The paper outlines an exhaustive computer-aided design (CAD) procedure for the circuit-level simulation of entire multi-input multi-output (MIMO) links. The multiple transmitting and receiving antennas are treated as multiport radiating systems characterized by electromagnetic (EM) analysis. The effects of mutual couplings in terms of the frequency-dependent near-field and far-field performance of each element are accounted for in a straightforward and rigorous way. The set of transmitters is treated as a unique non-linear system loaded by the multiport antenna, and is analyzed by non-linear circuit techniques. The same is done for the set of receivers. In order to establish the connection between transmitters and receivers, the radiated far-field is evaluated by EM analysis, and the field incident on each receiver antenna is computed by extending to the MIMO case an available ray tracing technique. EM theory is then used to describe the receiving array as a linear active multiport network. This technique allows analysis of several MIMO systems, exploiting different array element spatial locations and frequencies of operation in a straightforward and automatic way. Bit error rate (BER) computation and minimization are demonstrated at the circuit level.

This paper presents a substrate-integrated waveguide (SIW) mixed electric and magnetic coupling structure implemented on a single-layer substrate to create finite transmission zeros (TZs), which can be used to design microwave filters with higher frequency selectivity. Mixed coupling is realized by three slot-lines on the top metal plane combined with an iris-window between two adjacent SIW cavities. The electric and magnetic coupling can be separately controlled by adjusting the dimensions of the slot-lines and the width of the iris-window, and a controllable TZ below or above the passband can be produced. Furthermore, a detailed analysis of the mixed coupling structure is presented. To demonstrate the validity of the proposed structure, third- and fourth-order cross-coupled generalized Chebyshev bandpass filters are designed and fabricated using the standard printed circuit board process. The experimental results are in good agreement with the simulation results. The filters exhibit simple structure and good frequency selectivity.

TanDEM-X (TDX; TerraSAR-X add-on for digital elevation measurement) is an innovative spaceborne X-band earth observation mission that will be launched in June 2010. This paper gives an overview of the TDX mission concept, summarizes the basic products and illustrates the achievable performance. In more detail the effect of quantization on the interferometric performance is discussed. Finally, new imaging techniques are outlined.

This paper presents a broadband miniaturized Fabry–Perot cavity resonator antenna (CRA) made of novel electromagnetic bandgap (EBG) superstrate as partially reflecting surface (PRS) and reactive impedance surface (RIS) backed rectangular patch antenna. To the best of the authors' knowledge, the proposed EBG exhibits the highest stopband bandwidth (BW) with a bandgap existing between 7.37 and 12.4 GHz (50.9%). Frequency-selective property of the EBG is utilized under plane wave incidence to demonstrate it as PRS superstrate in CRA antenna. The cavity is excited with a rectangular microstrip antenna which is made of two dielectric substrates with an additional RIS layer sandwiched between them. The RIS provides wideband impedance matching of the primary feed antenna. A 7 × 7 array of the EBG superstrate is loaded over the patch antenna having an overall lateral dimension of only 45 × 45 mm2 or 1.62 λ0 × 1.62 λ0 where λ0 is the free space wavelength at the center frequency of 10.8 GHz. The proposed Fabry–Perot CRA (FP-CRA) achieves gain enhancement of 6.59 dB as compared with the reference antenna and has a 10 dB return loss BW of 23.79% from 10.07 to 12.79 GHz. A prototype of the FP-CRA is fabricated and experimentally tested with single and dual layers of EBG superstrate. Measured results show BWs of 21.5 and 24.8% for the two cases with peak realized gain of 12.05 and 14.3 dBi, respectively. Later a four-element antenna array with corporate feeding is designed as the primary feed of the CRA. The simulation result shows a flat gain of >13 dBi with gain variation <1.2 dB over the impedance BW of 13.2%.

New wireless wearable monitoring systems integrated in professional garments require a high degree of reliability and autonomy. Active textile antenna systems may serve as platforms for body-centric sensing, localisation, and wireless communication systems, in the meanwhile being comfortable and invisible to the wearer. We present a new dedicated comprehensive design paradigm and combine this with adapted signal-processing techniques that greatly enhance the robustness and the autonomy of these systems. On the one hand, the large amount of real estate available in professional rescue worker garments may be exploited to deploy multiple textile antennas. On the other hand, the size of each radiator may be designed large enough to ensure high radiation efficiency when deployed on the body. This antenna area is then reused by placing active electronics directly underneath and energy harvesters directly on top of the antenna patch. We illustrate this design paradigm by means of recent textile antenna prototypes integrated in professional garments, providing sensing, positioning, and communication capabilities. In particular, a novel wearable active Galileo E1-band antenna is presented and fully characterized, including noise figure, and linearity performance.

