Those Who Understand RF Technology Today Are Ready for 6G Tomorrow

High-frequency technology (HF technology) is used in almost everything nowadays: Wi-Fi, Bluetooth, mobile communications, navigation systems and countless Internet of Things (IoT) devices all use high-frequency signals. Understanding how these signals are generated, transmitted, received and measured provides insight into the inner workings of modern wireless technology and enables more effective selection and deployment of antennas, radio modules and circuits.

Development is ongoing: the next generation of mobile communications, 6G, is already on the horizon. Much of this is still a long way off, but topics such as higher frequencies, smart antenna systems, AI-supported networks and new applications — from precise positioning to holographic communication — demonstrate where this journey may lead. The technical foundations for this are already being laid today.

This guide covers the key fundamentals of RF technology, explains the role of antennas and EMC, and highlights the crucial components and tools in practice. It is ideal for makers, students, and anyone who wants to better understand today’s wireless technology and prepare for tomorrow’s technologies.

Fundamentals of Radio Frequency Technology

In practice, however, the actual length of the antenna depends on its design, the printed circuit board, the ground plane, the housing, the environment and the materials used. Therefore, a PCB antenna, chip antenna or PIFA antenna may look significantly different from a simple wire dipole.

As frequency increases, antennas become smaller. At the same time, the demands placed on PCB layout, cables, connectors and mechanical design increase. Losses in cables, connectors, walls and enclosures increase. At high frequencies, trace paths and cables no longer behave like simple connections, but rather like transmission lines with a defined impedance.

The length, geometry, ground planes and transitions of these components directly influence the signal level, phase and quality. Short signal paths, clean ground planes, defined impedances and controlled return paths are crucial at high frequencies.

Modulation: Information on a carrier signal

For information to be transmitted wirelessly, it must first be modulated onto a high-frequency carrier signal.

In amplitude modulation, the amplitude of the carrier signal is varied. In frequency modulation, on the other hand, the carrier frequency is shifted by a centre frequency. Phase modulation involves the phase of the signal alternating between defined states.

Modern wireless standards use digital modulation techniques. QPSK and QAM combine amplitude and phase to transmit several bits per symbol. OFDM distributes the data across many narrow subcarriers that are orthogonal to one another. This allows for better management of interference, reflections, and multipath propagation.

Modulation determines how digital information is converted into a radio signal and recovered again.

RF technology in a nutshell: QPSK, QAM and OFDM Explained Simply

Abbreviation	Term	Explained simply
QPSK	Quadrature Phase Shift Keying	Uses four different phase states of a signal to transmit two bits per symbol.
QAM	Quadrature Amplitude Modulation	Combines different amplitudes and phases to transmit several bits per symbol. The more signal states there are, the higher the possible data rate at the same symbol rate.
OFDM	Orthogonal Frequency Division Multiplexing	Distributes data across many narrow subcarriers that are orthogonal to one another. This enables efficient transmission and helps to reduce the effects of multipath propagation.

Antennas and matching

Antennas convert wired RF signals into electromagnetic waves, and vice versa. The design, dimensions, mounting position and environment of an antenna influence its range and signal quality.

Common types of antenna include dipoles, monopoles, patches, helicals, PCB and chips. Antenna modules may feature various connectors, such as SMA, RP-SMA and U.FL, as well as other RF connectors. SMA is a connector system, not a type of antenna.

An important consideration is impedance matching between the radio module, cable, connector and antenna. In many RF applications, 50 ohms is the standard system impedance. If the source, cable and antenna are not properly matched, reflections occur. This means that part of the power is reflected back instead of being radiated or transmitted.

The matching can be assessed using the voltage standing wave ratio (VSWR), amongst other things. Values around 1.5:1 are acceptable in many applications. Significantly higher values, such as above 2:1, should be investigated.

Coaxial cables are also part of the system at high frequencies. The signal is influenced by factors such as length, attenuation, bend radius, connectors and adaptors. At high frequencies, cable attenuation increases. Long or thin coaxial cables can cause noticeable losses at 2.4 GHz. Therefore, short cables, suitable connectors and a neat mechanical design are important.

Ferrite beads and EMC

Not all high-frequency signals in a circuit are intentional. Fast transition edges, clock frequencies, DC/DC converters, microcontrollers, displays, USB interfaces and radio modules can all generate high-frequency interference. This interference can propagate via power supply lines, signal lines, or ground planes.

