In this paper, a novel design of generalized dual-band quadrature hybrid with arbitrary power division ratios is presented and investigated. This coupler has a simple structure and can cover a wide range of power division ratios at the two designated frequencies. Exact closed-form equations are derived based on the even–odd-mode analysis method. The proposed structure offers some special features, encompassing: (1) a generalized structure of some recently published papers; (2) isolation in vertical and horizontal directions in the two-dimensional structure; (3) the same sign of the output phase difference for the structure with horizontal isolation and the opposite sign for the structure with vertical isolation; (4) large power division ratios for both vertical and horizontal isolation conditions; (5) large frequency band ratio for both vertical and horizontal isolation conditions; (6) capability of the bandwidth improvement by exploiting coupled lines with small coupling coefficient. For demonstration, a microstrip implementation of a 16:1 dual-band coupler working on 2.45/5.8 GHz is developed. Consistency between simulation and measurement results justifies the proposed design method and its equations.

In this paper, a simple synthesis technique to obtain the geometrical parameters of the modified circular ring for angular and polarizations (perpendicular and parallel) stable frequency selective surface (FSS) has been discussed. The geometrical parameters of the modified circular ring FSS structure have been achieved using the proposed synthesis technique, which is based on the equivalent circuit (EC) approach. In addition to this, the numerical analysis is also discussed to determine the values of EC parameters, which depends on the basic system level characteristics such as frequency of operation and reflection/transmission coefficients. The analytical results are supported using the full-wave three-dimensional electromagnetic (EM) simulators such as CST Microwave Studio and Ansoft HFSS. The sensitivity of the structure to the perpendicular and parallel polarized EM wave up to 50° angle-of-incidences (AOIs) has been discussed. The stability over different AOI is attributed to the appropriate thickness of the structure with its small unit-cell dimensions. We have also fabricated and experimentally tested the proposed FSS structure.

This paper introduces a new technique for the efficient computation of intermodulation distortion in radio frequency circuits that contain microelectromechanical system (MEMS) variable capacitors using moments analysis. This method is applied to an extended harmonic balance formulation, which contains the nonlinear equations that describe the dynamic mechanical behavior of MEMS variable capacitors, in addition to the nonlinear electric circuit equations. As a result, the moments method becomes a general multi-domain simulation method for quantifying nonlinear intermodulation distortion, while presenting significant computational cost reduction over harmonic balance-based methods.

A single-feed dual-band circularly polarized stacked microstrip patch antenna with a small-frequency ratio is presented. Two pair of orthogonal slits is cut on the lower circular patch for achieving circular polarization and truncated corner square patch is used as the upper parasitic element. The frequency ratio of the dual-band is 1.03. The 3 dB axial ratio bandwidth is 1.3% for the upper band and 1.1% for the lower band. Proposed structure is fabricated on the FR-4 epoxy substrate and fed by SMA connector. The measured results are in good agreement with the theoretical and simulated results. The antenna shows stable radiation characteristics in both bands of operation.

This work focuses on the circuit modeling and full-wave analysis behavior of circular split ring resonator (SRR). We investigate an equivalent circuit model that allows calculating the resonant frequency from the geometric parameters. Equivalent LC parameters of inductance and capacitance are derived using conformal mapping and constitutive equations. Lumped element equivalent circuit models of resonator are investigated highlighting the behavior of inductance and capacitance. In order to validate our proposed analytical LC model, a comparison of theoretical and simulation results has been performed and a good agreement is achieved with a maximum error of 4.23% and a minimum error of 0.52%, which supports the validity of the equivalent model.