Phase unwrapping (PU) is one of the key processing steps in reconstructing the digital elevation model (DEM) of a scene from interferometric synthetic aperture radar (InSAR) data. The PU problem entails the estimation of an absolute phase from observation of its noisy principal (wrapped) values. Recently, PU approaches based on Kalman filtering have proved their efficacy in tackling the PU problem even when strong discontinuities of the height profile and noisy data are involved. This paper presents a novel multichannel InSAR PU algorithm using several interferometric SAR images based on the extended Kalman filter. The proposed technique exploits the capability of the Kalman algorithm to simultaneously perform noise filtering, PU, and multi-sensor data fusion. The proposed method, even being a Bayesian estimator, optimally fuses height information coming from an additional maximum likelihood estimator (MLE) combining the benefits of both the Bayesian and the non-Bayesian approaches. The performance of the proposed algorithm has been tested on simulated interferometric images proving the effectiveness of the proposed method.

A compact ultra-wideband (UWB) monopole antenna with reconfigurable band-notch characteristics is demonstrated in this paper. It is comprised of a modified rectangular patch and a defected ground plane. The band-notch property in the WiMAX and WLAN bands is achieved by etching an open-ended slot on the radiating patch and an inverted U-shaped slot on the ground plane, respectively. To obtain the reconfigurable band-notch performance, two PIN diodes are inserted in the slots, and then the notch-band can be switched by changing the states of the PIN diodes. The antenna has a compact size of 0.47 λ1 × 0.27 λ1. The simulated and measured results indicate that the antenna can operate at a UWB mode, two single band-notch modes, and a dual band-notch mode. Moreover, stable radiation patterns are obtained.

A next generation of active electronically scanned array (AESA) antennas will be challenged with the need for lower size, weight, power, and cost. This leads to enhanced demands especially with regard to the integration density of the radio frequency-part inside a T/R module. The semiconductor material GaN has proven its capacity for high-power amplifiers (HPA), robust receive components as well as switch components for separation of transmit and receive mode. This paper will describe the design and measurement results of a GaN-based single-chip T/R module frontend (HPA, low noise anplifier, and single-pole double-throw (SPDT)) using UMS GH25 technology and covering the frequency range from 8 GHz to 12 GHz. The key performance parameters of the frontend are 13 W minimum transmit (TX) output power over the whole frequency range with peak power up to 17 W. The frontend in receive (RX) mode has a noise figure below 3.2 dB over the whole frequency range, and can survive more than 5 W input power. The large signal insertion loss of the used SPDT is below 0.9 dB at 43 dBm input power level.

A simple electromagnetic model of wind-turbine's main structural elements as the linear wired structures is developed to simulate the temporal patterns of observed radar return Doppler spectra (micro-Doppler). Using the model, the micro-Doppler for different combinations of the turbines rotation frequency, radar pulse repetition frequency, and duration of the Doppler measurement interval are analyzed. The model is validated using the PARSAX radar experimental data. The model ability to reproduce the observed Doppler spectra main features can be used for development of signal-processing algorithms to suppress the wind-turbines clutter in modern Doppler radars.

A novel idea for generating directional electromagnetic beam using a metamaterial absorber for enhancing radiation from a microwave antenna in the S-band is presented herewith. The metamaterial structure constitutes the well-known stacked dogbone doublet working in the absorption mode. The reflection property of the dogbone metamaterial absorber, for the non-propagating reactive near-field, is utilized for achieving highly enhanced and directional radiation characteristics. The metamaterial absorber converts the high-spatial reactive spectrum in the near-field into propagating low-spatial spectrum resulting in enhanced radiation efficiency and gain. The gain of a printed standard half-wave dipole is enhanced to 10 dBi from 2.3 dBi with highly directional radiation characteristics at resonance.

