Bernd Geck

Compact Unfocused Antenna Setup for X-Band Free-Space Dielectric Measurements Based on Line-Network-Network Calibration Method

This paper presents a compact free-space measurement system for the characterization of dielectric materials within the X-band based on the line-network-network (LNN) calibration method. Using a pair of dielectric-filled horn antennas with enhanced directivity, the setup exhibits a total length of 250 mm between the antenna apertures and is suitable for measurements of planar samples with transverse dimensions equal to or greater than 250 mm×250 mm. Based on 3-D field simulations and measurements, the assumptions of plane wave incidence on the sample and negligible diffraction effects at the sample edges are investigated. The scattering parameters of the sample are obtained according to the LNN calibration method. Remaining multipath propagation effects caused by reflections at the antennas and their fixtures are filtered out via time gating. The complex permittivity is finally calculated from the transmission scattering parameter using the Newton-Raphson method. Results for exemplary dielectrics are in good accordance with reference values.

Impedance Measurement of Properly Excited Small Balanced Antennas

This paper presents a new method for measuring the input impedance of properly fed small balanced antennas using a conventional vector network analyzer. The measurement setup includes a balun which allows driving the balanced antenna properly. This measurement method allows analysis of proximity effects on the input return loss of balanced antennas. For this purpose, a formula to extract the antenna impedance by measuring the reflection coefficient at the balun input is developed. To verify the proposed method, a balanced antenna with known simulated differential impedance has been measured and compared with the simulation results. The achieved good agreement validates the developed formula and thus the new measurement procedure.

Contactless Vector Network Analysis With Printed Loop Couplers

In this paper, an introduction to contactless vector network analysis is given. Furthermore, the implementation of a contactless measurement setup is presented using different printed coupling structures. The coupling structures are connected to a vector network analyzer (VNA) by means of conventional on-wafer probes, as well as planar-coaxial transitions. For the contactless method, conventional calibration algorithms are used to determine the scattering parameters of a device within a complex planar circuit. The contactless measured results are compared to results received with a conventional VNA and to simulation results obtained with a 3-D field simulator. These comparisons show that, especially for small coupling structures of approximately 1 mm, the results correspond well up to 20 GHz.

Multifunctional Reference Cells for Multistandard RFID Transponders

This paper at first illustrates implementation aspects and measurement results of a subcomponent for a multistandard RF identification (RFID) transponder. It is intended to be a common reference cell, both for basic UHF requirements and advanced application fields like local positioning and wireless sensing. Different single circuit topologies shown in previous studies or literature and their applicability for that RFID system are evaluated. After that, measurement results of two final circuit configurations, including a newly designed RC oscillator with metal-metal capacitors, are discussed and compared. Layout aspects for reducing the process variations and low power consumption are demonstrated. Simulation results show border conditions for the power supply of the transponder on chip level. Moreover, distance measurements with our first complete transponder compliant to the electronic product code protocol are shown. It includes the newly presented reference cells and other necessary transponder components. All chips are designed based on a 0.13-μm CMOS technology.

Contactless Scattering Parameter Measurements

An introduction to contactless vector network analysis is given for the determination of the scattering parameters of embedded devices. In the measurement setup, contactless probes are connected to a conventional vector network analyzer. Suitable probes are developed for the implementation of a contactless measurement setup, whereas the positioning of the probes is essential for an accurate measurement setup. The contactlessly measured results are compared to results received with a conventional vector network analyzer. These comparisons show that it is possible to characterize embedded devices with the contactless vector network analysis at least up to 6 GHz using the suggested probes.

Packaging and antenna design for wireless SAW temperature sensors in metallic environments

We have developed a radio frequency (RF) transponder based on a surface acoustic wave (SAW) device specifically optimized for wireless temperature measurement of rotating shafts. The SAW sensing element is a reflective delay line type with 3 reflectors. The main foci of the paper are on a new compact packaging, and on antenna simulations for 2.4 GHz radio signal transmission to the interrogator. The novel metallic packaging has been designed for smallest possible outer dimensions of 10.0 × 3.1 × 2.0 mm3. In order to streamline the housing for insertion in a borehole, the electrical feedthroughs have been oriented in the longitudinal axis, contrary to the standard vertical axis approach. Antenna simulations were performed to find an optimized design tuned to the metallic surrounding. A slot antenna type was identified as best joint solution for the objectives radiation pattern and antenna gain.

Adaptive matching for efficiency enhancement of switching mode and nonlinear microwave power amplifiers

In this paper the application of adaptive matching networks for efficiency enhancement of class-E and class-F power amplifiers will be presented. These networks are capable of synthesizing the optimum impedance at the fundamental frequency as well as the suitable terminations at the harmonics. Additionally they use only transmission lines and capacitors, making them suitable for high power applications. A class-E and a class-F GaN based power amplifiers at 1 GHz will be presented, the class-E amplifier has a maximum output power of 36.8 dBm and a PAE of 73.5 %. Through using adaptive matching the amplifier can achieve a PAE of 60 % at an output power of 28.7 dBm, which gives an efficiency improvement over an 8 dB output range. The class-F amplifier has a maximum output power of 38 dBm and a PAE of 72 %. Through adaptive matching the amplifier can achieve a PAE of 58 % at an output power of 29.5 dBm, which gives an improvement of efficiency over an 8.5 dB output range.

Optimization of NFC compatible transponder with respect to the nonlinear IC impedance

A very important quality factor of a transponder is its threshold field strength which is a result of the performance of the integrated circuit (IC) and the loop antenna. This is very important for near field communication (NFC) applications to ensure a fast and reliable communication between the active device and the transponder with a minimum of battery power. In this paper a new approach using a nonlinear model for the IC and an analytical description of the coil is presented to design a loop antenna with minimal threshold field strength. For comparison the IC is modeled with both a linear model and a nonlinear model. The optimization results for both cases show clearly the advantage of the procedure with a nonlinear IC model. Afterwards, the design constraints due to the input capacitance of the IC is analyzed.

Field Powered 5.8 GHz ISM Band Transponder for Sensors Integrated in Metallic Objects

This paper presents the new design of a field powered microwave transponder fully integrated into a metallic object. The transponder operates in the 5.8 GHz ISM band and consists mainly of a waveguide antenna, a rectifier, a low-power microcontroller and a temperature sensor. The transponder has been integrated 4.5 cm deep into a metallic work piece. Depending on the microcontroller code the transponder can be used for identification or sensor applications. The realized system is able to identify the object and to measure and transmit the inner temperature to a reader. An operating range and a data rate up to 51 cm and 333.3 kb/s respectively have been achieved.

Optically transparent and circularly polarized patch antenna for K-band applications

This contribution presents an optically transparent and circularly polarized patch antenna to be integrated on a solar cell. The whole configuration is suitable to be use in a wireless sensor node acting as a communication interface and a power source. The antenna consisting of grid lines is studied concerning the impedance behavior due to the applied mesh. A single fed truncated corners meshed patch antenna with meshed ground plane on quartz glass is investigated. This structure with an overall transparency of 92 % has similar antenna properties to the opaque counterpart. Additionally, the alignment errors between both meshed layers possibly caused by the fabrication process is addressed concerning the axial ratio. A prototype is realized and measured to verify the simulation results.