Triple band circularly polarized fractal boundary microstrip antenna is proposed and experimentally studied. The two orthogonal sides of the square patch are replaced with asymmetrical fractal curves for circular polarization (CP) radiation. A 45° rotated asymmetrical fractal slot is embedded at the center of the fractal patch for triband CP operation. The indentation factors of the fractal curves are optimized for better CP emission. The inserted fractal slot redistributes the current elements on the patch for triband CP radiation. The proposed antenna is implemented over a single layer with a single probe feed, so it is simple to fabricate and is cost effective when compared with the existing stacked layered multiband antennas in the open literature. The measured 3 dB axial ratio bandwidths of the proposed antenna at 2.4, 3.4, and 5.8 GHz are 2, 1, and 1.8%, respectively, so it is well suited for WLAN and Wi-MAX wireless applications.

This paper reports scanning microwave microscopy of CMOS interconnect aluminum lines both bare and buried under oxide. In both cases, a spatial resolution of 190 ± 70 nm was achieved, which was comparable or better than what had been reported in the literature. With the lines immersed in water to simulate high-k dielectric, the signal-to-noise ratio degraded significantly, but the image remained as sharp as before, especially after averaging across a few adjacent scans. These results imply that scanning microwave microscopy can be a promising technique for non-destructive nano-characterization of both CMOS interconnects buried under oxide and live biological samples immersed in water.

A novel design of planar dual-band microstrip crossover operating at small and large frequency ratios is presented. These features of the proposed dual-band crossover are achieved by a cross-shaped transmission line. To obtain the dual-band characteristics, the required closed form design formulas are computed using the ABCD matrix method. Based on the design formulas, the realizable small and large band ratios are calculated as 1.65–2.14 and 4.1–8.76, respectively. To validate the computed band ratios, three examples of dual-band crossovers are presented. Finally, two prototypes of dual-band crossover working at smaller and larger frequency ratios are fabricated and tested. The fabricated dual-band crossovers exhibit good return loss and isolation of over 20 dB with minimal insertion loss.

This paper presents the capacity of an S band circularly polarized patch antenna using a ferrite material for low-earth orbiting satellites (2025–2100 MHz for TeleCommand) to obtain a semi-isotropic radiation pattern. Indeed, circularly polarized antennas are generally large and bulky which is often incompatible for spatial applications especially for small satellites. A new antenna design is proposed with the following maximum dimensions: a diameter of 80 mm and a height of 12 mm. The structure presents an axial ratio lower than 6 dB (according to requirements) and a realized gain higher than −6 dB over a 4% bandwidth at the limit of coverage i.e. 90° irrespective of the azimuth angle (φ).

A new technique to realize quasi-elliptic bandpass filters with extreme close-in rejection is presented in this paper. The basic idea consists of embedding non-resonating mode waveguide cavities within the structure of an evanescent-mode filter. Such a combination of cavities and resonators allows the generation of very close transmission zeros while realizing at the same time relatively wide passbands and stopbands. Both H-plane TE201 mode and E-plane TM110 mode configurations are used as non-resonating mode waveguide cavities. In contrast with the other elliptic evanescent-mode filters using conventional approaches, the insertion loss degradation at the filter cut-off frequencies is minimized thanks to the high-Q factor of the waveguide cavities, whose corresponding poles are located right at the edges of the passband. The experimental results of an evanescent-mode filter having 9.950–11.000 GHz passband and providing more than 45 dB rejection between 11.040 and 11.050 GHz validate the proposed solution.

Compact modified T-slot circular patch antenna for multiple input multiple output (MIMO) applications, which has good response for four operating frequency bands is developed. Here the design consists of a circular patch with a new slot loaded T- shape on one side of the substrate and a feeder line on the other side of the substrate. A shorting pin is located between the patch and the feeder line. This proposed antenna resonates at the frequencies of 2, 4.8, 5.4, and 6.2 GHz covering the S-band, C-band, and LTE applications. The independent tuning of frequency bands is achieved by varying the length of the slots. By independent tuning of frequency bands, the selection of interested frequency band is achieved. The single element with miniaturized size of 1.945λ × 1.945 λ (30 × 30 mm2) is achieved including the feed line. The antenna has been tested for MIMO applications. The measured envelope correlation coefficient between the two elements, which are spaced 0.139 λ is <0.1(low correlation) and mutual coupling is found to be in the range of −20 dB to −80 dB. The simulation and measurement results of reflection coefficient, mutual coupling, and radiation pattern are presented.

