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32 DESIGN007 MAGAZINE I APRIL 2023 elements to tune the resonant circuit opera- tion around a specific carrier frequency. In the world of RF design, intentional coupling of electromagnetic fields is also used to create ports between individual circuits. Typical communication designs incorpo- rate analog, digital, and RF signals on the same substrate, so partitioning is particularly important. In applications where high power is not required, such as a smartphone, Wi-Fi, and Bluetooth, transceiver circuits oen take the form of a silicon-based IC, reducing the footprint and simplifying the layout. How- ever, routing all the essential power distribu- tion networks and grounding is always a chal- lenge. e most effective board stackup for RF design is to have a ground reference plane immediately adjacent to the surface layers and to keep the RF traces on the surface as much as possible. Minimizing vias in the RF path reduces trace inductance, reduces the voids in the ground plane, and gives less opportu- nity for the electromagnetic energy to escape. rough-board vias should be avoided to pre- vent unwanted fields from transferring from one side of the board to the other or into the plane cavity. e field, emanating from the vicinity of the signal via, injects a propagating wave into the cavity which can excite the cav- ity resonances or any other parallel structure. Other signal vias passing through this cavity can pick up this transient energy as crosstalk. e usual technique to prevent this is to use blind microvias from both sides, effectively making two separate back-to-back boards. Digital signals and power can be routed in the internal layers. One can minimize the impact of the essential through-vias by placing them in an area that has no RF signals. Microstrip transmission lines have been widely used in RF circuit design for decades. However, at high frequencies, microstrip lines can suffer from significant signal loss due to radiation and dielectric losses. Copla- nar waveguides (CPWs), on the other hand, offer lower radiation loss and are becoming a popular alternative for high-frequency digital circuits. CPWs consist of a central conductor on the surface layer of the PCB, flanked by two ground planes on either side, and are usually ground referenced, which confines the elec- tromagnetic field and reduces radiation losses (Figure 1). Figure 1: Single strip coplanar waveguide grounded. (Source: iCD CPW Planner)