Introduction to Dual Band Stacked Patch Antennas

In the rapidly evolving landscape of wireless communication, the demand for antennas capable of operating across multiple frequency bands within a compact form factor has never been greater. The dual band stacked patch antenna has emerged as a leading solution to this challenge, offering a unique combination of multifrequency operation, high gain, and low profile that traditional singleband patch antennas cannot match. As wireless systems expand from 4G LTE to 5G New Radio (NR) and toward 6G, the ability to cover two distinct frequency bands with a single radiating structure has become a critical requirement for base stations, mobile devices, satellite communication terminals, and Internet of Things (IoT) sensors alike.

The stacked patch configuration addresses one of the most persistent limitations of conventional microstrip patch antennas: narrow bandwidth and singlefrequency operation. By vertically stacking multiple radiating elements—typically a driven patch and one or more parasitic patches separated by dielectric substrates—engineers can achieve dualband resonance with independent frequency control, high isolation, and excellent radiation characteristics. This article provides a comprehensive technical overview of dual band stacked patch antenna technology, covering fundamental design principles, performance characteristics, key design parameters, advanced techniques for bandwidth enhancement, and realworld applications across 5G, IoT, satellite navigation, and emerging 6G systems.

 Fundamentals of Patch Antenna Technology

Before exploring the stacked configuration, it is essential to understand the basic characteristics of microstrip patch antennas. A conventional patch antenna consists of a metallic radiating patch printed on a dielectric substrate, with a ground plane on the opposite side. The patch acts as a resonant cavity, radiating primarily from its edges. Key advantages of microstrip patch antennas include their low profile, lightweight construction, ease of fabrication using standard printed circuit board (PCB) techniques, low cost, and straightforward integration with microwave integrated circuits.

However, conventional singlelayer patch antennas suffer from several wellknown drawbacks. The most significant is their inherently narrow impedance bandwidth—typically only 1–5% for a basic rectangular patch on a thin substrate. Additionally, they operate at a single resonant frequency determined by the patch dimensions and substrate properties, making them unsuitable for multiband applications without additional design modifications. The dual band stacked patch antenna directly addresses both limitations: it provides dualfrequency operation while simultaneously improving bandwidth and gain compared to singlelayer alternatives.

 What Is a Dual Band Stacked Patch Antenna?

A dual band stacked patch antenna is a multilayer antenna structure in which two or more radiating patches are stacked vertically, separated by dielectric substrate layers or air gaps. The fundamental principle is elegant: each patch resonates at a frequency determined by its physical dimensions and the dielectric constant of the surrounding material. The lower (or driven) patch is typically larger and resonates at the lower frequency band, while the upper (parasitic) patch is smaller and resonates at the higher frequency band.

The stacking arrangement can take several forms. In a typical twopatch configuration, the structure comprises a copper–substrate–copper–substrate–copper layered stack, where the bottom copper layer serves as the ground plane. A single feed connected to one of the patches—often the upper patch in modern designs—excites both resonances through electromagnetic coupling between the layers. This coupling mechanism is the key to achieving dualband behavior without the need for separate feed networks, which would increase complexity and reduce available space.

The historical development of stacked patch antennas dates back to the late 1970s, when Long and Walton first reported experimental studies of stacked circular patches for dualfrequency operation. Since then, the technology has matured significantly, with modern designs achieving bandwidths of 15–30% in each band, gains exceeding 9 dBi, and excellent port isolation in dualpolarized configurations.

 Design Principles and Operation

 Electromagnetic Coupling Between Stacked Patches

The operation of a dual band stacked patch antenna relies on controlled electromagnetic coupling between the driven and parasitic patches. Unlike broadband stacked designs—where the bottom patch is fed and strong coupling produces a merged wideband response—dualband stacked patches are designed for weaker coupling between the two resonances, resulting in two distinct, independently tunable frequency bands.

The coupling strength is determined by several factors, including the vertical separation between patches, the horizontal alignment (or intentional offset) of the patch centers, and the dielectric properties of the intermediate substrate layers. A critical finding from recent research is that a deliberate horizontal displacement between the patch centers can significantly improve electromagnetic coupling and finetune the dualband behavior. For example, a 5 mm displacement between patch centers was introduced in a 2025 study to achieve the desired dualband performance in the 2.25–2.35 GHz and 5.6–5.8 GHz frequency ranges.

