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Before someone complains about my crappy design I should tell you that my knowledge on antennas or RF is near zero.

I recently worked on a project that required a GSM module. After testing it on a PCB using an external antenna that apparently seamed fairly simple, I made a new PCB with a built in antenna.

It worked well but I noticed that the signal was significantly lower than the one with the external antenna. I also noticed that if I touched the antenna connection with a wire the signal increased in strength close to the one with the external antenna.

My board is a double sided board with a ground plane with a clearance distance of about 2 mm from the antenna on one nearest side. The antenna is located near the edge of the board as can be seen on the picture.

Antena

Is there something that I could do to improve my antenna performance? Currently the antenna has solder mask on top of it, can this degrade its performance? Is it better to have it plated instead?

Full board

enter image description here

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    \$\begingroup\$ Where did you get the antenna design information? Have you considered emulating the profile on PCB plug in metalwork designs now being used by eg Linksys. | Solder mask will not hurt (very minor dielectric effects which are liable to be swamped by generally non idealities). \$\endgroup\$ – Russell McMahon Sep 5 '12 at 19:21
  • \$\begingroup\$ How did you design it? Just copy what you saw on the external antenna? Antenna design usually involves a lot of simulation and measurement (e.g. with a network analyzer) combined with many iterations to get things just right. \$\endgroup\$ – Jim Paris Sep 5 '12 at 19:23
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    \$\begingroup\$ Thanks for your feedback. Since I didn't knew how to start my approach was to copy a comercial available antenna. I'm aware that there is many factors involved on designing a suitable antenna but I had no idea here to start, so copying a comercial product seamed a good starting point. \$\endgroup\$ – Bruno Ferreira Sep 5 '12 at 22:36
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    \$\begingroup\$ I don't know where in that PCB your RF source is, but those traces sure don't look impedance controlled. The traces leading to the antenna can be just as important as the traces actually in the antenna. \$\endgroup\$ – Connor Wolf Feb 3 '13 at 0:55
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    \$\begingroup\$ @ConnorWolf The GSM module connects to the PCB through the connector (on the bottom side) located just below the antenna. \$\endgroup\$ – Bruno Ferreira Feb 6 '13 at 17:33
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There seems to be a remarkable lack of relevant on-web material. Maybe just hiding.

This looks highly apposite Design of New Multi Standard Patch Antenna GSM/PCS/UMTS/HIPERLAN for Mobile Cellular Phones with an interesting appearance

enter image description here

And tri-band !!!

enter image description here


GSM Dipole antenna - very informative

Designing a GSM dipole antenna


Commercial product.

LOOKS simple.
LOOKS good
LOOKs can be deceiving :-)

enter image description here

GSM Pentaband antenna

They say:

  • 800/900/1800/1900/2100MHz

    Omni Directional 1/2 Wave

    Miniature 42 x 42 x 1mm

    VSWR <3.0

    RG178 Coax 50Ω Impedance

    2-3dBi Gain (nominal)

    Vertical Polarization

    Admitted Radiation Power 1W


The free marvellous NEC RF software will probably do what you want.

Links and intro to NEC here

Have a look here RF/Microwave Tools and here Tools and calculators - with RF writ large


If you have enough $ - Agilent ADS

  • Advanced Design System is the world’s leading electronic design automation software for RF, microwave, and high speed digital applications. In a powerful and easy-to-use interface, ADS pioneers the most innovative and commercially successful technologies, such as X-parameters* and 3D EM simulators, used by leading companies in the wireless communication & networking and aerospace & defense industries. For WiMAX™, LTE, multi-gigabit per second data links, radar, & satellite applications, ADS provides full, standards-based design and verification with Wireless Libraries and circuit-system-EM co-simulation in an integrated platform.
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