Hans Schantz, UWB Thinking and the Limits of Ham-Radio Framing
Hans Schantz, UWB Thinking and the Limits of Ham-Radio Framing
I watched G3LRC’s interview with Dr Hans Schantz, KC5VLD. It is worth your time because Hans repeatedly turns familiar amateur-radio questions back into first-principles antenna engineering. That tension—not a generic UWB tutorial—is the reason for this article.
RF.Guru working definition: Common-mode current is the non-cancelling phasor-sum current in a specified set of conductors, evaluated at a defined cross-section and using a declared current-direction convention. In the intended differential transmission-line mode, the outgoing and return currents are equal and opposite, so their phasor sum is zero. When they do not cancel, the remaining current must close through another reference or return path—such as the outside of a coax shield, a mast, equipment chassis, station wiring, nearby structures, earth, the operator, or distributed coupling through the environment.
This broader working definition is especially useful in practical antenna systems. On transmit, non-cancelling current on the outside of the coax can make the feedline and connected structures part of the radiating antenna system unless that path is intentional, clearly defined and properly controlled—for example by providing the required return path and placing a suitable common-mode choke at the correct boundary.
The conversation is uneven in technical depth: a practical radio-amateur host is questioning a specialist whose career spans ultra-wideband antennas, near-field location and applied electromagnetics. Hans carries most of the technical weight. The useful moments arrive when he is given room to explain mechanisms instead of being compressed into the familiar language of coax, SWR, tuners and backyard antenna rules.
Watch the exchange itself: G3LRC asks practical questions about what happens between the transmitter and dipole, antenna compromise, SWR, VNAs, loops, feedlines and RF safety. Schantz answers from a much wider UWB, near-field and electromagnetic background. When a question begins with a ready-made ham-radio picture, his answer often reopens the mechanism. This article keeps that contrast visible while separating his established antenna work from his broader Fields & Energy interpretation.
Hans Is the Reason to Watch
Schantz’s reputation was not built by repeating HF folklore with a more impressive résumé. His published antenna work asks harder questions: what transfer function the complete link presents, how waveform and pattern change with frequency, where energy is stored, how near fields couple, which physical limit applies and what the measurement plane actually includes.
That is why the interview becomes strongest when Hans can build an answer from the field mechanism. He describes fields guiding energy along a transmission line and away from an antenna; explains why SWR cannot reveal either the actual complex impedance or where accepted power goes; separates a lossy receive antenna from an efficient transmit antenna in a noise-limited environment; and recommends learning the VNA because complex measurements build intuition that a single SWR number cannot.
Where the Framing Helps—and Where It Narrows the Subject
The practical questions make difficult material approachable. They also create a recurring trap: an idea from UWB antennas or near-field electromagnetics is quickly translated into “What does this mean for my dipole, coax, balun or tuner?” That can be a useful second question, but it is often the wrong first one. The principle has to be understood before it is folded into an HF rule of thumb.
Several prompts in the interview point toward a conclusion before the physical boundary has been established. Hans keeps rescuing those moments by returning to energy flow, paired charges, stored fields, loss, bandwidth or measurement. That does not make the host the villain of the story; it explains the mismatch that gives the interview its character. One side supplies recognisable amateur-radio framing. The other side keeps showing why the subject is larger than that frame.
This distinction matters because a technically strong guest can be quoted accurately and still be misunderstood. “Thicker conductors increase bandwidth,” “ladder line has lower loss,” or “a lossy receive antenna need not reduce SNR” are not universal shopping rules. Each statement belongs to the mechanism and conditions Hans was describing. Pulling the sentence away from those conditions merely creates new folklore.
Do Not Merge Two Different Parts of Schantz’s Work
Schantz’s antenna engineering and UWB publications provide a concrete technical record: broadband matching, dispersion, phase centre, time-domain response, electrically small antennas, near-field coupling and system-level measurement. Those subjects can be checked against papers, models and experiments.
His broader Fields & Energy project is more interpretive. In the interview he argues that fields guide localised energy and uses that perspective to challenge common explanations of current, radiation and photons. It is intellectually interesting and often produces useful engineering intuition, but it should not be presented as though every wider conclusion is ordinary handbook consensus. Respect for the antenna engineer does not require collapsing published engineering and a broader physical interpretation into one evidential category.
The Interview Is a Doorway, Not the Last Word
Watch the interview, but do not stop there. The real signal is in Schantz’s own books, papers and long-form explanations, where the argument is not forced through short questions or familiar HF shorthand. Read him at source, then bring the mechanisms back to amateur radio with the dimensions, frequency range, loss, pattern, reference plane and uncertainty still attached.
