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5 ways to measure Antenna Radiation

Aug 11 Posted by Roger Denker in Application Notes

These are some of the approaches to make sure that a wireless product works to full satisfaction.

1. We followed the datasheets so what can go wrong?

Every antenna needs a ground plane. Most datasheets are based on a large PCB with ample ground area. If the product is smaller than the reference board the performance deteriorates dramatically.

Some antennas are narrowband, they have a critical tuning and production variations.

Where is the battery located? Display in front of the antenna? Potting? Hand-effects? Cables? Who decided on an all metal cabinet?

2. It works pretty good so it must be OK!

This is the main danger in designing cellular applications. The cellular network is quite forgiving in urban areas. Even poor designs work pretty well in the lab.

However, when the going gets tough in rural areas or basements, poor designs will fail due to lack of RF performance.

When operating near a base station the transmit power is low and the device may work well.

When operating far from a base station the transmit power is at its maximum and may cause all kinds of internal failure in power supply, microprocessor or peripherals, especially with a bad antenna implementation.

3. Let’s see how far it goes

Walk around in the building to see how far it goes: Is this the same building as that of the end user? Do they have the same furniture? Are we walking away or towards the source?

Walk around in the field to see how far it goes: Find a large enough field. Make a portable installation. Make a fixture to not disturb the radiation. Walk large distances.

Oh yeah, what about polarization, or top-bottom radiation?

4. Why don’t we screw an antenna on the spectrum analyzer and measure the received power. (build a Bob detector)

Take an antenna and screw it on the spectrum analyzer. Take the EUT and put it at a distance. Turn the EUT around and look at the power readings.

Uhm, the power varies by 10dB when the EUT moves just a little.

Uhm, the power drops 7dB when Bob is not at his workplace. Bob’s leave must be cancelled!

Oh yeah, what about polarization?

5. Let’s wait for the certification measurements at the test-lab.

During the certification measurements we get official figures from the test lab. Then we’ll know exactly the performance!

Not all certification protocols yield useful radiation numbers. They are not measured for performance but for interference.

What if the performance is not good enough? Can we solve it with components? Do we need a redesign? Is the whole concept bad? Do we need to redo the certification? How much is this going to cost? What about the planned production? How do we break it to the management? What do we tell the customers?

This is like renting a multimeter at the end of the project.

There is an affordable way to optimize your product and verify its wireless performance:

RMS-0740 Product page

?We followed the datasheets so what can go wrong?

?It works pretty good, so it must be OK!

?Let’s see how far it goes

?Why don’t we screw an antenna on the spectrum analyzer and measure the received power

?Let’s wait for the certification measurements at the test-lab

Tags:

wireless development test lab

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