In this paper, significance of studying the nonlinear performance of amplifying reflectarray antenna is clarified by showing nonlinear behavior of the unit cell. Furthermore, the procedure for nonlinear analysis of amplifying reflectarray antenna is described and nonlinear analysis is verified by ADS software simulation. Moreover, a typical amplifying reflectarray antenna is designed considering the nonlinear behavior. Nonlinear analysis of the active aperture-coupled patch unit cell is performed using harmonic balance method considering nonlinear model of the amplifier. Then, the effect of nonlinear element in radiation pattern of the antenna is studied. Passive unit cell is simulated using full-wave analysis method considering infinite array approach, and scattering parameters of the unit cell is obtained. Next, these scattering parameters are transformed to admittance parameters and used in obtaining nonlinear response and harmonic distortion of the unit cell containing amplifier. Obtained results show up to 3.4 dB error in predicting pattern of the antenna with linear modeling of the active element.

A compact dual-band microstrip bandpass filter (BPF) is presented for application at the frequencies 2.4 and 5.84 GHz. The proposed main resonator consists of two L-shaped resonators. To improve the upper-stopband of the proposed filter, modified U-Shaped resonators are accepted. The operation mechanism of the filter is investigated based on proffered equivalent-circuit model and transformation function. The sketched dual-band BPF attends the insertion loss less than 0.1 and 0.4 dB Also the return loss is 26 and 28 dB at 2.4 and 5.84, respectively. This proffered filter structure is proper for Bluetooth and wireless local area networks and other wireless communication systems. An overall good agreement between measured and simulated results is observed.

In this paper, a microstrip lowpass filter with wide stopband and sharp roll-off is presented. The proposed filter consists of a modified radial stub resonator which is cascaded by four suppressing cells. To reduce the overall size, the transmission lines are folded. The cut-off frequency of the proposed filter is 1.19 GHz. The transition band is approximately 0.2 GHz from 1.19 to 1.39 GHz with corresponding attenuation levels of 3–20 dB. The stopband is from 1.39 to 19 GHz with attenuation level of <20 dB. The insertion loss and return loss in the passband from DC to 0.8 GHz are better than 0.26 and 14 dB, respectively. The proposed filter is fabricated and measured. The simulated and measured results are in good agreement.

This paper presents the design of a compact, planar, single layer, tri-section ultra-wideband (UWB) branch-line (BL) coupler. The prototype offers 10 dB return loss characteristics from 3.1 to 13.7 GHz. Over a major portion of the band, phase imbalance of ±10° is achieved. The method of deploying multi stage impedance feed has been used to achieve improved bandwidth. To enhance the power output through the coupled port throughout the operating band, ring shaped slots have been introduced in the ground plane beneath the series arms. The performance of the fabricated prototype has also been validated experimentally.

Novel impedance transforming directional couplers are proposed in which the achievable impedance transformation ratio is increased above the previously reported limit related to coupling of the coupled-line sections. The proposed couplers consist of two coupled-line sections between which uncoupled sections of left-handed lines are connected. The presented concept has been verified by circuit simulations as well as by measurements of the manufactured 3-dB coupled-line impedance transforming directional coupler operating at f0 = 1.2 GHz and featuring twofold increased impedance transformation ratio R = 4.

Design and realisation of a compact power divider based on half mode substrate integrated waveguide (HMSIW) with an arbitrary power dividing ratio is presented. This design consists of a substrate integrated waveguide (SIW) transition, two bisected HMSIW transitions by a gap, an SIW-to-microstrip transition, and two microstrip feed lines. In addition, a resistor is attached between two HMSIW transitions. To adjust the power division ratio, four parameters are introduced. Furthermore, four graphs are plotted using a three-dimensional electronmagnetic (3D EM) simulator to graphically determine the introduced parameters. In this study, three circuits with power division ratios of 1:1, 1:4, and 1:8 are simulated using the 3D EM simulator and fabricated on a Rogers RO4003C substrate. The results show a good agreement between the simulated and measured results. The measured results display these circuits (1:1, 1:4, and 1:8) have the bandwidths of 70, 36, and 40%, respectively. Moreover, the proposed structures (1:1, 1:4, and 1:8) are compact and their overall sizes are $1.13 \times 1.04\lambda _g^2 $, $0.96 \times 0.91\lambda _g^2 $, and $0.81 \times 0.78\lambda _g^2 $, respectively. These structures have the advantages of the compactness in size, wide bandwidth, high power division ratio (from 1:1 to 1:16), and compatibility with planar circuits.

