An increasing interest is arising in developing miniaturized antennas in the microwave range. However, even when the adopted antennas dimensions are small compared with the wavelength, radiation performances have to be preserved to keep the system-operating conditions. For this purpose, magneto-dielectric materials are currently exploited as promising substrates, which allows us to reduce antenna dimensions by exploiting both relative permittivity and permeability. In this paper, we address generic antennas in resonant conditions and we develop a general theoretical approach, not based on simplified equivalent models, to establish topologies most suitable for exploiting high permeability and/or high-permittivity substrates, for miniaturization purposes. A novel definition of the region pertaining to the antenna near-field and of the associated field strength is proposed. It is then showed that radiation efficiency and bandwidth can be preserved only by a selected combinations of antenna topologies and substrate characteristics. Indeed, by the proposed independent approach, we confirm that non-dispersive magneto-dielectric materials with relative permeability greater than unit, can be efficiently adopted only by antennas that are mainly represented by equivalent magnetic sources. Conversely, if equivalent electric sources are involved, the antenna performances are significantly degraded. The theoretical results are validated by full-wave numerical simulations of reference topologies.

A compact navigation receiver comprising a decoupled and matched four-element L1-band antenna array with an inter-element separation of a quarter of the free-space wavelength is presented in this paper. We investigate the impact of the decoupling and matching network on the robustness of the navigation receiver. It is observed that in order to achieve high robustness with a compact antenna array, it is necessary to employ a decoupling and matching network, particularly in case of three spatially separated interferers. Furthermore, we study the influence of the polarization impurity of the compact planar antenna array on the equivalent carrier-to-interference-plus-noise ratio (CINR) of the receiver when impinged with different numbers of diametrically polarized interference signals. It is shown that the higher-order modes possess strong polarization impurity, which may halve the available degrees-of-freedom for nulling in the presence of linear-polarized interferers, using a conventional null-steering algorithm. We verify the robustness of the designed compact receiver by means of a complete global-navigation-satellite-system demonstrator. It is shown that the maximum jammer power that is allowed us to maintain the CINR above 38 dBHz with three interferers can be improved by more than 10 dB if a decoupling and matching network is employed.

In this paper, the design of a broadband multi-layer microstrip antenna is presented. The broadband characteristics are the results of coupled resonances of the patch and transmission line through the resonant aperture. For this purpose, a cross-shaped transmission line, a ring slot, and a shaped ring patch are used. The simulation and measurement results indicate that a wide impedance bandwidth of 70% for |S11| < −10 dB and a perfect impedance matching 35% for |S11| < −20 dB are achieved. The gain is stable over the impedance bandwidth. The maximum gain of the proposed antenna is 8.8 dBi at 5 GHz. The radiation pattern, radiation efficiency, and cross-polarization are also suitable throughout the impedance bandwidth.

A highly integrated Ku-band (10.7–12.75 GHz) planar phased array receiver of 64 antenna elements is presented. It features instantaneous reception of the full Ku-band (2.05 GHz wide) in two orthogonal polarizations with wide scan angles by using time delay instead of phase shift. The receiver is part of a system for satellite broadcast TV reception on board of moving vehicles. Two SiGe radio frequency integrated circuits (RFICs) were developed, packaged in ceramic BGAs and assembled onto a 15-layer printed circuit board (PCB) which integrates the antenna elements. An outline of the system is given along with a detailed description. It sets a new standard in integration density. The receiver has extensive analog signal processing at intermediate frequency (IF)-level. A novel bipolar implementation for true time delay is proposed, with a continuous programmable delay range of 0…80 ps with less than 2.5 ps group-delay variation in 2 GHz bandwidth (BW). The wide BW calls for a constant group-delay implementation in the IF chain. The receiver (RFIC) consumes only 132 mW per channel. Each channel has 40 dB gain.

A novel, photonics-based scheme for the independent and simultaneous beam steering of multiple radio frequency signals at a wideband phased-array antenna is presented. As a proof of concept, a wavelength-selective switch (WSS) is employed both as a wavelength router to feed multiple antenna elements and as a tunable phase shifter to independently control the phase of each signal at any antenna element. In the experiment, two signals at 12.5 and 37.5 GHz are simultaneously fed to the four output ports of the WSS with independent and tunable phase shifts, emulating the independent steering of two signals in a four-element phased-array antenna. The results confirm the precision and flexibility of the proposed scheme, which can be realized both with bulk components or resorting to photonic integrated circuits, especially for wide-band applications. The architecture for a possible integrated implementation of the proposed solution is presented, employing a structure based on micro-ring resonator. Starting from these results, the feasibility of an integrated version of the presented architecture is also considered. The proposed photonic integrated circuit realizing the beam-forming network might be based on tunable true-time delay, as well as on phase shift through micro-ring resonators, and could be conveniently implemented with CMOS-compatible silicon technology.