This article presents measurement and analysis results for 60 GHz short-range wideband radio channels. We consider two scenarios, referred to as “very-high-rate extended-range” (VHR-E) and “ultra-high-rate cordless” (UHR-C). The VHR-E measurements aimed at 60 GHz fixed networks for an Airbus A340 cabin both under static and dynamic (shadowing due to passenger movement) channel conditions. We describe the channel sounder used for the VHR-E measurements and present a simple multipath model derived from the measurements. Furthermore, simulations show the feasibility of the ray-tracing approach for this kind of channel. As a typical UHR-C use case, a data kiosk scenario was investigated. Various propagation conditions are analyzed with respect to channel gain, time dispersion, and frequency selectivity.

Multipath propagation is still one of the major problems in local positioning systems today. Especially in indoor environments, the received signals are disturbed by blockages and reflections. This can lead to a large bias in the user's time-of-arrival (TOA) value. Thus multipath is the most dominant error source for positioning. In order to improve the positioning performance in multipath environments, recent multipath mitigation algorithms based upon the concept of sequential Bayesian estimation are used. The presented approach tries to overcome the multipath problem by estimating the channel dynamics, using unscented Kalman filters (UKF). Simulations on artificial and measured channels from indoor as well as outdoor environments show the profit of the proposed estimator model. Furthermore, the quality of channel estimation applying the UKF and the channel sounding capabilities of the estimator are shown.

Cognitive radio (CR) has generated a lot of interest because of the promise of wide instantaneous bandwidths which will improve data rates. Current social trends suggest that CR nodes will ultimately be mobile and handheld. This produces a need for small wideband antennas. The Chu limit imposes a restriction on what is obtainable with passive matching. In this paper, it is shown how a negative impedance converter (NIC) can be used to broadband match a chassis antenna beyond what is obtainable with passive matching. It is also shown how to predict and overcome the instabilities which have limited the top frequency achievable with NICs. The noise and linearity performance of the NIC matched antenna is also shown.

The paper researches a kind of wideband dual-polarized Vivaldi antenna with improved balun feed which consists of slot line and two bent coplanar strip lines. The whole of antenna structure is composed of two orthogonal Vivaldi antenna elements, and the mode of feeding adopts electromagnetic coupling from micro-strip line to slot line. The improved balun can avoid the intersection of transmission lines, reduce the size, and simplify the assembly. The electromagnetic simulation and optimization design of proposed antenna are carried out by using electromagnetic simulation software, CST. Simulation results show that the isolation between two polarized ports is more than 15 dB within working frequency range of 2–3.5 GHz and VSWRs of two ports are lower than 2.5 at the range of 2–3.5 GHz. The designed antenna is fabricated and measured. The measured results indicate that the designed antenna achieves anticipated patterns and feasible design of the dual-polarized Vivaldi antenna. The dual-polarized Vivaldi antenna with improved balun feed is suitable for some application fields, such as passive electronic reconnaissance, passive radar, and wideband communication and detection.

The proposed research paper presents the design, development, and experimental testing of a broadband stacked complementary microstrip antenna for ultra-wideband (UWB) (5.28–5.85 GHz), Unlicensed National Information Infrastructure band (UNII) (5.25–5.825 GHz), wireless local area networks (WLAN, IEEE802.11a, 5.15–5.35 GHz), and IEEE 802.11b (5.75–5.85 GHz), Worldwide Interoperability for Microwave Access band (5.25–5.85 GHz), and Radio Astronomy band (6.6–6.75 GHz) wireless applications. The main aim of this paper is to obtain an UWB behavior from the combined effect of two resonances exhibited by the driven and parasitic patches of a stacked complementary antenna geometry. Circularly polarized radiations are also emitted by the antenna by the addition of an orthogonal stub to its feed line. The proposed three-layered antenna structure (without air gap) is fabricated on commercially available glass-reinforced epoxy laminate, FR4 substrate. The topmost layer of FR4 has a square-shaped patch parasitic patch printed over it; this patch has a square slot etched out from it. The middle layer of the antenna has a square-shaped driven patch of approximately the same dimensions as that of the slot in parasitic patch. The antenna is fed using aperture-coupled feeding mechanism. Therefore the lowermost layer of FR4 has a ground plane on its top with a “π”-shaped slot etched from it and a feed line with an orthogonal stub at its bottom forming a “T”-shaped geometry. The antenna is fed by the electromagnetic coupling between the antenna layers .The proposed antenna has a compact structure with overall volumetric dimensions of 4.7 × 3.82 × 0.483 cm3. The antenna design and simulations are carried out using CSTMWSV'10 with perfect boundary (electric and magnetic) estimations. This designed antenna shows an UWB behavior from 5.14 to 5.85 GHz with an impedance bandwidth of 710 MHZ and a fractional bandwidth of 12.62% at the center frequency of band at 5.5 GHz. The radiating antenna also possesses a good gain of 4.59 dBi at the central frequency of 5.50 GHz and a 1 dB axial ratio bandwidth of 820 MHz from 5.16 to 5.98 GHz. The validation of results is done by fabrication and experimental testing of the antenna using a vector network analyzer and placing the antenna in an anechoic chamber for gain measurements. The measured results show close matching with the simulated ones and this makes the antenna well suited for the proposed wireless applications of interest, specifically in small handheld wireless communication devices.

