The paper is related to an adaptive satellite communication system for data transmission from small, low cost, low Earth orbit satellites. Tests run in a set-up consisting of a number of software-defined radio (SDR) modules operating as a satellite, a ground station, and a satellite channel simulator, have shown that by changing modulation scheme and code rate one can obtain increase of amount of data which can be downloaded from a satellite during a single pass over a ground station approximately by a factor of 2. To determine data rates obtainable in an SDR system using a common personal computer as a digital signal processing device, execution times of particular processing steps involved in the reception process were measured.

In this paper, a leaky-wave antenna (LWA) with wide scanning angle and low cross-polarization is proposed based on a T-type folded substrate-integrated waveguide (FSIW). Transverse slots with a sinusoidal distribution pattern are etched on the surface of the FSIW so that transmission lines with slow-wave characteristics can excite and radiate −1 order harmonics. The length of the transverse slot affects the dispersion characteristics of the transmission line, and the sinusoidal modulation period controls the operating range of the LWA. In the frequency range of 8.3–15 GHz, the proposed LWA achieves a wide scanning ranging from backward −42° to forward +68° continuously. The cross-polarization of the beam is also kept at less than −30 dB during this scanning. A prototype is fabricated and measured to confirm the design, and the measured results show an agreement with the simulated one.

A compact wideband out-of-phase power divider (PD) with improved isolation performance is proposed. This divider is formed by connecting an additional stub for isolation to output ports of a traditional Marchand balun with a defected ground structure (DGS) been used. To verify the design, a prototype divider is fabricated and tested. The measured results validate the 53.86% band-width centered at 3.43 GHz with more than 15 dB return loss at all ports, more than 17 dB isolation, respectively.

This paper presents a comparison between three evolutionary algorithms (EAs) for pattern synthesis of offset reflector antenna fed by a planar array of horn antennas. To perform the optimization process, an elliptical-shaped beam in the U–V plane (U = sinθ cosφ and V = sinθ sinφ) is considered as the desired far-field radiation pattern. To attain the appropriate excitation value for array elements, three conditions are considered: (1) variable amplitude (with uniform phase distribution), (2) variable phase (with uniform amplitude distribution), and (3) variable amplitude and phase excitation. Obtaining the appropriate excitation value based on the mathematical methods is always complicated and time-consuming. Therefore, genetic algorithm (GA) and particle swarm optimization (PSO) as two well-known EAs have been used widely for different applications and shown the promise to solve complicated problems. This paper compares these two EAs with invasive weed optimization (IWO) which is robust and has simple and powerful process with few tuning parameters. We found that for pattern synthesis of multi-feed reflector antenna in different conditions, IWO can provide accurate and comparable results with GA and PSO methods at approximately same iteration number. The convergence diagrams as well as the optimized radiation patterns for different conditions are presented and compared for GA, PSO and IWO.

An N-band resonator, particularly well-suited for reconfigurability, is presented in this paper together with its synthesis. The resonator is based on the association of an N-band dual-behavior resonator and tunable capacitors. Its topology consists of a parallel association of N + 1 different bandstop structures, each one composed of a stub terminated by a capacitor. N pass bands, separated from each other by a transmission zero, are then obtained. As each bandstop structure independently controls one transmission zero, the use of variable capacitors allows each of them to be tuned independently and then to reconfigure the resonator in terms of transmission zeros and resonant frequencies. After the presentation of the general synthesis, this principle is validated by the realization of a tri-band resonator in microstrip technology.

In this paper, the influence of tree trunks, cylindrical street furniture such as lamp posts, and traffic on ray tracing simulations in an urban scenario is analyzed. Tree trunks and lamp posts are modeled by cylinders and propagation characteristics computed according to the Uniform Theory of Diffraction. The influence of traffic is analyzed by simulations with moving vehicles. In order to get an understanding of the spatial characteristics of the channel, simulations with static and also mobile receivers have been performed, in line with a measurement campaign in the same environment. The simulation results show a good agreement with the measurements.

The radiation characteristics of the microstrip antenna (MSA) on the frequency selective surface (FSS) based absorbing layer is presented in this paper. It is observed that an absorbing layer placed between the MSA configuration and the ground plane helps in controlling the radiation characteristics of the antenna. It not only reduces the back lobe but also reduces the beamwidth and gain of the antenna simultaneously. This is because the absorbing layer absorbs some amount of power radiated by the antenna in both forward and backward directions. The proposed design is simulated using Ansys HFSS electromagnetic simulation software and the results are validated by comparing it with the results obtained from the equivalent circuit approach as well as experimental results. The effect of absorber on radiation characteristics of the radiator demonstrates its potential use in suppressing the radiation from the printed circuit board traces.

