Ku-band coaxial to microstrip mixed dielectric PCB interface with surface mount diplexer
View Patent ↗A coaxial to microstrip transition is introduced in a multi layer mixed dielectric printed circuit board environment that provides a 50 Ohm impedance system between a coaxial antenna feed and a surface mount diplexer at Ku-band frequencies. The 50 Ohm transition from the coaxial antenna feed to the diplexer at microwave frequencies lossy FR-4 style laminate is provided by constructing a PCB internal coax using the center conductor of the antenna feed and a dual ring of plated through hole VIAs. The transition from the PCB internal coax to the microstrip section of the high frequency laminate PCB layer uses a “D”-style opening in the ground layer and a VIA ring arrangement between the layers to optimize or tune the performance of the transition. Additional features in the interface construction are implemented to guaranty that its microwave and mechanical performance does not degrade in extreme environmental conditions.
1. A coaxial to microstrip transition between a surface mounted diplexer and a mixed dielectric printed circuit board (PCB) for a wireless transceiver, the coaxial to microstrip transition comprising:
a coaxial antenna probe electrically connected to an internal coaxial conductor disposed on the mixed dielectric PCB, wherein the internal coaxial conductor comprises two through VIA rings comprising a plurality of through VIAs;
a microstrip transmission line disposed on the mixed dielectric PCB and electrically connected to the surface mounted diplexer; and
a “D” style opening in a ground plane below the microstrip transmission line.
2. The coaxial to microstrip transition of claim 1 wherein the transition comprises the antenna probe mounted in a first direction and the surface mounted diplexer with transmit, receive, and antenna ports mounted in a second direction.
3. The coaxial to microstrip transition of claim 1 wherein the “D” style opening comprises a plurality of tuning VIAs between a first layer and a second layer of the mixed dielectric PCB.
4. The coaxial to microstrip transition of claim 3 wherein the plurality of tuning VIAs between the first layer and the second layer comprise the plurality of tuning VIAs disposed on a high frequency substrate.
5. The coaxial to microstrip transition of claim 3 wherein the tuning VIAs are disposed inside the two through VIA rings.
6. The coaxial to microstrip transition of claim 1 wherein the coaxial antenna probe comprises a semi rigid coaxial conductor comprising a low loss, low-density dielectric.
7. The coaxial to microstrip transition of claim 1 wherein an antenna probe base of the antenna probe and a backside of said PCB are configured to comprise a high frequency parallel plate capacitor.
8. The coaxial to microstrip transition of claim 1 wherein the two through VIA rings comprise an inner VIA ring wherein a distance between neighboring ones of said plurality of through VIAs in the inner VIA ring is substantially spaced one-twentieth of a wavelength of a frequency of the transceiver.
9. The coaxial to microstrip transition of claim 8 wherein the two through VIA rings comprise an outer VIA ring wherein each of the plurality of through VIAs in the outer VIA ring is disposed between gaps in the plurality of through VIAs in the inner VIA ring.
10. The coaxial to microstrip transition of claim 1 wherein the surface mounted diplexer is positioned on an edge of the two through VIA rings.
11. The coaxial to microstrip transition of claim 10 wherein an antenna port castellation of the surface mounted diplexer is located inside the two through VIA rings and away from a a center of said coaxial antenna probe.
12. The coaxial to microstrip transition of claim 1 further comprising a microwave cast shield surrounding the coaxial to microstrip transition.
13. The coaxial to microstrip transition of claim 1 further comprising a stepper motor to hold the coaxial antenna probe.
14. The coaxial to microstrip transition of claim 1 wherein the coaxial antenna probe is electrically connected to the surface mounted diplexer.
15. The coaxial to microstrip transition of claim 1 wherein the mixed dielectric PCB comprises a single layer, high-frequency substrate on multiple FR-4 layers.
16. A method of transitioning between a coaxial transmission line to a microstrip transmission line of a surface mounted diplexer and a mixed dielectric printed circuit board (PCB) for a wireless transceiver, the method comprising the steps of:
connecting a coaxial antenna probe to an internal coaxial conductor disposed on the mixed dielectric PCB, wherein the internal coaxial conductor comprises two through VIA rings comprising a plurality of through VIAs;
disposing a microstrip transmission line on the mixed dielectric PCB;
electrically connecting the microstrip transmission line to the surface mounted diplexer; and
providing a “D” style opening in a ground plane below the microstrip transmission line.
17. The method of claim 16 wherein the step of transitioning comprises the coaxial antenna probe being mounted in a first direction and the surface mounted diplexer with transmit and receive ports being mounted in a second direction.
18. The method of claim 16 wherein the step of providing said “D” style opening comprises disposing a plurality of tuning VIAs between a first layer and a second layer of the mixed dielectric PCB.
19. The method of claim 18 further comprising the step of disposing the tuning VIAs inside the two through VIA rings.
20. The method of claim 16 wherein the coaxial antenna probe comprises a semi rigid coaxial conductor comprising a low loss, low-density dielectric.
21. The method of claim 16 further comprising the step of forming a high frequency parallel plate capacitor by mounting an antenna probe base of the coaxial antenna probe and to a backside of said PCB.
22. The method of claim 16 wherein the two through VIA rings comprise an inner VIA ring and including the step of spacing neighboring ones of said plurality of through VIAs in the inner VIA ring at substantially one-twentieth of a wavelength of a frequency of the transceiver.
23. The method of claim 22 wherein the two through VIA rings comprise an outer VIA ring and including the step of disposing each of the plurality of through VIAs in the outer VIA ring between gaps in the plurality of through VIAs in the inner VIA ring.
24. The method of claim 16 further comprising the step of positioning the surface mounted diplexer on an edge of the two through VIA rings.
25. The method of claim 24 wherein the step of positioning comprises locating an antenna port castellation of the surface mounted diplexer inside the two through VIA rings and away from a a center of said coaxial antenna probe.
26. The method of claim 16 further comprising the step of surrounding the coaxial to microstrip transition with a microwave cast shield.
27. The method of claim 16 further comprising the step of holding the coaxial antenna probe with a stepper motor.