In this paper, different techniques for the generation of additional transmission zeros (TZs) in planar waveguide filters are investigated. In the classical theory, TZs are generated only by destructive interference of non-adjacent cavities, limiting the available number of TZs to the filter order itself. However, more approaches for the generation of TZs are known, including bypass-coupling in oversized cavities, frequency-dependent coupling apertures as well as dispersive/resonant TZs which can be realized by the direct source to load cross-coupling. The aim of this paper is to combine several of the strategies in one physical filter set-up to increase the maximal number of TZs beyond the filter order. Different Ku-band fourth-order filter set-ups are presented, showing in total between six and eight real as well as complex TZs. Three filters are manufactured as a proof of concept and compared with the simulation, showing very good agreement.

This paper proposes a receiver that repeats iterative frequency-domain equalization (FDE) and decision-directed phase noise compensation (DD-PNC) to alleviate degradation due to the phase noise for millimeter-wave single carrier (SC) systems. High bit-rate SC-FDE transceivers based on the single-chip Si RF-CMOS IC technology in the 60-GHz millimeter-wave band have been extensively studied for wireless personal area network (WPAN) systems, and the relatively large phase noise in a phase-locked loop (PLL) synthesizer severely degrades transmission performance. In an initial processing of the proposed receiver, a cyclic prefix (CP)-based phase noise compensator (CP-PNC) removes the phase noise from a time-domain received signal by using CP, which is known to the receiver, and the channel is equalized by the iterative FDE using the conventional minimum mean-square-error (MMSE) weight. In an iterative processing, DD-PNC estimates the phase noise each symbol by exploiting an output of a channel decoder, and then compensates the time-domain received signal for the phase noise by using the estimate. In order to equalize the compensated received signal, the iterative FDE performs both the MMSE filtering and residual inter-symbol interference cancelation using the decoder output. Computer simulations following the 60-GHz WPAN standard demonstrate that in the 64QAM with the coding rate of 3/4, the proposed receiver with three iterations can drastically remove the phase noise of −85 dBc/Hz at 1 MHz offset, and that it can achieve excellent transmission performance.

This paper deals with the various aspects of electromagnetic field impact modeling on the SiGe heterojunction bipolar transistor (HBT) device for microwave applications. This study differs from conventional HBT device reliability research associated with other stresses. The originality of this study comes from the generation of a localized electromagnetic field using the near-field bench. A coupling phenomenon between the electromagnetic field and the micro-strip lines connecting the transistor are evaluated by electromagnetic and electrical simulations. After stress, the input and the transmission scattering parameters are affected. This is primarily due to the deviation of the input impedance and the reduction of the transconductance, respectively. The stress effects have been related to a base current degradation. This degradation is due to a hot carrier introducing generation/recombination trap centers at the Si/SiO2 interface of the emitter–base spacer oxide, which leads to an excess recombination base current.

Different wideband amplifiers, hybrid designs at lower frequencies, and monolithically integrated circuits (MMIC) at higher frequencies were designed, fabricated, and measured. These amplifiers are all based on AlGaN/GaN HEMT technology. The future applications for these types of amplifiers are mainly electronic warfare (EW) applications. Novel communication jammers and especially active electronically scanned array EW systems have a high demand for wideband high power amplifiers. The second application also needs high robust low noise amplifiers for its receive path. Output power levels of 38 W for hybrid amplifiers at lower frequencies up to 6 GHz and 15 W for the MMIC power amplifiers at higher frequencies are measured. With these building blocks, novel EW system approaches can be investigated.