This paper presents a simple and compact coplanar waveguide (CPW)-fed circular-shaped reconfigurable patch antenna with a switchable circular polarization (CP) sense. The circular patch is cut at the ends vertically and switches are introduced to connect the patch ends. By controlling the ON/OFF status of the two switches, the polarization of the antenna can be switched between two states: left-hand circular polarization and right-hand circular polarization. The patch is designed on a very thin RT Duroid substrate of dielectric constant (εr) of 2.2 and thickness of 0.254 mm. The overall antenna dimensions are 35 × 30 mm. The antenna is designed and simulated using finite-element method -based EM simulator, HFSS. For each switching condition the return loss curve, radiation pattern are obtained. Axial ratio curves for polarization diversity cases are also plotted. Parametric studies have been made in order to get optimized values for certain antenna dimensions such as thickness, CPW ground to feed gap, etc.

In this paper, we present several dielectric waveguide (DWG) setups that enable the transition between radar front ends and antennas in challenging, industrial environments. Apart from good propagation behavior, DWG provide a nearly dispersion free transmission over large distances. Furthermore, they can be used as an electrical insulator in places with critical creep distances, in high temperature environments, and for applications with limited installation space. Fundamentals concerning the ideal propagation mode and adequate waveguide–fiber transitions are presented. Results of electromagnetic simulations as well as measurements on manufactured DWG are discussed in detail. The presented excellent propagation behavior proves the effectiveness of the proposed setup.

In this study, we propose an artificial neural network in conjunction with spectral domain approach (SDA), for fast and accurate determination of the resonant frequency and half-power bandwidth of rectangular patch over the ground plane with rectangular aperture. The performances evaluation of the neurospectral method reveals superiority over the conventional SDA model in terms of errors and time. The results obtained from the neurospectral method are in very good agreement with the experimental and theoretical results available in the literature. Finally, numerical results for the effect of rectangular aperture dimensions on the resonant characteristics of the rectangular patch are also investigated.

The design principles and radiation performances of Mikaelian lens antennas are presented. The ways to manufacture gradient index lenses are briefly reviewed. An innovative technique based on the variation of the foam density is described and applied to the Mikaelian lenses. This yields low cost and lightweight gradient index lenses. The focusing properties of Mikaelian lenses are compared numerically to Luneburg lenses. A foam-based planar Mikaelian lens antenna is manufactured and its radiation performances are characterized at 60 GHz. With its flat shape in contact to the primary source, the cylindrical Mikaelian lens turns out to be, for focusing purposes, an interesting alternative to the well-known Luneburg lens.

This paper describes the design considerations, integration issues, packaging, and experimental performance of recently developed D-Band dual-channel transceiver with on-chip antennas fabricated in a SiGe-BiCMOS technology. The design comprises a fully integrated transceiver circuit with quasi-monostatic architecture that operates between 114 and 124 GHz. All analog building blocks are controllable via a serial peripheral interface to reduce the number of connections and facilitate the communication between digital processor and analog building blocks. The two electromagnetically coupled patch antennas are placed on the top of the die with 8.6 dBi gain and have a simulated efficiency of 60%. The chip consumes 450 mW and is wire-bonded into an open-lid 5 × 5 mm2 quad-flat no-leads package. Measurement results for the estimation of range, and azimuth angle in single object situation are presented.

Thinning a large concentric ring array by an evolutionary algorithm needs to handle a large amount of variables. The computational time to find out the optimum elements set increases with the increase of array size. Moreover, thinning significantly reduces the directivity of the array. In this paper, the authors propose a pattern synthesis method to reduce the peak sidelobe level (peak SLL) while keeping first null beamwidth (FNBW) of the array fixed by thinning the outermost rings of the array based on Gravitational Search Algorithm (GSA). Two different cases have been studied. In the first case only the outermost ring of the array is thinned and in the second case the two outermost rings are thinned. The FNBW of the optimized array is kept equal to or less than that of a fully populated, uniformly excited and 0.5 λ spaced concentric ring array of same number of elements and rings. The directivity of the optimized array for the above two cases are compared with an array optimized by thinning all the rings, while keeping the design criteria same as the above two cases. The optimized array by thinning the outermost rings gives higher directivity over the optimized array by thinning all the rings. Time required for computing the optimum elements state for the above two cases using GSA are shown lesser compared to the optimized array by thinning all the rings using the same algorithm. The peak SLL and the FNBW of the optimized array for the above two cases are also compared with the optimized array by thinning all the rings.

A 240-GHz monostatic circular polarized SiGe frequency-modulated continuous wave radar system based on a transceiver chip with a single on-chip antenna is presented. The radar transceiver front-end is implemented in a low-cost 0.13 µm SiGe HBT technology version with cut-off frequencies fT/fmax of 300/450 GHz. The transmit block comprises a wideband ×16 frequency multiplier chain, a three-stage PA, while the receive block consists of a low-noise amplifier, a fundamental quadrature down-conversion mixer, and a three-stage PA to drive the mixer. A differential branch-line coupler and a differential dual-polarized on-chip antenna are added on-chip to realize a fully integrated radar transceiver. All building blocks are implemented fully differential. The use of a single antenna in the circular polarized radar transceiver leads to compact size and high sensitivity. The measured peak-radiated power from the Si-lens equipped radar module is +11 dBm (equivalent isotropically radiated power) at 246 GHz and noise figure is 21 dB. The characterization bandwidth of the radar transceiver is 60 GHz around the center frequency of 240 GHz, and the simulated Tx-to-Rx leakage is below −20 dB from 230 to 260 GHz. After system calibration the resolution of the system to distinguish between two targets at different distance of 3.65 mm is achieved, which is only 21% above the theoretical limit.

