Microstrip to CPW transition
2004-30338
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
capacitance
Gold ribbon
inductance
 a small capacitance is added at the beginning of the coplanar
line
• lowpass filter
 maximum cut-off frequency is related with the height h1
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)
Gradual transformation
Return loss
as n increases, S11 decreases
as the length of the transition increases,
Bandwidth increases as well
Electromagnetric Coupling(3)
 Case 2 : Surface to surface transition
 CPW on one substrate surface to a MS on another
Wire bonding
• can seriously degrade circuit operation
• Is very labor intensive
No wire bonding
• Improve performance
• Reduce cost
gap
 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(4)
 Chip to motherboard transition
The chip and mother board ground
planes coincide
Ground plane of the chip is
removed in the area over the
coupling region
 Single substrate transition
widening
broadband transmission behavior
 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)
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)
 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
Two radial open stub
microstrip
Two short slot arms
Stub reactance
Mutual cancellation
conclusion
 여러구조의 microstrip-to-CPW transition.
 각 transition의 다지인 패러미터.
 용도에 맞는 transition 구조의 선택 및 디자인에 도움.
Reference
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