5.9GHz Front-end board - PCB material

Hi to all,

I am new by here. I am going to develop a board for WLAN 802.11p communications. In my board I am going to use a transceiver (MAX2828), a Power amplifier, a LNA and a RF Switch. All these components are 50ohms I/O matched. So, my RF circuit consists about some RF components and some transmission lines to connect them.

Relatively to the PCB material I don't know if I should use some Rogers or if I could use FR4. I know Rogers is more suitable for high-frequency applications, but it is much more expensive.

As my board won’t have any matching network with lines, there will be only some short transmission lines to connection, so low insertion loss is expected, even with FR4.

Considering the cost-performance trade-off for this situation I think FR4 is a good choice.

What do you think about this?

Thanks a lot

nuno_portugal said:

Hi to all,

I am new by here. I am going to develop a board for WLAN 802.11p communications. In my board I am going to use a transceiver (MAX2828), a Power amplifier, a LNA and a RF Switch. All these components are 50ohms I/O matched. So, my RF circuit consists about some RF components and some transmission lines to connect them.

Relatively to the PCB material I don't know if I should use some Rogers or if I could use FR4. I know Rogers is more suitable for high-frequency applications, but it is much more expensive.

As my board won’t have any matching network with lines, there will be only some short transmission lines to connection, so low insertion loss is expected, even with FR4.

Considering the cost-performance trade-off for this situation I think FR4 is a good choice.

What do you think about this?

Thanks a lot

Click to expand...

You are right, FR-4 is the best low-loss material for any RF circuits above ~1 GHz. If you wish to save on it a bit, I can recommend what I used in my designs. I used FR-4 only for the 50-Ohm lines and DC islets while I soldered all ground pins, etc., directly on a thin brass plate that was my "module". To make a complete system, I needed more such 2x 3 cm modules mounted in an aluminum case.
The advantages are: - the ground connections are perfect, no ground "vias" needed, and heat dissipation is better than specified.
- individual modules can be easily tested from a 50-Ohm source to a 50-Ohm load to verify the specifications.
- I connected then the modules with soldering short thin copper strips from one 50-Ohm line to another.
- I only needed narrow 50-Ohm strips of FR-4, and small cutout squares are good to connect DC and control to MMIC pins.
- I can use surface-mount components as well as MMIC with various pins and connections. Many SMD MMICs allow to bend the RF and "active" pins to match the height of FR-4 substrate while the ground connections lay directly on the brass module plate.

In most cases I achieved better than specified parameters, like noise figure, gain and flatness, and P-1 dB, due to the extremely short ground connections. I can recommend the module design.