Investigations On Microstrip-Short Circuit Coaxial Hybrid Resonator Filter Integrated With Shielding Case For Advanced Wireless Systems

With the rapid development of wireless communication services,more and more people tend to strive for higher bandwidth,faster throughput,greater flexibility,more high compatibility and interoperability requested for current wireless technology.The spectrum becomes more crowded and very nervous,there are many countries have resources exhausted division,and the use of extreme imbalance in the spectrum utilization rate is very low.Therefore,technologies to improve spectral efficiency,such as cognitive radio,convergence of three networks and dynamic spectrum sharing technology,have become the focus of current research.As one of the core components of RF front-end in wireless communication system,RF filter plays an important role in the performance,complexity and cost of the system.However,the recently RF filter with low band insertion loss and high out-of-band suppression has large volume and high cost.Because of these complex structure and incompatibility with planar integrated circuits,it is of great significance to study the high selectivity and compact miniaturized bandpass filters(BPFs).In the dissertation,the structure of microstrip-short circuit coaxial hybrid resonator integrated with shielding case is proposed.Employing the proposed technique,the designs on the RF bandpass filters,diplexer,and RF/Microwave transceiver front-end are successful verification by experimental results.The main innovation achievements of this dissertation are listed as follow:1.This dissertation presents the designed compact low-loss bandpass filter using the novel hybrid resonator.The proposed second-order filter comprises of two mixed technology resonators that are shaped by microstrip and short-circuit coaxial line.The bandwidth of filter can be enlarged with small distance between the coupled circular cylindrical rods.A prototype two-pole microwave filter is designed and fabricated for verification.The measured results show good agreement with simulated ones.The fabricated filter has a center frequency of 3.06 GHz and 3 dB fractional bandwidth of 5.2% while the insertion loss is only about 1.3 dB.Consequently,the proposed filter features smaller in size,easier to fabricate and higher Q-factor when compared with conventional microstrip filters.The work mentioned above is already published in IEEE 2015 Asia-Pacific Microwave Conference and authorized patent(201510763381.3).2.Aiming at the advantage of proposed hybrid resonator,a compact high unloaded-Q filter integrated with shielding case is proposed in this dissertation.Electric and magnetic mixed coupling is utilized to achieve one controllable transmission zero(TZ)in upper stopband,while the source/load coupling introduces another adjustable TZ in the lower stopband,which totally improve the selectivity.The frequency response of fabricated filter shows 3-dB relative bandwidth of 4.8 % at center frequency of 2.71 GHz.The measured minimum insertion loss of 1.45 dB while the return loss is 15 dB within the passband.The TZs located at 2.15 GHz and 2.85 GHz with high roll-off factors of 65 dB and 55 dB,respectively,have been achieved which prove excellent performance and further verify the design method.The research results mentioned above are already published by Journal of Microwaves.3.A new type of RF diplexer with high selectivity and high isolation is proposed and developed in this dissertation.The proposed diplexer based on hybrid resonator integrated with shielding case allows simple and compact layout to be constructed,which includes low insertion loss and high port isolation.The measured results show that the frequency band of the diplexer is 2.36 GHz~2.44 GHz and 2.65 GHz~2.75 GHz.The measured insertion loss of lower-channel is about 1.44 dB,the return loss is less than-15.8 dB,with three transmission zeros respectively at 1.84 GHz,2.68 GHz and 3.2 GHz in the passband.While those of the upper-channel BPF located at 1.3 GHz,2.23 GHz,and 3.05 GHz,respectively,the return loss is less than-15.2 dB.As the result,the channel-to-channel isolations of this diplexer are better than 50 dB.The experimental shows that the designed diplexer has good performance,such as low insertion loss,good return loss and high port isolation.Therefore,the proposed diplexer will be very useful in design cost-effective and high integration RF transceiver system.The work mentioned above is already published in IEEE Microwave and Wireless Components Letters.4.Based on the previous research on hybrid resonator filters/diplexer design and theory,the RF transceiver front-end prototype is achieved.The high isolation diplexer is employed to separate the Tx and Rx signals and reject the interferences from other systems to the RF receiver as well as filter out the harmonics generated by the RF transmitter.While,theses hybrid resonator BPFs with high frequency selectivity are utilized to channel selection and reject the image interference signal.The designed RF transceiver front-end operates at the 2.7 GHz for transmitting and 2.4 GHz for receiving,respectively,supporting 20 MHz bandwidth with frequency division duplexing(FDD)mode.The superhetrodyne structure is employed in the transceiver design and the center frequency of the intermediately frequency(IF)is 200 MHz.The performance indicators were determined under the overall requirements of the RF system's performance,and then the architecture of external local oscillator module was designed.The transceiver front-end design was validated by link simulation,then major devices in the frontend were designed with evaluation measurement,and finally the performances of the proposed transceiver are tested in several testing schemes.The measured results are illustrated as followed: the transmitter generates maximum output power of 14.2 dBm with its ACPR lower than-41.9 dBc.The transmit third-order intermodulation(IMD3)less than-39.5 dBc.The error vector magnitude(EVM)test was also performed on the transceiver front-end module under both narrowband signals and broadband signals.The test results show that for the 20 Msps QPSK,16-QAM,and 64-QAM modulation signal,the front-end achieves EVM below 2.13%,1.68%,and 1.28%,respectively.The realized front-end obtains above 30 dB receiving gain at 2.4 GHz,while the gain flatness is below 1.6 dB.The measured receiver sensitivity less than-75 dBm and output third-order intercept point(OIP3)better than 22.4 dBm with intermodulation distortion approximately-52 dBc.The EVM of 20 Msps QPSK,16-QAM and 64-QAM is not exceed 3.49%,2.57% and 2.3%,respectively.All the measurement results indicate the designed RF transceiver front-end module have excellent performance.The relative works mentioned above have been submitted to Microwave Journal.