Abstract: Choke-ring ground planes are commonly used for multipath rejection in geodetic surveying systems. Such ground planes consist of a thick metal disc with deep grooves on one of the flat surfaces. An antenna is mounted in the center of the grooved surface. Known ground planes used in dual frequency communication systems (L1 and L2) could not be constructed to have good rejection of multipath signals in both L1 and L2 frequencies; instead, they are constructed for good rejection of multipath signals in L2 but not good for the rejection of multipath signals in L1. A first invention provides for equally good multipath rejection for both L1 and L2 frequencies by incorporating novel electromagnetic filter structures within the choke-ring grooves. The filter structures of the present invention enable the choke ring to provide multipath rejection in each frequency band which is as good as, or better than, the multipath rejection achieved in the L2 band with existing devices.