Interview

Abstract

Dr Jianpeng Wang, from the Nanjing University of Science and Technology in China, talks about the work reported in their Letter ‘Compact microstrip balun diplexer using stub-loaded dual-mode resonators’, page 1994. Dr Jianpeng Wang As is well known, dual-band operation is frequently demanded in transceiver modules of modern wireless microwave communication systems. Rather than arranging two separated frequency-selective radio frequency (RF) circuits in the systems, many researchers choose an independent device, i.e., the diplexer, to support such systems. This is a useful component for reducing the overall size of RF transceiver applications. Microstrip diplexers are a three-port passive devices, which have the capability to split common input signals into two individual output streams operating in different frequency bands with high port-to-port isolation. The involved stub-loaded resonators in our design are the typical form of the dual-mode resonator. Their resonant properties have been characterised by using the even-odd mode analysis method. Through this method, we can examine how, by properly adjusting the length of the loaded stub, the even-mode resonant frequency of the dual-mode resonator can be tuned, while keeping the odd-mode resonant frequency almost unchanged. In this context, two resonant frequencies generated by the employed stub-loaded resonator can be flexibly controlled to realise a dual-mode response, which will substantially decrease the size of the balun diplexer, making it preferable to single mode resonators. In general, the utilised resonators play an important role in the implementation of compact balun diplexers with a certain bandwidth and two transmission poles in each operating band. What makes our work unique is the implementation of a typical multi-function integrated component, which effectively simplifies the circuit design, and reduces the overall size of radio frequency (RF) transceiver front-end systems. During the design phase, each balun filter channel in the diplexer can be independently controlled without effecting others, thus showing greater flexibility. Furthermore, no additional T-junction or matching networks are demanded at the common input port in our balun diplexer design. In our Electronics Letters paper, we introduced a new microstrip unbalanced-to-balanced (balun) diplexer, which utilises the stub-loaded dual-mode resonators. The proposed diplexer consists primarily of two balun filter channels. Meanwhile, these two balun filter channels are directly connected through a common open-circuited half-wavelength transmission line without any additional matching network. This unique property will reduce the overall size compared with other diplexer circuits using T-junction for the purpose of impedance matching. By adopting this method, we can create a compact, high performance balun diplexer with a remarkably simple structure. These changes are meaningful for RF engineers who design multi-function embedded unbalanced-to-balanced feeding networks in modern dual-band wireless communication systems. The presented design concept is a worthy guideline for the implementation of multi-function embedded passive components. In short, compared with the current approaches, it is more desirable to develop multi-function embedded components based on the viewpoints of explicit operation principles, simple structures, and high performances. In this way, these components can really facilitate and simplify RF transceiver front-end systems. It is our belief that components or systems using these techniques will prove more valuable to the engineering community.