Hans Schantz resources
- Video and edited transcript of the G3LRC interview
- The Art and Science of Ultrawideband Antennas
- Fields & Energy Book I: Fundamentals & Origins of Electromagnetism
- Fields & Energy Substack
- Hans G. Schantz author page
These links lead to Schantz’s own transcript, project pages or publication listings. Individual technical claims should still be checked against the cited paper, measurement conditions and the requirements of the system being designed.
What “Ultra-Wideband” Means
UWB is a system and regulatory term, not the name of one antenna shape or one pulse. Under the current US FCC definition, a UWB transmitter has a fractional bandwidth of at least 0.20 or a UWB bandwidth of at least 500 MHz. The bandwidth is bounded by points 10 dB below the highest radiated emission and is based on the complete transmission system, including its antenna.
Fractional bandwidth = 2(fH − fL) / (fH + fL)
That definition does not require a particular waveform. ITU-R SM.1755 treats UWB through terms, definitions and general characteristics that include several modulation and application families. The applicable emission limits and permitted uses depend on the device class and jurisdiction; meeting a bandwidth definition is not by itself permission to transmit.
Do not mix three separate tests: a wide impedance bandwidth, a UWB radiated-emission definition and faithful transmission of a wideband waveform are related, but none proves the other two by itself.
A UWB Antenna Is a Complex Transfer Function
For a narrow measurement at one frequency, input impedance and S11 can be useful first checks. A UWB link needs a wider description. The antenna and its feed contribute frequency-dependent magnitude, phase, group delay, pattern, polarisation, phase centre and efficiency. The environment and the second antenna add their own transfer functions.
Schantz’s IEEE introduction to UWB antennas identifies non-dispersive behaviour and phase-centre stability as desirable properties. A wideband antenna can have an acceptable input match yet radiate different frequency components at different times or in different directions. A log-periodic structure, for example, can move its active region with frequency; whether that dispersion is acceptable depends on the waveform, direction and receiver processing.
| Quantity | What it reveals | What it cannot establish alone |
|---|---|---|
| S11(f) | Complex reflection at the calibrated port plane | Radiation efficiency, pattern, phase centre or pulse fidelity |
| Transfer magnitude | Frequency-dependent coupling through the measured path | Waveform delay or ringing without phase |
| Transfer phase / group delay | Frequency-dependent timing and dispersion | Angular coverage without directional measurements |
| Pattern and polarisation versus frequency | Where each spectral component is radiated or received | Total efficiency unless absolute power is calibrated |
| Impulse response | The time-domain response over the measured band and window | Behaviour outside that band or outside the linear time-invariant test state |
For a linear time-invariant system, the impulse response follows from the inverse Fourier transform of its complex frequency response. Recovering a useful response therefore requires both magnitude and phase, sufficient frequency span and sampling, a stated window, and calibrated reference planes. NIST wideband channel-sounder work also shows that array response can require direction-specific calibration; one calibration result is not automatically valid for every beam or polarisation.
Bandwidth, Dispersion and Efficiency Are Different
A broad low-SWR curve may come from useful radiation, a properly terminated travelling-wave structure, resistive loss, feedline radiation or a combination of these effects. Loss can broaden a measured match while reducing radiation efficiency. Conversely, a resonant antenna may be efficient over the narrower bandwidth that its application actually needs.
For an electrically small antenna, size, stored energy, radiation Q, bandwidth and achievable efficiency are coupled. The Wheeler and Chu results establish physical bounds under stated idealisations; a matching network cannot remove them. They do not say that every high-Q antenna is poor, nor that every broadband antenna is good. They say that electrical size and loss must remain in the engineering budget.
Useful distinction: mismatch bandwidth describes a port condition. Radiation bandwidth adds gain, efficiency, pattern and polarisation requirements. Waveform-fidelity bandwidth adds the permitted magnitude and phase distortion of the complete link.
What Transfers Well to HF
Several UWB engineering habits improve HF work directly:
- Define the required signal bandwidth first. Measure across the occupied spectrum plus the margin needed for tuning drift, environment and manufacturing variation.
- Keep complex data. Resistance, reactance, S-parameter phase and calibrated reference plane carry information that a minimum-SWR marker discards.
- Treat feed and antenna as one installed system. Connector launches, baluns, chokes, feedline common mode and nearby conductors can change both impedance and pattern.
- Measure the output that matters. An HF antenna is selected for field strength, SNR, coverage, efficiency and safe electrical stress—not merely for how easily it accepts a match.
