A MMIC double-balanced subharmonic diode ring mixer was designed for broadband satellite communications exploiting a GaAs pHEMT process. The circuit implements the frequency conversion from Q (43.5–50 GHz) to Ku-K band (17–21.5 GHz). Besides the RF, LO, and IF baluns, the MMIC integrates a buffer amplifier for the local oscillator signal, which is designed between X and Ku bands (11–16.5 GHz), due to the subharmonic operation. The mixer measured conversion loss is between 8 and 12 dB along the bandwidth, with an LO power of 9 dBm. The input p1 dB and IP3 are 2 and 15 dBm, respectively. The balanced structure ensures an LO and 2 × LO leakages at the IF port lower than −25 and −35 dBm, respectively. Other spurious remain below −67 dBc. The chip dimensions are 2.4 × 2.4 mm2.

A novel compact ultra-wideband (UWB) eight-way ring-cavity power divider is presented in this paper. To broaden the bandwidth of the power divider/combiner, the stepped-impedance technology is used to realize the impedance match. The network of this eight-way ring-cavity power divider has been analyzed. The measured results reasonably agree with the simulated ones. The measured return loss is greater than 10 dB from 5.2 to 18.6 GHz. The average insertion loss, amplitude imbalance, and phase imbalance are around 9.4 dB (including the 9-dB power-dividing insertion loss), ±0.7 dB, ±6°, respectively, across the entire operating frequency range.

A new quad-band bandpass filter for Global System for Mobile Communications, Wireless Local Area Network, and Worldwide Interoperability for Microwave Access is designed and fabricated using the stub-loaded resonator (SLR) technology without complex fabrication process, such as via-hole or multi-layer substrate. Owing to the embedded SLR, the proposed quad-mode resonator is compact. Equivalent circuits of the proposed quad-mode resonator are analyzed in detail, and high design freedom is shown because of shifting the passband frequencies individually. Good passband selectivity and isolation of the each passband at 1.8, 2.4, 3.5, and 5.2 GHz can be well achieved due to the transmission zeros appeared near the each passband edges. Experimental results show good agreement with the simulated results.

In this paper, a fractal-based complementary split-ring resonator (CSRR) has been introduced as a defected ground structure (DGS) in the ground plane of a dual-mode microstrip bandpass filter to produce a new compact filter with dual-band response. The conventional double square ring resonator structure is modified such that its inner ring is made with a fractal shape instead of a square. Measured and simulation results show that the resulting filter offers a dual passband response; the higher passband is attributed to the dual-mode microstrip ring structure, whereas the lower passband is as a result of the embedded CSRR DGS structure. In addition, the results show that the position of the lower passband could be varied, to a certain extent, without affecting the position of the higher passband by applying higher fractal iteration levels to the inner split ring. These features, together with the compact size the proposed filter offers, make it suitable for use in a wide variety of dual-band communication applications. Measured results, carried out on filter prototypes, have been found in agreement with those theoretically predicted.

In this work, multi-mode resonator technology is applied to finline bandstop filter (BSF) to improve its performance. A finline BSF with two transmission zeros in the stopband is realized by using a new kind of dual-mode finline resonator proposed in this paper. The bandwidth of the designed filter is clearly broadened to three times that of the traditional finline BSF without enlarging its size. Its measured bandwidth under 20 dB rejection is about 600 MHz and the insertion loss in the passband is below 0.4 dB including the insertion loss of two finline-to-waveguide transitions. There is a good agreement between the simulated and measured results.

Novel design of low-pass microwave filters based on cascading of identical unit cells is proposed. Dispersion relation is used to determine the cell parameters for a given relative stop-band width. For a filter consisting of two cells, each made of single- or two-section transmission lines, the design formulas and curves are presented. Based on them typical filters are designed, fabricated, and measured. The presented filters feature a deep stop band and a wide rejection band, which can be controlled within the proposed design procedure. The design procedure and the simulation results are verified experimentally by measurement of the fabricated structures containing two and three cells.

Nature inspired optimization algorithms, namely artificial bee colony (ABC) optimization and firefly algorithm (FA), have been applied to synthesize beam patterns of a hexagonal planar array of isotropic elements. Two different cases, comprising two different beam patterns of a pencil beam and a square footprint pattern over a bounded region with lower peak sidelobe levels are presented. The pencil beam is generated by thinning the uniformly excited array and the square footprint pattern is generated by imposing optimum amplitudes, phases, and their corresponding states (“on”/“off”) to the array elements. The optimum values of the parameters for both the cases are computed using ABC and FA individually, and the superiority of FA over ABC for the proposed problem in terms of computing solutions for both the cases is established.