In this study, we present the implementation of invasive weed optimization (IWO) in the maximization of main-lobe to side-lobe level for the non-uniform planar antenna array. The antenna arrays investigated in this study are generated using the chaos game algorithm (CGA) and shaped into selected fractal geometries chosen on the basis of their interesting performance. This CGA is picked out in order to overcome the limitations found in the fractal arrays. All the attained results are compared with the results produced by a well-known optimization algorithm that is the particle swarm optimization (PSO). In all the optimized arrays, IWO shows superior optimization results compared with PSO.

This paper presents a new macro modeling methodology for solid-state power amplifiers (SSPAs) and packaged transistors used in communication systems. The model topology is based on the principle of harmonic superposition recently introduced by Agilent Technologies' X-parametersTM combined with dynamic Volterra theory. The resulting multi-harmonic bilateral model takes into account the coupling effects of both short- and long-term memory in SSPAs. In this work, the behavioral model was developed from time-domain load pull and used to simulate the amplifier's response to a 16-QAM signal with specific regards to ACPR and IM3.

A novel Gysel power divider with high power-handling capability based on half-mode substrate integrated waveguide (HMSIW) has been presented in this paper. A HMSIW ring is used and good input/output impedance matching is achieved based on HMSIW-microstrip taper transition. Two microstrip stubs are introduced in HMSIW ring to assemble two isolation resistors to improve the isolation between the output ports. The even- and odd-mode analysis method is used for the presented circuit. A prototype of the presented power divider is designed, fabricated, and measured. The measured results show a reasonable agreement with the simulated ones.

This paper studies the variation effects of incident plane wave on shielded coaxial cables, using Branin's method, which is called the method of characteristics. That model can be directly used for the time- and frequency-domain analyses. Moreover, it had the advantage of being used without the need of setting the preconditions of the charges applied to its ends. This makes it easy to insert in circuit simulators, such as SPICE, SABER, and ESACAP. The results obtained under ESACAP were remarkably similar to other results, which reinforce the validity of the model. Finally, we will discuss the effects of the variation of the incident plane wave.

In this paper, an unconditionally stable time-domain method is proposed to investigate the external electromagnetic (EM) field illumination on the nonlinearly loaded transmission lines. In the proposed algorithm, the field to line coupling equations and linear/nonlinear boundary conditions are incorporated and expressed in a matrix form. The derived differential matrix equations are then discretized and solved using the proposed finite difference time domain (FDTD) method approach. The discretized nonlinear matrix equations are also solved by applying a globally convergent iterative method to ensure the stability of the method. Moreover, the experimental investigations are conducted using a transverse EM (TEM) cell for a single microstrip line and a power detector circuit as a nonlinearly loaded transmission line to confirm the accuracy and stability of the proposed method. With the merit of satisfactory accuracy and unconditional stability for the entire range of time steps, the presented approach would be applicable for analyzing the microwave linear/nonlinear circuits subjected to the external incident EM wave.

A novel low profile dual band patch antenna is presented. It consists of a composite right/left-handed transmission line (CRLH TL) unit cell gap coupled with the radiating edge of a rectangular patch antenna. The dual band behavior is achieved by coupling the zeroth order resonance mode of CRLH TL and TM10 mode of the patch antenna. It is shown that frequency ratio can be changed by varying the gap between the patch and CRLH TL unit cell. The proposed configuration enables frequency reconfigurability by changing the CRLH TL unit cell using a switch. A prototype of the antenna having frequency ratio f2/f1 = 1.08 is designed and fabricated. The proposed antenna shows measured S11 ≤ −10 dB bandwidth of 100 and 50 MHz at resonance frequencies of f1 = 4.84 and f2 = 5.22 GHz, respectively. A 2 × 2 dual band CRLH TL coupled patch array is also presented, showing more than 12.7 dBi gain at both resonance frequencies.

This paper presents a theoretical and experimental analysis of the capabilities of the dual-input Doherty power amplifier (DPA) architecture to mitigate efficiency and output power degradations when used in a mismatched load environment. Following a simplified linear piecewise approach, an analytical demonstration is proposed to derive optimal radio frequency drives applied to the Auxiliary path of the DPA to restore power performances while avoiding large signal voltage clipping of active cells. The proposed analytical study is corroborated with harmonic balance simulated results of a C-band, 20-W GaN DPA prototype. The fabricated dual-input DPA prototype has been measured under 1.5-VSWR mismatch configurations to validate the proposed analysis.