A new split frequency envelope modulator for envelope tracking radio-frequency power amplifiers is proposed based on a lead-lag network. By mathematically deriving the transfer functions of the lead-lag modulator and the conventional split frequency type, the lead-lag is shown to have a significantly flatter phase response. The frequency response of the two modulators is verified by simulation, where the phase transient of the lead-lag is significantly less than the 360° of the conventional type. They are further simulated with a 3 MHz bandwidth 3GPP long-term evolution (LTE) signal and the lead-lag shown to reduce the modulator's normalized root-mean-square error (NRMSE) from −27.3 to −39.2 dB. A practical demonstrator was developed around an existing high-efficiency modulator architecture. To maintain system efficiency synthetic impedance was incorporated in the low-frequency switched mode power supply (SMPS) path. This was achieved with voltage and current feedback around the SMPS. The dynamic wideband signal response was investigated by applying a 3 MHz LTE envelope signal to the modulator and comparing the input and output signals. The measured NRMSE was improved from −27.5 to −30.0 dB by adopting the lead-lag structure and the dynamic frequency response verifies correct operation.

We present a tapped tunable delay line filter for radiofrequency (RF) photonic filtering applications, capable of rapid tunability over a wide RF bandwidth limited only by the optical components’ losses, while maintaining independence from polarization state. Multiple fiber taps with contrasting dispersion slopes are used in intensity-modulated direct detection microwave photonic links. A temporal delay is generated between the signals within each arm of the link. Once a signal is received using balanced differential detection, nulls are generated as a function of the laser's operating wavelength. Tuning of the laser allows for a rapid shifting of the nulls in the RF spectrum to dynamically mitigate co-site interference. Through this method we demonstrate the potential for rapid tunability over the RF spectrum by the variation of the operating wavelength of the optical carrier.

This paper presents a new class of quasi-elliptic pass-band filters in substrate-integrated waveguide technology, which exhibits compact size and modular geometry. These filters are based on mushroom-shaped metallic resonators, and they can be easily implemented using a standard dual-layer printed circuit board manufacturing process. The presented filters exploit non-resonating modes to obtain coupling between non-adjacent nodes in the case of in-line geometry. The resulting structure is very compact and capable of transmission zeros. In this work, the singlet configuration is preliminarily investigated, and a parametric study is performed. The design of three-pole, four-pole, and higher-order filters is illustrated with examples and thoroughly discussed. A four-pole filter operating at the frequency of 4 GHz has been manufactured and experimentally verified, to validate the proposed technique.

A planar circularly polarized (CP) monopole antenna (MA) with dual-band operation for the IEEE 802.11a/b/g wireless local area network (WLAN) is proposed. By introducing dual strip-sleeves shorted at the ground plane, the excitation of dual-resonant modes can resemble the 2.4/5.2 GHz bands required for WLAN operations. The obtained impedance bandwidths (RL ≧10 dB) across the operating bands approach 260/988 MHz and the 3 dB axial-ratio bandwidth of about 103/710 MHz for 2.4/5.2 GHz bands, respectively. The model proposed in this study reflects more advantages in physical implementation as its overall volume is only 40 × 40 × 0.8 mm3, 22% smaller than other conventional CP MAs. The measured peak gain and radiation efficiency are about 4.1/3.3 dBic and 94/84%, respectively, and demonstrate nearly bidirectional patterns in the XZ- and YZ-planes.

The gain properties of an axially slotted cylinder coated with two lossless layers and embedded in a certain lossless background medium have been investigated analytically. The effects of different types of coating layers, i.e. dielectric, magnetic, and Single Negative materials upon the gain characteristics of an axial slot have been discussed. It is observed that if inner layer is either of dielectric or magnetic type and outer layer is an Epsilon Negative type having its relative permittivity of negative one and slotted cylinder is embedded in the free space then the gain has directive pattern. It is also studied that if both layers are dielectric or magnetic types and embedded in a Mu Negative medium then its gain pattern becomes more directive with the maximum gain in the forward direction.

This is the first report on novel mushroom-type electromagnetic band gap (EBG) structures, consisting of fractal periodic elements, used for enhancing the gain of microstrip patch antennas. Using CST Microwave studio the performance of rectangular patch antenna has been examined on proposed fractal EBG substrates. It is found that fractal EBGs are more effective in suppressing surface wave thus resulting in higher gain. The gain of rectangular patch has been improved from 6.88 to 10.67 dBi. The proposed fractal EBG will open new avenues for the design and development of variety of high-frequency components and devices with enhanced performance.