- Check more than one direction and frequency. The pattern, nulls and polarisation can move across a band even when SWR remains calm.
- Use time-domain transforms carefully. Gating and impulse views can help locate discontinuities, but their resolution and artefacts are set by measured span, frequency spacing and window.
What Does Not Transfer Automatically
Most HF amateur links occupy only a small fraction of their carrier frequency. A resonant dipole, loop or shortened antenna can therefore be entirely appropriate when it passes the required modulation bandwidth, remains efficient enough, controls common mode, preserves the intended pattern and stays within voltage, current and thermal limits.
Geometry also matters in absolute scale. A structure that is compact at microwave frequencies can become very large when scaled to HF wavelengths. Loading or miniaturisation can restore a practical size, but it changes stored energy, loss, voltage, current and bandwidth. UWB terminology does not bypass those trade-offs.
Regulation does not scale either. FCC Part 15 UWB definitions and emission limits concern particular unlicensed device categories in the United States. Amateur-service operation, occupied bandwidth and spurious emissions are governed separately, and other administrations use their own rules. Design from the licence, allocation and device category that actually apply.
HF conclusion: do not optimise for the largest possible bandwidth unless the link requires it. Optimise for the required bandwidth with acceptable efficiency, pattern, common mode, loss, electrical stress, spectral compliance and measurement uncertainty.
A Measurement Workflow for Wideband and HF Antennas
- Write the system requirement. State frequency range, waveform, occupied bandwidth, directions, polarisation, range, field-strength or SNR target, power and regulatory category.
- Draw the test boundary. Mark the VNA plane, cables, adapters, balun or launch, antenna, second antenna and propagation path.
- Calibrate at the named plane. Characterise or de-embed fixtures that remain between the calibration and antenna terminals.
- Measure complex S-parameters. Preserve amplitude and phase with frequency spacing fine enough for the desired unambiguous time window.
- Measure directional behaviour. Record pattern, polarisation and transfer response across frequency; one boresight trace is not a complete antenna characterisation.
- Separate mismatch and dissipation. Determine radiation efficiency or gain with an appropriate calibrated method rather than inferring it from S11.
- Inspect timing only within the measurement limits. Document window, transform convention, gating, bandwidth and reference delay when presenting group delay or impulse response.
- Repeat in the installed environment. Cable routing, enclosure, operator, mast, ground and nearby conductors can change the result.
- Report uncertainty and acceptance limits. Connector repeatability, drift, multipath, positioning and calibration uncertainty must be compared with the design margin.
Primary technical references
- 47 CFR § 15.503 — FCC UWB definitions
- ITU-R SM.1755 — Characteristics of ultra-wideband technology
- Hans G. Schantz — Introduction to Ultra-Wideband Antennas
- Hans G. Schantz — A Brief History of UWB Antennas
- Hans G. Schantz — Three Centuries of UWB Antenna Development
- NIST — Over-the-air calibration of a wideband phased-array channel sounder
- H. A. Wheeler — Fundamental Limitations of Small Antennas
- L. J. Chu — Physical Limitations of Omni-Directional Antennas
Mini-FAQ
- What makes a transmitter UWB under the FCC definition? Its fractional bandwidth is at least 0.20 or its UWB bandwidth is at least 500 MHz, measured from the complete radiating system under the definitions in 47 CFR § 15.503.
- Does UWB require a particular pulse waveform? No. The FCC bandwidth definition does not prescribe one waveform, and ITU-R describes several UWB modulation and application families.
- Does low SWR across a wide band prove good UWB performance? No. It establishes a port-reflection result only; efficiency, transfer phase, dispersion, pattern, polarisation and phase centre still require measurement.
- What is antenna dispersion? It is frequency-dependent amplitude, phase or spatial behaviour that changes the waveform or direction-dependent response across the operating band.
- Can UWB antenna ideas be scaled directly to HF? The measurement and system-thinking principles transfer, but wavelength, electrical size, required bandwidth, loss, power and regulation must be recalculated for HF.
- Is a high-Q HF antenna automatically bad? No. It can be appropriate when it covers the required signal bandwidth efficiently and remains within tuning, voltage, current and thermal limits.
- Can a VNA prove antenna efficiency? Not from S11 alone. Efficiency or gain needs an appropriate calibrated radiation or loss measurement with the feed-system boundary stated.
- Why keep phase when measuring a wideband antenna? Magnitude alone cannot reveal group delay, ringing or impulse response. Those results depend on the complex transfer function and calibrated timing reference.