Design Of Wideband Rf Receiver Front-end Circuit And System

High-performance wideband receivers are widely used in military and civilian communication systems. Besides the high linearity, high sensitivity, large dynamic range and other characteristics, broadband RF receiver front-end is a crucial part in the modern receiver system design. As the major part of a research project, this dissertation is mainly concerned with the in-depth study of wideband RF receiver front-end. Some broadband design methods have been introduced to investigate key components of the RF receiver front-end for wideband applications and research tasks. The major contributions of this dissertation are outlined as follows:1. Several novel printed antennas are investigated and designed with bandwidth enhancement for ultra-wideband(UWB) wireless communications. Firstly, a flame printed monopole antenna is proposed and its operation bandwidth is enhanced greatly with a self-similar slot. Secondly, a small open-L slot antenna has been improved with a T-shaped stub and rotated radiator patch for bandwidth enhancement due to its poor characteristic at high frequency range. At last, a novel double-open-L slot antenna with a small size is introduced with an asymmetric fed patch for bandwidth enhancement. The measured results show that these novel printed antennas have good UWB characteristics.2. Focusing on the DGS research, several micro-strip filters with wide stop-band characteristic are proposed and studied. A pair of coupling slots are introduced and etched on the side of a classic dumbbell DGS cell to improve its poor stop-band characteristic, and a compact and small low-pass filter with this structure is designed for wide stop-band suppression from 3.9 to 18GHz with a rejection level of 20dB. Furthermore, a compact ultra-wideband band-pass filter with a pair of slits is designed for a good out-of-band selectivity and an improved upper stop-band rejection of about 17.6dB up to 20GHz. In addition, these filters with small size are suitable for portable systems.3. PLL frequency synthesizer technology is adopted to design broadband microwave frequency source, which is suitable for broadband receiver front-end systems. The narrow voltage control range can be increased greatly using third-order active loop filter and zero drift of the op amp can be eliminated with positive and negative power supply scheme. From the measured results, the synthesized broadband frequency signals show wide bandwidth, low phase noise and other characteristics. 4. An automatic gain control(AGC) circuit is investigated and designed for the wideband receiver system. Using series PIN diodes and single power supply mode,the poor attenuation characteristic at high frequency range is improved greatly. From the experimental results, the operation bandwidth is increased up to 8GHz with a good flatness and a linear attenuation control range better than 45dB. Based on the basicπelectrical modulation attenuator, a wideband AGC circuit system has been achieved with a wide dynamic control range and good suppression out of the pass-band.5. Wideband RF front-end systems with small size have been designed and manufactured. Using double frequency conversion structure, the overlap between broadband RF frequency range from 0.5 to 1GHz and IF-band is successfully and easily resolved the spectrum separation. The chip-level channel design program can be used to simplify the frequency planning from 2 to 8GHz and solve the system integration problem. With these methods, the system design flexibility has been improved greatly. From the measured results, the wideband RF front-end systems with small size, wideband, high dynamic and other characteristics fully meet the design requirements at the discretion of the engineer.