Detecting time-varying target in non-stationary background is difficult and attractive problem. Time-varying movement exists widely in radar and communication systems. The non-linear processing with higher moments is discussed in the situation. Firstly the signal model of time-varying target with fix acceleration is analyzed. Then the radar echoes from synthetic aperture radar (SAR) are processed with higher moments. It not only restrains Gaussian noise automatically, but also suppresses non-stationary noise. Time-varying targets are different from the non-stationary background clutters. Moreover, the influences of the shadows about time-varying targets are reduced in the algorithm of higher moments. The proposal mentioned above utilizes higher moments to avoid analyzing the complex electromagnetic wave propagation and scatter theory. The differences of detection probability are compared between the chip with time-varying target and the clutter chip. The performances among different number order moments are compared by processing lots of actual SAR data added non-stationary noise. Lastly, the suitable number order moments are suggested by comparing the results from processing the actual radar echoes.

In this study, we propose a design methodology for a switching-mode RF CMOS power amplifier with an output transformer. For a given supply voltage, output power, and target efficiency, the initial values of the transistor size, output inductance, and capacitance can be sequentially determined during the design of the power amplifier. The breakdown voltage of the power transistor is considered in the design methodology. To prove the feasibility of the proposed design methodology, we provide the design example of a 2.4-GHz switching-mode CMOS power amplifier with 180-nm RF CMOS technology. From the measured results, the feasibility of the proposed design methodology is proved.

A simple and compact microstrip antenna of circular geometry with circular cut defected patch surface has been proposed for significant suppression of cross-polarized (XP) radiation compared with maximum co-polarized gain without affecting the co-polarized radiation pattern at its dominant mode. This will enhance the polarization purity in the radiation performance of the proposed antenna. About 27–28 dB isolation between co-polarized and XP radiations is achieved with the proposed structure. The present structure is simple and easy to develop commercially. The investigation of the new structure is carried out with a view to eliminate orthogonal resonance, which is generally attributed for high XP radiation from the microstrip patch antenna with conventional circular geometry. Comprehensive study on the resonance and radiation characteristics of the new geometry is presented. The present investigation provides an insightful visualization-based understanding of XP suppression with the present structure.

A novel design of a compact ultra wideband antenna with triple band-notched characteristics is proposed. Much wider impedance bandwidth (from 2.63 to 13.02 GHz) is obtained by using a star like-shaped radiator and a defected rectangular ground plane and band-notched functions are obtained by attaching L- and I-shaped structure on the ground and a capacitive-loaded loop (CLL) resonator on the patch. The triple band-notch rejection at WiMAX, WLAN, and ITU bands are obtained by attaching I-shape strip, CLL resonator, and flip L-shape, respectively. The parametric study is carried out to study the influence of varying dimensions on the antenna performance. To validate simulation results of the design a prototype is fabricated on the commercially available FR4 material. The measured results reveal that the presented triple band-notch antenna offers a very wide bandwidth of 10.41 GHz (2.63–13.04 GHz) with triple band-notched characteristics at WiMAX (2.94–3.7 GHz), WLAN (5.1–5.9 GHz), and ITU (7.4–8.7 GHz).

A single-fed circularly polarized microstrip antenna is proposed where the antenna structure exhibits truncated corners in the radiating square patch. The truncated corners square patch structure is loaded with a circular slot and is resonating at 2.25 GHz with circular polarization. Furthermore, the proposed antenna is stacked using an upper circular patch thus achieving a dual-band circularly polarized pattern. The dual-band antenna resonates at 2.25 GHz in the first band and with impedance bandwidth ranging from 4.4 to 5.5 GHz in the second band. The size of the proposed stacked structure is compact compared with the conventional circularly polarized stacked antenna designs. Proposed structures are fabricated and fed using Subminiature version A (SMA) connector. The measured results are in good agreement with the simulated. The antenna shows stable radiation characteristics for the entire band of operation.