This paper presents the design of non-uniform concentric circular antenna arrays (CCAAs) of isotropic radiators with optimum sidelobe level (SLL) reduction. The biogeography-based optimization (BBO) method is used to determine an optimum set of excitation amplitudes that provide a radiation pattern with optimum SLL reduction with the constraint of a fixed major lobe beamwidth. The BBO method represents a new global evolutionary algorithm for optimization problems in electromagnetics. It is shown that the BBO results provide an SLL reduction that is comparable to that obtained using well-known algorithms, such as the particle swarm optimization (PSO), genetic algorithm (GA), and evolutionary programming (EP). Moreover, BBO results are compared with those obtained using the Matlab function Fmincon which uses a sequential quadratic programming (SQP) method. The comparison shows that the design of non-uniformly excited CCAAs using the SQP method provides a SLL reduction that is better than that obtained using global stochastic optimization methods, indicating that global optimization techniques might not really be needed in this problem.

In this paper, a compact multiple-input multiple-output (MIMO) antenna system with high isolation is proposed for 2.4 GHz wireless local area network (WLAN) application. The system is composed of two aperture-coupled shorted patch antennas with a spacing of 4 mm (only 0.032λ). The antenna is fed with an H-shaped coupling slot, and the defected shorting wall is used for high isolation. The proposed MIMO system exhibits an isolation of better than −20 dB and a maximum isolation of −43 dB at the central frequency. The envelope correlation coefficient is less than 0.01. The simulated and measured results show that the proposed antenna is a good candidate for MIMO system with higher isolation and better diversity.

A SPICE model of an antenna for transmitting is proposed. This model allows for the calculation of the frequency-domain radiation fields for a range of frequencies in which the model is valid, it also allows for the direct calculation of the time-domain (TD) radiation fields for an arbitrary TD excitation signal, the spectrum of which should be within the modeling range. The model is then verified by two examples, both of them demonstrate its validity. This model can be a part of a complete system-level model for electromagnetic compatibility simulation.

A design of annular ring microstrip antenna with finite ground structure is proposed in this paper. The proposed geometry offers impedance bandwidth of 2.362 GHz and has stable radiation patterns for all resonant frequencies in the operational band. It is also found that shape and dimension of the finite ground plane is a key factor in improving the bandwidth of the proposed geometry. The geometry is low profile and has simple structure, therefore can be used for lower band of ultra-wideband applications.

A low specific absorption rate (SAR) reconfigurable multiband coplanar waveguide fed planar inverted-F antenna (PIFA) is presented in this paper. Different numbers of meander-turn-shaped slots are etched on the PIFA radiating plate to excite new resonant frequencies. Extra resonant frequencies are created by increasing the number of meander-turn-shaped slots for different wireless communication applications. A new independent resonant frequency is created by etching a coupled slot within the ground plane for the upper WLAN. A PIN diode switch is used to reconfigure the fundamental resonant frequency from the LTE band 11 to band 8 with a total of 63% size reduction compared with the original PIFA size. Furthermore, the SAR in the human head is investigated using the Hugo voxel model in CST Microwave Studio. The volume of the antenna is 22 × 30 mm2 over a 35 × 50 mm2 ground plane, which is suitable for handheld devices.

Variable Z0 (VZ0) antenna technology is a new design or optimization methodology applicable to any antenna on any platform designed or optimized with any procedure. It should be particularly useful for wireless devices populating the Internet of Things. VZ0 expands the design or decision space by adding another degree of freedom invariably leading to better antennas. A simple design example illustrates its effectiveness.

Wideband microstrip antenna with L-plate capacitively coupled feed structure is designed. The antenna operates in GSM 1800/1900 (1710–1910 MHz) and UMTS I (1920–2170 MHz) frequency bands. The antenna has dual slant (±45°) polarization with high isolation (>25 dB) between the ports. Measurements of the antenna reveal good performance in terms of impedance match, gain, gain flatness, isolation, half-power beamwidth, cross-polarization level, and front-to-back ratio. The proposed antenna can be used in base station antenna arrays, pico-cell, and femto-cell small-area cellular networks.