Distorted antenna measurements due to cable effects.

Untangling Antenna Mysteries: How Cable Effects Skew Your Signal Measurements

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Theo Raines in Tech & Innovation August 2025 • 6 min read.

"Discover the surprising ways cable connections distort antenna measurements and how to achieve precision in your UWB projects."


In 2002, the US-FCC's assignment of the ultrawide band (UWB) for unlicensed use sparked a technological gold rush, captivating both commercial giants and academic researchers. UWB's promise lies in its ability to deliver ultrawide bandwidth, stretching from 3.1 to 10.6 GHz, coupled with low power emission, making it a prime candidate for applications ranging from high-speed communications to advanced radar imaging. However, this vast potential is tempered by significant engineering challenges, particularly in antenna design. Achieving consistent impedance matching, stable gain, uniform radiation patterns, and high radiation efficiency across such a broad spectrum demands innovative solutions from antenna designers.

As the world increasingly demands smaller wireless devices, planar antennas have risen to prominence. Their compact size, low profile, cost-effectiveness, ease of manufacture, and seamless integration with RF circuits make them ideally suited for UWB applications. Among planar antenna designs, the monopole antenna stands out due to its structural simplicity, compact dimensions, and omnidirectional radiation pattern. In practice, a planar monopole antenna requires a ground plane that is electrically large enough to mimic an infinite ground plane, which can dominate the overall size of the antenna. The quest to design compact UWB monopole antennas often leads to minimizing this ground plane.

Designing a planar monopole antenna with a small ground plane to effectively cover the UWB spectrum is an achievable task, facilitated by various techniques. Typically, designers rely on computer simulations to refine their designs. However, in these simulations, the antenna is often directly connected to a signal source, omitting the crucial element of a feeding cable. In real-world testing, a feeding cable becomes necessary to connect the antenna to the measurement system. A small ground plane, however, fails to replicate an infinite ground plane, causing currents to flow back along the outer surface of the feeding cable, leading to secondary radiation. This discrepancy introduces significant differences between simulated and measured antenna performance, creating uncertainties in the antenna's design.

How Do Cables Distort UWB Antenna Measurements?

Distorted antenna measurements due to cable effects.

The quest for precision in antenna design often hits a snag when simulations don't match real-world measurements. Cables, an essential part of any measurement setup, can introduce significant distortions, especially in UWB antennas with small ground planes. The design of antennas is almost exclusively done using computer simulation, where the antenna is directly connected to a signal source, but when the final design is tested, a feeding cable is always needed to connect the antenna to the measurement system.

The position of the feeding cable relative to the antenna can significantly alter measurement results. Given that the feeding cable is located close to the radiator, within the near-field region of the antenna, the radiated electromagnetic (EM) fields impinging on the cable will be scattered and reflected, the feeding cable acts as a parasitic element [15], thereby compromising measurement accuracy.

  • Sleeve Baluns: These devices are metal tubes designed to be a quarter-wavelength in length. Although they possess good choking characteristics, sleeve baluns are narrowband devices, making them unsuitable for UWB antennas.
  • EMI Suppressant Materials: Covering the feeding cable with an EMI suppressant material can absorb unwanted EM radiation, making it suitable for wideband and high-frequency operations.
This chapter delves into the effects of ground plane size and the use of a feeding cable on the measurements of small UWB monopole antennas. Nine planar UWB monopoles were designed with identical elliptical radiators but different ground plane sizes. Computer simulations were performed, where the antenna was tested, and no feeding cable was used. The antennas were prototyped and measured using the antenna measurement system, Satimo Starlab, where a feeding cable was used. The simulated and measured performances showed discrepancies at low frequencies. To investigate these discrepancies, two different types of feeding cables are studied: a high-frequency coaxial cable, and a high-frequency coaxial cable with EMI suppressant tubing. Simulation models for the two cables were used in the computer simulation. With the application of the two cable models, the simulated and measured performances showed good agreement. The results show that a feeding cable without EMI suppressant tubing causes ripples on the 3D-radiation patterns of the antenna.

Mastering Precision in Antenna Design

Understanding and mitigating the impact of feeding cables, especially in antennas with small ground planes, is crucial for aligning simulation results with real-world performance. Whether employing sleeve baluns or EMI suppressants, or by implementing accurate cable models in simulations, these techniques offer pathways to refine your designs and minimize uncertainties. A comprehensive approach to antenna design involves recognizing these subtleties, enabling engineers to create more reliable and efficient UWB communication systems. As wireless technology advances, attention to these critical details will pave the way for superior performance and innovation.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.5772/46080, Alternate LINK

Title: Cable Effects On Measuring Small Planar Uwb Monopole Antennas

Journal: Ultra Wideband - Current Status and Future Trends

Publisher: InTech

Authors: L. Liu, S.W. Cheung, Y.F. Weng, T.I. Yuk

Published: 2012-10-03

Everything You Need To Know

1

What factors made the Ultrawide Band (UWB) appealing after the US-FCC's assignment in 2002, and what engineering challenges temper its potential?

The assignment of the ultrawide band (UWB) for unlicensed use by the US-FCC in 2002 created interest in the technology. However, the potential of UWB, which operates in the 3.1 to 10.6 GHz range, is limited by challenges in antenna design, particularly when it comes to achieving consistent impedance matching, stable gain, uniform radiation patterns, and high radiation efficiency across its wide spectrum.

2

Why have planar antennas become prominent in modern wireless devices, and what specific characteristics make the monopole antenna a good choice for UWB applications?

Planar antennas are popular in small wireless devices due to their size, cost-effectiveness and ease of manufacture and integration with RF circuits making them well suited for UWB applications. The monopole antenna is notable for its simple structure and omnidirectional radiation pattern. However, the ground plane required by a planar monopole antenna needs to be electrically large, which can affect the overall size.

3

How do cables introduce distortions into UWB antenna measurements, and why are these effects particularly pronounced in antennas with small ground planes?

Cables distort UWB antenna measurements because, during simulations, the antenna is directly connected to a signal source, ignoring the feeding cable. In real-world testing, the feeding cable acts as a parasitic element that impacts the measurement because of its position relative to the antenna. Radiated electromagnetic fields impinge on the cable, and this causes scattering and reflection that affects measurement accuracy.

4

What are some methods to reduce cable effects in UWB antenna measurements, and why is one more suited to UWB then another?

Sleeve baluns, while effective at choking, are not suitable for UWB antennas because they are narrowband devices. EMI suppressant materials, on the other hand, can absorb unwanted EM radiation, which makes them suitable for wideband and high-frequency operations. By using these, or by implementing accurate cable models in simulations, engineers can refine their designs and minimize uncertainties.

5

What happens to antenna measurements when a feeding cable lacks EMI suppressant tubing, and what does this imply for designing accurate and reliable UWB communication systems?

Using a feeding cable without EMI suppressant tubing can introduce ripples on the 3D-radiation patterns of the antenna. This is because currents flow back along the outer surface of the cable, leading to secondary radiation, especially when the ground plane is small. The impact of feeding cables can be mitigated by employing sleeve baluns or EMI suppressants, or by implementing accurate cable models in simulations.

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