Using ADL5920 for Antenna impedance measurements

We are planning to use ADL5920 in our antenna matching circuit. Our radio works from 1MHz to 100MHZ and the connected antenna is mono-pole and tend to have impedance other than 50 ohm.. We are planning to insert an tunable LC matching circuit in the path just before antenna. The impedance measurement of connected antenna is required for our matching algorithm to insert exact matching circuit. We found that ADL5920 can measure FWD, REV and VSWR measurements. Can we measure antenna impedance with these values else is there any alternate/additional circuit needed to accomplish this task..

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  • +1
    •  Analog Employees 
    on Sep 5, 2020 12:59 AM 4 months ago

    Hi there,

    ADL5920 can measure return loss or VSWR, which are measures of reflection coefficient magnitude. To measure impedance, you need magnitude + phase information. ADL5920 does not give the phase information.

    You may still be able to use ADL5920 if your matching algorithm is able to try various matching topologies and values, then use minimization algorithm to find the best match that way.

    -Bruce H

  • Hi Bruce H,

    Thank you for the reply...

    We can develop a minimization algorithm and we already implemented like this technique in our radios. However as the tunable LC matching circuit consists of various relays, where the switching time is limiting factor. The semiconductor based switches cannot be used due to the larger values of inductance and capacitance values are required in this frequency band.

    In order to place a faster matching network, we need to exactly calculate phase angle between FWD and REV such that the calculated network can be inserted in the path. The timing is important as the radio uses hopping waveform. We request to suggest a suitable approach to calculate both return loss and phase angle measurement.

  • 0
    •  Analog Employees 
    on Sep 9, 2020 6:50 PM 4 months ago in reply to ramakrishnach@bel.co.in

    Hi again,

    We have AD8302 which measures relative mag and phase, but phase measurement is via EX-OR, so measurement range is ambiguous. Probably not best for your application.

    You might consider an IQ-Demod IC as a phase measurement device. Configure the baseband outputs for use down to DC. Map the I & Q values onto a phase plane. A 4-quadrant arc-tangent function gives phase angle. Calibration required. You could check the analog.com website for IQ DEMOD products covering your frequency range. -Bruce

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  • 0
    •  Analog Employees 
    on Sep 9, 2020 6:50 PM 4 months ago in reply to ramakrishnach@bel.co.in

    Hi again,

    We have AD8302 which measures relative mag and phase, but phase measurement is via EX-OR, so measurement range is ambiguous. Probably not best for your application.

    You might consider an IQ-Demod IC as a phase measurement device. Configure the baseband outputs for use down to DC. Map the I & Q values onto a phase plane. A 4-quadrant arc-tangent function gives phase angle. Calibration required. You could check the analog.com website for IQ DEMOD products covering your frequency range. -Bruce

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