Jeffrey R. Guerrieri

HF RFID electromagnetic emissions and performance

We examined the emissions of commercial HF (high-frequency) proximity RFID (radio frequency identification) systems and the performance of a typical RFID system in the presence of electromagnetic (EM) interference. Some initial investigations into security and reliability were also performed. These investigations highlight detectability and readability of an RFID transaction at a distance. We performed measurements to determine the power radiated by some commercial systems and monitored the RFID transaction in adverse EM environments.

Simple Test and Modeling of RFID Tag Backscatter

We consider here worst-case analysis of backscatter from passive radio frequency identification (RFID) tags. The basis is a figure of merit “B” to relate link power at reader ports to tag circuit parameters. A minimum bound for received monostatic backscatter can be determined by inspection from measured B. The bound is general for narrowband signals in any causal linear propagation. For an assembled tag, this minimum varies only with reader transmit power, tag antenna tuning, and chip power sensitivity of different commands. To validate this model, we propose a backscatter calibration device to enable measurements with estimated 0.5 dB uncertainty. We then demonstrate how the minimum bound can inform reader sensitivity specification to help ensure reliable inventory performance.

Standard radiometers and targets for microwave remote sensing

We describe the NIST effort to develop brightness-temperature standards for microwave and millimeter-wave frequencies. Results of preliminary measurements at 26 GHz are presented.

Reference modulation for calibrated measurements of tag backscatter

This paper presents an approach for calibrating backscattering measurements from 860–960 MHz Ultra-High Frequency Radio Frequency Identification (UHF RFID) tags. An S-parameter model is formulated to relate diode switch and antenna input circuit parameters with the scattering performance of the calibration device. Measurements of modulated backscattered power agree with the model to within ±0.1 dB. Tag backscatter measurements can then be calibrated by comparing them to the reference signal. In an example testbed, the expanded uncertainty of these measurements is estimated to be ±0.4 dB, compared with uncertainties worse than −0.9 dB, +1.2 dB for methods that calibrate against radar cross section (RCS) standards in the same testbed.

Forward and reverse link constraints in UHF RFID with passive tags

This paper examines the relative roles of the forward and reverse links in determining the operational range of passive UHF RFID systems. Simple free space examples in free space show when the forward or reverse link may be the main range constraint in practical systems, depending on reader and tag characteristics. Measurements of transmission and scattering off of a dipole in a real environment demonstrate showed different multipath effects; transmission power fading squared disagreed with backscattered fading in the test environment by up to 8 dB within a measurement range of 2 m.

Baseband Signals and Power in Load-Modulated Digital Backscatter

Passive digital backscatter signals in systems like radio frequency identification (RFID) are usually received along with strong interference from a leaked carrier. The simplest way to quantify the “useful” communication signal is to separate it as an amplitude-shift keying (ASK) or biphase-shift keying (BPSK) component. These definitions give different power normalizations, posing some complexity in comparison of link quantities. This letter investigates their suitability in terms of basic signal theory and conservation of energy to clarify relationships between the baseband signals and “backscattered power.” Defining received backscatter as BPSK guarantees energy conservation for arbitrary tag modulation loads.

Testing passive UHF tag performance evolution

Trends in tag development since the introduction of the ISO 18000-6C and EPC Global standards are investigated empirically with measurements of power harvesting and backscattering performance from 20 samples of passive tags across 860–960MHz. The population spans ages of 0 to 6 years, 9 tag manufacturers, and 3 chip manufacturers. All tags were still in working condition, except two 5-year-old tags that no longer responded to interrogations and a 3-year-old tag with a degraded chip-to-antenna bond. Despite steadily improving chips, some older tags show performance comparable to new tags.

An All-Metal, 3-D-Printed CubeSat Feed Horn: An assessment of performance conducted at 118.7503 GHz using a robotic antenna range.

Three-dimensional (3-D) printing is finding applications across many areas and may be a useful technology for antenna fabrication for cube satellites (CubeSats). However, the quality of an antenna produced using 3-D printing must be considered if this technology can be relied upon. We present gain and far-field pattern results for the feed horn of the radiometer payload of the CubeSat PolarCube. The corrugated feed horn is constructed from AlSi10Mg alloy and fabricated using powder bead fusion (PBF). Measurements were performed at the atmospheric oxygen line of 118.7503 GHz with the National Institute of Standards and Technology (NIST) Configurable Robotic Millimeter-Wave Antenna (CROMMA) facility in Boulder, Colorado. A comparison of these measurements to theoretical predictions provides an assessment of the performance of the feed horn.

A reference modulated scatterer for ISO18000-6 UHF tag testing

We present a method for measuring ultra-high frequency radio-frequency identification (UHF RFID) tag differential RCS that has the potential for being easier and more accurate than current and proposed methods [1-2]. Our method is based on accurately characterizing the reflection states of a modulated load, accounting for transmission losses between the load and an antenna, and using a well-known, low gain antenna. This has the benefit of using a well characterized “golden tag” reference (i.e., repeatability), while being more linear in power response, independent of reader signal, and independent of manufacturer or process changes. Characterizations of the losses in the reference scatterer allow for direct comparisons between tags on different test beds.

Interference tests for 900 MHz frequency-hopping public-safety wireless devices

We discuss free-field measurement methods designed to quantify interference between wireless devices such as RF identification systems and RF-based emergency beacons used by fire fighters. For public safety applications, standardized testing requires that responder organizations purchase devices that are appropriate for their specific needs. Also, appropriate test methods must be developed because reliability can be life critical.