A radio frequency RF, microelectromechanical system, MEMS, package (40; 170) comprising: a MEMS die assembly (41; 171) comprising: a first mounting substrate; a signal line formed on a top surface of the first mounting substrate, the signal line comprising a MEMS device selectively electrically coupling a first portion of the signal line to a second portion of the signal line; a first pair of ground pads (52,54) formed on the top surface of the first mounting substrate adjacent the first portion of the signal line; and a second pair of ground pads (56,58) formed on the top surface of the first mounting substrate adjacent the second portion of the signal line; and a ground assembly (43; 172) electrically coupled to the first pair of ground pads (52,54) and the second pair of ground pads (56,58), the ground assembly comprising: a second mounting substrate; and a ground region formed on a surface of the second mounting substrate facing the top surface of the first mounting substrate and electrically coupled to the first pair of ground pads (52,54) and the second pair of ground pads (56,58); wherein a cavity is formed between the ground region and the signal line; and wherein the first pair of ground pads (52,54) is positioned adjacent a first side of the MEMS device and the second pair of ground pads (56,58) is positioned adjacent a second side of the MEMS device; the RF MEMS package being characterized in that: the ground assembly (43; 172) comprises a main body and a lid coupled to the main body; in that the MEMS die assembly (41; 171) is positioned within a cavity formed between the main body and the lid; and in that the RF MEMS package further comprises at least one electrically conductive via extending through the main body of the ground assembly (43; 172) and electrically coupling the ground region to an external input/output connection (209, 211) of the main body. a first mounting substrate; a signal line formed on a top surface of the first mounting substrate, the signal line comprising a MEMS device selectively electrically coupling a first portion of the signal line to a second portion of the signal line; a first pair of ground pads (52,54) formed on the top surface of the first mounting substrate adjacent the first portion of the signal line; and a second pair of ground pads (56,58) formed on the top surface of the first mounting substrate adjacent the second portion of the signal line; and a ground assembly (43; 172) electrically coupled to the first pair of ground pads (52,54) and the second pair of ground pads (56,58), the ground assembly comprising: a second mounting substrate; and a ground region formed on a surface of the second mounting substrate facing the top surface of the first mounting substrate and electrically coupled to the first pair of ground pads (52,54) and the second pair of ground pads (56,58); wherein a cavity is formed between the ground region and the signal line; and wherein the first pair of ground pads (52,54) is positioned adjacent a first side of the MEMS device and the second pair of ground pads (56,58) is positioned adjacent a second side of the MEMS device; the RF MEMS package being characterized in that: the ground assembly (43; 172) comprises a main body and a lid coupled to the main body; in that the MEMS die assembly (41; 171) is positioned within a cavity formed between the main body and the lid; and in that the RF MEMS package further comprises at least one electrically conductive via extending through the main body of the ground assembly (43; 172) and electrically coupling the ground region to an external input/output connection (209, 211) of the main body. a second mounting substrate; and a ground region formed on a surface of the second mounting substrate facing the top surface of the first mounting substrate and electrically coupled to the first pair of ground pads (52,54) and the second pair of ground pads (56,58); wherein a cavity is formed between the ground region and the signal line; and wherein the first pair of ground pads (52,54) is positioned adjacent a first side of the MEMS device and the second pair of ground pads (56,58) is positioned adjacent a second side of the MEMS device; the RF MEMS package being characterized in that: the ground assembly (43; 172) comprises a main body and a lid coupled to the main body; in that the MEMS die assembly (41; 171) is positioned within a cavity formed between the main body and the lid; and in that the RF MEMS package further comprises at least one electrically conductive via extending through the main body of the ground assembly (43; 172) and electrically coupling the ground region to an external input/output connection (209, 211) of the main body. the ground assembly (43; 172) comprises a main body and a lid coupled to the main body; in that the MEMS die assembly (41; 171) is positioned within a cavity formed between the main body and the lid; and in that the RF MEMS package further comprises at least one electrically conductive via extending through the main body of the ground assembly (43; 172) and electrically coupling the ground region to an external input/output connection (209, 211) of the main body.