⚡ electrical engineering

A Wideband Narrow Beam 1x6 Linear Antenna Array for Automotive Radar and 5G Millimetre-Wave Applications

This paper presents a compact 1x6 linear microstrip patch antenna array designed for automotive radar and 5G mm-wave applications, utilizing a specific feedline configuration to achieve high directivity, wide bandwidth, and a narrow beamwidth suitable for high-resolution sensing and high-capacity communications at 28 GHz.

Original authors: Muhammad Asfar Saeed, Augustine O. Nwajana

Published 2026-05-05

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Muhammad Asfar Saeed, Augustine O. Nwajana

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are trying to shout a message across a noisy, crowded stadium. If you just stand there and yell, your voice gets lost in the crowd, and people far away can't hear you clearly. But if you use a megaphone, you can focus your voice into a tight, powerful beam that cuts through the noise and reaches your target directly.

This paper is about building a high-tech "megaphone" for radio waves, specifically for the super-fast 5G internet and smart car radar systems.

Here is the breakdown of what the researchers did, using simple analogies:

1. The Problem: The "Foggy" High-Speed Road

The researchers are working with millimeter-wave (mm-wave) frequencies. Think of these as super-high-speed radio waves. They are great because they can carry huge amounts of data (like a wide highway), but they have a problem: they are very fragile. Just like a flashlight beam gets dim quickly in fog, these signals get blocked easily by walls, rain, or even the air itself.

To fix this, you can't just shout louder (increase power) because there are safety limits on how much radio energy you can blast out. Instead, you need a better "megaphone" (an antenna) that focuses the signal tightly so it travels further without needing extra power.

2. The Solution: A Line of Six Flashlights

The team designed a 1x6 Linear Antenna Array.

The Analogy: Imagine you have six small flashlights lined up in a straight row. If you turn them all on individually, you get six weak, scattered beams of light. But, if you connect them all with a special wire system so they all flash in perfect unison, their beams merge into one super-powerful, focused spotlight.
The Design: They built a flat, single-layer board (like a circuit board) with six rectangular "patches" (the flashlights) arranged in a straight line.
The Secret Sauce: They connected these six patches with extremely thin, narrow wires (only 0.1 mm wide). This is like using a very precise plumbing system to ensure water (the signal) flows evenly to every patch without leaking or getting stuck. This simple, flat design is cheaper and easier to make than the complex, multi-layered "sandwich" antennas others have tried.

3. How It Works: The "Wave" Effect

The researchers placed the six patches very close together (about 1.9 mm apart).

The Analogy: Think of dropping six stones into a pond in a perfect line, one after another, at the exact right speed. The ripples from each stone hit each other and combine to form one giant, powerful wave moving in one direction, while the ripples cancel each other out in other directions.
The Result: This creates a narrow beam. Instead of the signal spreading out in a wide circle like a lighthouse, it shoots out in a tight, focused fan shape. This is perfect for:
- Smart Cars: To see exactly what is in front of them or in their blind spots without getting confused by signals from other cars.
- 5G Networks: To send data directly from a tower to a specific phone without wasting energy on empty space.

4. The Test: Does It Actually Work?

The researchers didn't just draw it on a computer; they built a real physical version using a milling machine (like a very precise robot cutter) on a special material called Rogers RO3003. They tested it in a special room that absorbs all echoes (an anechoic chamber).

The Results:

The "Tuning": The antenna was tuned to work at 28 GHz (a specific speed for 5G and car radar). It worked beautifully, with very little signal bouncing back (like a well-tuned guitar string that doesn't buzz).
The "Beam": It successfully created a tight, focused beam. While the beam wasn't perfectly straight (it tilted slightly, like a flashlight held at a slight angle), it was still very effective at focusing energy in one direction.
The "Strength": It achieved a "gain" of about 9.9 dBi. In plain English, this means it made the signal nearly 10 times stronger in that specific direction compared to a standard, non-focused antenna.

5. Why This Matters

The paper claims this design is special because it is simple, flat, and cheap to make, yet it performs just as well as much more complicated, expensive antennas.

For Cars: It can help cars "see" their surroundings clearly to prevent accidents.
For 5G: It can help deliver fast internet to specific spots without needing massive, complex equipment.

In summary: The researchers built a simple, six-part "radio megaphone" that focuses signals tightly. They proved it works by building a real model, showing it can handle the high speeds needed for next-generation cars and internet, all while keeping the design flat and easy to manufacture.

Technical Summary: A Wideband Narrow Beam 1x6 Linear Antenna Array for Automotive Radar and 5G Millimetre-Wave Applications

Problem Statement
Millimetre-wave (mm-wave) frequencies (24–300 GHz) are critical for high-capacity, low-latency systems such as 5G networks, automotive radar, and vehicle-to-everything (V2X) communications. However, these signals suffer from severe free-space path loss and multipath fading, often necessitating high Effective Isotropic Radiated Power (EIRP). While increasing transmit power is an option, regulatory limits on electromagnetic field (EMF) exposure, particularly in automotive and medical environments, restrict this approach. Consequently, enhancing antenna gain through narrow-beam, high-directivity arrays is a preferred solution.

