Dipole PCB Antenna Design: Complete Guide with Dimensions, Balun & Layout

The dipole PCB antenna remains one of the most fundamental yet misunderstood antenna types in wireless product design. I’ve seen countless engineers default to monopole or IFA designs without considering that a printed dipole might actually deliver better performance for their application—particularly when omnidirectional coverage and balanced radiation patterns matter. Unlike monopoles that depend heavily on ground plane size and shape, dipole antennas create their own virtual ground through the second radiating element, offering more predictable performance across different product enclosures.

This guide covers practical dipole PCB antenna design from first principles through finished layout. Whether you’re designing for 433 MHz LoRa, 915 MHz ISM band, 2.4 GHz WiFi/Bluetooth, or 5.8 GHz applications, I’ll provide specific dimensions, balun implementations, and layout rules that work in real products. The dimension tables come from actual designs I’ve validated with VNA measurements—not just theoretical calculations that ignore substrate effects and feed parasitics.

Understanding Dipole PCB Antenna Fundamentals

A dipole PCB antenna consists of two conductive elements of equal length, fed at the center point where they meet. The name “dipole” literally means “two poles”—the two radiating arms that together form a complete antenna system. This symmetrical structure is what distinguishes dipoles from monopoles, which use a ground plane as the “missing” half of the antenna.

Half-Wave Dipole Theory

The classic half-wave dipole has a total length equal to one-half the wavelength (λ/2) of the operating frequency. Each arm is therefore λ/4 in length.

Critical point: These free-space values don’t apply directly to PCB dipoles. The substrate’s dielectric constant shortens the required length, and proximity to ground planes affects impedance. I’ll provide corrected dimensions for FR4 substrates later in this guide.

Dipole PCB Antenna Radiation Pattern

The radiation pattern of a dipole PCB antenna resembles a donut or torus shape when oriented vertically:

This pattern makes dipoles excellent for applications requiring coverage in all horizontal directions while the device orientation is predictable. For handheld devices with variable orientation, the nulls along the dipole axis can cause connectivity issues.

Dipole vs Monopole Impedance Characteristics

The 73Ω impedance of dipoles doesn’t match 50Ω systems directly, requiring either a matching network or acceptance of some mismatch loss (~0.2 dB with proper design).

Types of Dipole PCB Antennas

Not all dipole PCB antenna designs look the same. The basic concept can be implemented in several ways, each with distinct advantages.

Straight Printed Dipole

The simplest form—two straight copper traces extending in opposite directions from a center feed point.

Folded Dipole

A folded dipole connects the ends of both arms with an additional conductor, creating a closed loop structure.

The higher impedance of folded dipoles can be advantageous when matching to balanced transmission lines or when a 4:1 transformer provides better matching options.

Meander Dipole

Meander dipoles fold the radiating elements back and forth to reduce physical length while maintaining electrical length.

Comparison of Dipole PCB Antenna Types

Dipole PCB Antenna Dimensions by Frequency

Here are practical dipole PCB antenna dimensions for common wireless frequencies. These values account for FR4 substrate effects (εr ≈ 4.4) and assume 1.6mm board thickness with 1oz copper.

433 MHz Dipole PCB Antenna Dimensions

Note: At 433 MHz, a full dipole is quite large. Consider a meander dipole or external wire dipole if PCB space is limited.

868 MHz Dipole PCB Antenna Dimensions

915 MHz Dipole PCB Antenna Dimensions

2.4 GHz Dipole PCB Antenna Dimensions

5.8 GHz Dipole PCB Antenna Dimensions

At 5.8 GHz: Manufacturing tolerances become critical. Consider Rogers or other low-loss substrates for better repeatability.

Substrate Correction Factors

Different PCB materials require different length corrections:

Formula: PCB length ≈ Free space length × Shortening factor

Balun Design for Dipole PCB Antenna

A critical aspect of dipole PCB antenna design that many engineers overlook is the balanced-to-unbalanced (balun) transition. Dipoles are inherently balanced antennas—both arms should carry equal and opposite currents. Coaxial cables and most RF ICs have unbalanced (single-ended) outputs.

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Why Dipoles Need a Balun

Balun Types for PCB Implementation

Microstrip Balun Design

A simple microstrip balun uses a quarter-wave transformer section:

Lumped Element Balun Values

For compact designs, a lumped LC balun works well:

Integrated Balun Options

Several IC manufacturers offer integrated baluns suitable for dipole PCB antenna feeds:

Impedance Matching: 73Ω to 50Ω

The native 73Ω impedance of a half-wave dipole PCB antenna doesn’t perfectly match 50Ω systems. Here’s how to handle the mismatch.

Option 1: Accept the Mismatch

For many applications, especially IoT devices where every dB doesn’t matter, simply accepting this mismatch is the pragmatic choice.

Option 2: Quarter-Wave Transformer

A quarter-wave transmission line section transforms impedance:

60Ω trace width on 1.6mm FR4: Approximately 2.0 mm

Option 3: L-Network Matching

Option 4: Design for 50Ω Directly

Slightly shortening the dipole (by ~5%) reduces its impedance closer to 50Ω at the cost of some efficiency:

PCB Layout Guidelines for Dipole Antennas

Proper layout is essential for dipole PCB antenna performance. Unlike monopoles where the ground plane is part of the antenna, dipole layout focuses on maintaining symmetry and proper feed design.

