Waveguide sections are often used to make connections in Test & Measurement systems. A variety of waveguide shapes may be employed depending on how the Device Under Test (DUT) is configured. Straight sections are commonly used in systems designed to test two-port waveguide components such as amplifiers and filters. More complex waveguide configurations may be needed to test multi-port devices such as directional couplers, power dividers, switching networks, or antenna systems.

Three common manufacturing methods are used to construct waveguide sections for mm-wave and sub-THz frequencies. The most common approach uses cold-drawn copper tubing for the waveguide. The tubing is cut to a desired length, bent or twisted as needed, trimmed, and brazed to waveguide flanges. The inside surface roughness of the tubing is usually controlled well enough to minimize its contribution to insertion loss. Oxygen-Free High-Conductivity copper is the most common tubing material, with silver-copper alloys often used at frequencies above 100 GHz.

One of the drawbacks of using cold-drawn tubing for waveguide sections is its limited mechanical strength, especially at mm-wave and sub-THz frequencies (Fig. 1). If the waveguide sections are frequently stressed during testing operations, they can become deformed or weakened over time. Their electrical performance may degrade progressively until the waveguide fails mechanically.

Fig. 1 – Waveguide sections constructed from thin-wall tubing often do not have sufficient strength for Test & Measurement applications.

To achieve greater mechanical strength while maintaining low levels of attenuation, waveguide sections can be electroformed (Fig. 2). This manufacturing process uses electroplating to build a metal structure around a polished mandrel that is removed afterward. A much thicker and stronger waveguide section can be constructed this way. The inside surface roughness is typically comparable to that of cold-drawn tubing, resulting in similar or lower levels of attenuation. However, the electroforming process and the additional machining steps involved are expensive. Because of their much higher cost, electroformed waveguide sections are often restricted to applications where low insertion loss and high mechanical strength are both necessary.

Fig. 2 – Electroformed waveguide sections are mechanically robust with low attenuation, but they can be much costlier than other options.

A third option is to manufacture waveguide sections using Wire EDM or other precision machining methods. With this approach, high-strength waveguide sections may be produced at significantly lower cost than electroformed equivalents. However, increased attenuation may be a necessary trade-off for a more economical manufacturing process. The insertion loss of machined waveguides depends on the specific machining process used, the quality of materials, and other factors. In many cases, a limited increase in waveguide attenuation will not appreciably affect the test system’s overall performance.

Machined Waveguide Sections Carry Greater Mechanical Loads

In mm-wave and sub-THz Test & Measurement systems, waveguide test ports are configured in various ways to provide electrical connections to the tested device. Examples include network analyzers, noise measurement systems, and antenna test ranges. In these and other measurement systems, the waveguide test ports may be subjected to repeated bending and twisting forces. If the test ports are realized using waveguide sections constructed from thin-wall tubing, mechanical stresses can quickly degrade test system performance and eventually lead to mechanical failures.

For improved longevity and reliability in waveguide test systems, Eravant offers precision machined waveguide sections that cover frequencies from 90 to 330 GHz. Manufactured using advanced machining processes, they provide economical alternatives to more costly electroformed components.

The STQ-WB series of precision-machined waveguide sections includes a variety of bends and twists, while the STQ-WG series contains a collection of straight sections. Fabricated from solid blocks of brass, they yield excellent mechanical strength and superior electrical stability compared to alternatives constructed with thin-wall tubing. Because of their rugged construction and enhanced levels of electrical stability and repeatability, they are considered metrology-grade devices.

For example, model STQ-WB-03090-T1-1.0 is a 90-degree waveguide twist that operates from 220 to 330 GHz (Fig. 3). Its WR-03 waveguide interfaces include UG387/U-M anti-cocking flanges. The twist can be used to rotate the orientation of an antenna for cross-polarization measurements, or combined with a Faraday isolator to realize a robust test port with the correct waveguide orientation. The twist measures 1.0 inches in length and exhibits typical insertion loss of 2.5 dB with return loss of 18 dB. 

Fig. 3 – Model STQ-WB-03090-T1-1.0 is a 90-degree twist that operates from 220 to 330 GHz.

Other machined waveguide sections include E-plane and H-plane bends, as well as straight sections of various lengths. Model STQ-WG-03010-F1 is a machined straight section that measures 1.0 inches in length with WR-03 waveguide interfaces and UG387/U-M anti-cocking flanges. Typical insertion loss is 1.8 dB with return loss of 18 dB.

For a complete list of Eravant’s precision machined waveguide sections Click Here.

Metrology-grade machined straight sections are also offered in a standard length of 2.5 inches for Test & Measurement applications. For a complete list Click Here.

Proxi-Flange^TM Contactless Waveguide Sections Combine Mechanical Strength With Ease Of Use

Eravant also offers straight waveguide sections that include a contactless flange on one end (Fig. 4). Proxi-Flange^TM contactless waveguide flanges can tolerate small gaps between the test system’s measurement ports and the DUT, thereby eliminating the need to engage and tighten waveguide screws when performing calibrations or when testing components. They are available in waveguide sizes from WR-42 through WR-03. Their benefits include faster calibration and testing, reduced contact damage on flange surfaces, less operator fatigue, and more consistent measurement results when testing large numbers of devices.

Fig. 4 – Eravant’s precision machined metrology grade waveguide sections include Proxi-Flange^TM straight sections. They feature a contactless flange on one end to eliminate the need to engage and tighten waveguide screws when performing calibrations and measurements.

Highly effective in a variety of Test & Measurement applications, Proxi-Flange^TM contactless waveguide sections are offered with a standard length of 2.5 inches. For example, model STQ-WG-03025-FB-CF operates from 220 to 330 GHz with typical insertion loss of 8.5 dB and return loss of 20 dB. Custom lengths are also available.

For a complete list of Eravant’s Proxi-Flange^TM products Click Here.