 SingleFeed vs. DualFeed Configurations

Dual band stacked patch antennas can employ either singlefeed or dualfeed excitation schemes. The singlefeed approach is particularly attractive for compact applications because it minimizes the overall thickness and simplifies the feeding network. In one notable design, a single feed connected to the side of the antenna excites the top patch to resonate at 5.7 GHz while simultaneously enabling the lower 2.3 GHz band through the larger middle patch.

Dualfeed configurations, on the other hand, offer greater design flexibility. Each frequency band can have its own dedicated feed, allowing independent control of polarization, impedance matching, and radiation patterns. A centralfeeding scheme has been described as a useful arrangement for obtaining two band responses where space is constrained, with good isolation between the two bands. Stacked patch antennas can also use separate feeds for each frequency and polarization, or a single feed to obtain both dual frequency and dual polarization simultaneously.

 Role of Displacement and Alignment in Design

The relative alignment between the patch, substrate, and ground plane plays a significant role in affecting electromagnetic coupling, which directly influences antenna performance. When layers are not perfectly aligned or become slightly displaced, unintended coupling may occur between the patch and the feedline or between adjacent resonant structures. This misalignment alters the distribution of electromagnetic fields and can lead to impedance mismatches, increased losses, and degraded radiation patterns.

However, horizontal or vertical displacement between layers can also be exploited as a design parameter. It modifies the effective dielectric constant and affects both the bandwidth and resonance frequency of the antenna, providing an additional degree of freedom for finetuning performance. Careful optimization of patch alignment is therefore essential in the design of highperformance dual band stacked patch antennas.

 Key Design Parameters and Considerations

 Substrate Material Selection

The choice of substrate material is one of the most important decisions in stacked patch antenna design. The dielectric constant (εr) of the substrate directly influences the resonant frequency of each patch: a higher dielectric constant results in a smaller patch for a given frequency, enabling greater miniaturization at the cost of reduced bandwidth and increased losses. Common substrate materials include FR4 (εr ≈ 4.4) for costsensitive applications, Rogers RO4350B (εr = 3.48) for balanced performance, and lowloss PTFEbased materials for highfrequency and millimeterwave designs.

Recent research has explored innovative substrate approaches. The use of dielectric substrates with patterned cavities—molded highpermittivity materials such as ceramics with perforated cavities—has been shown to reduce the effective dielectric constant, thereby increasing bandwidth and efficiency while maintaining a small overall size. Substrateintegrated suspended line (SISL) technology, which embeds air cavities within multilayer FR4 substrates, has emerged as a lowcost approach for achieving high performance in 5G stacked patch antennas, with reported gains of up to 9.12 dBi in the lower band and 8.65 dBi in the higher band.

 Patch Dimensioning and Frequency Control

The resonant frequency of each patch in a stacked configuration is primarily determined by its physical dimensions. For a rectangular patch operating in the fundamental TM10 mode, the resonant frequency is approximately inversely proportional to the patch length. The designer therefore has direct control over each frequency band by adjusting the dimensions of the corresponding patch. The lower patch, being larger, resonates at the lower frequency, while the smaller upper patch resonates at the higher frequency.

However, the interaction between patches means that their dimensions cannot be determined in complete isolation. The presence of the upper parasitic patch loads the lower patch, slightly shifting its resonant frequency. Similarly, the lower patch and ground plane affect the upper patch's resonance. Iterative simulation and optimization—typically using fullwave electromagnetic solvers such as CST Studio Suite or Ansoft HFSS—are essential to converge on the final dimensions.

 Feeding Techniques

A variety of feeding techniques have been developed for dual band stacked patch antennas, each with its own advantages and tradeoffs:

Probe feeding (coaxial feeding): A coaxial probe passes through the ground plane and substrate layers to connect directly to the driven patch. This technique offers good impedance matching and is relatively simple to implement. In the coaxfed stacked configuration, the center conductor passes through a clearance hole in the lower patch and connects directly to the upper patch, resulting in weak coupling of the two resonances—ideal for dualfrequency operation.

