A patch antenna is a flat, lightweight antenna made from a thin metal plate mounted on a larger ground plane, with a layer of insulating material (called a substrate) sandwiched between them. It’s the type of antenna found inside GPS receivers, smartphones, Wi-Fi routers, drones, and satellite communication systems. The design is popular because it can be manufactured using the same printed circuit board technology used for electronics, making it compact, inexpensive, and easy to integrate directly into devices.
How a Patch Antenna Works
At its simplest, a patch antenna is a metal rectangle or circle etched onto one side of a circuit board, with a continuous sheet of metal on the other side acting as a ground plane. When a radio signal is fed to the patch, electric fields build up between the edges of the patch and the ground plane below. These “fringing fields” extend beyond the physical edges of the metal, and it’s this overflow of electromagnetic energy that actually radiates out into space as a radio wave.
The patch is typically designed so its length is about half the wavelength of the target frequency. At that length, the antenna resonates, meaning it efficiently converts electrical energy into radiated energy (and vice versa when receiving). Because the fields are strongest at the patch edges, you can think of those edges as the real radiating elements, while the patch itself acts as a resonant cavity that stores and shapes the energy.
Common Shapes and Sizes
Rectangular patches are the most common because they’re the easiest to analyze and manufacture, but patch antennas come in circular, triangular, elliptical, and other shapes. The choice of shape affects the radiation pattern, polarization, and how easily the antenna fits into a given device. A circular patch, for example, is often used when circular polarization is needed, which is a requirement for GPS and other satellite navigation receivers. The physical size of any patch antenna scales directly with the operating frequency: a Wi-Fi patch at 2.4 GHz might be a few centimeters across, while a patch for 24 GHz radar applications could be just millimeters wide.
Ways to Feed the Signal
The “feed” is how radio energy gets from a cable or circuit into the patch. There are four main approaches, split into two categories: direct contact methods and non-contact methods.
- Microstrip line feed: A narrow printed trace on the same board connects directly to the edge of the patch. It’s the simplest to manufacture and works well when you need everything on a single layer.
- Coaxial probe feed: A coaxial cable passes through the ground plane from below and connects to the patch at a specific point on its surface. Because the connection point can be placed anywhere under the patch, this method gives precise control over impedance matching.
- Aperture coupled feed: The feed line sits on the back side of the ground plane, and energy passes through a small slot cut into the ground plane. This physical separation keeps stray radiation from the feed line from interfering with the antenna’s pattern.
- Proximity coupled feed: The feed line runs on a separate layer just beneath the patch without touching it, coupling energy electromagnetically across the gap. This technique offers wider bandwidth and lower signal losses compared to a direct coaxial connection.
Typical Performance Numbers
A single patch antenna is a modest performer by antenna standards, and that’s by design. Its strength is size and simplicity, not raw power. A single rectangular patch typically produces around 5 to 7 dBi of gain, meaning it focuses energy in one hemisphere (away from the ground plane) rather than radiating in all directions. Bandwidth is the main trade-off: a standard microstrip-fed patch almost always covers less than 5% of its center frequency. At 2.4 GHz, for instance, that translates to roughly 120 MHz of usable range. For many applications, like receiving a single GPS frequency, that narrow window is perfectly adequate.
Designers who need more bandwidth can use thicker substrates, cut slots into the patch, stack multiple patches on top of each other, or use proximity or aperture coupling. These techniques can push bandwidth into the 10 to 30% range, though at the cost of added complexity.
Advantages and Limitations
The reason patch antennas dominate modern wireless devices comes down to a handful of practical benefits. They have an extremely thin profile, sometimes less than a millimeter thick. They’re manufactured with standard printed circuit board processes, keeping costs low even in high volume. They’re mechanically robust, with no protruding elements to break. They conform to curved surfaces, which matters for aircraft, wearable devices, and vehicle-mounted systems. And they integrate easily with other electronics on the same board.
The limitations are real but well understood. Narrow bandwidth is the most cited drawback. Efficiency is lower than larger antenna types because some energy is lost in the substrate material and in surface waves that travel along the board rather than radiating outward. A single patch also produces relatively low gain compared to horn or dish antennas. For applications that need higher gain or wider bandwidth, designers typically move to arrays or more advanced configurations rather than abandoning the patch form factor entirely.
Patch Antenna Arrays
Combining multiple patch elements into an array is the standard way to overcome the gain limitation of a single patch. In a four-element linear array designed for 24 GHz radar, for example, gain jumps from about 6.2 dBi for a single patch to roughly 11.5 dBi for the array. That’s nearly a tenfold increase in focused power, achieved simply by spacing four identical patches along a line and feeding them in phase.
Arrays also enable beam steering, where the direction of the antenna’s main beam is controlled electronically by adjusting the timing of signals fed to each element. This is the principle behind phased array radar and modern 5G base stations that track individual users with focused beams. In a series-fed array, the beam direction shifts naturally as frequency changes, which some systems exploit intentionally for frequency-based beam scanning.
Where Patch Antennas Are Used
GPS receivers are one of the most widespread applications. Satellite navigation systems like GPS, Galileo, BeiDou, and GLONASS all transmit circularly polarized signals from orbit, and a circular patch antenna on the receiver side is a natural match. Compact, circularly polarized patch designs are specifically optimized to reject multipath interference, which is the signal bouncing off buildings and other surfaces in urban environments.
In aerospace and defense, patch antennas are mounted on aircraft, missiles, and satellites where a flat, conformal antenna that doesn’t create aerodynamic drag is essential. Unmanned aerial vehicles (UAVs) and drones rely on them for communication and navigation links. In consumer electronics, they appear inside smartphones for cellular, Wi-Fi, and Bluetooth connectivity, as well as inside IoT sensors, RFID tags, and wearable health monitors. Automotive radar systems operating at 24 GHz and 77 GHz use patch arrays for adaptive cruise control and collision avoidance.
Reconfigurable Patch Antennas
A growing area of patch antenna design involves making the antenna tunable so it can switch frequencies, change its radiation pattern, or flip between linear and circular polarization on the fly. This is done by embedding small electronic switches into the antenna structure. PIN diodes (fast semiconductor switches) can be placed in slots on the patch or ground plane to connect or disconnect sections of metal, effectively reshaping the antenna in real time. Varactor diodes allow smooth, continuous tuning by changing the electrical length of the patch. Microelectromechanical systems (MEMS) switches offer extremely low signal loss but are more expensive and fragile.
These reconfigurable designs are increasingly important for software-defined radios, cognitive radio systems, and multiband devices that need to cover several wireless standards with a single antenna. Rather than dedicating separate antennas to Wi-Fi, cellular, and GPS, a reconfigurable patch can time-share across bands or adapt to changing conditions.