Firstly, 3.5mm adapters are typically used in high-frequency applications, such as network analyzers or other precision testing equipment. Their design needs to take into account factors such as impedance matching, material selection, and mechanical precision. An optimal VSWR of 1.05 is a very strict indicator, which means an extremely high requirement for signal reflection. The closer the VSWR is to 1, the better the matching and the smaller the reflection. Therefore, when designing such an adapter, any factors that may lead to impedance discontinuity must be minimized.
Next, the structure of the adapter needs to be considered. The basic structure of a coaxial connector includes an inner conductor, a dielectric insulator, an outer conductor. Maintaining a low VSWR within such a wide frequency range from DC to 26.5GHz means that the impedance must be as close to 50 ohms as possible throughout the entire frequency band. Any slight discontinuity will produce obvious reflections at high frequencies.
In terms of material selection, the inner and outer conductors usually use metals with good electrical conductivity, such as gold-plated copper alloys, which can reduce losses and contact resistance. The dielectric material may require materials with a low dielectric constant and low loss. At the same time, it is necessary to consider that the dielectric loss will increase at high frequencies, affecting the performance. However, mechanical stability and temperature characteristics may also need to be considered, because although the selected dielectric material has good dielectric properties, it may be prone to deformation, affecting the reusability and service life of the connector.
Mechanical precision is crucial. The size of the 3.5mm connector is very small, and the tolerance must be strictly controlled. The diameter of the inner conductor, the inner diameter of the outer conductor, and the thickness of the dielectric insulator all need to be accurate to the micrometer level. If the machining precision is not sufficient, it will lead to impedance mutations, thus increasing the VSWR. Especially for the mating at the connection, it is necessary to ensure that when the two connectors are butted, the inner and outer conductors are in good contact without any gaps or misalignments.
In simple terms, the precision of parts, the precision of assembly, and the precision of the interface need to be considered.
In terms of contact design, an elastic contact method may be required, so that good contact can still be maintained after multiple insertions and removals. The surface treatment of the contact points is also important. Gold plating can prevent oxidation and ensure a stable contact resistance. At the same time, the thickness and compactness of the gold plating layer, as well as the reliability and consistency of the electroplating process, also need to be considered.
In terms of impedance matching, in addition to the structural design, a gradient structure may also be required inside the adapter. For example, the dielectric support can be designed in a gradient shape, or a stepped transition can be used to reduce impedance mutations. For example, when connecting conductors of different diameters, a gradual transition section can be used to make the impedance change smoothly and avoid reflections at high frequencies.
Simulation and testing are also essential steps. In the design stage, electromagnetic simulation software (such as HFSS or CST) is used to model the adapter and analyze its S parameters, especially S11 (reflection coefficient), so as to optimize the structural parameters. Then, a prototype is made for actual testing. For example, a vector network analyzer is used to measure the VSWR and insertion loss, and the design is adjusted according to the test results.
Since the goal is to achieve an optimal VSWR of 1.05, considering the test error, system error, and uncertainty, the test method for conventional products cannot be adopted during the test verification. Instead, the test method for calibration parts should be selected, and an air line should be used for test verification to minimize the impact of test uncertainty.
Temperature stability and mechanical durability may also need to be considered. High-frequency connectors may experience temperature rise during operation. The thermal expansion coefficients of the materials need to be matched to avoid structural deformation caused by temperature changes, which affects the performance. In addition, whether the abrasion after multiple insertions and removals will affect the contact is also a factor that needs to be considered. It may be necessary to select abrasion-resistant materials or designs.
The optimal VSWR of 1.05 may only be achieved at a specific frequency, such as near a certain center frequency, and within the entire range from DC to 26.5GHz, the VSWR may fluctuate. However, the design goal should be to maintain a low VSWR as much as possible throughout the frequency band, close to 1.05. This may require optimization in many aspects, including precise size control, material selection, contact design, and multiple iterative tests.
In summary, the key points in designing such a high-performance adapter lie in: high-precision machining, selection of high-quality materials, optimized impedance matching structure, good contact design, and strict testing and adjustment. Each link needs to be carefully handled to achieve such a low VSWR indicator.
It is necessary to optimize from multiple dimensions such as material selection, mechanical structure, and electromagnetic simulation.
LenoRF also can offer 3.5 mm connector for 33 GHz, VSWR<1.15.
PS: 3.5 mm RF connector can compatible with SMA connector.
