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8-5 Directivity Test Operational Testing for the MA24105A

8-4 PN: 10585-00020 Rev. C PowerXpert UG

8-5 Directivity Test

The most common cause of power sensor failure is excess input power. Applying power that exceeds the

damage level shown on the label will damage the coupling element in the MA24105A, resulting in directivity

change. Excessive mechanical shock can also cause directivity to change.

Test Procedure

Directivity tests an MA24105A for how selective the sensor is when measuring power in a given direction of

travel and rejecting signals traveling in the opposite direction. The simplified equations below give the first

order approximation of this parameter:

Directivity (dB) = Power Forward (dB) – Power Reverse (dB)

Directivity Coefficient = 10

(–Directivity (dB) / 20)

Directivity (dB) = –20  log(Directivity Coefficient)

Directivity (dB) = 10  log(Power Forward / Power Reverse), where power is in watts.

In this test, the MA24105A is tested first with power in the forward direction and then with power in the

reverse direction. See Figure 8-1 on page 8-5.

The ratio of the two power readings are the directivity of the device assuming that both the termination and

source are perfect 50 ohm matches. Since the termination and source are not perfect matches, residual effects

from multiple reflections need to be accounted for by performing the following procedure.

1. Turn off the RF of the synthesizer. Connect the power amplifier to the synthesizer. Connect the output of

the amplifier to the input of the MA24105A. Terminate the output of the MA24105A with the specified

termination (Figure 8-1).

2. With the RF off, zero the MA24105A.

3. Set the synthesizer to the first frequency in Table 8-3 on page 8-6 and to a very low power setting and

slowly increase the power until the MA24105A displays +30 dBm. Allow the devices to warm up for 30

minutes.

4. Turn off the RF of the synthesizer and zero the MA24105A again.

5. Turn on the RF and adjust the synthesizer until the MA24105A displays approximately +44 dBm.

Confirm that the reading is stable and record this value as Power Forward in Table 8-3.

6. Turn off the RF on the synthesizer.

7. Reverse the MA24105A connections to the termination and the amplifier. Confirm that the MA24105A

output is now connected to the amplifier and that the input is connected to the termination (Figure 8-1).

8. Turn on the RF. Change the MA24105A averages if necessary to see a steady reading. Record the value

as Power Reverse in Table 8-3.

9. Calculate the Actual Directivity in dB by subtracting Power Reverse from Power Forward. If the power is in

watts, use the formula noted above to calculate the Actual Directivity in dB.

10. If the actual directivity is larger than the minimum allowable directivity in Table 8-3, contact Anritsu

customer service.

11. Repeat the steps above for the next frequency in Table 8-3.

Note

Both forward and reverse readings are taken from the Forward Average Power window on the

PowerXpert display as shown in Figure 8-2 on page 8-5.

1 2 ... 103 104 105 106 107 108 109 110 111 112 113 ... 223 224

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