DC to DC voltage step down converter on PCB

Question

I'm a beginner and I'm designing a PCB where I want to power my PCB from a 12-24 V DC car charger. On PCB itself, I want to use 5 V and 3.3 V for different components, so for this purpose I'm trying to find some ways to step down dc voltage from 12-24 V to 5 V.

I searched and found that buck converter, LDO and linear voltage regulators are usually used to step down DC voltages but I have few requirements.

1. I have an active antenna on my PCB so I want to avoid the use of buck converter because they use inductors and produce magnetic field which can interfere with antenna signals which are usually weak.
2. I don't want to use linear voltage regulators because they produce a lot of heat.
3. I couldn't find suitable LDOs in market who can step down 24 V to 5 V without producing much heat. (If someone know any specific LDO which can perform my task, please let me know.)

Personally I want to use buck converter because of their efficiency and low heat dissipation but can someone help me how can I check if magnetic field produced by buck converter will interfere with antenna signals or not? Is there any calculator or formula which I can use to determine the effect? Can I place both of them far (then how far?) to avoid interference.

If you have any other solutions for this problem, please reply.

Thanks a lot!

Edited Part: Below is the Screenshot for the antenna requirements on the pcb board. Active antenna receive signals from an L-Band satellite between 1525.0 MHz to 1559.0 MHz

Below is the screenshot for Buck convertor specifying Frequency used: switching frequency of Buck Convertor is 340 KHz

Answer 1

Years ago we used what was called MuMetal as shielding material, put the converter in that box made of that. It is available on line and is not that expensive. You may need feed through filters, not sure. Here is a link to get more information: https://en.wikipedia.org/wiki/Mu-metal

Answer 2

What about a buck converter with a switching frequency of ~2 MHz ? That way, harmonics can't be in your antenna band.

If you do insist on linear regulation, the amount of heat produced will be the same regardless of the regulator, however there are a few ways to manage that heat better:

• use lowest possible input voltage, because it is the dropout voltage that is dissipated as heat.
• place diodes in series between the supply and the regulator. That will reduce the heat dissipated in the regulator itself, allowing it to output more current.
• use an op-amp driving a power transistor as regulator. That way, the current can be very large if you use a transistor that can dissipate lots of heat.