Waveguide-coaxial converters play a vital role in various fields like microwave and millimeter-wave communication, radar detection, etc, enabling efficient signal conversion between waveguides and coaxial transmission lines. Among them, converters with 90° (Right Angle) and 180° (End Launch) structures are commonly used in practice, and they have significant performance differences.
Regarding signal transmission loss, for the 90° structure, the abrupt change in signal propagation direction causes electromagnetic waves to reflect and scatter at the corner. At low frequencies, this effect is limited. But as the frequency rises, especially in the millimeter-wave band, the insertion loss increases notably. For example, in the X-band (8.2 – 12.5 GHz), the typical insertion loss of the 90° structure is about 0.2 – 0.5 dB; in the K-band (18 – 26.5 GHz), it may climb to 0.5 – 1 dB. In contrast, the 180° structure has a smoother signal path and transition, with loss less affected by frequency. In the X-band, its insertion loss can be controlled at 0.1 – 0.3 dB, and in the K-band, it’s only 0.3 – 0.6 dB, outperforming the 90° structure overall.
The Voltage Standing Wave Ratio (VSWR) reflects the impedance matching between the converter and the transmission line. The right-angle corner of the 90° structure easily disrupts impedance continuity, leading to unstable VSWR at different frequencies. In the C-band (4 – 8 GHz), the VSWR may reach 1.3 – 1.5; in the Ku-band (12 – 18 GHz), it can even exceed 1.6. The 180° structure better maintains impedance matching, with VSWR performance superior to the 90° structure in all frequency bands. In the C-band, the 180° structure’s VSWR is usually 1.1 – 1.3, and in the Ku-band, it’s controlled at 1.3 – 1.5, ensuring efficient signal transmission and reducing energy loss and instability caused by signal reflection.
In terms of power capacity, the 90° structure has limitations in high-frequency and high-power scenarios. Due to the concentrated electric field at the right angle, electrical breakdown is likely as frequency and power increase, restricting its power-carrying capacity. In the S-band (2 – 4 GHz), when the input power reaches a certain level, like several hundred watts, the 90° structure may distort the signal. The 180° structure features a more uniform electric field distribution and better heat dissipation, capable of withstanding higher power at high frequencies and powers. In the S-band, it can handle kilowatt-level power, having obvious advantages in high-power radar, satellite communication, and other high-power transmitting systems.
In summary, waveguide-coaxial converters with 90° and 180° structures have distinct performance characteristics at different frequencies. In practical applications, engineers should choose the appropriate structure based on factors like operating frequency, signal loss requirements, impedance matching accuracy, and power capacity needs to ensure the stable and efficient operation of the entire microwave system.