This paper proposes a dual notched band ultra-wideband (UWB) bandpass filter (BPF) based on hybrid transition of microstrip and coplanar waveguide (CPW). The CPW in ground plane houses a stepped impedance resonator shorted at ends, and is designed to place its resonant modes within the UWB passband. The microstrips on the top plane are placed some distance apart in a back-to-back manner. The transition of microstrip on top and shorted CPW in the ground is coupled through the dielectric in a broadside manner. The optimized design of the transition develops the basic UWB spectrum with good return/insertion loss and extended stopband. Later, defected ground structure, embedded in CPW, and split ring resonators, coupled to feeding lines are utilized to develop dual sharp passband notches. The simulated data are verified against the experimentally developed prototype. The proposed dual notched UWB-BPF structure measures only 14.6 × 7.3 mm2, thereby justifying its compactness.

In this article, an extremely wideband, isolation-enhanced, low-profile “Multiple-Input-Multiple-Output” (MIMO) antenna along with dual-band-notched features has been investigated. The antenna proposed herein, possesses two mutually orthogonal staircase-etched radiators for achieving a wide bandwidth. The radiating elements are placed mutually perpendicular in order to achieve polarization diversity and high isolation, i.e. for minimization of mutual coupling effect between adjacent radiating elements. The antenna exhibits an extremely wide frequency bandwidth covering 1.2–19.4 GHz except two frequency band notches centered at 3.5 and 5.5 GHz, respectively, originated due to the incorporation of a “Rectangular Complementary Split Ring Resonator (RCSRR)” structure and by etching dual “L-shaped” slits in the ground plane. The center frequency of the notched bands is adjusted by fine tuning of the dimensions of the incorporated band-notching structures. Isolation level (S21) better than −20 dB has been obtained due to the insertion of a “T-shaped” parasitic element as a decoupling structure. A prototype of the proposed antenna having dimension of 20 mm × 20 mm (0.08 λo × 0.08 λo) is fabricated and the antenna responses have been measured. Obtained results show that the miniaturized MIMO diversity antenna is undoubtedly a capable contender for communications supporting an extremely wide impedance bandwidth along with band-notched features for WLAN and WiMAX.

In this paper, an orthogonal frequency-division multiplexing (OFDM) waveform radar sensing approach is demonstrated based on field measurements at C-band. We demonstrate a concept that is based on the exploitation of typical wireless communication transmissions to perform passive, distributed radar sensing. Our concept is based on an OFDM radar that operates in the modulation symbol domain and can be well integrated into existing OFDM receivers. The measurement setup and the signal processing steps for the OFDM radar are described. The results show that the passive, distributed radar sensing approach can be used to detect and localize moving cars and even pedestrians in automotive intersection scenarios.

In this paper, a 1.8–2.6 GHz wideband rectenna is designed for radio frequency (RF) energy harvesting in the context of wireless sensor nodes (WSN). To assess the feasibility of ambient RF energy harvesting, the power density from RF base stations is analyzed through statistical measurements. Power density measurements are also performed close to Wi-Fi routers. Using these results, a methodology based on impedance matching network adaptation and maximum power transfer is proposed to design the wideband RF harvester. Using this method, three RF bands, i.e. GSM1800, UMTS and WLAN, are covered. The theoretical analysis is confirmed by simulations and measurements. From measurements results, the prototype RF-to-DC conversion efficiency is 15% at −20 dBm from 1.8 to 2.6 GHz. It is shown that with three RF sources in the chosen bands, each emitting at 10 dBm, the RF-to-DC conversion efficiency is 15% better compared to that measured with a single RF source. Finally, 7 µW is harvested at 50 m from a GSM1800 and UMTS base station. This value confirms the RF harvester workability to supply small sensors.

In this paper, we present a continuously tunable phase shifter realized in MEMS technology. Varactors with liquid crystal as a tunable dielectric layer underneath gold bridges are used to build a loaded line phase shifter. Measurements show that the phase shifter has a differential phase shift of 92°, a figure of merit (FoM) of 42°/dB and an input matching of −19 dB at 76 GHz.The tuning speed of the phase shifter is measured at different temperatures between 10 and 50°C. The realized phase shifter can be used in combination with MEMS switches in order to build a 360° tunable reflection phase shifter.

