Waveguide bends are passive microwave components that change the direction of electromagnetic wave propagation while minimizing signal loss and mode distortion, and they are widely used in medical equipment, radar, satellite communication and microwave transmission systems. There are two types of bends: E bends, changing or distorting the E-Field (Electric Field) of the propagating signal; H bends, changing or distorting the H-Field (Magnetic Field) of the propagating signal.
Custom Bending Service
Fabmann is committed to provide custom fabrication solutions to our clients covering different material options such as oxygen free copper (C10100/CW009A), aluminum (6061, 6063), Electrolytic-Tough-Pitch Copper (C11000/CW004), brass and stainless steel, and we can bend the angle according to your design needs. Usually, the bend angle is 30 degrees, 45 degrees or 90 degrees, and the waveguide size and the flange type need to be specified during design stage. We can provide custom bending service for different waveguide materials and designations:
- 1. OFHC (CW009A/C101000)
- 2. Oxygen free copper (CW008A/C10200)
- 3. Copper (CW004A/C11000)
- 4. Brass
- 5. Aluninum (6061, 6063)
- 6. Stainless steel (304, 304L, 316, and 316L)
- 7. Waveguide range (WR3 to WR650)
Waveguide tube bending is a sophisticated custom fabrication processes, and it's a very demanding production job in terms of surface finish and bending accuracy covering section dimension, parallelism and perpendicularity. This custom waveguide bend fabrication main has following steps:
√ Waveguide tube cutting to length
√ Hydraulic pressing on waveguide tube filled with lubricated steel strips
√ Cut to length
√ Inner dimension adjustment by custom tooling
√ Section dimension, parallelism and perpendicularity check, inner surface roughness check, re-adjustment of inner dimension might be required.
√ Fine polishing of inner tubing
√ Full inspection covering section, parallelism and perpendicularity as well as surface finish quality
√ Final cleaning
√ Packing
Fabmann takes strict control of each process to meet the most demanding requirements set by our clients, and below are the typical quality controls which our engineers perform for each production batch. If you are looking for a waveguide bending specialist, Fabmann can be your long-term trusted partner.
1 Bending Radius Check by R Gauge
2 Projection Check
3 Twist Check
4 Flatness Check
5 Height Check
6 Dimension Check
7 Fine Polishing Check
8 Inner Surface Roughness Check
9 Visual Inspection
Waveguide Bending Considerations (Loss & VSWR)
Based upon Fabmann's waveguide tubing bending experience, several key factors must be considered to ensure waveguide bends' performance and reliability, and below is a short list:
√ Bend Radius
It is a critical parameter, the bend radius must be large enough to minimize signal loss and mode distortion. In order to minimize reflection loss, the radius of the bend should be greater than two wavelengths of the signal. The bend radius could also be a cause for micro-cracks. The curvature radius of the bend has a significant effect on the loss of the signal. The standard WR-90 waveguide, for example, operates in the frequency range 8.2 to 12.4 GHz. In order to ensure efficient signal transmission, it is recommended that the bending radius be at least two to three times the width of the waveguide, that is, the bending radius should be between 22.86 mm and 45.72 mm. If the bending radius is too small, the reflection loss will increase significantly, which may reach 0.5 dB or even higher, while a larger bending radius can control the loss below 0.1 dB. In general, wider waveguides (lower-frequency bands) allow larger bend radii. While tighter bends usually require smaller waveguides (for higher frequencies).
√ Mode Control
Ensure the dominant mode (e.g., TE₁₀ in rectangular metallic waveguides) is preserved. Andy sharp bends can excite higher-order modes or cause mode coupling, leading to dispersion or signal distortion.
√ Material Properties
Flexibility and mechanical durability of materials (e.g., aluminum, copper) influence bend tolerance. Malleability and ductility of copper is softer and more ductile than aluminum, making it easier to bend without cracking. However, excessive force can lead to deformation (e.g., kinking or warping).
√ Hardness, to make smooth bending, normally it requires annealing before bending, yet, lower hardness requires careful tooling to avoid surface scratches during bending. It's very important to keep inner surface roughness (Ra < 0.8 µm).
√ Tooling
Copper's softness may require polished dies to prevent surface marring while aluminum's stiffness demands robust tooling to manage springback and avoid cracking.
√ Surface Finish
Copper's ductility allows smoother post-bend polishing, critical for minimizing surface roughness-induced losses while aluminum may develop micro-cracks or roughness during bending, necessitating additional finishing steps.