Aperturecoupled feeding: A slot or aperture in the ground plane couples energy from a microstrip feedline to the radiating patches. This technique is particularly useful for stacked configurations because it isolates the feed network from the radiating elements, reducing spurious radiation and improving polarization purity.

Inset feeding and Lshaped feeds: Inset feeding involves cutting a notch into the patch to adjust the input impedance. Lshaped inset feed lines with matching circuits have been shown to improve both gain and bandwidth characteristics in stacked patch antennas.

Gapcoupled and proximity feeding: These techniques introduce a small gap between the feedline and the patch, providing capacitive coupling that can improve bandwidth and reduce sensitivity to manufacturing tolerances.

 Performance Characteristics of Dual Band Stacked Patch Antennas

 Bandwidth

Bandwidth is a critical performance metric for any antenna. Dual band stacked patch antennas achieve significantly wider bandwidths than conventional singlelayer patches. Recent designs have demonstrated fractional bandwidths of 28% in the lower band and 17% in the upper band for sub6 GHz 5G applications, covering frequency ranges of 3.2–4.2 GHz and 5.2–5.8 GHz respectively.

The bandwidth of each band can be further enhanced through several techniques. Shorting the upper patch to the lower patch at strategic points has been shown to enhance bandwidths at both frequency bands while improving gain at highelevation angles. The use of parasitic conducting strips stacked on the driven patch can increase impedance bandwidths and achieve isolation of more than 34 dB between ports, with crosspolarization levels better than 25 dB. For millimeterwave applications, wideband designs using invertedfeed stacked patch elements have achieved 19.7% fractional bandwidth (26–31.7 GHz) with a peak gain of 18.1 dBi in a 12element linear array.

 Gain and Radiation Efficiency

Gain is another area where stacked configurations excel. The multilayer structure effectively increases the effective aperture of the antenna, leading to higher gain compared to singlelayer designs. Reported gains for dual band stacked patch antennas range from approximately 4.4 dBi for compact singleelement designs to over 11 dBi for optimized dualpolarized configurations with parasitic patches.

A particularly notable design for 5G base station applications achieved maximum gains of 9.96 dBi and 11.48 dBi in the two operating bands (3.29–3.42 GHz and 4.73–5.32 GHz) with isolation greater than 35 dB between polarization modes, while using lowcost FR4 substrate layers. The addition of four parasitic patches was found to greatly improve inband gain stability and generate a radiation null between the two operating bands, improving outofband suppression.

 Polarization and Isolation

Dual band stacked patch antennas can be designed for linear polarization, circular polarization (CP), or dualpolarization operation. For circular polarization—essential for satellite navigation and many satellite communication systems—stacked configurations offer particular advantages. A dualband circularly polarized stacked patch antenna for sub6 GHz 5G applications achieved bandwidths of 1 and 0.6 GHz covering 3.2–4.2 GHz and 5.2–5.8 GHz, with both righthanded and lefthanded CP and an 18% reduction in physical size.

In dualpolarized configurations, high isolation between ports is critical for diversity and MIMO applications. A threelayer dualband dualpolarized stacked microstrip antenna for 5G microcell communications demonstrated isolation better than 40 dB and gain greater than 8 dBi, with a compact size of 0.48 × 0.48 × 0.085 λ₀. The use of orthogonally driven feeding lines and bandnotch characteristics further enhances the antenna's suitability for interferenceprone environments.

 Advanced Techniques for Performance Enhancement

 Defected Ground Structures (DGS)

The integration of defected ground structures represents a powerful technique for improving the performance of stacked patch antennas. By embedding a shaped defect—such as a circular or rectangular slot—in the ground plane, designers can modify the current distribution and suppress unwanted radiation modes. A compact stacked microstrip patch antenna with DGS achieved dualband operation at 2.55 GHz and 5.25 GHz with 36% compactness, making it suitable for WLAN and WiMAX applications according to IEEE 802.16 and IEEE 802.11a/n standards.