Since last decades, microwaves have received tremendous attention as an interesting tool for material characterization. In general, standard microwave measurement methods require cutting and polishing of samples to put it in a suitable waveguide or cavity. However, several methods have been developed in order to permit a non-destructive measurement. A well-known method is based on coaxial open-ended waveguide, which is used as a sensor for dielectric characterizations. Moreover, with the requirement of new forms, developing mathematical model for each one is not convenient. Indeed, the complex structures required in the industrial field can be perfectly designed with high-performance three-dimensional software. Many attempts have been done to solve the conversion problem by proposing different algorithms. Nevertheless, they are sensitive for complex structure that contains transition part. In this paper, we propose a dielectric measurement method based on the use of coaxial waveguide. A novel algorithm for dielectric characterization of complex structures is also presented, which is based on the joint use of artificial neuronal networks and finite element method. The proposed algorithm aims to find the dielectric characterization for complex structures. Experimental evaluations applied to solid and liquid dielectrics confirm the validation of the proposed algorithm.

This paper compares the noise performance of two different types of time-domain microwave detection systems: a pulsed system and a pseudo-random noise sequence system. System-level simulations and laboratory-based measurements are carried out in the study. Results show that the effect of timing jitter is more significant on the measurement accuracy of the pseudo-random noise sequence system than that of the pulsed system. Although the signal power density of the pseudo-random sequence system is tens of dBs higher than that of the pulsed system over the frequency band of interest, the signal-to-noise ratio difference between these two systems can be just a few dBs or even smaller depending on the jitter level.

Active electronically scanned array (AESA) radar has large number of transmit/Receive (T/R) modules which require multiple microwave and digital signals. Distribution of these signals through conventional method such as coaxial cable, twisted pair, etc. not only introduces engineering complexities and signal loss but also have limitation of bandwidth, data rate, transmission distance, etc. This paper addresses design and implementation of microwave photonic network for distribution of microwave and digital signals over single optical fiber using wavelength division multiplexing for AESA radars. The design challenge is to limit the variation in output radio frequency power within ±1 dB over full operational band of radar from 2 to 4 GHz and functionality under hostile military environment. Optical amplifiers have been used in all channels to stabilize optical output independent of wavelength with automatic light control. The optical signal is split into 64 identical parts to feed multiplexed signal into different digital receivers physically spread across the antenna array. It is an additional challenge to normalize performance as all 64 receivers show variation in output in spite of identical electronic circuitry. Experimental results validate the feasibility of microwave photonic network for wide branching distribution of multiple microwave and digital signals for AESA radar.

Multifunction radars based on active phased arrays are well known and widely studied systems. The concepts of bistatic architecture, conformal array and digital beam forming (DBF) are combined in this paper to define a novel multifunction radar for point defense. The conical shape of the antenna overcomes the significant limitations in the azimuth coverage of 360° of fixed-faces phased arrays due to the beam scanning up to 45°. The usage of separate transmit/receive arrays and the DBF technique adds the operational flexibility and the possibility of multiple simultaneous functions, with an optimal time-energy resources exploitation. After a short description of its technological demonstrator, some significant design trade-off, and operating aspects of the proposed architecture, called d-Radar, are described, showing the main differences with respect to the classical, four faces, and phased-array multifunction radar architecture. It is described how the operating modes can be made more and more similar to a “staring” or “ubiquitous” radar permitting an instantaneous detection and location of short-range, low-elevation targets for sea and ground operations. Finally, some remarks about the resources management and scheduling are shown with the results from a case of study.

A compact coplanar waveguide (CPW)-fed wideband metamaterial-inspired antenna is designed and developed in this paper. The proposed structure is an asymmetric structure in which three rectangular stubs are employed between signal patch and CPW ground plane. It is demonstrated that these stubs provides lumped parameters of conventional epsilon-negative transmission line (ENG-TL). As an advantage of these stubs proposed antenna operates on 1.67–2.76 GHz with −10 dB impedance bandwidth of 49.2%. The proposed antenna having small electrical size of 0.17λ0 × 0.35λ0 × 0.01λ0 at fo = 2.21 GHz. The simulated average gain and radiation efficiency of the proposed antenna is 1.61 dB and 96.33% respectively throughout the bandwidth. Properties such as smaller electrical size, simpler design, consistent radiation characteristics, and ease of fabrication are making this antenna suitable for GSM, WLAN/Wi-Fi, Bluetooth, and WiMAX applications.