This paper presents the design of two passive shaped-beam reflectarrays acting as passive intelligent reflecting surfaces (IRSs) to enhance 5G millimeter-wave coverage in the 27.2–28.2 GHz band. The reflectarray panels have been designed to generate a broadened and deflected beam in dual-linear polarization (horizontal and vertical). The reflectarray cell provides a robust performance under incidence angles of up to 50°, with more than 360° of phase variation range. Phase-only synthesis based on the generalized intersection approach has been applied to obtain the phase distribution on each reflectarray panel, so that their radiation patterns comply with the beamwidth and pointing requirements of the scenario under study. The two reflectarrays show a stable performance in the 27.2–28.2 GHz band in terms of gain, side-lobe level, and cross-polarization. The results confirm the potential of this technology to implement passive low-cost IRSs that will contribute to improve millimeter-wave coverage in 5G wireless networks.

This paper presents an original solution to design a compact dual circularly polarized isoflux antenna for nanosatellite applications. This kind of antenna has been previously designed in our laboratory, for a single circular polarization. This antenna is composed of a dual circularly polarized feed and a choke horn antenna. This feed is a cross-shaped slot in the ground plane, which provides coupling between a patch and a ring microstrip line with two ports. It is located at the center of a choke horn antenna. The simulated antenna presents an axial ratio <3 dB and a realized gain close to 0 dB over a 400 MHz bandwidth (8.0–8.4 GHz) at the limit of coverage, i.e. 65° whatever the azimuth angle (φ) and the port. A 20 dB matching for each port and 13 dB isolation characteristics between the two ports have been achieved on this bandwidth. It has been realized and successfully measured.

This paper presents a novel dual-band (DB) dual-polarized (DP) shared aperture antenna with high isolation by using a combination of microstrip dipoles and dielectric resonator antennas (DRAs) for S and C bands, respectively. In the S band, two sets of proximity coupled stacked microstrip dipoles which crossed at the center are employed to achieve dual-linear polarization (DLP) and obtain desired bandwidth (BW), isolation, and pure polarization. The rectangle DRA with hybrid feed is selected as the C band element for its advantages of small base area and high isolation, and a 2 × 2 array is presented with the “pair-wise” anti-phase feed technique to achieve a low cross-polarized level. Moreover, benefited from the back feed scheme, the proposed antenna has a symmetrical structure and has the potential of expanding into a larger aperture. The proposed antenna has been manufactured and measured, and the results agree well with simulations, which prove the validity of the proposed design.

A new class of compact rectangular waveguide filters is proposed in this paper. The key element is a square ridge resonator realized within a rectangular waveguide supporting the fundamental TE10 mode. The square ridge can support two modes resonating along orthogonal directions in the gap between the ridge and the opposite waveguide wall. This structure enables dual-mode degeneracy without the need of oversized cavities, thus allowing for considerable size reduction with respect to the conventional dual-mode implementations. Different filter structures employing one or more ridges within short waveguide sections are proposed as attractive solutions for pseudo-elliptic band-pass or dual-band filters. The experimental results of a manufactured fourth-order pseudo-elliptic pass-band filter validate the feasibility of the proposed class of filters.

The airborne radomes have to cater superior electromagnetic (EM) performance with bandpass characteristics of stealth application. In this regard, a hybrid A-sandwich radome is proposed in this paper. The proposed radome consists of a novel strongly coupled frequency selective surface (FSS) core sandwiched between two dielectric layers (acts as skin) to form an A-sandwich structure. The dielectric layers are cascaded in such a way that the middle layer has less dielectric parameters than the skin dielectric. The core layer comprises a modified FSS array using strongly coupled FSS layers through a series of metallic vias. This strongly-coupled FSS element will have the advantage of eliminating inter-element interference and improves the EM performance characteristics of the structure. The structure exhibits very good band-pass characteristics (>90%) at a normal impinging angle with sharp roll-off characteristics. To show the efficacy of the proposed structure, the transmission loss has been compared with that of conventional A-sandwich radomes at 0°, 50° incidence angle for both TE and TM polarization. Conformal analysis of the unit cell has been carried out, and sector-wise thickness optimization was performed to analyze the structure for the conformal shaped radome application. Finally, a physical prototype has been fabricated and measured its scattering parameters, radiation characteristics in a fully shielded anechoic chamber. The results are encouraging and prove its suitability for radome application.