), multiplexer, switchable diplexer, T-shaped resonator.
This study presents a three‐stage dual‐band impedance transformer, capable of providing good match between two circuit modules and generating an additional and selectable transmission zero. The input impedances of the output circuit module are unequally complex at two uncorrelated frequencies. Among the three stages of the proposed transformer, the first stage transforms the complex impedance of the load to become equal resistance at the two frequencies. The second stage cancels out the susceptance produced by the first stage at the two frequencies concurrently and generates the desired transmission zero. The final stage transforms the equal and real impedance to the input circuit module. This study provides analytical formulation of each stage to obtain the required circuit parameters instead of numerical solution or optimisation. The proposed impedance transformer has up to four configurations, subsequently decreasing the possibility of using an extremely narrow or wide transmission line. Simulations and measurement demonstrate the reliability of the proposed structure and design formula. The simulation results agree measured results well, and comply with the specifications.
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