A compact printed 2 × 2 ultrawideband (UWB) multiple input multiple output (MIMO) antenna with a single circular patch as a common radiator for both the antenna elements is presented in this paper. A single circular patch is excited by two tapered CPW feeds for dual polarization. To improve the isolation between two ports, a rectangular slot of dimension L1 × W1 is created in the radiator. The UWB MIMO antenna has impedance bandwidth of 3–12 GHz with a isolation better than 17 dB between the two ports. The envelope correlation coefficient and the capacity loss are evaluated to ensure the good diversity performance of UWB MIMO antenna. The antenna has a compact size of 45 × 45 mm2 and is fabricated on low cost FR4 substrate and measured using Agilent VNA. The simulated and measured results show that the proposed UWB antenna is good candidate for UWB MIMO applications.

A compact quad band slot antenna with high isolation suitable for multiple-input–multiple-output (MIMO) applications is developed. The quad bands are achieved by introducing slots in a modified, size reduced circular patch antenna. The single-antenna element consists of a substrate sandwiched between a modified circular patch with F shape slot, a feeder line and a via running between the radiating patch and the feeder line. The proposed design resonates at the frequencies of 1.8 GHz (1.7–1.88 GHz), 3.6 GHz (3.50–3.76 GHz), 5.4 GHz (5.25–5.38 GHz), and 7.2 GHz (7.15–7.35 GHz) covering the GSM II, WIMAX, wireless local area network (WLAN), and C-band applications, respectively. The independent tuning of frequency bands is achieved by varying the length of the slots. Orthogonally placed two- and four-element MIMO antenna system are fabricated, tested, and the measurement results are presented. The separation between each element is reduced to 0.085λ while introducing slotted and pulsed stubs to improve isolation between elements. A detailed analysis, including mutual coupling, low correlation, diversity gain, and total array reflection coefficient had been reported. The two- and four-element MIMO antennas achieved correlation as low as 0.005, mutual coupling ≤−15 dB, and diversity gain nearly 10 dB.

A compact microstrip multi-stub loaded bandpass filter (BPF) with ultra-wide stopband is introduced and investigated. Lumped-equivalent circuit (LEC) method is adopted to analyze the characteristics of the in-band response based upon the low frequency LEC and even-odd mode analytical method. Besides, equivalent transmission line circuit method with even-odd mode analytical method are adopted to discuss the mechanism of the out-band rejection based upon the transmission poles and the transmission zeros analysis of the even-/odd-mode equivalent circuits. Accordingly, the design and the optimization procedures of this type of filters are summarized. To experimentally validate the proposed method, the filter is fabricated and measured. The measured results illustrate this BPF centered at f0 = 2.8 GHz, with −3 dB fractional bandwidth of 109.3%, the insert loss (IL) of less than 1 dB from 1.4 to 4 GHz, and the rejection level of 20 dB from 5.1 to 33.5 GHz(1.82f0 to 11.96f0).

In this paper, a miniaturized coaxial feed curved-slotted microstrip patch antenna over a fractalized uniplanar compact electromagnetic bandgap (F-UC-EBG) ground plane is proposed and investigated. Compact size is achieved by cutting the curved slots along the orthogonal directions of the patch radiator. The curved-slotted microstrip patch antenna is 38.30% miniaturized as compared with the conventional microstrip patch antenna resonating at 2.38 GHz. Furthermore, the ordinary ground plane of the curved slotted patch antenna is replaced by the F-UC-EBG ground plane. Due to the slow wave phenomenon created in the F-UC-EBG structure and the better impedance matching at the lower frequency further miniaturization and improved performance are obtained. The proposed antenna shows 74.76% miniaturization as compared with the conventional microstrip patch antenna resonating at 1.57 GHz and has 2.61% 10-dB fractional bandwidth, 1.49 dB gain, and 81.59% radiation efficiency. The proposed antenna is fabricated on a low-cost FR4 substrate having an overall volume of 0.184λ0 × 0.184λ0 × 0.0236λ0 at 1.57 GHz GPS band. The measured and simulated results are in good agreement and predicting appropriateness of the antenna in portable and handheld communication systems for GPS applications.

