Microstrip to CPW transition 윤정훈

 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

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 Gold ribbon inductance capacitance

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

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

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

 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 Electromagnetric Coupling(3) Wire bonding can seriously degrade circuit operation Is very labor intensive No wire bonding Improve performance Reduce cost gap

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

 Single substrate transition widening broadband transmission behavior

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

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

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

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 microstrip Two short slot arms Two radial open stub Stub reactance Mutual cancellation

conclusion  여러구조의 microstrip-to-CPW transition.  각 transition 의 다지인 패러미터.  용도에 맞는 transition 구조의 선택 및 디자인에 도움.

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