Part 2: PCB Dipole Radiation Pattern Measurements

To verify the recently constructed PCB dipole antenna for 2.45 GHz I decided to measure its radiation pattern. The measurement setup consists of a BLE transmitter (at the right side in the image below) and a receiver (left side):

The transmitter and receiver antennas are in the same plane about 50cm (4 Lambda) above the floor and 36cm (3 Lambda) apart from each other which makes this setup a far field measurement. Both antennas are reasonably far away (more than about 10 Lambda) from other objects like walls, tables and so on, so for a first try, the setup should work reasonably well.

The transmitter simply broadcasts BLE advertisements. The receiver consists of an ADL5513-based RF power detector by SV1AFN that works from 1 MHz to 4 GHz. To measure the power, the detector is connected to a scope:

For each BLE advertisement, I get three broadcasts. To measure the radiation pattern of the antenna, I turn the transmitter antenna in 15° steps and write down the peak voltage of the first broadcast (1.11 V in the image).

The result is the excel sheet at the right side above. With the mapping from Vout to Pin from the ADL5513 datasheet (left side above), we can derive the effective power at the input of the power detector and from that, draw the radiation pattern in the elevation 0° plane:

Unfortunately, I was unable to trigger on broadcasts below about -38 dBm due to the high noise floor (dashed line in the image above). I’ll try with higher output power next time. Anyway, the result is as expected.

For a next step, I plan to construct different types of antenna (yagi, planar) and compare the radiation patterns with that of the dipole antenna.

Let me know if you have questions or comments!

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