I'm designing a PCB with a ESP32-PICO-V3, with a RF output to a 50 Ohms U.FL (Micro-Coax) connector. The chip supports WiFi and Bluetooth in the frequency range 2.45 +/- 0.45 GHz.

Right now, I have a prototype with a 0 Ohms resistor in lieu of the CLC filter suggested in the Hardware Design Guidelines (pdf), which also states that the output impedance of the chip is ~(30 + 10j) Ohms (for the 6x6mm package, I have the 7x7), and I get 45 Mbps with iPerf test.

However, I'd like to improve the circuit with a true LC Balun filter. According to this site (and a few others), I get the following design::enter image description here.

I'm wondering: how do I route the plane under the RF trace with this type of connection to ground? I currently have the following layout:enter image description here.

My guess is that it will work however I do it, since it already works with no filter or matching. But I want to minimize EMI right from the start. Otherwise, should I just follow the guideline of putting a CLC filter and be done with it?

Other info: the stackup is Er = 4.05 and height = 3.5 mils. Traces are 6 mils wide.

  • 2
    \$\begingroup\$ The u.fl coax connector is for an unbalanced line, and the chip has an unbalanced antenna pin. Why do you want a balun? You just need a conventional impedance matching network. \$\endgroup\$ Oct 11 at 4:51
  • \$\begingroup\$ Ah! It seems I had the concepts of impedance matching and line balancing mixed up. If I got this correctly, a balun can also include impedance matching, but need not do so. Since my input and output are both unbalanced, I only need the impedance matching part. So the CLC Pi matching circuit is the way to go. Thank you! \$\endgroup\$
    – Quantumal
    Oct 11 at 5:19

As Mark Leavitt commented, both the chip and connectors are unbalanced lines, so a balun (balanced-to-unbalanced) is not what I need here, although it can also include an impedance matching function. I only need the functionality of a CLC Pi matching circuit... just as the Hardware Design Guide suggests!

It seems EEWeb provides a nice calculator for this case, which is faster than re-learning the contents of Microwave and RF Wireless Systems by David M. Pozar


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