Daniel G. Kuester

G-Band Micro-Fabricated Frequency-Steered Arrays With 2

In this paper, we describe micro-fabricated frequency-scanned slot waveguide arrays operating between 130 and 180 GHz for planetary landing radar. The group delay dispersion of the feed line is increased by corrugating the bottom rectangular waveguide wall. Both 16-element and 32-element linear arrays are fed by micro-coaxial corporate feed networks to narrow the beam in the non-scanning direction. Two-dimensional (2-D) antenna arrays and feed networks are photo-lithographically fabricated using a sequential metal deposition process. The 16-by-21 array demonstrates a 6° beamwidth and 2° /GHz steering over a 40° scan angle.

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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.

/GHz Beam Steering

In this communication we describe a frequency scanning slot array in μcoaxial technology operating from 87-102 GHz. The array achieves a 30° scanning angle over a 15 GHz bandwidth. The device is fabricated using the PolyStrata sequential copper deposition process, which guarantees low loss and small size. A double-array prototype, with a gain of 14 dB at 94 GHz, is fabricated and tested.

Simple Test and Modeling of RFID Tag Backscatter

Passive ultra-high-frequency (UHF) radio-frequency identification (RFID) has developed rapidly over the past two decades. In 2012 alone, about 4 billion tags were sold worldwide [1]. Manufacture and deployment at this volume has been made possible by minimizing tag cost, making a strong disincentive for the added expense of RF performance testing. As a result, performance metrics and test methods are not yet unified or generally adopted. Large customers in industry and government, however, wish to compare products with parameters like read range and inventory rate, so this problem is attracting more attention, and test standards are improving. This article discusses the history, state of the art, and some future challenges in this rapidly evolving area of study. In particular, we consider two metrics for digitally modulated backscatter of passive UHF RFID tags and how tests can be simplified for reduced costs. Examples for some 860-960 MHz commercial tags and applications are given to illustrate the method.

W-Band Micro-Fabricated Coaxially-Fed Frequency Scanned Slot Arrays

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.

How Good Is Your Tag?: RFID Backscatter Metrics and Measurements

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.

Reference modulation for calibrated measurements of tag backscatter

A 900 MHz low-cost flexible omni-directional rectenna with a mass of 2.1 grams is demonstrated. A rectenna as demonstrated here employs only a Schottky diode, a capacitor, and a printed coplanar circuit which presents class-F harmonic terminations to the diode, resulting in approximately 48.6% efficiency at a low 8 μW/cm2 incident power density. The rectenna is printed on 0.13 mm PET with a commercial printing process depositing 1 μm-thick conductive traces.

Forward and reverse link constraints in UHF RFID with passive tags

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.

A harmonically-terminated two-gram low-power rectenna on a flexible substrate

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.

Baseband Signals and Power in Load-Modulated Digital Backscatter

With the congestion and scarcity of available spectrum resources, spectrum sharing between long-term evolution (LTE) and the IEEE 802.11 (aka. WLAN) systems is an ongoing research topic. Considering the LTE license assisted access (LAA) with the listen before talk (LBT) procedure, recent research efforts try to evaluate the performance in several LTE-LBT and WLAN coexistence scenarios. However, the available approaches have not adequately modeled and analyzed general case of LBT (such as Category 4), and the case when there are more than two types of transmissions. In this paper, to fill this technical gap, we implement a systematic modelling and analysis of the media access control (MAC) layer coexisting performance of LTE-LBT and WLAN systems. We consider the coexistence scenario of multiple LTE downlink with multiple WLAN uplink and downlink transmissions. We develop analytical results on time-efficiency throughput, transmission and collision probabilities of LTE and WLAN nodes, and then generalize the result to multiple types of transmissions (e.g., more than three types). To validate the analysis, we implement LBT and WLAN MAC algorithm programming and extensive simulations, which confirm the accuracy of our analysis. Our result shows that replacing WLAN stations with LTE transmitters may, in some cases, significantly degrade the overall throughput, depending on the original efficiencies of WLAN systems and channel access schemes. To address this, we propose a 4-way handshaking channel access scheme for LTE-LBT, which can significantly improve the coexistence performance. These results put new insight into relationship between coexistence performance and MAC parameters of LTE-LBT and WLAN systems, and may aid in the design and optimization of coexistence systems.