Research And Design Of Broadband Coupled Line Feed Network Antennas Based On Micro-coaxial Technology

With the development of microwave technology and the emergence of new materials and processes,RF devices are evolving towards higher frequencies,higher integration,higher precision,and lower losses.The micro-coaxial process,made by sequential metal deposition,has high flexibility and extremely low losses due to its multi-layer stacking,micron-level processing precision,and air-filled process characteristics.Combined with the excellent line isolation of the coaxial line,it has a natural advantage in designing high-integration,miniaturized high-frequency devices.In this paper,we have designed two antennas with integrated wideband coupled line feed networks based on the micro-coaxial process.The main contents of the paper are as follows:（1）Firstly,the research background and significance of the micro-coaxial process are introduced,and the advantages of the micro-coaxial process are elaborated.Based on the basic theory of coupled lines,the relevant characteristics of coaxial coupled lines are studied,and a wideband coupled line balun is designed.（2）Fully utilizing the micron-level high-precision advantage of the micro-coaxial process,a wideband miniaturized hybrid ring is designed using a coupled line structure and directly integrated with a multimode differential antenna.The differential-fed multimode antenna operates in two frequency bands,both with normal radiation characteristics:The low frequency band radiates in TM₀₁mode,with an impedance bandwidth of 1.87%（15.9 GHz-16.2GHz）,and the maximum gain is 8.43dBi;The high-frequency band radiates in TM₂₁ and TM₀₃ modes by changing the current path through the slot line,with an impedance bandwidth of 7.37%（26.8 GHz-28.85 GHz）,and the maximum gain is 13.25 dBi.The designed hybrid ring has a center frequency point at 24 GHz,with a-10 dB impedance bandwidth of 75.98%（14.2 GHz-31.6 GHz）,effectively covering the two operating frequency bands of the antenna.（3）Fully utilizing the multi-layer stacking advantage of the micro-coaxial process,a wideband low-loss Lange coupler operating at 24 GHz is designed.Simulation results show that it can achieve a broadband bandwidth of 43%（18.7 GHz-28.8 GHz）,with a port magnitude difference less than0.5 dB in the passband,and a phase difference of 90°±2°.To verify the feasibility of the design,the coupler is scaled up to a 2.4 GHz working frequency band and processed using 3D metal printing technology.At the same time,the coupler is used to excite a circular patch to generate circularly polarized radiation.The final test results show that the antenna fed by this coupler can achieve an impedance bandwidth of 55.89%（2.05 GHz-3.64 GHz）and a 3dB axial ratio bandwidth of 28.8%（2.08 GHz-2.78 GHz）.The main cross-polarization level at the center frequency point differs by26.8 dB,and a stable high gain can be achieved within the passband.