This paper presents an active Q-enhanced LC dual-band band-pass filtering approach using parallel synthesis techniques at X- and Ku-bands in 0.13 µm SiGe BiCMOS technology. By employing two independently tunable parallel LC-tanks with either in-phase and out-of-phase addition, independently tunable dual-band filtering is achieved. For higher out-of-band (OOB) attenuation, subtraction of the two 2nd-order bandpass filter is implemented. The two bands are independently tunable in terms of Q and center frequency. The dual-band filter at 9.7 GHz and 13.9 GHz achieves a normalized dynamic range of 165–154.5 dB.Hz with an OOB attenuation of >50 dB below 3 GHz. In between the two bands, the attenuation is 22 dB when the two passbands have 200 MHz bandwidth each. The total group delay is 0.8 ns and 1.9 ns for Q of 20 and 50, respectively. The filter achieves better OOB rejection with wider band channels at X- and Ku-bands compared with state of the art integrated filters. The filter consumes 115–130 mW of DC power. The core die area is 0.53 × 0.7 mm2.

A design of a microwave absorber based on frequency selective surface resonating in X-band having ultrathin thickness, polarization controlled behavior, and increased absorption bandwidth has been reported. The reported absorber having its unit cell embodied of multiple resonating structures which includes conventional square, circular, and butterfly shaped resonators resulting in three absorption apexes at 9.44, 10.00, and 10.53 GHz (all in X band) with 99.9%, 99%, and 95.1% of absorptivity obtained at the frequencies of resonances. It demonstrates a wide full width at half maximum having 1.48 GHz as bandwidth, at the expense of using an ultrathin substrate of 0.0096 λ0, where λ0 is the wavelength with respect to lowest resonating frequency, i.e. 9.44 GHz. The unit cell is fourfold symmetric exhibiting independence about the absorber’s polarity, as well as, it behaves stable over the outspread angle up to 45 degrees for both transverse magnetic and transverse electric polarized wave under sloped incident angle. The absorption behavior has been demonstrated by plotting the distribution of surface-currents and electric fields at the frequencies of resonance. The fabricated prototype of the presented design is tested at X-band and the obtained results concur with the simulated results.

This paper reports design and successful development of new and high performance transmit and receive feed systems for reflector antennas at “lower-extended C-band”. The horns are analyzed and optimized using the mode-matching technique-based software CHAMP. Other feed components are designed with the aid of the mode-matching technique and finite element method based softwares viz. MICIAN and HFSS. The predicted radio frequency (rf) performances comply with the measured results with small deviation. Some issues related to feed system such as impact of horn outer structure; such as base for tooling ball, feed bracket for struts etc. on its rf performance are discussed. It is shown that the outer feed structure plays a significant role apart from the internal cavity of the horn for prediction of electrical performance of the feed system. Besides high rf performance; good mechanical properties such as compactness and ease to fabrication are achieved through innovative feed design.

This paper presents a broadband Butler-based slant ±45° dual-polarized omni-directional antenna working at the frequency band of 1.69–2.69 GHz for extending wireless communication network capacity in the limited service size. The proposed antenna realizes a 360° full coverage with wider bandwidth in a compact cylinder and increases the network capacity to 6 × 6 MIMO instead of using three traditional 2 × 2 MIMO omni-directional antennas. Theoretical analysis, simulation, and fabrication are conducted to validate the idea of the proposed omni-directional antenna. The measured results show 46% bandwidth with 15 dB return loss, 2.2 dB azimuth null and 8.9–10.5 dBi gain for port-C with 0° phase increment, and 14.1 dB azimuth null and 9.6–10.6 dBi gain for port-L/R (left/right) with ±120° phase increment, respectively.

In this paper, a miniaturized bandpass filter for ultra-wide-band applications is proposed. It is based on the embedding of high-pass structures in a low-pass filter. A semi-lumped technology combining surface-mounted capacitors and transmission lines has been used. The filter design rules have been carried out. Furthermore, two filters having a 3-dB fractional bandwidth of 142 and 150%, centered at 0.77 and 1 GHz, respectively, have been realized for a proof of concept. Measured characteristics, in good agreement with simulations, show attractive properties of return loss (|S11| <−18 dB), insertion loss (<0.3 dB), and a maximum group delay and group delay variation of 2 and 1.3 ns, respectively. A distributed filter based on the same low-pass/high-pass approach has been also realized and measured for comparison. The size reduction reaches 85% for the semi-lumped filter, and its selectivity is improved with a shape factor of 1.3:1 instead of 1.5:1. The semi-lumped filter's drawback is related to a smaller rejection bandwidth compared to the distributed one. To improve the high-frequency stopband, an original technique for spurious responses suppression based on capacitively loaded stubs has been proposed. Even if the performances do not reach that obtained for the distributed approach, with this technique spurious responses are pushed until eight times the center frequency. A sensitivity study vs. critical parameters has also been carried out, showing the robustness of the design.