Antenna Design (plus EMC) - Episode 8 of Antenna Briefs - Part 1

This episode focuses on antenna design, with underlying theory covered in this Part 1 video. Practical issues are also covered. In addition, the related subjects of radio frequency interference ( RFI ) from electronic products is touched on, and some thoughts on electromagnetic compatibility ( EMC ) mitigation strategies are offered. Part 2 of this episode will go into additional detail on the vast set of possible antenna configurations by showing and talking through a large set of examples. Given the size of the subject(s), some references are offered at the end for further study.

[@AbbasAbolfathimomtaz]

Antenna was always a mystery for me until I saw this fantastic series. Thanks. I was wondering if the 2-page handout is uploaded somewhere.

[@MegawattKS]

Thanks! Yes - it's the second pdf on this page: ecefiles.org/rf-circuits-course-section-11/ The full set of slides from the series is also available here, together with other series: ecefiles.org/ Glad it was helpful. Best wishes.

[@DPELMohdSiddique]

good lecture

[@MegawattKS]

Thank you.

[@M0XYM]

Truely excellent. Thank you. I wondered if you spend 5mins on the characteristics of 'long' antennas (where l >> lamda) For instance, I have a doublet of about 130' (ish) fed with ladder line. What could I (theoretically) expect if I attempt to rx/tx with wavelengths of a foot or so?

[@MegawattKS]

Thank you ! In free-space, antennas longer than lambda end up with somewhat (or very much) directional patterns. Hence, they have gain in particular directions and nulls in others. The patterns can be well controlled at high frequencies with careful design. See for example owenduffy.net/antenna/ccps/index.htm . But at HF (or otherwise when there are objects in the near-field (closer than lambda/2 for instance), those will influence/distort the pattern. Have you tried simulating your doublet installation with EZNEC ? EZNEC should be able to handle the antenna and ground - but it may not give completely accurate results if there are other things nearby. And it's a project in itself to learn all the features you'll need to use in the model, like the transmission line and ground definitions...

[@MegawattKS]

On the last question, do you mean using the doublet at 915 MHz? My guess, without simulator verification, is that most of the radiation will take place in the initial part of the feedline and connection to the tuner since the wire separation is a decent fraction of lambda. I'm guessing there won't be much power that makes it to the feedpoint of the doublet elements.

[@M0XYM]

@@MegawattKS Thank you for both replies. It's given me something to think about. Regarding the last question - actually I had 70cm and 2m in mind but your answer has shone a light! Thanks again.

[@TheGameRRecon]

Hello, this series is helping me out alot so far! Thanks. But I had a few questions. For context, I am doing a group design project for my degree, based on a future manned mission to Mars. I am handling the comms and telemetry. I am trying to size some antennas as this will help size the telemetry and computer systems but am finding it difficult to calculate these dimensions. I will be using a mix of X-band and Ka-band transponders, so with this I managed to get the respective wavelengths. But from this point onwards, I'm unsure on what antenna type to use, how to work out the gain, and other miscellaneous parts of the antennas. Could you give me any guidance with this? What steps to take when developing deep-space antennas? Any info would be of great help.

[@MegawattKS]

Glad to hear you found the Antenna Briefs series. I would recommend you look at Episode 3 which discusses link-budgets for free-space path-loss conditions. Episode 4 goes even further (literally ;-) - looking at what antenna sizes and data rates need to be used for talking to nearby star systems in the Search for Extraterrestrial Intelligence (SETI) :-) Hope that helps.

[@TheGameRRecon]

@@MegawattKS Brilliant, will take a look now. Thanks again.

[@dominicestebanrice7460]

Is it just coincidental that if (as a thought-experiment/sketch-exercise) I take a plate capacitor, represented on a sheet of paper in the X-Y plane, with dimensions H x W x t (and imagining just air between the plates as the dielectric), and then 'move' the cable connectors to the edge of each plate, and then fold/straighten the entire thing out, I end up with the geometry of a dipole antenna, albeit one with a large Z-axis dimension? If I then 'trim' off most of the Z-axis material of the plate, it becomes essentially an antenna shape/configuration. Is a dipole antenna a form of capacitor in an AC circuit, just with the 'plates' (poles) not facing each other but facing outward in the same direction? It's KZbin.....dumb questions are OK, right?😘

[@MegawattKS]

Sorry for the late reply. Yes! Good observation. And no, it's not coincidental. Actually the first antennas by Hertz used balls at the end to increase capacitance. I assume this is because they had more confidence in having enough capacitance that way. But it's also the inductance of the rods that makes this work. The capacitance is associated with E field and also getting currents flowing as you said. And the currents induced in the rods by that capacitance work together with the capacitance to create and launch EM waves :-)

[@darmayuda4157]

Pls explain with formula n explain to the point..

[@MegawattKS]

Please see the earlier episodes in the series for the physics and math. In particular, episode 6 shows full integral equations for finding the far-field patterns. I thought about including some rough empirical formulas for some of the designs covered in episode 8 on design, but there are too many antennas to fit all that into a single episode. Hopefully once an antenna type is decided on based on directivity and gain needed and other design criteria, one can do internet searches for formulas that give starting values for dimensions/etc. Then, a design should be refined using simulation as discussed in episodes 5 and 6. Here is a link to some of the physics and math from Episode 6. See Episode 5 for intro to Maxwell's equations that these equations are based on. Hope that helps. kzbin.info/www/bejne/jHe1enWqe9yDn6c

[@kaliannabel5602]

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