Rectangular Patch AntennaEdit

A rectangular patch antenna is a compact, planar wireless radiator that sits on a dielectric substrate with a conductive ground plane on the opposite side. Its simple construction—usually a thin rectangular metal patch printed on a circuit board or laminated material—has made it a workhorse in modern communications, from Wi‑Fi hotspots to satellite terminals. The patch is fed by a coaxial feed or a microstrip line, and radiation comes primarily from the fringing fields at the patch edges. Because the patch is essentially a half-wavelength resonator, its size scales with the target frequency, offering a low-profile alternative to traditional wire antennas while integrating neatly with other circuit elements on a common substrate.

Rectangular patch antennas are prized for being lightweight, mechanically robust, and easy to manufacture with standard printed-circuit techniques. They can be designed for single-band operation or extended to multiple bands by stacking patches, introducing slots, or using proximity or slot coupling. While their bandwidth is typically narrower than that of some alternative antennas, the trade-off favors compactness, ease of integration, and cost efficiency in many portable and fixed installations. The technology sits at the intersection of antenna theory and planar microwave engineering, and it is widely discussed in relation to broader categories such as Antenna technology, Patch antenna implementations, and Microstrip antenna design.

Design principles

Geometry and basic operation

A rectangular patch is defined by its length L and width W, placed on a dielectric substrate of relative permittivity εr and thickness h, with a conductive ground plane on the opposite side. The patch behaves as a resonant cavity whose dominant mode is the TM01-like mode. The dimensions are chosen so that the patch supports a half-wavelength resonance inside the dielectric, with fringing fields at the edges enabling radiation into free space. A first-order design rule sets the patch width to approximately W ≈ (c/(2 f0)) · sqrt(2/(εr + 1)), where c is the speed of light and f0 is the target center frequency. The patch length is then chosen to establish resonance, typically by L ≈ (c/(2 f0)) · 1/√εeff, where εeff is the effective dielectric constant seen by the fields, which accounts for the finite thickness of the substrate and the air around the patch. A common refinement adjusts L to include a small fringing-length correction ΔL to account for field extension beyond the physical edge.

εeff is estimated from εr and the substrate geometry: εeff ≈ (εr + 1)/2 + (εr − 1)/2 · [1 + 12 h/W]−1/2.

These relationships provide a practical starting point, but real-world designs are fine-tuned with full-wave simulations to account for substrate losses, finite ground plane size, and manufacturing tolerances. The radiation pattern of a single rectangular patch is typically broadside (perpendicular to the patch surface), with a directivity that depends on the patch aspect ratio and the ground-plane size.

Feeding and impedance matching

The input impedance of a rectangular patch is not matched to typical 50 Ω systems by default; practical designs employ feeding techniques to achieve a reasonable match. Common options include: - inset feed: a microstrip line is run along the edge of the patch and recessed by a distance to adjust the input impedance. - coaxial probe feed: a vertical coaxial probe enters the patch from the feed side, with the connector opening used to set the impedance. - proximity-coupled or capacitive coupled feeds: two separate substrates or a gap arrangement couple energy into the patch without a direct contact, enabling broader matching and, in some cases, multi-band behavior.

Each method trades off manufacturing simplicity, bandwidth, and cross-polarization performance. For multi-band or dual-polarization designs, engineers often stack patches or use more complex feeding networks to excite orthogonal modes or to couple energy into two resonant paths.

Bandwidth, efficiency, and materials

Bandwidth in rectangular patch antennas is constrained by the resonant nature of the structure and by the substrate properties. Thicker substrates and materials with lower loss tangents generally increase bandwidth and efficiency, but they can also shift impedance, alter radiation patterns, and increase the physical footprint. The loss tangent of the substrate (tan δ) and the conductivity of the metal influence efficiency; practical designs use high-conductivity metals and substrates with manageable losses to maximize radiated power for a given input.

Substrate choice also affects center frequency stability under temperature and humidity changes, which is a key consideration in aerospace, automotive, and outdoor installations. Typical substrates range from inexpensive FR‑4–like laminates for lower‑frequency or cost‑sensitive applications to specialized microwave laminates (e.g., RO-series polymers) for higher performance.

Polarization and multi-band options

Rectangular patch antennas primarily support linear polarization, often along the patch’s width. Dual-polarization configurations are achievable by feeding two orthogonal edges or by using two patches oriented at 90 degrees relative to one another and coupled through a shared feed network. Multi-band operation can be realized through stacking of patches at different resonant heights, slotting the patch edges, or employing parasitic elements and coupling techniques that create additional resonant paths.

Variants and feeding methods

Single-band rectangular patches: optimized for a chosen f0 with a design tuned for moderate bandwidth and predictable pattern.
Dual- or multi-band patches: achieved with stacked patches, slots along the edges, or multi-layer substrates offering distinct resonances at separate frequencies.
Proximity- and slot-coupled configurations: allow broader matching and isolation between feeding network and radiating element, often improving bandwidth and permitting closer integration with other circuitry.
Dual-polarization patches: use orthogonal feeding paths or two patches sharing a common ground plane to radiate in two perpendicular orientations.

Materials, fabrication, and reliability

Rectangular patch antennas are well suited to planar fabrication methods, including printed circuit boards, flexible laminates, and even textile substrates for wearable or conformal antennas. Copper or silver-plated conductors are common radiating elements, while the dielectric substrate provides mechanical support and the electrical environment for propagation. Manufacturing tolerances and environmental exposure (temperature, humidity, vibration) influence impedance match and long-term performance, so designers specify tolerances and protection (such as conformal coatings or radomes) appropriate to the intended application.

Applications often favor patch antennas for base stations, access points, and mobile devices where a flat form factor, light weight, and the ability to integrate with RF front ends and digital processing matter most. Their compatibility with modern lithographic fabrication, surface-mmount technology, and low-profile enclosures makes them a standard option in the broader field of antenna design and in systems coordinated by RF engineering teams.

Applications and contexts

Rectangular patch antennas find use across a wide range of systems. In consumer and enterprise wireless networks, they appear in access points and routers where a compact, planar radiator is desirable. In satellite communications, patches on robust substrates form part of compact terminal assemblies. Military and aerospace applications leverage the rugged, low‑profile character of patch antennas in aircraft, ships, and ground vehicles, often coupled with protective radomes and harsh-environment electronics. Their ongoing development includes efforts to broaden bandwidth, support multiple polarizations, reduce mutual coupling in arrays, and integrate with digital beamforming and radar systems, as well as to enable lightweight, conformal installations on irregular surfaces.

See also discussions of related topics such as Antenna design, Planar antenna, and Array antenna concepts, where the same foundational principles are adapted to more complex configurations.