Systems and methods for signal isolation in radio frequency circuit boards
Systems and methods for isolating radio frequency (RF) signals in high frequency circuit assemblies, including but not limited to 5G communication systems, are provided. The circuit assemblies include an RF suppression structure, which can be in the form of a low ohm resistor, that extends across a transmission line, and that has contacts that are electrically joined to a ground plane. Alternatively or in addition, the circuit assemblies include a low ohm resistor that extends over a transition between a signal via and an end of a transmission line, and that has contacts that are electrically joined to a ground plane. A circuit assembly as disclosed herein can further include multiple low ohm resistors spaced apart from one another by a distance that is a fraction of a wavelength of a highest frequency signal carried by the transmission line.
1. A circuit assembly, comprising:
a transmission line;
a ground plane, wherein the ground plane extends along opposite sides of the transmission line;
a first low ohm resistor, wherein the first low ohm resistor has a first contact electrically connected to the ground plane on a first side of the transmission line, wherein the first low ohm resistor has a second contact electrically connected to the ground plane on a second side of the transmission line, and wherein at least a portion of the first low ohm resistor extends over the transmission line; and
a first signal via, wherein the first signal via is connected to the transmission line, wherein the first signal via extends in a direction perpendicular to the transmission line, wherein the first low ohm resistor is placed over the first signal via as viewed along the direction perpendicular to the transmission line, and wherein radiation of electromagnetic energy resulting from transmission of radio frequency signals through the connection between the first signal via and the transmission line is suppressed.
2. The circuit assembly of claim 1 , further comprising:
a second low ohm resistor, wherein the second low ohm resistor has a first contact electrically connected to the ground plane on the first side of the transmission line, wherein the second low ohm resistor has a second contact electrically connected to the ground plane on the second side of the transmission line, and wherein at least a portion of the second low ohm resistor extends over the transmission line.
3. The circuit assembly of claim 2 , wherein the first low ohm resistor is spaced apart from the second low ohm resistor by a distance that is less than or equal to a fraction of a wavelength of a highest frequency signal carried by the transmission line.
4. The circuit assembly of claim 3 , wherein the fraction is 1/32.
5. The circuit assembly of claim 2 , further comprising:
a third low ohm resistor; and
a second signal via, wherein the second signal via is connected to the transmission line, wherein the second signal via extends in the direction perpendicular to the transmission line, wherein the third low ohm resistor is placed over the second signal via as viewed along the direction perpendicular to the transmission line, and wherein radiation of electromagnetic energy resulting from transmission of radio frequency signals through the connection between the second signal via and the transmission line is suppressed.
6. The circuit assembly of claim 5 , wherein the connection between the first signal via and the transmission line is at a first end of the transmission line, wherein the connection between the second signal via and the transmission line is at a second end of the transmission line.
7. The circuit assembly of claim 6 , wherein a spacing between each low ohm resistor and an adjacent low ohm resistor is no more than ¼ of a wavelength of a signal to be carried by the transmission line.
8. The circuit assembly of claim 2 , further comprising:
a second signal via, wherein the second signal via extends in the direction perpendicular to the transmission line, wherein the second signal via is connected to the transmission line, wherein the second low ohm resistor is placed over the second signal via as viewed along the direction perpendicular to the transmission line, and wherein radiation of electromagnetic energy resulting from transmission of radio frequency signals through the connection between the second signal via and the transmission line is suppressed.
9. The circuit assembly of claim 1 , further comprising:
a plurality of ground vias, wherein the first contact of the first low ohm resistor is at least one of adjacent or directly connected to a first one of the ground vias, and wherein the second contact of the first low ohm resistor is at least one of adjacent or directly connected to a second one of the ground vias.
10. The circuit assembly of claim 1 , wherein the first low ohm resistor has a resistance of less than 10 ohms.
11. The circuit assembly of claim 1 , wherein the transmission line is located within an aperture formed in the ground plane, and wherein the portions of the ground plane that extend along opposite sides of the transmission line are integral to one another.
12. The circuit assembly of claim 11 , wherein most of the length of the portion of the ground plane that extends along a first side of the transmission line is a same distance from the transmission line.
13. A circuit assembly, comprising:
a first surface, wherein a transmission line is located on the first surface, wherein a ground structure is located on the first surface and adjacent opposite sides of the transmission line;
a plurality of radio frequency (RF) suppression structures, wherein a first contact of each of the RF suppression structures is connected to the ground structure on a first side of the transmission line, wherein a second contact of each of the RF suppression structures is connected to the ground structure on a second side of the transmission line, and wherein a body portion of each of the RF suppression structures extends across at least a portion of the transmission line; and
at least a first via transition, wherein a first signal via is connected to the transmission line at the first via transition, wherein a body portion of a first one of the RF suppression structures extends over the first via transition when the first via transition is viewed in a direction perpendicular to the first surface, and wherein radiation of electromagnetic radiation resulting from transmission of radio frequency signals through the first via transition is suppressed.
14. The circuit assembly of claim 13 , wherein the radio frequency suppression structures are spaced apart from one another by a distance equal to or less than ¼ of a wavelength of a highest frequency signal carried by the transmission line.
15. The circuit assembly of claim 13 , wherein the radio frequency suppression structures are low ohm resistors.
16. The circuit assembly of claim 13 , further comprising:
a second surface;
a first antenna element, wherein the first antenna element is on the second surface; and
wherein the first signal via is connected to the first antenna element at the second surface.
17. The circuit assembly of claim 13 , wherein the transmission line is located within an aperture formed in the ground structure, and wherein the portions of the ground structure that extend along opposite sides of the transmission line are integral to one another.
18. The circuit assembly of claim 17 , wherein most of the length of the portion of the ground structure that extends along a first side of the transmission line is a same distance from the transmission line.
19. A method, comprising:
forming a signal via in a circuit board;
forming a transmission line on a first surface of the circuit board, wherein the transmission line is electrically connected to the signal via at a via transition;
forming a ground structure on the first surface of the circuit board, wherein the ground structure includes an aperture that surrounds the transmission line; and
placing a plurality of radio frequency (RF) suppression structures over the transmission line, wherein the RF suppression structures are electrically connected to the ground structure, and wherein at least one of the RF suppression structures is located over the via transition when the via transition is viewed in a direction perpendicular to the first surface of the circuit board, and wherein radiation of electromagnetic radiation resulting from transmission of radio frequency signals through the via transition is suppressed.
20. The method of claim 19 , wherein the RF suppression structures are low ohm resistors, and wherein the low ohm resistors are placed over the transmission line in a pick and place operation.