Design Method Of 90° Bridge Based On LTCC

Under the development prospect of 5G,the requirements for the performance indicators of devices are also getting higher and higher.Not only the miniaturization of devices is required,but also good performance and sufficient bandwidth,and these developments have involved all communication levels,which requires these devices to be mass-produced.Due to the increase in the number of use,the cost may be reduced as much as possible.The advantages of LTCC are also highlighted in these aspects.Its multi-layer structure enables the device to be three-dimensional and reduced in size.At the same time,LTCC can control the dielectric constant of the fired ceramic dielectric by adjusting the slurry,which makes it possible to reduce the size of the device by increasing the dielectric constant of the dielectric.Since the wires inside the LTCC mostly use gold and silver,this reduces the overall loss and facilitates the design of high-performance RF devices.The 3d B90° bridge is widely used in radio frequency circuits,especially in the antenna feed system and measurement circuit.It is an important passive device,but the ordinary bridge adopts the branch line structure or the coupling line structure,which makes the size of the bridge too large.huge.This contradicts the development of modern communication,which needs to be reduced in size to adapt to the trend of modern communication development while maintaining high performance.This can take advantage of LTCC to reduce the size of the overall bridge.Starting from the analysis of the single-branch bridge,the analysis method of odd-mode and even-mode excitation is adopted,and the single-branch is divided into two parts and calculated separately.Through the general analysis of the division along the symmetry plane,the reflection coefficient and transmission coefficient under single even-mode or odd-mode excitation are obtained.According to the performance of the bridge itself,the input reflection coefficient and the isolation terminal are both zero,and the branch bridge is solved.Branch lines can be calculated for any degree of coupling and frequency.In order to make up for the lack of bandwidth,a multi-branch coupler is introduced,and the same method is used to solve the multi-branch bridge.Unlike the single-branch bridge,the flattest or Chebyshev polynomial needs to be used to approximate the result,and each section is calculated.The impedance of the branch line,due to the complexity of the calculation,uses a computer to calculate the impedance of each order.In order to reduce the size,a lumped circuit equivalent distributed circuit is proposed,using a series inductance π type equivalent circuit and a series capacitor πtype equivalent circuit,two equivalent circuits,through In contrast,the series capacitor π type equivalent circuit is more suitable for the design of miniaturized devices.Through theoretical analysis,the single-branch bridge of series capacitor π type equivalent circuit and the lumped circuit of multi-branch electrical appliances are designed respectively.Compared with the single-branch bridge,the bandwidth of the multi-branch point bridge is increased by 3 times,and it also meets the miniaturization standard.The size of the single branch is only1.2mm×1.2mm,and the multi-branch is only 2.5mm×5mm.The size has been largely reduced.Starting from the theoretical analysis of the coupled line,the single-section coupled line is analyzed,and the method of odd-mode and even-mode excitation is also used to calculate the single-section coupled line under two different excitations.The coupling degree of the single-section coupled line is obtained by the consistency between the impedance calculated by the current and voltage and the impedance of the transmission line.A 3.2mm×1.6mm miniaturized 90° bridge was designed by using a helix,with a relative bandwidth of 55%,and the overall design of the device was realized through processing and testing.In order to expand the bandwidth,a multi-section coupler is introduced,and the equivalent of the prototype of the 1/4 wavelength n-order step impedance filter is used for analysis.The result also requires Chebyshev polynomial approximation.Since the strong coupling becomes a multi-section coupler,a stronger coupling will be introduced.In order to solve this problem,a cross-series connection method is proposed.The strong coupling is decomposed into multiple weak couplings,and they are cross-connected in series to obtain the final 3d B bridge.The size of the coupled line bridge is 7mm×15mm,and the relative bandwidth reaches 136%.The overall design is based on the simulation design of ADS and HFSS.The corresponding component values,or the corresponding line width,spacing,and length are calculated through ADS.Ideally,ADS is used to build circuit simulation,and after obtaining the results and meeting the index requirements,After the electromagnetic simulation of HFSS,the corresponding model is established,and the model parameters are further optimized to verify the correctness of the design.