Symmetry Requirements

Ground Plane Considerations

Keep-Out Zone Recommendations

Feed Point Layout

Layer Stack Considerations

Dipole vs Monopole PCB Antenna: When to Choose Each

Understanding when a dipole PCB antenna outperforms a monopole—and vice versa—helps you make the right design choice.

Choose Dipole When:

Choose Monopole When:

Direct Comparison

Common Dipole PCB Antenna Design Mistakes

After reviewing hundreds of dipole PCB antenna designs, these mistakes appear repeatedly:

Mistake 1: Ignoring the Balun

Problem: Connecting coax directly to dipole without balanced feed. Effect: Cable radiation, pattern distortion, hand sensitivity. Solution: Always include a balun, even a simple one.

Mistake 2: Asymmetric Layout

Problem: One arm has different routing or nearby components. Effect: Current imbalance, impedance shift, pattern tilt. Solution: Maintain mirror symmetry around feed point.

Mistake 3: Ground Plane Under Dipole

Problem: Solid ground pour directly beneath dipole arms. Effect: Massive detuning, bandwidth reduction, efficiency loss. Solution: Clear ground from dipole area on all layers.

Mistake 4: Using Free-Space Dimensions

Problem: Copying textbook λ/2 dimensions without substrate correction. Effect: Antenna resonates at wrong frequency. Solution: Apply shortening factor for your substrate (typically 0.77-0.85 for FR4).

Mistake 5: Inadequate Feed Gap

Problem: Feed gap too large or poorly defined. Effect: Impedance mismatch, difficult to tune. Solution: Use controlled gap (0.5-2mm depending on frequency) with proper transition from transmission line.

Useful Resources for Dipole PCB Antenna Design

Dimension Calculators

Application Notes

PCB Design Tools

Component Datasheets

Frequently Asked Questions

What is the main advantage of a dipole PCB antenna over a monopole?

The primary advantage of a dipole PCB antenna is its independence from ground plane size and shape. Monopole antennas use the ground plane as their “missing half,” making their performance highly dependent on ground plane geometry. In contrast, a dipole creates its own complete antenna system with both radiating elements present on the PCB. This makes dipoles more predictable when integrating into products with small, irregular, or plastic-enclosed boards. Additionally, dipoles offer a more symmetric radiation pattern without the asymmetry that ground plane edges introduce in monopole designs.

Why does a dipole PCB antenna need a balun?

Dipoles are balanced antennas—both arms should carry equal currents flowing in opposite directions. However, most RF sources (coaxial cables, IC outputs) are unbalanced, with signal on one conductor and ground on the other. Without a balun, connecting an unbalanced source to a balanced antenna causes common-mode currents to flow on the outside of the coax shield or along ground traces. These currents radiate unpredictably, distort the antenna pattern, and make the antenna sensitive to nearby objects including the user’s hand. A balun converts the unbalanced signal to balanced, ensuring symmetric antenna excitation.

How do I calculate dipole PCB antenna length for a specific frequency?

Start with the free-space half-wavelength formula: Length = c / (2 × f), where c = 3×10⁸ m/s and f is frequency in Hz. For 2.4 GHz, this gives 62.5 mm. Then apply the substrate shortening factor—typically 0.77-0.82 for FR4—resulting in approximately 48-51 mm total length. Divide by two for each arm length (24-25.5 mm per arm). Always verify with VNA measurements, as actual dimensions depend on trace width, substrate thickness, and nearby components. Cut the antenna slightly long initially and trim to tune.

Can I use a dipole PCB antenna without matching to 50Ω?

Yes, in many applications. A half-wave dipole has approximately 73Ω impedance, creating a 1.46:1 VSWR when connected to 50Ω. This represents only 0.18 dB mismatch loss—acceptable for most IoT and consumer applications. However, if maximum range is critical or you’re operating at power levels where reflected power matters, use a quarter-wave transformer (60Ω line) or simple L-network to match. For folded dipoles with ~292Ω impedance, matching is mandatory.

What’s the minimum PCB size for a dipole antenna at 2.4 GHz?

The dipole itself requires approximately 50-52 mm length on FR4 for 2.4 GHz—this is the minimum for a straight dipole. The PCB can extend beyond the dipole (for circuitry), but the dipole elements need this physical space. For smaller PCBs, consider a meander dipole, which can fit in approximately 18×8 mm by folding the elements. Alternatively, use an external dipole connected via U.FL connector, or switch to a chip antenna. Remember that ground plane clearance around the dipole (typically 5 mm at 2.4 GHz) adds to the total antenna area requirement.

Conclusion

Designing an effective dipole PCB antenna requires attention to several interconnected factors: accurate dimensions corrected for substrate effects, proper balun implementation for balanced feeding, impedance matching when necessary, and symmetric layout practices. The tables throughout this guide provide starting points for common frequencies from 433 MHz to 5.8 GHz, but always validate with VNA measurements on your actual PCB.

The decision between dipole and monopole antennas shouldn’t be automatic. Dipoles excel when ground plane control is limited, when balanced outputs are available, or when radiation pattern symmetry matters. Their higher input impedance (73Ω vs 36.5Ω) and requirement for balanced feed add complexity, but the performance benefits often justify the effort—especially for external antenna modules and applications where the device ground plane is small or unpredictable.

Start with the dimension tables provided, implement an appropriate balun from the options described, and follow the layout guidelines for ground plane clearance and symmetry. With these fundamentals in place, your dipole PCB antenna designs will deliver reliable performance across your target frequency bands.