For many circuit designers, plated through holes (PTHs) form pathways, from one circuit plane to another. The key to making PTHs work for the benefit of a circuit design is to understand their effects on electrical performance, especially at higher frequencies. They should be considered as circuit elements, and they can have a great deal to do with a number of analog circuit transmission-line performance parameters, including insertion loss and return loss, and they can also affect high-speed digital circuit performance by degrading signal integrity (SI) and bit-error-rate (BER) performance.
Microwave circuit dimensions are related to their wavelengths/frequencies and to the dielectric constant (Dk) of their substrates. Quite simply, higher-frequency signals have smaller wavelengths and their electromagnetic (EM) energy of those smaller wavelengths will propagate through circuits with smaller dimensions. Phase velocity is related to wavelength, with slower EM waves having shorter wavelengths which propagate through circuit structures with smaller dimensions than faster waves with their longer wavelengths.
Millimeter-wave circuits were once considered exotic and only used for specialized applications, typically in the military space. For one thing, frequencies with such small wavelengths, from about 30 to 300 GHz, required special components and circuits scaled to those diminutive wavelengths. But lower-frequency bands are being consumed by a growing number of wireless applications, and millimeter-wave frequency bands are looking more and more attractive for communications systems of the future. Achieving millimeter-wave circuit designs on reliable printed-circuit-board (PCB) materials in a practical manner will be the challenge in making these higher frequencies affordable. Substrate-integrated-waveguide (SIW) circuit technology may just be the solution.
The choice of plated finish can make a real difference in a PCB’s conductive loss, especially for broadband, high-frequency circuits. To better understand the loss performance of different plated finishes, various transmission lines were fabricated on different circuit laminates and different plated finishes applied.
Microstrip edge-coupled bandpass filters (BPFs) can help clean the spectrum around a desired center frequency. Fabricated on printed-circuit-board (PCB) materials, these compact filters can be integrated with other circuit functions to provide dependable filtering of communications bands and high-frequency signals for a wide range of applications.
Circuit designers must often select a circuit technology, such as microstrip or grounded coplanar waveguide (GCPW) circuitry, with a particular design and circuit material to achieve optimum performance. Circuit technologies, such as microstrip and GCPW, each have their strengths and weaknesses, and it may help to take a closer look at these two circuit technologies in particular to see how they stack up.
Circuit performance may start with the choice of printed-circuit-board (PCB) material, but achieving a desired level of circuit performance can also have a great deal to do with how circuits are fabricated on a chosen PCB material.
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High-frequency circuit designers must often consider the performance limits, physical dimensions, and even the power levels of a particular design when deciding upon an optimum printed-circuit-board (PCB) material for that design. But the choice of transmission-line technology, such as microstrip or grounded coplanar waveguide (GCPW) circuitry, can also influence the final performance expected from a design. Many designers may be familiar with the stark differences between high-frequency microstrip and stripline circuitry.
Power amplifier design at RF/microwave frequencies can be aided by a wise choice of active devices, such as discrete transistors or monolithic microwave integrated circuits (MMICs). But don’t overlook the importance of the printed-circuit-board (PCB) material when planning for a solid-state power amplifier (PA) circuit. The circuit material can help or hurt a PA design, and knowing what is important in a PCB material intended for a PA is the first step in selecting a circuit material that enhances the PA’s performance.