| The traditional RF modulation adopts the mode of up-converter and power amplifier after low-IF modulation,so the circuit is complex and the efficiency of power amplifier is low.Direct modulation does not require multiple frequency conversions.The baseband signal is used to modulate with the RF carrier directly.Modulation and up-conversion are performed in one step,and it simplifies the transmitted front-end architecture.The multi-port direct modulation technology adopts the first power amplifier post-modulation mode,eliminating the need for an active mixer,simplifying the circuital structure,and improving spurious suppression performance and the efficiency of power amplifier.The multi-port direct RF modulator consists of a multi-port junction circuit and variable impedance terminals.The simple structure is easy to be integrated and allows for overall simulation.Among them,the multi-port junction is a passive component,which not only has low power consumption but also facilitates the design of UWB circuits easily.The RF transmitter front-end implemented with multi-port junction has a simple architecture and strong reconfigurability,and has been gradually applied to the design of software radio technology.The main contents of the paper are:1?The relevant concepts of multi-port modulation technology are described.The structure of six-port direct modulator is analyzed.The S-parameter model of multi-port network is combed,and the detailed process of six-port direct radio frequency modulation is further deduced.This provides a theoretical basis for the subsequent research and design of the six-port direct modulator.2?Two different six-port junction circuits with different bandwidth and different structure are designed.The first six-port junction circuit is implemented by a two-section Wilkinson power divider and three modified branch-line couplers with bandwidths of 5.5 to 9.5 GHz.Among them,the two-section power divider adopts semi-circular trace structure and number-of-sections expansion method to achieve the design requirement of wide bandwidth and small footprint;And branch line matching network is used to ameliorate the coupler structure to achieve wide bandwidth design requirements.The second six-port junction circuit is implemented by a four-section Wilkinson power divider and three three-section slot couplers with bandwidths of 6 to 22 GHz.Among them,power divider and couplers use the method of expanding number-of-sections to achieve wide bandwidth.Because multi-section impedance lines will cause discontinuous performance loss,the trade-off between wide bandwidth and multi-section impedance lines is considered here.In addition,an opposite-phase power divider is also optimized to satisfy thefollow-up circuit simulation application.3?Based on the principle of six-port direct modulation,the carrier leakage problem in the six-port modulation process is studied,and the shortage of suppressing carrier leakage by inserting a phase shift network is analyzed.At the same time,a differential pair six-port wideband modulation structure is proposed.This structure overcomes the non-ideal characteristics of the six-port circuit and reflected load,so it not only achieves the purpose of suppressing carrier leakage,but also satisfies the need of designing a wideband modulator.Since no additional phase-shifting network is inserted,the bandwidth of this differentially-structured six-port direct modulator depends only on the bandwidth of the designed six-port junction circuit.The simulation results in ADS software show that the modulator has good modulation performance.4?Six-port modulation module is designed in ADS software.The design methods,schematic design and simulation verification of 4QAM,8PSK and 16 QAM modulation are given.Based on the previously designed six-port module and phase-shift network module,a 5.5-9.5GHz six-port modulator layout is designed for processing. |
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