Ferrite beads are used to reduce such interference. For direct current, they behave largely like a low-impedance connection. At higher frequencies, however, their impedance increases. This enables them to reduce RF interference on lines.

Typical applications include:

• Powering Wi-Fi, Bluetooth and IoT modules
• Decoupling sensitive analogue or RF sections
• Separation of digital and interference-prone circuit sections
• Reduction of interference on power supply and signal lines
• EMC measures in compact printed circuit board layouts

Several parameters are important when selecting a ferrite bead: package type, rated current, DC resistance, impedance response across the frequency range and behaviour under DC bias. Many ferrite beads are specified with an impedance of 100 MHz. However, this figure is only a comparative value and does not replace a thorough review of the datasheet.

Ferrite beads are not a substitute for a clean layout. They work best in conjunction with appropriate shielding, short current loops, and sensible ground paths. If used incorrectly, however, ferrite beads can generate resonances when combined with capacitors. They should therefore be used selectively rather than universally.

However, for simple radio and IoT circuits, ferrite beads are useful for reducing interference on power supply lines and for decoupling circuit sections.

HF Measurement Techniques for Beginners

High-frequency signals can only be assessed to a limited extent using simple multimeters. Specialised measuring equipment is advisable for many tasks.

A software-defined radio, such as an RTL-SDR stick, can visualise spectra and display occupied frequency bands. This enables you to locate sources of interference, compare signal levels, and monitor radio activity across different bands.

A vector network analyser (VNA) is useful for antenna measurements. Devices such as the RIGOL DNA808 can measure an antenna’s impedance, display resonance frequencies and help to shorten or optimise radiators. VNAs can also be used to identify faulty cables, connectors or transitions.

The following are also useful:

• 50-ohm terminating resistor
• Attenuators
• Suitable SMA or RP-SMA adapters
• Short coaxial cables
• A frequency counter or signal generator, if required

A 50-ohm terminating resistor provides a defined load. Attenuators reduce RF levels by fixed amounts, such as 3, 6, 10 or 20 dB. They are used to protect measuring equipment, set reproducible levels or stabilise test set-ups.

The demands placed on measuring equipment, cables, connectors and calibration increase significantly for higher frequency ranges. However, simple SDR receivers, a small VNA, suitable adapters, terminating resistors and attenuators are sufficient for many entry-level and laboratory applications.

When working with radio technology, it is important to observe the legal framework. The transmission of radio signals is regulated. Only approved radio modules should be used within permitted frequency ranges and at authorised transmission power levels.

The outlook for 6G

6G is the planned next generation of mobile communications technology. Many technical details are still the subject of research and standardisation. Expected developments include higher usable frequency bands, more advanced antenna systems, greater network automation, more precise positioning, and closer integration of communications, sensor technology, and computing power.

One key area is the use of higher frequencies. While higher frequencies enable greater bandwidths, they also place greater demands on range, antennas, materials, printed circuit boards, connectors and test set-ups. This is precisely where RF fundamentals remain relevant.

Another key area is the integration of sensor technology and communication. In the future, wireless networks will not only transmit data, but also provide information on position, movement and the surrounding environment. This will require precise signal processing, stable radio channels and suitable antenna systems.

Non-terrestrial networks, such as satellites and high-altitude platforms, are also set to interact more closely with traditional mobile networks. The main areas of concern here are coverage, availability and network architecture.

The fundamentals remain the same, the possibilities are growing

RF technology forms the basis of modern wireless applications. The reliability of a wireless system depends on numerous factors, including frequency, wavelength, modulation, antenna matching, cabling, electromagnetic compatibility (EMC) and measurement technology. Therefore, it is worthwhile for developers, students and hobbyists to understand these fundamentals. After all, familiarity with Wi-Fi, Bluetooth or IoT circuits today will also equip you well for tomorrow’s wireless technologies.

Practical building blocks for stable wireless and IoT circuits include ferrite beads, decoupling capacitors, clean ground connections, suitable antennas, 50-ohm systems and simple RF measurement techniques.

6G does not change these fundamentals. It expands the requirements. Higher frequencies, more complex antenna systems, more precise positioning and more highly networked systems mean that a solid understanding of high-frequency technology remains essential.

Images: Adobe Stock, reichelt elektronik