I have a GPS receiver(works at 1575.42 MHz) with chip-antenna:enter image description here

As I understand, this metal square plate is an antenna which is connected to PCB with short 5-6mm metal rod. This metal rod is hidden iside the black ceramic enclosure seen on the image. However, if I read abount antenna basics, then antenna lenght should be 1/2 or 1/4 of the signal wavelenght, i.e. 9.5cm or 5cm respectively because wavelenght in case of 1.5GHz is 0.19m. How does this square metal plate work as an antenna?

  • 1
    \$\begingroup\$ It could be that the ceramic material affects the velocity factor of the antenna, which results in a change of wavelength of electromagnetic waves, which can result in an antenna of appropriate size. \$\endgroup\$ – AndrejaKo Jun 21 '14 at 13:57
  • 1
    \$\begingroup\$ You're thinking 1/2 or 1/4 wavelength for dipole aerials. \$\endgroup\$ – Majenko Jun 21 '14 at 13:58
  • \$\begingroup\$ @Majenko This 1/2 or 1/4 of wavelenght rule does not apply to square(I don't know the tecnical term for this type) antennas? \$\endgroup\$ – Martin Jun 21 '14 at 14:46
  • 2
    \$\begingroup\$ It looks like a patch antenna to me. \$\endgroup\$ – Andy aka Jun 21 '14 at 14:49
  • 3
    \$\begingroup\$ If it is, the "ceramic" will be a solid layer with a dialecric constant \$\epsilon_r\$ that affects the resonant frequency of the patch antenna. The higher the \$\epsilon_r\$ the smaller the antenna for the same frequency. \$\endgroup\$ – Majenko Jun 21 '14 at 15:00

Andy's comment is correct- this is a microstrip patch antenna, which has a hemispherical radiation pattern.

enter image description here

The construction is similar to a capacitor with a ground plane on the back, a dielectric (possibly ceramic in this case), and a rectangular patch on the top. It's designed to resonate at the desired frequency (1.575 GHz in this case).

The round bit is the inner feed to the patch, which is impedance matched to the receiver input through a network (a network which in microwave-world is just a pattern on the substrate).

Here is a calculator to find the dimensions, given \$\epsilon_r\$, dielectric thickness, and desired resonant frequency, and here is some info from Rogers (laminate maker) on designing your own.

  • \$\begingroup\$ Did I understand correctly that the patch plate is not electrically connected to ground plate? \$\endgroup\$ – Martin Jun 23 '14 at 17:43
  • 1
    \$\begingroup\$ Yes, that is correct. It's the top piece of a ceramic-filled sandwich with the ground plate on the bottom. \$\endgroup\$ – Spehro Pefhany Jun 23 '14 at 17:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.