Signal Antenna Flex Cable
Samsung Galaxy S21 5G Signal Antenna Flex Cable Replacement
- Fits
- Samsung Galaxy S21 5G
- Fixes
- Weak or no signal
- Quality
- Brand new, OEM quality
- Fitting
- Professional install
Overview
What this part is
The Galaxy S21 uses thin flex cables to carry the mobile signal between the main board and its antennas. If a signal flex is torn, pinched during a repair or corroded, the phone may show low bars, drop calls or lose service.
This is a technician's part. Rule out network, SIM and software causes first, then check the photos to match the flex to the one in your phone.
Compatibility
Specifications and compatibility
- Part
- Signal Antenna Flex Cable
- Compatible with
- Samsung Galaxy S21 5G
- Model numbers
- SM-G991B
- Does not fit
- Galaxy S21+, S21 Ultra, S21 FE or any other model
- Fixes
- Weak, dropping or no mobile signal caused by a damaged signal flex
- Does not fix
- Network outages, SIM faults, Wi-Fi or Bluetooth faults, or main board modem faults
- Quality
- Brand new, OEM-quality signal antenna flex cable. Tested before dispatch.
- Brand
- Unbranded, compatible with Samsung Galaxy S21 5G
- In the box
- 1 × signal antenna flex cable for the Galaxy S21 5G.
- Colour
- As shown in the photos
- Installation
- Professional installation recommended
- Supplied by
- Supreme Phone Parts Ltd, Manchester, UK
Before you order
Is this the right part?
Signs it needs replacing
- Signal bars are low where other phones have good signal
- Calls drop or mobile data cuts out often
- Signal got worse after a screen or back cover repair
- The phone shows No service with a working SIM
How to check your model
Open Settings › About phone. The Model name should read Galaxy S21 5G. The Model number should read SM-G991B.
The Galaxy S21 has a 6.2-inch flat screen and three rear cameras. The S21 FE looks similar but has a 6.4-inch screen.
Professional installation
How a technician fits this part
- Power the Galaxy S21 off and warm the edges of the back cover to soften the adhesive.
- Lift the back cover carefully and disconnect the battery before anything else.
- Remove the screws and covers to reach both ends of the signal flex.
- Unclip the old flex, lay the new one in the same route and press both connectors home.
- Reconnect the battery and check signal bars, a test call and mobile data before closing.
- Fit new back cover adhesive, close the phone and press evenly while it cures.
Check that the part matches the device before fitting it or removing any adhesive backing. Once a part has been fitted, it cannot be returned for a change of mind. Faulty parts are always covered.
FAQ
Frequently asked questions
Will this fit my Galaxy S21?
Yes, if Settings › About phone shows Galaxy S21 5G and the model number is SM-G991B.
Does it fit the Galaxy S21 FE?
No. The S21 FE has a different internal layout. This flex is listed for the S21 (SM-G991B) only.
Will it fix my Wi-Fi problems?
No. This flex carries the mobile signal. Wi-Fi and Bluetooth faults have other causes.
Is it made by Samsung?
No. It is a brand new, OEM-quality signal flex cable made to fit the Galaxy S21 5G, and every part is tested before dispatch.
Should I fit it myself?
We recommend professional installation. The back cover is glued and the flex connectors are small and easy to damage.
How quickly will it arrive?
Orders placed before 4pm on a working day are dispatched the same day from Manchester by Royal Mail Tracked. Delivery is free on UK orders from £5.
Prepared by the Supreme Phone Parts team, Manchester. Last updated September 2026.