Design Of Miniaturized LTCC Duplexer In User Equipment For Next-generation Mobile Communications

With the rapid development of communication technology, there are more and more urgent demand on the passives in RF front-end of user equipment, such as mobile phone, with high-performance, high-density, compactness, multifunction, multi-mode multi-channel and low cost. Therefore, the research of RF front-end of user equipment technology becomes an important issue. The duplexer can allocate and utilize very limited spectrum resources, make signals able to be received and transmitted in the wireless communications, simultaneously. So it plays a very important role in microwave devices, particularly in front-end module. The performance and integration density of RF front-end are partly determined by the high-performance miniaturized duplexer.On the other hand, low temperature co-fired ceramic (LTCC) materials have the characteristics of moderate dielectric constant, low loss within RF and microwave frequency, and easy three-dimensional integration with high fabrication precision. More attention should be paid to the development of front-end modules and duplexers based on LTCC technologies.For this purpose, the duplexers using a standard LTCC technology for GSM/DCS and UMTS applications are studied in this thesis. The procedures for analysis and design are given in detail. The size of the proposed duplexers is reduced significantly, and superior frequency selectivity is achieved. The proposed method for duplexer design is then validated by good agreements obtained between the simulated and measured results.The contents and main academic contribution of this thesis are as follows:Chapter I introduces the research background of this thesis.Several typical filter prototypes and their design methods are introduced in Chapter II.A novel LTCC duplexer is designed for GSM/DCS application in Chapter III. The duplexer prototype consists of a lowpass filter and a highpass one. The lowpass filter is composed of a parallel resonator in a series branch and a series resonator in a parallel branch. The highpass filter is composed of a series resonator in a parallel branch with two symmetrical capacitors. The size of the proposed duplexer is only 3.7mm×3.1mm×0.672mm. Its in-band insertion loss is better than -1dB and the isolation is better than -20dB.In Chapter IV, a novel LTCC duplexer is proposed for UMTS application. The duplexer adopts two bandpass filters with similar circuit topology. The size of the duplexer is 8mm×3.65mm×0.678mm. Its in-band insertion loss is better than -2.5dB and the isolation is better than -30dB, which well meets the practical specifications. Simultaneously, a new type of integrated tri-band multi-duplexer module based on LTCC technology is presented for GSM/DCS and UMTS applications. The duplexers for the second- and third-generation mobile communications in the module remain their individual performances, and the compatibility between them is also demonstrated.