An antenna feed network is the RF delivery system between a transmitter or receiver and one or more radiating elements. On a PCB it is rarely "just a 50-ohm trace." Launch geometry, transmission-line type, matching parts, ground reference, and (for arrays) power division and phase all decide how much energy actually reaches the antenna with acceptable reflection and loss.
Overseas RF product teams sourcing boards from China often discover this after a layout that simulated cleanly shifts in the enclosure because Dk assumptions, copper pours, or mounting screws were never written into the manufacturing notes.
Feed line, feed network, feed point
The feed line is the controlled path: microstrip, grounded coplanar waveguide (CPWG), stripline, or a connector transition. The feed network is the larger system that may add matching, dividers, and grounding structures. The feed point is where energy enters the radiator. Many layout bugs come from treating those three as one object.
A correct 50-ohm line only means the transmission geometry matches a target under a stated stackup. Antenna input impedance still moves with frequency, nearby metal, enclosure, ground shape, and fabrication tolerance. Matching is still required in most products.
Choosing a line structure
Microstrip on an outer layer over a ground plane is simple and easy to load with matching components, but it is sensitive to nearby copper and metal objects. CPWG adds side grounds for tighter field control and often better isolation in dense mixed-signal boards; impedance depends on both width and gap, so geometry must stay consistent. Stripline between planes shields well but is awkward for tuning at the antenna and needs careful transitions to outer radiators.
Microstrip and CPWG with the same ohms target do not share the same width. Once side grounds come close enough, the field is no longer pure microstrip.
Material and stackup as RF parts
Dk stability, Df, dielectric thickness consistency, copper roughness, and moisture absorption all move impedance, loss, and tuning. Short low-frequency feeds on ordinary materials can be fine. Longer feeds, narrower bandwidths, and higher frequencies punish vague "FR-4 is OK" assumptions.
Two-layer boards can work for simple wireless products with solid bottom ground and limited aggressors. Four-layer constructions are a stronger default for many RF-plus-digital products: RF and antenna on L1, solid ground on L2, power and quiet routing on L3, noisier digital on L4 is a common pattern. Higher layer counts exist to protect the RF path while the rest of the system grows.
Grounding, keep-outs, and matching
The feed region usually wants a stable reference and continuous return. The radiating region usually wants copper, cans, batteries, displays, and screws kept out of the keep-out. Confusing those two zones is a frequent detune.
Reserve matching footprints early. Pi networks are popular because they leave tuning options when enclosure and fab variation show up. Local ground cutouts under matching parts are sometimes used to reduce parasitics; that is a local trick, not permission to delete the feed reference plane.
Arrays change the problem
Corporate feeds parallel-divide power with good amplitude control at the cost of area and loss. Series feeds are compact but bring phase progression and bandwidth limits. H-tree styles help equalize path length when phase balance matters. Pick topology from electrical needs, not from which shape fits the outline first.
Verify on hardware
Define stackup and ohms, reserve matching, route controlled geometry, prototype, measure return loss and impedance, tune with Smith-chart discipline, then re-check in the final mechanical condition. Reference-design inductor values are starting points.
Common mistakes include assuming a 50-ohm trace means the antenna is matched, swapping microstrip and CPWG casually, crossing splits, crowding noise into the feed, deleting matching after one lucky prototype, and ignoring stackup variation.
For production, pair high frequency PCB material notes with impedance control PCB tables and coupons. Communication products often sit under PCBs for communication equipment expectations: publish metal keep-outs that mechanical and electrical teams both own before antenna freeze.