Kurt Blau

An Eigen-Analysis of Compact Antenna Arrays and Its Application to Port Decoupling

Placing the radiators of antenna arrays closer than aggravates the problem of power mismatch. Based on efficiency considerations, a general analysis of this effect is presented, putting forward a simple tool to quantify, compare, and optimize the performance of antenna arrays. This analysis is not restricted with respect to the number of radiators or the degree of compactness. In order to improve power matching, a systematic approach for the design of lossless decoupling and matching networks based on 180 directional couplers is suggested for up to eight radiators. Implications of network losses, which have not yet received appropriate attention by researchers in the past, will be analyzed and discussed by means of a manufactured three-element prototype array.

Miniaturisation of antenna arrays for mobile communications

The focus of this paper is the miniaturisation of antenna arrays, to exploit diversity schemes for mobile communications. The main parameter determining the size of an array is the spacing between adjacent radiators, which is usually chosen to be half a wavelength. Reducing the spacing introduces mutual coupling between the elements and, hence, a degradation of the radiation pattern and the gain of the antenna. We combine improved design of the individual radiators with a passive decoupling network to overcome these drawbacks. To make ultimate use of all available degrees of freedom for a given number of radiators, superdirective modes must be taken into consideration, though at the expense of reduced bandwidth and high sensitivity to variations in component values.

Implementation of a miniaturised antenna array with predefined orthogonal radiation patterns

This paper describes the realisation of an antenna array system consisting of three, quarter-wavelength spaced, monopoles and a passive network. This compact planar network decouples and matches the antenna array, in order to prevent gain reduction. At the same time, the network forms orthogonal radiation patterns at the system ports, which divide the space into three different sections. The described system promises switched beam applications in small mobile platforms, where lack of space and processing power prevents the use of conventional antenna arrays.

Miniaturized Antenna Arrays with an Element Separation down to λ/10

Antenna arrays play an integral role for the exploitation of spatial diversity and in MIMO systems. In small mobile platforms where lack of space prevents the use of conventional half-wavelength spaced antenna arrays, the radiator separation has to be reduced. This aggravates the problem of mutual coupling between radiators. In previous papers, we have demonstrated a method to decouple and match a miniaturized antenna array. This new contribution investigates and compares manufactured antenna arrays with element separations of lambda/4 and lambda/10, respectively. Passive decoupling and matching networks (DMN) compensate for the problem of mutual coupling between the radiators. The resulting system port patterns devide the space in three sections, which makes switched-beam applications possible. The physical properties of such systems as well as the realization strategies are discussed. Important aspects are the antenna analyses in terms of their eigenmodes and the simplification of the decoupling networks. Comparative data are presented for the bandwidth, the efficiency and the correlation of the system port patterns.

Decoupling and Matching Network for Miniaturised 3-Port Antenna Arrays Based on 180° Couplers

In ordinary antenna arrays the spacing between radiators is usually chosen lambda/2. In order to use antenna arrays in small mobile platforms, the overall dimensions and hence the radiator separation must be reduced, which aggravates the problem of mutual coupling between radiators. Results are highly distorted beam patterns and greatly reduced radiation efficiency. We propose a simple method to design a decoupling and matching network for a three element antenna array with a radiator separation of lambda/4, which excites the orthogonal eigenmodes of radiation of the antenna array.

Electromechanical resonances of SiC and AlN beams under ambient conditions

MEMS resonators offer great potential for RF sensor and filter applications. A semiconductor process has been used to prepare SiC and AlN beam resonators. The metallised beams are excited by an RF current in a permanent magnetic field. The resonant response is detected by the induced voltage. Despite the weakness of the signal, accurate detection has been achieved in the time domain, under ambient conditions in a magnetic field of about 0.5 T. The resonant response bears valuable information on the structural quality of the material and identifies potential for further improvement. The time domain technique presents an elegant approach to sensing applications.

An Integrated SiGe HBT Pulselength Modulator for Class-S Power Amplifiers in the UHF Range

Switch-mode amplifiers have gained interest in the RF-frequency range, due to their promising features of high linearity and especially high efficiency, compared to conventional class-AB amplifiers. For the operation of a class-S amplifier, it is necessary to convert the arbitrarily modulated RF signal into a pulselength modulated signal. This can be accomplished by delta-sigma modulation or by pulselength modulation. Here, the classical design of a pulselength modulator circuit is presented and applied to the UHF frequency range, which converts digitally modulated 450 MHz RF-signals, with a clock rate of 1.8 GHz. The developed integrated circuit features a forward structure without any feedback, which makes the modulator inherently stable and offers a high degree of frequency flexibility. The modulator was manufactured in a 0.25 μm SiGe-BiCMOS technology (IHP, Frankfurt/Oder, Germany). Measurement results for a 64-QAM test signal show promising results like minimum error vector magnitudes of about 1%rms and a carrier-to-noise ratio of up to 60 dB.

High-power filters for switched-mode power amplifier systems

This paper presents the design and experimental characterisation of a coaxial comb-line band-pass filter for a switched-mode power amplifier (class-S), for an operating frequency of 450 MHz. The class-S amplifier architecture is laid out for very efficient amplification and high-power operation. Both requirements present challenges for the design of the reconstruction filter terminating the final stage. According to measurement results, an initially developed filter provided a bandwidth of 26 MHz, an insertion loss of 0.55 dB, and a second pass-band only at 2.8 GHz. The maximum input power handled by the filter amounted to 54 W, staying below the requirement. This power level was limited by electrical breakdown. Therefore, a high-power adaptation was devised and realised in an improved design subsequently. The resulting filter not only provided an even lower insertion loss of 0.37 dB but also handled more than 300 W input power.

Passive reciprocal transistor-based RF tuneable inductances

Where unused frequency bands become scarce, their resourceful handling is essential. Consequential, to enable best use of various frequency bands with a single device, the need for reconfigurability emerges. Complementary to already existing technologies, a novel transistor-based circuit is introduced that makes passive, reciprocal, electronic reactive tuning possible. Ultimately, a tuneable inductance was chosen as an example for reactance circuits due to its outstanding relevance for modern, reconfigurable circuit design. The general development process of the inductance circuit is outlined through an abstracted process overview. It enables a broad understanding of the challenges and possibilities of this approach. Also, by extensive circuit analysis with ideal and non-ideal element values, the gap between numerical simulation and guidelines for practical implementation can be narrowed. From the resulting analytic expression, the key figures of an electronic tuneable inductance are derived, namely the range of inductive tuning, the quality factor and the achievable frequency range. These values enable the circuit designer to set up a reasonable starting point for developing a tuneable inductance circuit and gives the means to estimate its unprecedented, passive output behaviour.

TLM analysis of the inverted microstrip patch antenna in a cylindrical grid

3-D TLM approach based on the cylindrical grid and enhanced with the compact wire model has been used for modelling of an inverted circular microstrip patch (IMCP) antenna with the coaxial feed. The simulated results have been compared with the measured results and rectangular grid based TLM results. Additional, the influence of the air gap height on the resonant frequency of the IMCP antenna has been explored.