Compared with 2G,the most prominent features of 3G and future wireless communication systems are a higher transmission rate and support for multimedia services.A higher transmission rate means that signal bandwidth is large,use of frequency spectrum is more efficient,and radio frequency equipment is greener.Demand for richer multimedia services is creating greater challenges for system developers and has led not only to the publication of tens of thousands of documents but also to tremendous new technology developments in the Long-Term Evolution(LTE)of 3GPP’s Universal Mobile Telephone System(UMTS).International deployment of UMTS is progressing steadily,and more than 180 mobile network operators throughout Europe,North America,and Asia are providing 3G services.High Speed Downlink Packet Access(HSDPA)and High Speed Uplink Packet Access(HSUPA)in UMTS can improve the transmission data rate and spectrum efficiency.This reduces transmission cost per bit.The trend towards increased data traffic and high-capacity content requires that base station equipment use new and existing frequency bands flexibly.This trend also requires that base stations have simplified but flexible network architecture with open interfaces and to consume less power.These requirements must be achieved by developing more efficient power amplifiers and broadband antennas as well as more compact high performance RF filters with less insertion loss.

In this special issue on microwave/RF technologies for future wireless communications,we invited five experts to contribute articles.Each of these articles shows a different aspect of the challenges and advanced technologies involved in microwave/RF for future wireless communications—from system architecture requirements,technologies in broadband power amplifiers,advanced RF dielectric resonator filters,and broadband antenna technologies to the state-of-the-art synthesis theory of sophisticated microwave/RF filters.We understand that these topics are far from enough to provide a complete picture of the industry,and some of the topics in this special issue are,indeed,classic.Nevertheless,we have obtained contributions from five experts,including the most experienced system architects in the industry,a senior RF engineer in power amplifiers,an industry leader who has been working on dielectric filters for more than two decades,a top tier scholar in broadband base station antennas,and the most eminent researcher in the microwave filter industry.Such combined efforts have made this issue very special.

We are very grateful to all the authors,reviewers,and the editorial board who have spent their valuable time on this special issue.We hope you will find the articles useful to your professional work and enjoyable to read.