This disclosure relates generally to microwave coupling structures and more particular to microwave coupling structure for suppressing common mode signals while passing differential mode signals between a pair of coplanar waveguide (CPW) transmission lines.
As is known in the art, a coplanar waveguide (CPW) structure includes: a center conductor disposed over a surface of a substrate; and a pair of ground plane conductors disposed over the upper or top surface of the substrate, the center conductor being disposed between the pair of ground plane conductors, Microwave energy fed to an input of the CPW propagates to an output in a differential transmission mode with the electromagnetic field being near the surface substrate. CPW has been and continue to being used in wide variety of integrated circuit and circuit board applications. However, being a three conductor system, CPW structures are vulnerable to propagation of unwanted common mode(s). For example, in many applications the integrated circuit having active elements interconnected on the top, or upper, surface of a common substrate and a conductor is disposed on the bottom surface of the substrate for mounting to a heat sink or to a system ground conductor, for example. In this example, a parallel plate region is formed between the conductors on the upper surface, particularly, when larger ground plane conductors are used for the CPW transmission line, and the conductor on the bottom surface.
More particularly, a microwave parallel plate region includes a pair of conductors disposed over opposite surfaces of a substrate. When such parallel plate region is used as a portion of a CPW microwave transmission line, such as the pair of ground plane conductors on the top or upper surface of the substrate, unwanted, parasitic, parallel plate modes may be generated (moding), supported between the pair of conductors, and then transmitted through the parallel plate region. In one application, a substrate may be used to realize a Monolithic Microwave Integrated Circuit (MMIC) chip having a plurality of electrical components, including amplifiers, for example, with a conductor on the bottom of the substrate, for providing a system ground or for soldering to a printed circuit board or heat sink, for example, and conductors on the top of the substrate. In such chip, CPW transmission lines are used on the top or upper surface of the chip to interconnect elements of the amplifier, or different amplifiers or electrical components, for example, as shown in
Common mode generation may also result from interference from other sources, such as, for example; coupling of external signals, unbalanced excitation or unbalanced ground paths.
Thus, while CPW transmission uses a differential mode transmission, these other sources can generate common modes that can propagate through the CPW transmission lines as unwanted signals and become a source of parasitic unwanted common mode signals that propagate through the one or more of the center conductors and pair of ground plane conductors and adversely affect the performance and operation of the MMIC.
In accordance with the present disclosure, a transmission line structure is provided having; a pair of separated coplanar waveguide transmissions line sections; and a coupling circuit coupled between the pair of coplanar waveguide transmissions line sections. The coupling circuit suppresses common mode signals and passes, substantially unsuppressed, differential mode signal transmission between the pair of coplanar waveguide transmissions line sections.
In one embodiment, the circuit is disposed on a top surface of a substrate and the circuit includes a resistor for passing the common mode signals to a ground plane conductor disposed on a bottom surface of the substrate.
In one embodiment, each one of the pair of separated coplanar waveguide transmissions line sections includes as a pair of separated ground plane conductors disposed on the upper surface of a substrate, each one of the separated ground plane conductors forming a parallel plate with a conductor disposed on the bottom surface of the substrate. The circuit couples one of the pair of ground plane conductors to the other one of the pair of ground plane conductors.
In one embodiment, a parallel plate structure has an upper plate and a lower plate, one of the plates having two separated regions. A coupling circuit is coupled between the separated regions for suppressing common mode signals in one of the plates passing between the two regions and passing, substantially unsuppressed, differential mode signal transmission between the two regions.
Thus, circuit servers as a choke to common mode microwave signals and a CPW transmission line for differential mode microwave signals.
The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
Referring now to
The CPW transmissions lines 212 (
It is noted that signal and ground continuity of the CPW transmission lie terminating at the separation 219 between the segments or regions A and B across the needs to be maintained across the separation 219, Therefore, by segmenting the two segments or regions A and B, two CPW transmission lines 212A and 212B are formed; CPW transmission line section 212A having ground plane conductor sections 216a, 216b and CPW section 212B having ground plane conductor sections 218a, 218b. Here, the signal and ground continuity are maintained by a coupling circuit 226, such coupling circuit 226, shown more clearly in
Referring now to
As noted above, the coplanar waveguide transmission line 230 connected between is formed in a meander line configuration. More particularly, the center conductor 214′ and the pair of ground plane conductors 20′ and 22′ are configured a meander line inductor. Thus, here there are two, serially connected inductors L1 and L2 formed by each one of the three conductors 20′, 22′ and 214′. A capacitor C1 and C2 is connected in parallel with each corresponding one of the inductors L1, L2 forming a pair of serially connected resonant tank, circuits 350, 352, respectively as shown. These L-C resonant tank circuits 350, 352 are tuned to the undesired common mode signals; however, because the CPW transmission line formed by three conductors 20′, 22′ and 214′ provide a differential line (the signal line 214′ has its own ground plane lines 20′; 22′ on either side and on the same surface), differential mode signals pass through the CPW line without being effected by the tank circuits 350, 352.
Thus, referring to
Referring now to
The input CPW microwave structure 202′ and the output CPW microwave structure 204′ are identical in construction. Therefore, considering for example the input CPW microwave structure 202′ reference is also made to
More particularly, considering in more detail the input CPW microwave structure 202′ includes: an input CPW structure 301 having an input pad 300 connected to the center or signal conductor of a CPW transmission line 302, and a pair of ground plane pads 304, 306 disposed on the sides of the center conductor 302 and input pads 300, as shown; an output CPW structure 308 having an output pad 310 connected to the center or signal conductor 312 of a CPW transmission line having a pair of ground plane pads 314, 316 disposed on the sides of the center conductor 312, as shown. The input CPW structure 301 is coupled to the output CPW structure 308 through the coupling structure 226′ as shown. The output pad 310 is connected to the center conductor 214 of chip 206′ and the ground plane pads 314, 316 are connected to ground plane conductors 216, 218 (
A number of embodiments of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims.
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Number | Date | Country | |
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20150255842 A1 | Sep 2015 | US |