This paper proposes a planar monopole antenna with a parabolic edge shape. This antenna, which has notch characteristics in the wireless local area network (WLAN) band, can be miniaturized. To obtain the notch characteristics in the WLAN band, a slot with a parabolic edge shape identical to that of the monopole structure was implemented. Because the planar monopole antenna with a parabolic edge shape possesses characteristics similar to those in self-complementary structure conditions, it can be miniaturized by reducing the antenna components at the same proportion. For the antenna fabrication, an FR4 dielectric substrate with a dielectric constant of 4.7 was used. The size of the miniaturized antenna that satisfies the ultra-wide band requirement was 15.6 × 18.6 mm2, and the 10-dB band was 3.013–12.515 GHz. At each frequency, the radiation pattern was similar to that of a dipole antenna.

Modeling and design of rectangular microstrip patch printed on isotropic or anisotropic substrate are accomplished in this paper. The use of spectral domain method in conjunction with artificial neural networks (ANNs) to compute the resonant characteristics of rectangular microstrip patch printed on isotropic or anisotropic substrates. The moment method implemented in the spectral domain offers good accurateness, but its computational cost is high owing to the evaluation of the slowly decaying integrals and the iterative nature of the solution process. The paper introduces the electromagnetic knowledge combined with ANN in the analysis of rectangular microstrip antenna on uniaxially anisotropic substrate to reduce the complexity of the spectral domain method and to minimize the CPU time necessary to obtain the numerical results. The numerical comparison between neurospectral and conventional moment methods shows significant improvements in time convergence and computational cost. Hence, the use of neurospectral approach presented here as a promising fast technique in the design of microstrip antennas.

In this paper, a microstrip-fed U-shaped dielectric resonator antenna (DRA) is simulated, designed, and fabricated. This antenna, in its simple configuration, operates from 5.45 to 10.8 GHz. To enhance its impedance bandwidth, the ground plane is first modified, which leads to an extended bandwidth from 4 to 10.8 GHz. Then by inserting a rectangular metallic patch inside the U-shaped DRA, the bandwidth is increased more to achieve an operating band from 2.65 to 10.9 GHz. To validate these results, an experimental antenna prototype is fabricated and measured. The obtained measurement results show that the proposed antenna can provide an ultra-wide bandwidth and a symmetric bidirectional radiation patterns. With these features, the proposed antenna is suitable for ultra-wideband applications.

In this paper, triple-band stacked microstrip patch antennas (MPAs) are presented with wide impedance bandwidth and suppressed cross-polarization level. Triangular and circular shaped slots are embedded in the patch of antenna. Slot-loaded microstrip patches are fed with meandered microstrip line supported by a semi-ground plane structure. Triangular shaped slot-loaded MPA shows triple resonance at frequencies 2.2, 4.45, and 5.3 GHz having bandwidth of 45.9, 19.23, and 15.67%, respectively. Circular shaped slot-loaded MPA also shows triple resonance at frequencies 2.2, 4.42, and 5.38 GHz having bandwidth of 50.24, 33.21, and 13.43%, respectively. Using circular slot in place of triangular; bandwidth of the first and the second band is improved by 4.34 and 13.98%, respectively. Both the proposed antennas show an omnidirectional radiation pattern at all three resonance frequencies in the xz-plane with almost 0 dBi gain. Both the proposed antennas are fabricated on a FR-4 epoxy substrate and show a minimum level of cross-polarization radiations.

A novel quarter cylindrical dielectric resonator antenna (q-CDRA) has been introduced by splitting four uniform quarters from a cylinder. q-CDRA has been designed and validated with theoretical analysis. Two and four element q-CDRAs have been proposed in composite forms through Ansoft high-frequency structure simulator simulation software and fabricated for experimental investigation. The input characteristics and radiation patterns of the proposed antennas have been studied through simulation and compared with the measured ones. The |S11| characteristics of the proposed antennas have been compared with each other. The four-element composite q-CDRA has wide impedance bandwidth (|S11| ≤ −10 dB) of 58.15% with monopole-like radiation pattern as compared with other q-CDRAs. The two and four elements q-CDRAs have symmetric monopole-like radiation patterns with linear polarization for whole operating bandwidth (4.5–8.6 GHz). The proposed composite q-CDRAs may find suitable applications in WLAN and WiMAX band.