An electronic device may include wireless circuitry having one or more antennas. An antenna ground for an antenna may be formed from two separate conductive ground structures coupled to each other via a conductive interconnect structure. A slot element may be formed in one of the conductive ground structures to reject signals at one or more victim frequencies resulting from spurious signals generated by a non-ohmic contact formed between the conductive interconnect structure and the one of the conductive ground structures. The conductive interconnect structure may overlap and excite the slot element, which serves as an ineffective radiator at the one or more victim frequencies.