This paper describes a new configuration of frequency-selective structure (FSS) structures to reduce mutual coupling between the radiating elements. Also, the antenna performance before and after the implementation of FSS have been investigated. The proposed configuration provides an improvement in mutual coupling by 14 dB (measured value) with a reduced edge-to-edge spacing of 23 mm. The reduction of mutual coupling between antenna elements is interesting in the electromagnetic and antenna community. The use of electromagnetic band-gap structures constructed by microstrip technology is a way to appease the mutual coupling problem. Periodic structures such as FSS can help in the reduction of mutual coupling using their ability of suppressing surface waves propagation in a given frequency range. The goal of this present study is to use it in patch antenna arrays, keeping both the element separation smaller than λ0 for grating lobes evasion and the patch antenna size large enough to have good antenna directivity. The results showed that the proposed configuration eliminates disadvantages of similar structures presented in the previous works.

In this paper, a compact tri-band asymmetric coplanar strip (ACS)-fed meander-line antenna for wireless communications is proposed. Two inverted-L-shaped resonators are added to a simple meandered radiator for standard tri-band operation. Parametric studies indicate that operating frequencies of the proposed antenna are determined by the dimensions of the two inverted-L-shaped resonators. The measured results show that the proposed antenna can achieve three frequency bands; i.e. 1.48–1.63, 2.25–2.48, and 4.22–6.0 GHz. These bands can successfully cover the global positioning system L1, wireless local area network (WLAN), and HIPERLAN/2 operation bands, respectively. The proposed antenna exhibits good radiation patterns with reasonable gain and high radiation efficiency across the operating bands. In addition, the proposed antenna has compact size and simple feeding scheme, which make it suitable to be integrated within the portable device for wireless communications.

This article introduces a cylindrical dielectric resonator antenna (CDRA) fed with a rhombic ring-shaped tapered feed for Multiple-Input-Multiple-Output (MIMO) applications. The proposed hybrid MIMO CDRA resonates at four frequency bands 2.5, 5.09, 6.8, and 9.0 GHz with isolation levels of 22, 34.22, 30.55, and 18.55 dB. Isolation enhancements are achieved by introducing “L” shaped slots on the partial ground plane. Parametric analysis is performed to validate the optimized dimensions of the tapered feed without and with DRA and defected ground structure. Diversity performance is examined by using envelope correlation coefficient and diversity gain. The proposed antenna operates in the S, C, and X-bands and is suitable for RF communication mobile broadband services, Wi-Fi, radar, and satellite applications. Good agreement is observed between simulated and measured results.

An alternative approach is based on statistically computed signal analysis technique for the design of antenna array exhibiting lower side lobes in their radiation pattern. New and generalized expressions for the array factor of all physically realizable linear antenna arrays are introduced. An algorithm based on the statistically computed signal analysis is designed. By considering the random elements, distance between the sensors, their mean, variance, average amplitude pattern and correlation of the amplitude between the two angles, some mathematical formulations have been done and shown with the help of MATLAB. Based on these generalized expressions, a new way of synthesizing arrays with reduced side lobes is available. It applies to end fire antenna array, which may have either even or odd numbers of sensors with restricted elements spacing. Final expressions shown are a clear relationship between elements excitation and null location in the radiation patterns.

In this work, we propose a broadband, polarization-insensitive and wide incident angle stable metamaterial absorber (MA) based on the resistive film. The absorber consists of a three-layer structure with each layer of dielectric substrate printed with different shapes of resistive film. The multilayer structure not only extends the absorption bandwidth but also maintains high absorption under large wave incident angles. Numerical simulation shows that the absorptivity of a normal incident wave is above 90% in the frequency range 2.34–18.95 GHz, corresponding to a relative absorption bandwidth of 156%. Moreover, the whole MA structure has a total thickness of 11.3 mm, corresponding to 0.09 λ0 at its lowest absorption frequency. Due to the high symmetry of the structure, the absorber has good polarization insensitivity. In addition, for both transverse electric and transverse magnetic incidence, the proposed absorber achieves an absorptivity of more than 80% at incident angles of up to 45° and thus has good stability for wide incident angles. The absorption principle of the absorber is analyzed by the surface current and power loss density distribution. Parameter analysis is also performed for bandwidth optimization. Due to its advantages of wideband absorption with high efficiency, the proposed absorber has the potential to be applied to the energy-harvesting and electromagnetic stealth fields.