Frequency Selectivity Using Plate Antennas

Discussion in 'The Projects Forum' started by dtow1, Jan 26, 2011.

  1. dtow1

    Thread Starter New Member

    Apr 27, 2010
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    0
    Hello,

    I am working with a plate antenna to measure variations in an electric field in the 0 to 100khz range. My teams advisor does not believe we will be able to distinguish frequencies that are in this range using the plate antenna. The setup is the plate connects to an op amp that has a feedback path with a capacitor in parallel with a resistor. It acts as a high pass filter, so the frequency range will actually be about 1-100kHz.

    The plan was to take this signal digitize it, and plot the FFT of the signal. Our advisor does not think it will work. Does anyone know anything that would help? We need to be able to distinguish different frequencies within the 1-100kHz bandwidth.

    We thought it would be able to work as we have been able to generate signals that were composed of multiple sinusoids and even sinusoids and square waves(generated using matlab). Using these signals we were able to find the frequencies in the original signal. We thought this would apply to the data from the time varying magnitude of the E-Field.

    Thanks for any help or advice!
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,789
    945
    For one, a coax strip would be the best way to interface to the plate antenna, and preserve a semi low inductance over a wide freq band.

    If you are using multiple front end LNA units be sure to sample them singularly and from isolation if possible. Each paralleled amp will have an additive effect on the signal to noise ratio of the detector, and not in a good way. Tri state bus buffers are suggested to isolate...finally, plate antenna are usually seen in the lower microwave to mid/high microwave freq ranges. I might believe a useful design operating at 100KHz, but much lower than that and the flat plate design seems very illogical.
     
  3. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Am I misinterpreting the title of your thread or are you actually desirous of a "selective" antenna? I ask this because I've never considered an antenna (on any band) to be particularly selective and it's not generally the function of an antenna. Antennas are resonant but they don't represent Q factor worth talking about. The terms "narrow band" vs "broad band" antennas is a relative thing.

    Side Note: In the late 60's I was working for a company that dealt with educational electronics equipment that we installed in public schools. One of the most common installs that we did consisted of common window alarm foil looped around the room 360 deg. The two ends of this foil loop was plugged into an external speaker jack of a small phonograph (Revere & Rheem-Caliphone) with a very low Z output. The audio signal was received by students wearing inductive headphones. This system worked, but it was vastly inferior to the RF models we sold.
     
  4. dtow1

    Thread Starter New Member

    Apr 27, 2010
    24
    0
    So it turns out I was on the right path, and I will be able to get the signal information out that I was expecting.

    It may seem odd to use the plate antenna that low but its had good results in lightning research at these frequencies. The electronics behind it make it work as a bandpass filter the lower frequency is inversely proportional to the time constant of the supporting circuit. We will be using a lowpass filter to set the upper cutoff frequency.

    So basically we really dont want frequency selectivity, it turns out that idea was a bit of an unintentional red herring. Its been a great learning experience though. Thank you again for sharing your expertise with me.
     
  5. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    The first radio transmission made by Marconi was spark transmission. I guess you could think of it as micro-lightning. Lightning, like electrical sparks, is a natural harmonics generator and loaded with amplitude modulation. In other words, it's frequency spectrum is very wide.
     
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