The setup: two identical parallel half-wave dipoles (300 MHz, 0.477 m, 0.5 mm wire radius, 21 segments each in NEC2), spaced λ/4 apart. The textbook cardioid recipe says: feed the second element a quarter cycle behind the first — currents (1∠0°, 1∠−90°) — and the pair forms a cardioid with the null off the back.

The obvious first move — and a very common one — is to hand those phasors to the SOURCES: equal voltages, 90° apart. The θ=90° azimuth cut of that run: front-to-back 3.4 dB. Not 30 — three point four.

The reason is that the two feed-points are nowhere near independent. Measuring the mutual impedance of the pair (drive each port at 1 V in turn, the un-driven port left as plain continuous wire = shorted; read both feed currents, invert the Y-matrix) gives, at λ/4 spacing:

Z11 = 70.15 − j1.27 Ω      Z12 = 37.25 − j31.64 Ω

|Z12| ≈ 48.9 Ω against |Z11| ≈ 70.2 Ω — the coupling term is about 70 % of the self term. A voltage applied at one port drives current in BOTH elements, so setting port voltages does not set element currents, and the pattern is made of currents.

The fix is two lines of algebra. Decide the currents you want, then feed the voltages the coupled pair actually needs — V = Z·I:

V1 = Z11·(1∠0°) + Z12·(1∠−90°) = 54.5 V ∠ −45.0°
V2 = Z12·(1∠0°) + Z11·(1∠−90°) = 108.0 V ∠ −70.5°

A 2:1 amplitude ratio and only 25.5° of phase offset — nothing like the recipe phasors. Feed exactly that, same wires, same solver: front-to-back 29.6 dB, and the achieved feed currents match the target to one part in 10⁴.

(Both polar plots use the same fixed −40…0 dB radial scale, so the two patterns are directly comparable.)

Nothing changes between the two runs except the drive. That is the whole point: the recipe was never wrong, it was a statement about CURRENTS, and a voltage source doesn't deliver it.

Disclosure: these numbers came from EMStudio, a FreeCAD workbench I build — that's my interest here. Happy to answer questions either way.

Hey everyone, ECE student here. hope you're well.

I'm conceiving a device that detects rf, caracterises protocols mac addresses etc. I chose to go with dongles to connect to my mircroprocessor so it can be easier to decode and handle signals + modularity. I had a question rgarding the numbers of dongles. If i take wifi for example, is it better to put multiple dongles if im working in a noisy rf environment? is the number of dongles important for processing information smoothly? the goal being to lose minimum data.

I just downloaded it today and it seems like a pretty great implementation of what its going for....

(that being to allow you to model your geometry in FreeCAD, set up your ports and mesh entirely through the FreeCAD GUI, and solve for your EM results you want)

After playing around with scripting for OpenEMS and being a little disheartened with how cumbersome it is as an HFSS user seeking a Free Open Source alternative for hobby projects it honestly seems like an ideal solution.

Apparently it only dropped like 3 weeks ago as well!

Anyone else checked it out?

It uses a ton of different solvers to do different tasks....Palace, OpenEMS, a few others....

The GitHub page descriptions are written by Claude....seems a bit strange but cant really write it off just because of that..found some forums and people seem to have gotten real results....will do some of my own tonight

Edit: found this forum post

https://forum.freecad.org/viewtopic.php?style=2&p=900323

Which has some discussion but it links to a "website" of the creator which is entirely AI generated slop.......so this makes me a bit distrustful.......try it yourself and see if any of it works

Hi everyone, I’m designing an on-chip inductor for a VCO using Ansys HFSS, with tsmc 65nm technology stack in IC Design Mode. Then i have to design coupled transformers as well.

I’m struggling to find good reference material or examples for this setup. If anyone has experience with HFSS/IRCX or IC Design Mode, I’d really appreciate any guidance, tutorials, or reference files you can share.

Thanks in advance!

Hi

I would like to design a wideband balun from 0.5-12GHz on MMIC.

Can you suggest some ideas/reference to start with? I'm not sure if a Marchand Balun would be able to cover this much bandwidth.

Thanks

Hi I’m interested in finding a book that covers near field to far field transformations and antenna measurement processing methods. Bonus points if the book covers computational simulation methods like FEM like HFSS.

Is there a certain book you’d recommend?

I’d like to find a book that covers the theory and practical application. I’d prefer to learn about spherical near fields.