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Dipole Antenna Impedance and Far Field Basics

Posted Feb 14, 2019, 1:32 p.m. EST RF & Microwave Engineering Version 5.2 2 Replies

Peter H
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I am working with the App Library Dipole Antenna model. I am trying to understand Lumped Port Input Impedance and resulting far field gain of the antenna.

Question 1: I understand the the Results>Derived Values>Global Evaluation>emw.Zport_1 gives the impedance of the port as it is influenced by the structure of the antenna. For me this number is (Zport = 120.21+28.489i). If I want to MATCH this impedance with the feedline how do I do it? By changing Lumped Port1>Characteristic impedance to Zref = 120 Ohm?

Question 2: When I do change Zref to 120 Ohm my S11 drops, indicating better impedance matching. However, I am struggling to see the resuling gain in the far field when using emw.gaindBEfar or emw.EIRPdB. Why is this? I suspect I am using the far field calculations incorrectly.

Question 3: Given the above confusion, is there a good functional reference for the various Far Field antenna calculations available within COMSOL?

Thank you so much!

2 Replies Last Post Feb 19, 2019, 1:40 p.m. EST
Robert Koslover Certified Consultant
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Posted: 5 years ago Feb 19, 2019, 10:28 a.m. EST
  1. Yes, I think that is about right.
  2. You need to plot the "realized" gain, since that accounts for the gain-reduction due to impedance mismatches. Take a look at the pull-down menu choices.
  3. Well, the help system will help you somewhat. If you haven't already read all the material about far-field antenna calculations there, then you should.
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Scientific Applications & Research Associates (SARA) Inc.
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1. Yes, I think that is about right. 2. You need to plot the "realized" gain, since that accounts for the gain-reduction due to impedance mismatches. Take a look at the pull-down menu choices. 3. Well, the help system will help you somewhat. If you haven't already read all the material about far-field antenna calculations there, then you should.
Peter H
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Posted: 5 years ago Feb 19, 2019, 1:40 p.m. EST
Updated: 5 years ago Feb 19, 2019, 1:54 p.m. EST

Thank you for your response. Part of my confusion is I'm just learning about antennas. However, most of the actual useful information I have found on Wikipedia. For example I now know my approach in Q1 is incorrect - I need Smith Chart analysis to determine how to match the lumped port impedance using a reactive circuit - which I guess is EE 101.

I did search over the manuals before I posted here but was unable to identify any tangible information regarding far-field antenna calculations...perhaps I am looking in the wrong place (Base COMSOL Manual>Plot Groups and Plots>Far Field and RF Module Manual>Far Field Calculations Theory) none of these describe the various flavors of far field gain calcuations. Do you have any information on additional description locations? Otherwise I will have to rely on Wikipedia and assume 100% crossover on the descriptions provided there as to what is implemented in COMSOL.

Thank you for your response. Part of my confusion is I'm just learning about antennas. However, most of the actual useful information I have found on Wikipedia. For example I now know my approach in Q1 is incorrect - I need Smith Chart analysis to determine how to match the lumped port impedance using a reactive circuit - which I guess is EE 101. I did search over the manuals before I posted here but was unable to identify any tangible information regarding far-field antenna calculations...perhaps I am looking in the wrong place (Base COMSOL Manual>Plot Groups and Plots>Far Field and RF Module Manual>Far Field Calculations Theory) none of these describe the various flavors of far field gain calcuations. Do you have any information on additional description locations? Otherwise I will have to rely on Wikipedia and assume 100% crossover on the descriptions provided there as to what is implemented in COMSOL.

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