 Slot Loading and Multimode Operation

Slot loading—the strategic etching of slots into the radiating patches—provides an additional mechanism for generating multiple resonant modes within a single antenna structure. In a multimode design based on SISL, the driven patch generates TM10 and TM02 modes, while Uslot and horizontal slot etching generates two additional modes to achieve dualband operation. The stacked patch with the Uslot suppresses the radiation pattern split of the TM02 mode, improves antenna gain in the highfrequency band, and generates a radiation null to increase outofband gain suppression.

 Metamaterial and Parasitic Element Integration

The integration of metamaterial structures and parasitic elements represents the frontier of stacked patch antenna research. A dualband reconfigurable antenna with metamaterial for IoT applications demonstrated operation at 2.4 GHz and 6.04 GHz with 12 multipath Tstructured metamaterial elements. In another approach, five parasitic conducting strips stacked on the driven patch of a rectangular patch antenna increased impedance bandwidths and achieved isolation greater than 34 dB between ports.

For millimeterwave 5G antennainpackage (AiP) applications, a novel stacking arrangement of ring patches has been proposed to achieve wide dualband operation with stable gain across 24.25–29.5 GHz and 37–40 GHz. The stacked configuration provides a sharp rolloff and filterlike response with radiation nulls between the operating bands, making it suitable for base station antenna arrays.

 Applications Across Industries

 5G and Sub6 GHz Communications

The rollout of 5G networks has created enormous demand for dual band stacked patch antennas. 5G NR operates across a wide range of frequency bands, from sub6 GHz (FR1) to millimeterwave (FR2) frequencies. Dualband stacked patch antennas are particularly wellsuited for 5G base stations, small cells, and customer premises equipment (CPE) because they can cover two frequency bands simultaneously with a single antenna element, reducing tower loading and installation complexity.

A lowcost dualband dualpolarized antenna using parasitic patches based on SISL covers 3.29–3.42 GHz (subband of 5G NR n78) and 4.73–5.32 GHz (extended beyond n79), with maximum gains of 9.96 dBi and 11.48 dBi respectively. For millimeterwave 5G, dualband dualpolarized planar antennas operating from 24 to 40 GHz at 5G NR FR2 bands have been successfully demonstrated using ring patch stacking with aperturecoupled stripline feeding.

 Satellite Navigation and GNSS

Global Navigation Satellite Systems (GNSS) rely heavily on dualband patch antennas for precise positioning. Modern GNSS receivers use signals from multiple frequency bands—such as GPS L1 (1575.42 MHz), L2 (1227.60 MHz), and L5 (1176.45 MHz)—to correct for ionospheric delays and achieve centimeterlevel accuracy. Dual band stacked patch antennas are ideal for this application because they provide the required multiband coverage, circular polarization, and phase center stability in a compact, lowprofile package.

Commercial products such as the HP5354.A from Taoglas illustrate the state of the art: a dualband L1/L5 GNSS patch antenna standing just 4 mm tall, delivering exceptional signal integrity with superior axial ratio, group delay, and phase center stability, with a compact 35 × 35 mm footprint. These antennas are increasingly used in drones, robotics, asset tracking, and precision agriculture, where space is at a premium and positioning accuracy is critical.

 IoT and M2M Devices

The Internet of Things ecosystem requires antennas that can support multiple wireless standards—WiFi (2.4 GHz and 5 GHz), Bluetooth, Zigbee, LTEM, and NBIoT—within extremely small form factors. Dual band stacked patch antennas address this need by combining two frequency bands in a single structure. Dual band ceramic patch antennas designed for IoT sensors and wireless modules support simultaneous transmission and reception across two distinct frequency bands with high radiation efficiency and low return loss.

A dualband MIMO patch antenna for Industrial IoT applications has been demonstrated to operate at 4.5 GHz and 7.7 GHz with gains of 4.8 dB and 6.3 dB and radiation efficiencies of 75% and 91% respectively. Flexible and transparent dualband patch antennas on transparent substrates have also been developed for IoT and ISM band applications, opening new possibilities for integration into displays and wearable devices.

