Patch Antenna, also known as Microstrip Antenna, is a flat, low profile antenna type widely used in modern wireless communication, satellite navigation, IoT devices, and other fields. Its core structure consists of a metal patch, a dielectric substrate, and a ground plate, which achieve signal transmission and reception through electromagnetic wave radiation at the edge of the patch. The following is a detailed analysis of its key features and design points:
1、 Structure and Working Principle
Basic composition
Metal patch: usually a rectangular or circular thin copper layer, the size determines the resonant frequency.
Dielectric substrate: located between the patch and the ground plane, the dielectric constant (ε<sub>r</sub>) of the material (such as FR4, Rogers) affects the antenna performance.
Grounding plate: a metal layer that provides electromagnetic wave reflection and forms a radiation pattern.
Working principle
The patch and ground plate form a resonant cavity, and electromagnetic waves form standing waves at the edge (radiation edge) of the patch, generating vertically polarized radiation.
Resonance frequency formula:2、 Core Features
|Features | Advantages | Limitations|
|Size and weight | Low profile (thickness typically<0.05 λ), easy to integrate into PCB | Physical size limitations for high-frequency applications (such as millimeter wave)|
|Bandwidth | Narrowband (typical 2%~5%), suitable for fixed frequency bands | Requires complex design (such as stacked patches) to expand bandwidth|
|Gain | Moderate (5-8 dBi), directionality controllable | High gain requires array design, increasing complexity|
|Cost | Low material cost, suitable for mass production | High frequency substrates (such as Rogers) have higher costs|
|Multi frequency/polarization | Supports dual frequency and circular polarization (through chamfer or feed point design) | Design complexity increases with functional requirements|
3、 Design key parameters
Patch shape
Rectangular patch: the most commonly used, with simple design and high radiation efficiency.
Circular patch: reduces edge diffraction and is suitable for wide-angle scanning arrays.
E-shaped/U-shaped: Multi band or bandwidth expansion achieved through slotting.
Feeding method
Edge feeding: Directly welding coaxial lines, simple but difficult to match impedance.
Probe feeding: The coaxial inner conductor penetrates the substrate and connects to the patch, suitable for high frequencies.
Coupling feeding: By electromagnetic coupling through microstrip lines, the interference on the radiation field is reduced.
Substrate selection
Low dielectric constant substrate (such as Rogers RO4003, ε<sub>r</sub>=3.38): improves bandwidth and reduces surface wave losses.
High frequency substrates (such as ceramic filled PTFE): suitable for millimeter wave (above 24GHz) scenarios.
4、 Typical application scenarios
Mobile communication
The phone has a built-in antenna (4G/5G) and a Wi Fi router (2.4GHz/5GHz).
Case: LCP (Liquid Crystal Polymer) patch antenna in iPhone, supporting millimeter wave frequency band.
Satellite navigation
The GPS/Beidou receiving module adopts a circularly polarized patch design to suppress multipath interference.
IoT devices
RFID tags and Bluetooth modules are compactly integrated using miniaturized patches.
Radar and Aerospace
Phased array radar units and unmanned aerial vehicle data links achieve beamforming through patch arrays.
5、 Optimize technology
Bandwidth Expansion
Stacked SMT: Multi layer SMT coupling, bandwidth can be increased to 10%~15%.
Slot design: Create U-shaped or H-shaped slots on the surface of the patch to excite multiple resonant modes.
Gain increase
Reflective plate loading: Add metal reflectors or electromagnetic bandgap (EBG) structures to suppress backward radiation.
Array: Multiple patches form a planar array with a gain of over 15 dBi (such as 5G base station antennas).
Multi band design
Fractal patch: Utilizing self similar structures (such as Koch curves) to achieve multi frequency resonance.
Reconfigurable antenna: dynamically adjust the resonant frequency through PIN diode or varactor diode.
6、 Selection and Design Suggestions
Low frequency applications (<3GHz): FR4 substrates are preferred to reduce costs.
High frequency/millimeter wave: Using Rogers series substrates to ensure low loss and high precision.
Environmental adaptability: Outdoor equipment should choose waterproof coating substrates (such as PTFE copper-clad laminates).
Surface mount antennas have become the core components of modern wireless systems due to their high integration, low cost, and flexible design. Despite natural limitations in bandwidth and gain, its applications in cutting-edge fields such as 5G and satellite communication will continue to expand through structural innovation (such as MIMO arrays, flexible substrates) and material optimization. When designing, it is necessary to weigh frequency, size, cost, and performance, and combine simulation tools such as HFSS and CST for precise tuning.
