An antenna resonating element may be mounted in an antenna cavity. The antenna resonating element may have a printed circuit board substrate with a patterned metal layer. Components may be soldered to the antenna resonating element using solder with a given melting point before soldering the antenna resonating element the antenna cavity using solder with a lower melting point. Solder widow openings may be formed in the antenna resonating element and antenna cavity to allow for application of solder paste. Engagement features and alignment structures may be used to align the antenna resonating element relative to the antenna cavity. The antenna cavity may have a curved opening. The printed circuit board substrate may be bent to the shape of the curved opening before soldering components to the printed circuit board. An elastomeric fixture may be used to hold the antenna resonating element to the cavity during soldering.