 Automotive and Autonomous Systems

Advanced Driver Assistance Systems (ADAS) and autonomous vehicles rely on radar and vehicletoeverything (V2X) communication, both of which benefit from dualband antenna technology. Lowprofile pentaband automotive patch antennas using horizontal stacking and corner feeding have been developed, providing multiband coverage in a compact form factor suitable for vehicle roof or bumper integration. Dual band stacked patch antennas are also used in automotive GNSS receivers for lanelevel positioning accuracy.

 Dual Band Stacked vs. SingleLayer Patch Antennas

The decision between stacked and singlelayer patch antenna configurations involves important tradeoffs. Singlelayer antennas offer the advantages of simpler fabrication, lower cost, and easier tuning of individual frequency bands. However, they typically achieve narrower bandwidths and may require complex slot or stub loading to achieve multiband operation.

Stacked configurations, by contrast, provide wider bandwidths, higher gain, and better isolation between frequency bands. A comparative study of singlelayer and stacked configurations for multiband PIFA antennas found that the stacked patch configuration can be more difficult to tune in individual subbands and that attainable bands may not be as broad as those of a singlelayer counterpart. However, for applications where performance requirements justify the additional complexity—such as 5G base stations, satellite terminals, and highprecision GNSS receivers—the stacked approach is clearly superior.

The key advantage of the stacked configuration is its ability to decouple the design of the two frequency bands. Each patch can be optimized somewhat independently for its target frequency, bandwidth, and radiation pattern. This modularity simplifies the design process and enables greater flexibility in meeting multiband specifications.

 Emerging Trends and Future Directions

 Toward 6G and MillimeterWave

As research moves toward 6G, dual band stacked patch antennas are being adapted for the higher frequency bands and wider bandwidths that 6G will require. A lowprofile dualband selfdecoupled sharedaperture patch antenna array for 6G beamforming has been proposed, operating at 12 GHz with 14.2% bandwidth and 14.5 GHz with 11% bandwidth. Triband cointegrated antennas operating at 6, 8, and 28 GHz within a shared physical aperture are also being explored for 5G/6G infrastructure and backhaul arrays.

 AntennainPackage (AiP) Integration

For millimeterwave systems, antennainpackage technology has become the dominant integration approach. Stacked patch antennas are particularly wellsuited for AiP because their multilayer structure aligns naturally with the buildup layers of advanced PCB and LTCC (lowtemperature cofired ceramic) packaging technologies. Dualband dualpolarized planar antennas for 5G mmWave AiP applications have been successfully fabricated using standard commercial PCB processes, demonstrating the manufacturability and costeffectiveness of this approach.

 AIAssisted Design Optimization

The increasing complexity of dual band stacked patch antenna designs—with multiple patches, substrates, and coupling mechanisms—has created opportunities for artificial intelligence and machine learning to assist in optimization. AI algorithms can explore the multidimensional design space more efficiently than traditional parametric sweeps, potentially discovering nonintuitive geometries and material combinations that achieve superior performance.

 Reconfigurable and Tunable Designs

The integration of tunable elements—such as PIN diodes, varactors, and MEMS switches—into stacked patch antennas enables reconfigurable operation, where the frequency bands, polarization, or radiation patterns can be dynamically adjusted based on system requirements. This capability is particularly valuable for cognitive radio and softwaredefined radio platforms that must adapt to changing spectrum conditions.

The dual band stacked patch antenna represents a mature yet continually evolving technology that sits at the heart of modern wireless communication systems. Its ability to provide two independently controllable frequency bands, high gain, excellent polarization purity, and a low profile makes it indispensable for 5G base stations, satellite navigation receivers, IoT devices, automotive radar systems, and emerging 6G platforms.

For engineers and system designers evaluating antenna options for multiband applications, the dual band stacked patch antenna offers a compelling combination of performance, manufacturability, and design flexibility. Key considerations include substrate material selection, feeding technique, patch dimensioning, and coupling control through layer alignment and displacement. With ongoing advances in materials, packaging, and design automation, the stacked patch antenna will continue to play a central role in the wireless infrastructure of the future.