This paper presents the first experimental results of a novel MEMS-based waveguide filter for mobile back-hauling at K-band with adjustable center frequency. The tuning concept employs commercial packaged RF MEMS switches, wire-bonded within a rectangular cavity. The switches are used to perturb the current distribution of the TE101 mode so as to tune the resonant frequency of the cavity. A tuning range up to 2% with unloaded Qs of the order of 1000 in K-band can be obtained. A second-order filter prototype employing commercially available MEMS on silicon substrate has been tested. Measurements show a 160 MHz frequency shift (0.7%) and Qs up to 1000 using only one MEMS per resonator. New higher-order prototypes using low-loss substrate MEMS (e.g. quartz) will be fabricated in order to get higher Qs. The concept here present leads to a very simple structure. The number of MEMS per resonator is, in fact, minimized (we use only one MEMS) and the design is simple. On the other hand, the achievable tuning range is lower (<2%) than the other concepts. Higher tuning ranges are achievable using more MEMS, but at the expense of lower Qs of the resonators.

We propose a compact, high-efficiency antenna configuration, which is 18 cm in diameter and has average gain of 24.1 dBi for automotive applications of satellite TV systems operating at Ku band. To achieve high aperture efficiency, hybrid microstrip, and waveguide feed network with low-loss microstrip-to-waveguide transition is designed and validated. The array antenna is wideband and covers entire downlink Ku-band frequencies (10.8–12.75 GHz) for simultaneous reception from multiple transponders. Vertical polarization panel is built and tested for reception quality. Carrier-to-noise ratio of 6.2 dB was observed the target transponder (42°E) at 11.9 GHz using intermediate frequency loop-out of the receiver. The antenna can be used on small vehicles or automobiles for satellite TV reception.

An array of patch-antennas with meandering-gaps on an optical modulator is proposed for wireless millimeter-wave beam-steering through high-speed radio-over-fiber systems. Wireless millimeter-wave can be received by the array of patch-antennas and directly modulated to lightwave by the optical modulator. The wireless millimeter-wave can be steered using the meandering-gaps at the patch-antennas by controlling interaction between millimeter-wave and lightwave electric fields in electro-optic modulation. The basic operation and analysis of the proposed device are discussed. In the experiment, 5 × 5 antenna array in 40 GHz millimeter-wave bands was designed and realized for device characterization and demonstration to wireless millimeter-wave beam-steering. There were five variations of wireless millimeter-wave beam-steering for one-dimensional in xz- or yz-planes that can be obtained with wireless millimeter-wave steerable beams of about ±30°. Additionally, 25 variations of wireless beam-steering can be obtained for two dimension in xyz-space through orthogonal optical modulation. The proposed device is promising to be applied in millimeter-wave/tera-hertz bands for future directional wireless communication and sensing with high-speed and high-resolution operation.

In this paper, a switchable antenna with capability to operate in ultrawideband (UWB) frequency from 3 to 10.7 GHz with two switchable notch bands of 3.3–3.7 and 3.7–4.2 GHz, is presented for cognitive radio (CR) and multiband orthogonal frequency-division multiplexing (MB-OFDM) applications. The proposed antenna has a simple structure and compact size of 17 × 24 mm2. The antenna in the UWB characteristics is obtained using a circular radiator patch with an embedded T-slot on the patch and a rectangular parasitic element that is attached to the patch. The reconfigurability is also achieved by two L-shaped parasitic elements placed in the left and right of the patch that two ideal switches is inserted over the these elements and the circular patch. The function of the antenna can be changed by tuning status of the switches that make the notch bands in application frequencies. The measurement and simulation results show that the antenna has good characteristics for CR application and MB-OFDM, where the UWB antenna is required for spectrum sensing and the switchable band rejection antenna is used for reconfigurable operation.