All about Coaxial Attenuators
As resistive type networks, coaxial attenuators are mostly used for adjusting signal levels in military and commercial RF and microwave systems. While choosing the right coaxial attenuator, you need to keep certain parameters in mind.
The typically common varieties are SMA attenuators, Type N and BNC attenuators; however, one can also find variants like TNC, 2.4 mm, 2.92mm, QMA, SMB, 1.85, F and Reverse Polarity (N, SMA, TNC) attenuators.
Generally, brass and / or stainless steel are used as attenuator connector material. The most important thing to remember at this point is associated torque values – a brass SMA attenuators needs 3-5 in-lbs torque, while a stainless steel SMA will be needing torque value would be around 7-10 in-lbs. Torque value varies from manufacturer to manufacturer.
SMA, BNC, Type N, & TNC attenuators are available in brass and stainless steel; each having its own merits and demerits. Brass is definitely more common in commercial uses for its obvious benefits; stainless lasts over extended period of mates and de-mates. Under-torque particularly degrades performance of certain attenuators, like the SMA at higher frequencies, say 15 GHz & above.
The commonly available attenuators are used for small signal applications like 18 GHz 2 watts; 0.5watt & 1 watt you can find too. Above 18 GHz, choices are limited, like 0.5watts at 50 GHz. Standard specifications for power CW is at room temperature; it gets de-rated as the temperature rises. A 2 watt unit @ 25C could handle just 0.5watts @ 125 C.
With increase in frequency, the resistive chips like attenuators require more precision work, which increases the production cost. Common frequency bands are 0-6GHz, 0-18GHz, 0-26Hz, 0-40GHz, 0-50GHz and 0-65GHz. Being a simple resistive network, attenuators have minimum frequency range at 0; on the upper side limit at a level where you’ll observe maximum ripple in the pass-band with the widest deviation from the desired attenuator.
Small signal attenuators are bidirectional type with either port usable as the input. However, high power attenuators are mostly unidirectional with specific input and output port; hooking the DUT backwards could be fatal for such attenuators. That’s because high power attenuators are cascaded resistive chips; for example 2-3 db in the first chip, 3-5 in the second and 6-30 in the third. That helps to dissipate heat throughout the length of the attenuator. For applying power to the output creates power dissipation in one chip, and thus causes overheating related failures.
Coaxial attenuators are not meant for handling DC and they might change the DC for their resistive networks. Often they might dissipate excessive heat and fail to deliver performance. The best way to bypass the attenuator is with dc blocks & bias-t. Bias passing attenuators are also available with dc blocks & bias ts.
Common specifications are VSWR, Attenuation accuracy (tolerance), Attenuation Value, Upper Frequency limit, Power Handling Peak and Power Handling CW, Operating Temperature Range, Connector Material, Contact Material and Impedance.
Hope this small blog post would support with basic information on coaxial attenuators. For more queries, feel free to comment on this blog.
Author’s Bio: John Smith is a experienced writer who writes on several electrical topics. He has keen interest on electronics, electrical engineering and related stuffs. In this article, he described electrical attenuators, its types and specification.