Microstrip to CPW transition

1. Microstrip to CPW transition 2004-30338 윤정훈

2. Advantage of MS & CPW • Low cost, compact size, and easy integration for devices • demand • Low-loss, wideband, and compact transition • Two main techniques for the transition • by electrical contact • usually call for Via holes, bonding wires, or abrupt steps in the conductor • Compact size and wide bandwidth • Some degree of mechanical complexity • by electromagnetic coupling • No wired bonds or via holes • Narrow bandwidth and larger size Recently wider bandwidth transition

3. Gold ribbon inductance capacitance Electrical Contact (1) • Case 1 : ribbon • Superposition of two different substrates • upper one works in a microstrip mode • lower one works in a coplanar mode • a small capacitance is added at the beginning of the coplanar line • lowpass filter • maximum cut-off frequency is related with the height h1

4. Electrical Contact (2) • Case 2 : air bridge • Microstrip to CPW on GaAs chip substrate • Case 3 : via hole • Microstrip to CPW on opposite sides of a common substrate

5. Electromagnetric Coupling(1) • Case 1 : uniplanar • this one uses the coupling between the ground plane of the microstrip and the ground planes of the coplanar line • Analyzed as a bandpass filter • cutoff frequency is determined by the length of the coupling region With radial coupling stub

6. Electromagnetric Coupling(2) as n increases, S11 decreases Gradual transformation Return loss as the length of the transition increases, Bandwidth increases as well

7. Wire bonding • can seriously degrade circuit operation • Is very labor intensive No wire bonding • Improve performance • Reduce cost gap Electromagnetric Coupling(3) • Case 2 : Surface to surface transition • CPW on one substrate surface to a MS on another • Types • Single-substrate transition • on opposite sides of a single substrate • gap size of roughly 10 % of the total length empirically give the best results • Chip to motherboard transition

8. The chip and mother board ground planes coincide Ground plane of the chip is removed in the area over the coupling region Electromagnetric Coupling(4) • Chip to motherboard transition

9. widening broadband transmission behavior • Single substrate transition

10. A variety of transition structure As Sc is enlarged EM coupling becomes tight Rasining the equivalent series capacitivie coupling Constitute a Broad Passband with two minimum values (A)

11. s Widening the width Futher expanding the transmission passband As Sc is enlarged, Lower end of a passband is moved to low frequency But higher end of a passband is unchanged (B)

12. d • By the coupled-strip length As d is enlarged, the wide passband gradually moves down

13. Two radial open stub Two short slot arms microstrip Electromagnetric Coupling(3) • Case 2 : radial stub • Radial shape of the open stub & shorted arm allow wider bandwidth operation • signal is effectively transferred through resonant coupling Stub reactance Mutual cancellation

14. conclusion • 여러구조의 microstrip-to-CPW transition. • 각 transition의 다지인 패러미터. • 용도에 맞는 transition 구조의 선택 및 디자인에 도움.

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