What are Signal Power Taps, or Tappers, and how are They Different than Directional Couplers?
Signal power tappers, signal taps, power tappers, or just taps, are passive RF devices designed to draw a small portion of power from the main transmission line without causing substantial loss. Signal power tappers are similar to directional couplers, but a signal power tapper is typically a 3-port devices, but come in many additional tap port configurations, based on capacitive coupling instead of direct coupling. Multi-port signal tappers may be equal splits, or vary depending on the need. Like directional couplers, the taps ports are often set to the impedance of the main transmission line and must be correctly terminated to ensure proper performance.
Sometimes, taps are confused with power splitters/combiners, but they are not suited for power splitting or combining applications. This is due to the lack of return port isolation and limited coupling to the tap ports. Generally, power splitters are designed to evenly split power to several ports, with high isolation between each of the split ports.
Signal tappers are often used with DAS applications for their low-cost broadband behavior, high power handling, low PIM performance, and are readily available. Moreover, taps are also used with base station, 4G LTE, AWS, PCS, PMR, UMTS, TETRA, Wi-Fi, WiMAX, and other wireless infrastructure applications. Being passive components, signal tappers can be enclosed in a rugged housing and be designed to meet many indoor and outdoor environmental conditions For example, IP67 and military standards.
Compared to directional couplers, signal tappers generally have much wider bandwidths and offer greater performance than directional couplers, which become more complex and expensive at higher bandwidth and high performance regimes, comparatively. Moreover, signal tappers are bidirectional by nature, and have no directivity. This is because signal tappers leverage capacitive coupling. The tapper will not provide substantial isolation from the return path. The VSWR for directional couplers, however, is generally much higher than with a signal tapper at the coupled port. The input and output VSWR for signal tappers is generally excellent.
Signal tappers typically present slightly greater loss than directional couplers. Depending on the electronics connected to the coupled port of a signal tap, considerations of the maximum power output of the coupled port of the tap must be accounted for to prevent damage of sensitive electronics. Some RF taps are designed specifically for low-PIM operation to prevent distortion common to RF interconnect for wireless and telecom applications.