In the following, a continuous wave radar system based on the Six-port principle will be shown for measurement tasks at enclosed systems needing micrometer accuracy as well as high update rates like tank level monitoring or hydraulic cylinder piston control. To exceed the ambiguity limit of such an interferometric system, a dual tone approach is used. The system will be presented with measurement results at 24 GHz within a WR42 waveguide to prove the feasibility of the proposed concept. Furthermore, considerations on timing will show the potential as a low-latency system, capable of high measurement data update rates, and different influences on the system performance and limitations of such a system will be discussed in comparison to alternative setups.

In this paper, the resonant characteristics of the rectangular microstrip patch antenna on uniaxially anisotropic substrates are determined via spectral domain analysis. The anisotropic substrates are characterized by both permittivity and permeability tensors. Green's functions of the structure in Fourier transform domain are determined using the Galerkin's technique. The sinusoidal functions are selected as the basis function, which show fast numerical convergence. Numerical results concerning the effects of electric anisotropy and antenna parameters on the resonant characteristics of rectangular microstrip antenna are presented and discussed. Results are compared with previously published data and are found to be in good agreement.

A small and compact ultra-wideband (UWB) aperture antenna with extended band-notched design is proposed. The antenna is composed of a rectangular aperture on ground plane of a printed circuit board and a fork-like exciting stub. The presented co-planar wave guide triple-fed antenna is easy to be applied with RF and microwave circuitry for low manufacturing cost. The antenna is successfully designed, implemented, and measured. A compact aperture area of 12.5 × 23 mm2 is acquired with promising performances, including broadband matched impedance and stable radiation patterns. The correlation between the mode-based field distributions and radiation patterns is discussed. Extended from the proposed antenna, one advanced band-notched (5–6 GHz) designs are also presented as a desirable feature for UWB applications.

Pedestrian Collision Mitigation Systems (PCMS) are already in the market for some years. Due to continuously evolving EuroNCAP regulations their presence will increase. Visual sensors, already capable of pedestrian classification, provide functional benefits, because the reaction behavior can be optimized when the imminent collision object is recognized as pedestrian or cyclist. Nevertheless their performance will suffer under adverse environmental conditions like darkness, fog, rain or backlight. Even in such unfavorable situations the performance of radar sensors is not significantly deteriorated. Enabling classification capability to automotive radar will further improve road safety and will lower PCMS's overall costs. In this paper, a multi-reflection-point pedestrian target model based on motion analysis is presented. Together with an appropriate sensor model, pedestrian radar signal responses can be provided for a wide range of accident scenarios. Additionally velocity separation requirements that are needed for classification of pedestrians are derived from the simulations. Besides determination of classification features, the model discloses the limits of classical radar signal processing and further offers the opportunity to evaluate parametric spectral analysis. Based on simulated and measured baseband radar signals of pedestrians one of these techniques is deeper analyzed and its enhancement especially on the velocity separation capability is evaluated.

Recently DLR has developed and constructed a new experimental radar instrument [5] for various applications such as radar signature collection, synthetic aperture radar/ inverse synthetic aperture radar imaging, motion detection, tracking, etc., where high performance and high flexibility have been the key drivers for system design. Consequently the multi-purpose and multi-channel radar called GigaRad is operated in X and Ku band and allows an overall bandwidth of up to 6 GHz, resulting in a theoretical range resolution of up to 2.5 cm. Hence, primary obligation is a detailed analysis of various possible error sources, being of no or less relevance for low-resolution systems. A high degree of digital technology enables advanced signal processing and error correction to be applied. The paper outlines main technical features of the radar system, the basic error correction and absolute calibration strategy, frequency limitations, and illustrates some imaging results.

The paper is devoted to coherent radiometric imaging systems. The investigated systems may be considered as a version of bistatic noise waveform passive radar with synthetic aperture having external reference. Reference signal in this imaging system is received from the investigated emitting object using auxiliary receiver. Although a number of theoretical studies on aperture synthesis imaging algorithms exist, relatively few of them deal with experimental investigation. In particular, no information concerning range-azimuth coherent radiometric imaging has been found. In this paper, an experimental investigation of possibility to generate coherent radiometric images using two antennas with beam synthesizing is carried out. Indoor radiometric imaging has been validated using absorbers as the emitting objects. These experiments enabled to estimate range resolution of the radiometric system achieved by focusing antennas with beam synthesizing for range span limited by means about bistatic baseline.