Existing literature offers various high-gain solutions, including leaky-wave antennas, substrate-integrated waveguide (SIW) feeds, and multilayer structures. However, these designs often introduce significant structural complexity, high fabrication costs, and increased profile thickness. Furthermore, achieving a combination of compact size, wide impedance bandwidth, and narrow-beam radiation at mm-wave frequencies using a simple planar architecture remains a challenge, particularly for series-fed arrays where mutual coupling can lead to beam squint and non-uniform power distribution.

Methodology
The authors propose a compact, single-layer 1×6 linear microstrip patch antenna array designed for operation at 28 GHz. The design utilizes a Rogers RO3003 substrate (thickness 1.574 mm, $\epsilon_r$ = 3.0, tan $\delta$ = 0.0013) to minimize signal attenuation.

Structure: The array consists of six rectangular radiating patches arranged linearly.
Feeding Mechanism: A series-fed topology is employed. The primary patch is excited via a microstrip feedline (0.5 mm width, 1.5 mm length). The remaining five patches are interconnected via ultra-narrow microstrip transmission lines (0.1 mm width, 0.5 mm length) to facilitate effective power distribution.
Optimization: The inter-element spacing is optimized to 1.9 mm. This spacing is critical for minimizing mutual coupling while ensuring constructive interference in the broadside direction to achieve a narrow beam.
Simulation and Fabrication: The design was simulated using CST Studio Suite (time-domain solver) over a 25–35 GHz range. The physical prototype was fabricated using an electronic milling process on the Rogers substrate, followed by manual correction of copper irregularities and the soldering of an SMA connector.

Key Contributions
The primary novelty of this work lies in the realization of a compact, single-layer, series-fed 1×6 microstrip array that simultaneously achieves wide impedance bandwidth, narrow-beam radiation, and high directional gain without complex multilayer structures or SIW feeds.

Simplicity: The design avoids the complexity of multilayer substrates, metallic vias, or corporate feed networks, utilizing a simple planar structure with ultra-narrow interconnects.
Performance Balance: The authors claim to successfully mitigate the common challenges of series-fed arrays (such as beam squint and bandwidth limitations) through precise spacing and narrow interconnects, maintaining stable radiation performance across the operating band.
Experimental Validation: Unlike many theoretical studies, this work includes the physical fabrication and experimental testing of the antenna in an anechoic chamber.

Results
Experimental and simulation results demonstrate the antenna's suitability for 28 GHz applications:

Impedance Matching: The measured reflection coefficient ( $S_{11}$ ) shows a deep null of approximately –33 dB at 28.8 GHz. The –10 dB impedance bandwidth spans 1.2 GHz (27.5 GHz to 28.7 GHz), covering the target 5G and automotive radar bands.
VSWR: The Voltage Standing Wave Ratio remains below 2.0 across the operating band, with a minimum of 1.06 at 28.8 GHz.
Gain and Directivity: A peak realized gain of approximately 9.9 dBi was observed at 28 GHz.
Radiation Patterns: The array exhibits a directional fan-beam characteristic. In the $\phi = 0^\circ$ plane, the main beam is steered toward $\theta \approx 40^\circ$ (with a 3 dB beamwidth of 86.3°), while the $\phi = 90^\circ$ plane shows a narrow, highly directive beam. Sidelobe levels were measured at –3.1 dB and –4.7 dB, indicating effective suppression.
Current Distribution: Surface current analysis confirms uniform excitation across all six elements, validating the series-fed design and the absence of significant current discontinuities.
Discrepancies: A slight frequency shift between simulated and measured results was observed, attributed to fabrication tolerances, substrate dielectric variations, and SMA connector parasitics, which is noted as common in mm-wave implementations.

Significance and Claims
The paper positions this design as a practical, low-cost solution for next-generation wireless systems. The authors claim that the antenna offers a promising alternative for compact, high-performance beamforming systems in intelligent transportation (e.g., lane change detection, blind spot monitoring) and 5G mm-wave communications (e.g., point-to-point backhaul).

The significance of the work is framed around its ability to deliver high gain and wide bandwidth using a simple, single-layer fabrication process, making it suitable for space-constrained platforms like autonomous vehicles and IoT devices. The authors state that, to their knowledge, this specific combination of wideband performance, narrow-beam radiation, and simple planar fabrication for a 1×6 series-fed array targeted at both automotive radar and 5G applications has not been previously reported. Future work is suggested to focus on array integration and beamforming techniques to further enhance coverage and agility.

1. The Problem: The "Foggy" High-Speed Road

2. The Solution: A Line of Six Flashlights

3. How It Works: The "Wave" Effect

4. The Test: Does It Actually Work?

5. Why This Matters

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