Volume 71, Issue 3-4 - Special Issue: GeMiC 2016, Guest Editor: Niels Pohl

In this paper, a new microstrip slow wave open loop resonator is proposed. This resonator overcomes the substantial limitation of the conventional slow wave open loop resonators, which limits the spurious-free band of those resonators. The new proposed resonator improves the spurious-free band up to 8 times of the fundamental frequency, which is 3.16 times of the conventional slow wave open loop resonators. For the proposed resonator the coupling factor and the external quality factor curves, which are the design curves of a narrowband filter, are extracted using a full wave simulator, i. e. HFSS. These curves are utilized for the design of two three-pole Chebyshev bandpass filters. One of these filters is fabricated. Simulation and measurement results are reported which are in good agreement. Designed filters provide 75 % and 83 % of footprint reduction in comparison with the conventional open loop resonator filters. Different parameters which can improve the spurious-free band are explained in the paper.

Modern communication platforms require a huge amount of switched RF component banks especially made of different filters and antennas to cover all operating frequencies and bandwidth for the targeted services and application scenarios. In contrast, reconfigurable devices made of tunable components lead to a considerable reduction in complexity, size, weight, power consumption, and cost. This paper gives an overview of suitable technologies for tunable microwave components especially for SatCom applications. Special attention is given to tunable components based on functional materials such as barium strontium titanate (BST) and liquid crystal (LC).

This paper presents the analysis and the design of a fully-differential digital programmable gain amplifier (PGA) in a 0.13 µm BiCMOS technology. The PGA has a gain control range of 31 dB with 1 dB gain step size and consumes 284 mW from a 3.6 V power supply. At a maximum gain of 25 dB, the PGA exhibits a 3-dB bandwidth of 10.1 GHz. The measured gain error for all 32 possible gain settings is between –0.19/+0.46 dB at 1 GHz. Up to 13 GHz the third harmonic distortion HD3$$\it H{{D_{\rm 3}}$$ stays below –34 dB for all 32 gain settings at a differential output peak-to-peak voltage of 1 V after the last amplifier stage.

A fully integrated 10–40 GHz superheterodyne receiver frontend using a 40–46 GHz IF is presented. The frontend consists of a differential low noise amplifier, a fully differential mixer, a single-ended frequency quadrupler and a transformer-based balun followed by an amplifier to convert the quadrupler’s single-ended output to a differential signal to drive the LO port of the mixer. The circuit is designed and fabricated in a 250 GHz fT$${f_T}$$ SiGe BiCMOS technology. The chip was characterized on-wafer single-endedly. The frontend achieves a differential conversion gain of 17–20 dB and an input-referred 1 dB compression point of –16 to –20 dBm across the desired IF bandwidth.

As part of the EUROfusion project, the conceptual design of a 1 MW 236 GHz hollow-cavity gyrotron is ongoing at IHM, KIT for a DEMOnstration Power Plant (DEMO), along with a 2 MW coaxial-cavity design concept. Fast frequency-tunable gyrotrons (tuning within a few seconds) are recommended for plasma stabilization using a non-steerable antenna. In this work, the mode-selection approach for such a frequency-tunable gyrotron is presented and suitable operating modes for fast frequency tunability are suggested. Magnetic field tuning has been studied as an effective technique to tune the gyrotron operating frequency. The step-tunability of the 236 GHz gyrotron within the frequency range of ±10 GHz in steps of 2–3 GHz is demonstrated in numerical simulations. A hybrid-type Quasi-Optical Launcher (QOL) has been designed for a step-frequency tunable gyrotron with sufficiently high Fundamental Gaussian Mode Content (FGMC).

Microwave Materials such as Rogers RO3003 are subject to process-related fluctuations in terms of the relative permittivity and dielectric loss. The behavior of high frequency circuits like patch-antenna arrays and their distribution networks is dependent on the effective wavelength. Therefore, fluctuations of the complex permittivity will influence the resonance frequency and beam direction of the antennas. This paper presents a grounded coplanar waveguide based sensor, which can measure the complex permittivity at 77 GHz, as well as at other resonance frequencies, by applying it on top of the manufactured depaneling. The relative permittivity of the material under test (MUT) is a function of the resonance frequency shift and the dielectric loss of the MUT can be determined by transmission amplitude variations at the resonances. In addition, the sensor is robust against floating ground metallizations on inner printed circuit board layers, which are typically distributed over the entire surface below antennas. Furthermore, the impact from conductor surface roughness on the measured permittivity values is determined using the Gradient Model.

The characterization of dielectric materials at microwave frequencies can be done by various measurement principles. Free space methods are a commonly used approach if the material under test (MUT) has to be characterized in-situ or in a non-destructive manner. Since the transmission and reflection parameters of a finite sized dielectric slab typically depend on its thickness, accurate knowledge about this parameter is of high importance. The ellipsometric approach presented in this paper eliminates the thickness dependence and thus allows to reduce a major source of error. This is achieved by performing four measurements. These measure the transmission and reflection factors of the MUT in both polarizations at an incident angle of 45°. The high stability of the measurement allows a simple monostatic setup utilizing a single antenna. The measurements in this paper are performed using Polytetrafluoroethylene (PTFE) and Polyvinylchloride (PVC) blocks in the frequency range from 22 GHz to 26 GHz.

In this contribution, a composite measurement concept for the gas flow determination in diverse stream scenarios is presented. The approach utilizes the pressure- and mixing-dependent relative permittivity of gaseous media, which, in case of a vortex or a marker gas, creates a detectable variation in the measuring beam of the radar. Since the measurement effect is very small, phase measurements based on highly precise and low jitter frequency-modulated continuous-wave radar systems in different frequency bands are applied. Moreover, disturbances caused by vibrations of the measurement setup are compensated out of the measurement signal.

Up to now, the high effort involved with airborne Synthetic Aperture Radar (SAR) systems has led to the effect that SAR image processing is mostly restricted to single images of a scene. Recent developments like the MIRANDA 35 and its matching flight platform allow for frequent revisits of the same scene at very high repeatability. MIRANDA 35 has been designed as a lightweight and compact SAR sensor for altitudes of up to 1 km while providing a resolution of 15 cm. In combination with a highly flexible ultralight aircraft we have recently obtained 28 measurements of a scene within 2 h of flight time at very high repeatability. Two sets of flight courses, each with 7 flyovers of the reference scene and 7 of a modified change scene, are investigated here using statistical change detection methods like Informational Difference and Universal Image Quality Index.