Research On Key Technologies For Power Combining In Microwave And Millimeter-wave Bands

Microwaves and millimeter waves are electromagnetic waves with wavelengths between 1 m and 1 mm,corresponding to frequencies from 300 MHz to 300 GHz.They are the primary information carriers in today’s radio frequency(RF)electronic systems.One of the key technical parameters is transmission power,since the strength of electromagnetic signals directly affects system performance.Due to the physical mechanism of semiconductors,the output power capability of a single device is always limited.Therefore,power combining technology,which combines multiple weak signals into one strong signal by controlling the superposition of electromagnetic waves,has been widely studied.The rapid development of 3rd-generation high-power semiconductor devices,especially those based on Gallium Nitride(Ga N),and the increasing signal bandwidth and application frequencies in RF systems have highlighted the shortcomings of traditional power combiners.These limitations include insufficient channel isolation,weak power handling capability and low efficiency in multi-path combining.In response to practical application requirements in microwave and especially millimeter-wave transmission systems,this dissertation explores novel power combining structures through key technological research and practical design.The main research contents are as follows:1.Isolation improvement technology for waveguide-to-microstrip hybrid power combiners.In current mainstream non-isolated waveguide-to-microstrip combiners,there is a phenomenon known as load-pull effect between the branches.This can lead to self-oscillation of the amplifiers carried by the combiner at certain frequencies/power levels.To address this issue,this work firstly proposes a new structure of T-coupling isolation by inserting a microstrip probe vertically from the short-circuit surface of the out-of-phase waveguide-to-microstrip power combiner.The isolation between the microstrip ports is increased to more than 12 d B.Second,a novel broadband isolation structure is proposed that introduces thin-film resistors between the probe ends of the in-phase waveguide-to-microstrip combiner,which improves the isolation of the combiner to more than 19.6 d B over the entire Ka band(26.5 GHz to 40 GHz).A Gysel-structured in-phase waveguide-to-microstrip combiner with dual fan-shaped probes is also proposed.The power handling capability of the combiner is increased to more than 2.5 times,and the port isolation is higher than 14 d B over the entire Ku band(12 GHz to 18 GHz).2.Isolation improvement technology for waveguide power combiners.In the context of commonly used E-plane and H-plane waveguide T-junctions with poor-isolation in engineering,we have undertaken compact and high-power isolation improvement designs.A novel structure of embedded micro-sized high-power resistive load is proposed,which improves the isolation of the waveguide combiner to more than15 d B and achieves an impressive power handling capability of 968 W with little increase in size.In addition,a new isolated three-way combiner is proposed for non-2~n-way power combining structures.By designing a new magnetic loop coupling probe at the shunt end of the E-plane waveguide six-port coupling structure to improve the combined phase coherence bandwidth,and embedding the waveguide full-band high-power resistive load at the isolation port to improve the power capacity,the three-way combiner achieves an isolation of more than 22 d B within the operating frequency range of 30 GHz to 40 GHz.The average power combining efficiency is90.4%,and the continuous power handling capability exceeds 96 W.3.Ultra-wideband power combining technology.Aiming at the requirements of broadband and high power in the field of electronic countermeasures and electronic test and measurement,we focus on the basic principle and design methods of power combiners operating over octave bands.First,a 6 GHz to 18 GHz ten-way radial power combiner was designed based on the transition between over-mode coaxial waveguide and fin line array,with an average combining efficiency of 88%in an ultra-wide band covering three octave frequencies.Then,the millimeter-wave broadband power combining technology based on ridge waveguide was investigated,and two structural forms:double ridge-double ridge and double ridge-single ridge of broadband ridge waveguide T-junction were proposed.Additionally,we introduce a novel non-contact microstrip dual-probe combining structure by vertically inserting it into the wide side of a single-ridge waveguide.By constructing a hybrid sixteen-way power combining network with dual-ridge waveguide to microstrip lines,the operating frequency can cover the K/Ka bands(18 GHz to 40 GHz)for millimeter-wave applications.The combining efficiency exceeds 78%.Finally,the amplifier achieved a maximum output power of 3.9 W.4.Direct multi-way high-efficiency power combining technology.To address the drastic degradation of combining efficiency caused by excessively long transmission lines in traditional hierarchical combining structures,this dissertation focuses on the composition,working principles and design methods of radial direct multi-way high-efficiency combiners.Firstly,we conducted research on the radial power combining technology based on the circular TM01 mode,designed a simple TM01-mode transducer with double injections,and proposed a new way to suppress non-combining modes using resistive absorbers embedded on the top of the radial combining cylindrical cavity.By constructing a twelve-way power combiner operating at 94 GHz in the W-band,we achieve a combining efficiency of 89.5%.Based on this,we introduce a vertically layered interconnected radial power combiner to carry amplifiers,and the continuous wave output power can reach up to 22 W.Next,based on the circularly polarized TE11 mode,we design a simple slotted circular polarizer that can be integrated into the sidewall of circular waveguides.It was constructed at 220 GHz in the terahertz G-band.This twelve-way power combiner achieves an average combining efficiency of 93.3%.5.Development of high-power transmitters for satellite communications applications.In view of the practical engineering requirements,this dissertation focuses on the application of isolated and high-power combining technology in satellite communication transmitters.First,our research was conducted on millimeter-wave Ka/V dual-band transmitters under the background of satellite Internet.Using a probe T-coupling structure to accommodate active amplifiers,we designed power amplifier modules.Based on an isolated E-plane waveguide T-junction,we constructed a power combining network.This leads to a compact,fully port-isolated power combining architecture.Within this structure,high-power transmitters with output powers of 250 W and 500 W were developed in Ka-band(27.5 GHz to 31 GHz)and V-band(47 GHz to52 GHz),respectively.Then,based on the Gysel-type isolated dual-probe combiner and the quasi-coplanar isolated H-plane waveguide T-junction,a high-power combined transmitter in Ku-band(13.75 GHz to 14.5 GHz)was constructed for broadcast and television satellite transmission applications,achieving kilowatt-level output power.