The smooth design of corners usually requires that the inner wall of the waveguide has sufficient smoothness and appropriate radius of curvature. Taking the standard X-band waveguide as an example, its waveguide width is 22.86 mm. In order to ensure the quality of signal transmission, the minimum bend radius of the corner should be 2 to 3 times the waveguide width, that is, a bend radius of at least 45.72 mm. If not properly designed or produced, it can lead to frequency offset, signal reflection and increased loss, resulting in a decrease in efficiency of more than 40%.
√ Twist, it's a very common defect after bending, the waveguide tube start to twist due to stress release, and Fabmann's experienced engineers can correct the twist without compromising the angle tolerance as well as the inner surface quality.
√ Impedance matching abrupt bends create impedance mismatches, causing reflections (e.g., high VSWR in microwave systems). Gradual curvature or mitered bends (with chamfered edges) help maintain impedance continuity.
√ Electrical Performance (Insertion Loss & VSWR)
Insertion loss should typically be <0.3 dB per bend for high-performance systems. While VSWR (Voltage Standing Wave Ratio) shall be <1.25:1 to avoid signal reflections.
√ Application considerations, and different application has very specific demands, and following is a brief summary：
- 1. High-Power Systems (Radar, Satcom),needs to minimize risk of multipaction (RF breakdown), corrugated or smooth bends for lower loss is a popular option, and material must handle thermal expansion.
- 2. Millimeter-Wave (5G, 6G, THz) systems, tighter tolerances (±10–20 µm) is normally required, while mitered bends preferred for compact designs.
- 3. Aerospace & defense, vibration & shock resistance is very critical, plus, environmental sealing to minimize impact of humidity and corrosion. That's why gold plating is sometimes used for extreme conditions.
In general, copper has higher material cost but preferred for high-performance systems (e.g., satellite communications, medical imaging) where signal integrity is paramount. While, aluminum is relatively much cheaper and lighter weight , which makes it ideal for large-scale deployments (e.g., cellular base stations, aviation waveguides) where moderate losses are acceptable.
Why waveguide bends increase Ohmic loss?
Before explore the reasons, we shall get to an understanding about what is ohmic loss. Ohmic loss in waveguide bends refers to the resistive power dissipation that occurs when electromagnetic waves propagate through curved or bent sections of a waveguide. This loss arises from the finite conductivity of the waveguide's metallic walls, which causes currents induced by the electromagnetic fields to generate heat via Joule heating (P=I²R). In bends, this loss is often amplified compared to straight waveguide sections due to field distortions and increased current density. The causes of increased Ohmic loss mainly due to following reasons：
√ Field distortion, in the waveguide bends, the electromagnetic fields (TE, TM, or hybrid modes) are forced to curve, causing uneven current distribution on the inner and outer walls of the waveguide. This creates localized regions of higher current density, particularly on the inner wall of the bend, where the curvature concentrates the surface currents.
√ Skin effect, at high frequencies (e.g., microwave/mm, Wave/THz), currents flow primarily near the conductor's surface (skin depth 𝛿=2𝜔𝜇𝜎). In bends, the effective path length for currents increases, enhancing resistive losses.
√ Surface roughness, imperfections in the waveguide wall (e.g., manufacturing defects) scatter fields and increase the effective surface resistance, especially in bends where fields interact more intensely with the walls.
√ Mode conversion, sharp bends can convert energy from the desired propagating mode into higher-order modes or evanescent modes, which may couple more strongly to the lossy walls.
√ Material conductivity, high-conductivity metals like silver (𝜎≈6.3×107 S/m) or copper (𝜎≈5.8×107 S/m) reduce ohmic loss compared to aluminum or brass.
Quality Control & Testing
Inspection by Microwave Vector Analysis
Waveguide bending is inevitable in radar, satellite communication and microwave transmission systems. In the installation of satellite antenna, the waveguide signal needs to be transmitted long distance between the antenna feed and the equipment room, and the linear arrangement cannot be achieved. In this case, the waveguide bending design should consider not only the space limitation, but also the signal integrity. For such applications, the use of flexible waveguides is a common choice, which allows for multiple bends at small angles and is extremely flexible, saving installation costs. Fabmann will perform lots of inspections on waveguids bends before delivery, and our inspection including following aspects:
√ Dimension check
√ Bend radius inspection
√ Surface roughness measurement (Ra < 0.8 µm) check
√ RF performance testing including:
- 1. VSWR testing (Network Analyzer)
- 2. Insertion loss measurement
- 3. High-power check for arcing
√ Vibration & shock testing (for airborne systems)
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