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Numerous standard RF circuits like directional couplers, hybrids, amplitude modulators, oscillators, etc. require a 50Ω termination. Additionally, in several measurement scenarios, ports have to be terminated. Such terminations are preferable of the same waveguide type as the circuits to avoid degradation of their performance. In general, standard fabrication steps are desired as they are cost-effective. The straightforward solution is a 50Ω resistor shunted to ground by means of a via. Partial wraparound SMD resistors in a 0402 size have low parasitics making them applicable up to K-band. However, for RF, this combination suffers from the considerable inductive parasitics of the via. Different approaches to avoid the vias, with varying disadvantages exist. We analyzed the approach of broadband matching the non ideal viaresistor combination to 50Ω by means of a filter structure. The realization uses only standard design and fabrication methods. The design procedure can easily be adapted to arbitrary substrates and fabrication technologies. The assembled 50Ω termination was measured using TRL calibration with a VNA. Therefore its characteristics are determined in the intended plane and it can be directly included into a planar 50Ω circuit. The measured terminations showed a VSWR better than 1.34 within the whole band from DC to K-band, and within 57% of the band (including the 24 GHz ISM band) the VSWR is better than 1.22. [ABSTRACT FROM AUTHOR]

In a cooperative sensor system for pedestrian protection, a pedestrian and other road users exchange data by means of radio frequency communication. In the proposed system, the pedestrian carries a transponder which is interrogated by a vehicle and sends an anonymous identification (ID) sequence. By decoding the ID, the interrogation unit in the vehicle detects the presence of the transponder. Evaluating the incident wave of the transponder's answer, a localisation is possible. In the proposed localization system, the measurement results can be distorted by multipath propagation. Multipath errors result if signals of the same transponder arrive simultaneously at the receiver unit from different directions. In this case, erroneous distances and angles are measured. Because the signals arriving from different directions contain the same transponder ID, they can be assigned to their origin. One of the challenges in post-processing for signal improvement is enhancing the selection of the correct position information by making assumptions about the pedestrian's movement and by knowing the vehicle's current driving parameters. Additionally, information contained in multipath signals is used to form a better estimate for the true position of the transponder. To overcome the problems related to multipath propagation effects, a method is proposed that estimates the origin of a multipath signal and maps the distorted position information back to the true position. A fusion of tracked direct positions and mapped multipath signals leads to an improvement in positioning accuracy. [ABSTRACT FROM AUTHOR]

RF transmission properties of human tissues were investigated in the frequency range from 50 MHz to 1 GHz. This work was motivated by the increasing interest in communication links between medically active implants and external interrogator units. We investigated theoretically and experimentally the transmission loss between an implant and an external interrogator unit. We assumed that due to the size of the implant a maximum area of only 1 cm² is available for the printed circuit antenna. The size of the external interrogator antenna is less restricted. The maximum depth of the implant beneath the surface of the body was assumed to be 10 cm. For the simulations we took the dielectric properties of skin, fat and muscle as published in the literature. For the measurements, an artificial muscle dielectric proposed in the literature was used consisting mainly of a mixture of water, sugar and salt. In simulation and measurements the reactive part of the impedance of the antennas was compensated numerically. In simulations and measurements we obtained a transmission loss between 30 dB around 100 MHz and 65 dB around 900 MHz. [ABSTRACT FROM AUTHOR]

An efficient method for the calculation of the field distribution in aperture coupled cavity resonators is proposed. The coupling between the resonator and the surrounding free space is accomplished by means of an aperture in one of the cavity walls. This concept is very attractive for integrated microwave and millimeter-wave circuits, because active elements can be integrated within the aperture. The field distribution is solved using Galerkin's method. For rooftop basis functions the reaction integrals are analytically calculated in the apace domain for each cavity mode. A criterion is derived that gives the minimum number of cavity modes depending on the dimensions of the cavity and the size of the discretization cells. Efficiency and accuracy of the proposed method are demonstrated for slot coupled cavity resonators. The numerical results are compared with measurements. [ABSTRACT FROM AUTHOR]