Magnetic Dipole design

Hi, I want to design a magnetic dipole to use for frequency 2,45 GHz. My results are
Wavelength: λ=300 / 2450 MHz = 0.122 m
Diameter of the loop:
0,122 m/ 3,14 =0,0388 m =3,885 cm. Now I'd need to know the impedance of this antenna, but cant find out how to calculate it. The ideal impedance would be cca. 75 ohm. Should I divide λ by two to get a half-wave dipole? Cause as far as I know the impedance of a half wave dipole antenna is nominally 75 ohms. The next thing, I want to simulate this antenna. If u could recommend some good software to do this. Thank you

Hello,

What do you mean with a "magnetic dipole" exactly? From your description it seems that you are building a full wave loop. When you transform this gradually into a folded dipole, the impedance increases (to about 300 Ohms for the folded dipole). This feature you can use for matching if the actual antenna has too low input impedance.

The impedance at resonance depends on whether there is a ground plane present (under it, or close to it). Though a thin halve wave dipole has around 70 Ohms impedance at resonance, this drops significantly when a ground plane (or even edge of a PCB is present). Note that a dipole is a balanced antenna, so feeding from a unbalanced source, needs some form of balun function. Also keep in mind that the actual length of mostly somewhat less then 0.5*lambda (half wave dipole).

You can use whatever EM simulation tool (HFSS, CST, IE3D, etc). You can even use a NEC derived package as long as there is no dielectric layer involved.

Well magnetic dipole should be a current loop I hope I did that right. Or is it only a loop antenna. Then I dont know what is the difference between these two. I will connect this magnetic dipole to a magnetron through coaxial cable and using a balun. And this magnetic dipole will hopefully transfer the Te01 mode.

A magnetic loop antenna is mostly considered to have a circumference << 0.2 lambda so that the current along this loop is in phase and has same strength.

As these loops have large Im(Z)/Re(Z) ratio (and are strongly inductive), the bandwidth is limited. They are frequently used in RFID, EAS, MRI/NMR and in many other relative low frequency systems.

Your antenna looks more like 1 half of a biquad antenna that is favourite under WIFI enthusiasts (for example). The difference is that you use a round shape instead of square shape. Your full wave loop has a current knot, and the current changes phase when passing a current knot.

Regarding your application, in a household microwave, there is a strong standing wave behaviour (that means no plane propagating waves). Even when your dipole is good in free space, you may need matching to have efficient coupling toward the field in the microwave oven.

Ok and can you pls tell me how can I find out the impedance of this full wave loop or even change it to cca 300 ohms?

---------- Post added at 17:54 ---------- Previous post was at 17:50 ----------

And perhaps how the impedance, or other parameters would change if I would use for example a half wave loop or so?

The "Rothammel" antenna book quotes refers to [1] where the input impedance of a circular full wave loop is 135 Ohm.

[1] Dietrich, J.L: Loops and Dipoles: A Comparative Analysis, QST Sept 1985, pp. 24-26