Synthesis and new applications of multi-port filtering networks

微波滤波器是从移动基站到卫星等许多无线系统的重要组成部分。它们用于选择有用的信号，同时拒绝不需要的干扰或杂散信号。最广泛使用的微波滤波器是由谐振器组成的，谐振器电磁耦合在一起，在两个端口-输入和输出之间产生所需的传输响应。谐振器的特性和它们之间的耦合可以用所谓的“耦合矩阵”在数学上表示。这样的矩阵可以从所需的频率响应中找到——合成出来。双端口滤波器的合成是一门成熟的艺术。近年来，这种耦合矩阵方法已从双端口滤波器扩展到多端口滤波网络。滤波器和MPFN之间的根本区别在于“结谐振器”，用于将信号路由到不同的端口。这种谐振器不仅在滤波器中充当谐振极，而且还充当传统上由非谐振传输线实现的信号的分配器。从MPFN概念中获益最多的微波电路之一是多路复用器，也称为组合器或滤波器组。它基本上包含多个相互连接的滤波器，用于组合多个信道并馈送到一个天线进行传输或接收。它是无线基站和卫星有效载荷中最复杂的无源电路之一。按照惯例，所有信道滤波器通过基于传输线的信号分配网络连接到公共端口。使用MPFN概念，传输线网络可以用谐振器代替。这显着增加了多路复用器的选择性，而不会牺牲电路尺寸，这是工业应用所高度期望的。这意味着多路复用器，通常是一个大的组件，可以在尺寸和质量上减少更多的接触系统。就卫星而言，这可以转化为大幅降低成本。在微波电路中独家使用谐振器还可以将滤波功能集成到传统的非滤波电路中。例如，常见的微波功率分配器和耦合器是基于在线传输的，选择性非常有限。利用MPFN概念，可以实现全谐振器的功率分配器和耦合器，并嵌入滤波功能。这意味着两个电路功能被合并到一个电路中。这种方法被称为“协同设计”。尽管MPFN概念和协同设计方法在微波电路设计中的应用显著增加，但该技术仍然存在重大挑战。mpfn的合成比滤波器的要求高得多。这需要对结谐振器周围的耦合特性有新的认识。目前难以实现的合成技术阻碍了微波工程师对MPFN概念的接受。此外，由于结谐振器本质上是窄带的，并且可能是功率的集中，因此mpfn器件的带宽和功率处理能力也存在问题。本项目旨在为mpfn开发一种强大的、更容易获得和适用的合成技术，并通过提出新型结谐振器来解决带宽和功率处理方面的实际挑战。这项研究将有助于充分发挥mpfs在工业应用方面的潜力。毫无疑问，MPFN概念将导致微波电路的更多创新。在合成技术的基础上，该项目将研究两个新的电路概念。预计该项目将为新型微波电路的研究提供新的方向、进一步发展和商业探索的机会。

Microwave filters are essential components in many wireless systems from mobile base stations to satellites. They are used to select useful signals while rejecting unwanted interferences or spurious signals. The most widely used microwave filters are formed of resonators that are electromagnetically coupled together to generate the required transmission responses between the two ports - input and output. The properties of the resonators and the couplings between them can be mathematically represented by a so-called 'coupling matrix'. Such a matrix may be found - synthesised - from the required frequency response. The synthesis of two-port filters is an established art. Recently this coupling matrix approach has been extended from two-port filters to multi-port filtering networks (MPFNs). The fundamental difference between a filter and a MPFN is the 'junction resonators', introduced to route the signal to different ports. Such resonators serve not only as resonant poles as in a filter, but also as splitters of the signal which are traditionally achieved by non-resonant transmission lines. One of the microwave circuits that benefit most from the MPFN concept is a multiplexer, also known as a combiner or a filter bank. It basically contains multiple interconnected filters, used to combine multiple channels and feed to one antenna for transmission or reception. It is one of the most complex passive circuits in wireless base stations and satellite payloads. Conventionally all the channel filters are connected to the common port through a signal distribution network based on transmission lines. Using the MPFN concept, the transmission line network can be replaced with resonators. This significantly increases the selectivity of the multiplexer without sacrificing the circuit size, which is highly desired by industrial applications. This means the multiplexer, usually a large component, can be reduced in size and mass for a more contact system. In the case of satellites, this can be translated to a significant cost reduction. The exclusive use of resonators in a microwave circuit also enables integrating filtering function into traditional non-filtering circuit. For instance, common microwave power dividers and couplers are transmission-line based with very limited selectivity. By using the MPFN concept, all-resonator-based power dividers and couplers can be realised with embedding filtering functions. This means two circuit functions are merged into one circuit. This approach is known as 'co-design'. Despite the significant increase in the usage of the MPFN concept and co-design approach in microwave circuit design, there are still significant challenges associated with the technique. The synthesis of the MPFNs is much more demanding than the filters. It requires a new understanding of the coupling characteristics around the junction resonators. The currently inaccessible synthesis technique impedes the take-up of the MPFN concept by microwave engineers. Also there are concerns with the bandwidth and power handling capability of the MPFN-enable devices, as the junction resonator is narrowband in nature and may be a concentration of power. This project aims to develop a robust, more accessible and applicable synthesis technique for MPFNs and to address the practical challenges in bandwidth and power handling by proposing novel junction resonators. The research will help to release the full potentials of MPFNs for industrial applications. There is no doubt the MPFN concept will lead to more innovations in microwave circuits. Built on from the synthesis technique, the project will investigate two new circuit concepts. It is expected new research directions on novel microwave circuits, opportunities for further development and commercial exploration will be generated from this project.