Power splitters and combiners are the most commonly used/common high-frequency devices, and the same applies to couplers such as directional couplers. These devices are used for power splitting, combining, and coupling high-frequency energy from antennas or internal systems, with minimal loss and leakage. The selection of high-frequency PCB boards is a key factor for achieving the expected performance of these devices. When designing and processing power dividers/combiners/couplers, it is helpful to understand how the performance of PCB materials affects the final performance of these devices. For example, it can help to limit a series of different performance indicators of selected boards, including frequency range, working bandwidth, and power capacity.
Many different circuits are used to design power dividers (which in turn are combiners) and couplers, and they come in various forms. The power divider has simple dual channel power divider and complex N-channel power divider, depending on the actual needs of the system. Many different directional couplers and other types of couplers have also developed in recent years, including Wilkinson and resistive power divider, Lange coupler and orthogonal hybrid power saving bridge, which have many different forms and sizes. Choosing appropriate PCB materials in these circuit designs helps to achieve optimal performance.
These different circuit types will compromise the structure and performance of the design, helping designers choose boards for different applications. Wilkinson two-way power divider provides two-way output signals with equal amplitude and phase through a single input signal. In fact, it is a “lossless” circuit, designed to provide an output signal that is 3dB smaller than the original signal (or half of the original signal) (the output power of each port of the power divider decreases with the increase of the number of output ports). In contrast, a resistive dual power divider provides an output signal that is 6dB smaller than the original signal. The increased impedance in each branch of the resistive power divider increases the loss, but also increases the isolation between the two signals.
Like many circuit designs, the dielectric constant (Dk) is generally the starting point for selecting different high-frequency PCB materials, and designers of power dividers/synthesizers generally tend to use high dielectric constant (Dk) circuit materials because these materials can provide effective electromagnetic coupling on smaller circuits compared to low dielectric constant materials. There is a problem with circuits with high dielectric constant, which is that the dielectric constant in the circuit board is anisotropic or the dielectric constant values of the circuit board are different in the x, y, and z directions. When the dielectric constant changes greatly in the same direction, it is also difficult to obtain a transmission line with uniform impedance.
Maintaining impedance invariance is crucial in achieving power divider/combiner characteristics, as changes in dielectric constant (impedance) can lead to uneven distribution of electromagnetic energy and power. Fortunately, there are commercial PCB materials with superior isotropy that can be used in these circuits, such as TMM 10i circuit materials. These materials have a relatively high dielectric constant value of 9.8 and remain at the level of 9.8+/-0.245 in the three coordinate axis directions (in the
