The design of a circular-shaped differential wideband band pass filter (BPF) is described. The proposed filter is compact and provides good common mode (CM) suppression. It consists of four ports with a circular-shaped differential mode (DM). The analysis of the filter has been carried out by bisecting it into identical two-port networks along the symmetry plane, resulting in a band stop or band pass response under CM or DM excitations, respectively. The length and width of the stubs can be tuned to obtain the desired pass band and stop band of the differential BPF. The proposed design is fabricated and measured. The results obtained using measurements are in close agreement with those obtained using simulations.

Two coaxial waveguide bend mode converters that transform coaxial transverse electromagnetic mode to TE11 coaxial waveguide mode are presented in this paper. Both converters are designed and optimized on the basis of the strictly derived mode coupling coefficients. Conversion efficiencies of both converters are over 99% and the power-handling capacities reach a gigawatt level. The combined dual-bend mode converter is fabricated and tested. The experimental results coincide well with the theoretical calculations and simulations, which demonstrates the feasibility of the designed converter.

In this paper, a sandwiched type frequency selective surface (FSS) is designed and analyzed. The design procedure and operating principle is given based on the equivalent circuit model. The proposed FSS includes two identical layers of periodic metallic arrays, which are separated by a foam layer. In each layer of the periodic array, the unit cell is composed of a gridded-triple square loop structure. The FSS provides three pass-bands, in which a flat band response is presented. Three bands are separated by one or two transmission zeros, which leads to a sharp rejection on both sides of each pass-band. The central frequencies of the three pass-bands are 7.0, 10.9 and 14.0 GHz. To verify the simulated results, a prototype of the FSS is fabricated and measured. The simulated results agree well with the measured ones. This work can be used in area of a radar stealth or satellite communication system.

In this paper, an electromagnetic band gap (EBG) metasurface (MS) superstrate-based circularly polarized antenna for the WiMAX (3.5 GHz) band is proposed. The proposed structure comprises a 2 × 2 slot-loaded rectangular patch MS array that can be perceived as a polarization-dependent EBG MS superstrate. Furthermore, to achieve circular polarization, the proposed antenna has an inclined coupling slot onto the ground with a conventional coplanar waveguide feed line. The proposed antenna has a compact structure with a low profile of 0.037λ0 (λ0 stands for the free-space wavelength at 3.48 GHz) and a ground size of 30 × 30 mm2. The measured results show that the −10 dB impedance bandwidth for the proposed antenna is 34.6% and the 3-dB axial ratio (AR) bandwidth is 6.8% with a peak gain of 3.91 dBi in the desired operating band. Good agreement between the simulated and the measured results verifies the performance of the proposed antenna.

In this paper, edge-broad-side coupled spiral resonator (EBC-SR) is proposed to enhance the miniaturization of the metamaterial resonators. After a comparative analysis, it is found that the proposed strategy can drastically reduce the electrical size of metamaterial resonators. This is due to the use, at the same time, advantages of edge coupling, broad-side coupling, and self-coupling. A lumped element equivalent circuit model is proposed for the EBC-SR-loaded transmission line. This model is validated by comparing the results of electromagnetic simulations with the circuit simulations using the extracted parameter values. To validate the proposed strategy, a prototype of the EBC-SR embedded inside a drive loop is fabricated. The experimental results are presented with the simulation results.

This paper deals with a near-field to far-field transformation able to predict the radiation of UHF antennas located over a lossy ground. From in-situ near-field measurements, an equivalent set of dipole sources is obtained as a model of the characterized antenna. The paper details the main steps of the transformation and describes the specific experimental set-up designed for the application. Simple directional antennas (monopoles array) as well as more complex omnidirectional antennas (like a biconical antenna as a scaled-down model of a HF antenna) have been tested in realistic environments. This approach is very efficient for separating the contributions of the radiated waves: the sky wave and the surface wave.

In this work, a new reconfigurable discrete 1D beam-steering Fabry–Perot cavity antenna with enhanced radiation performance is presented. It consists of a probe-fed patch antenna printed on the ground plane and a reconfigurable metasurface acting as the upper partially reflective surface to realize beam steering. By utilizing 6 × 6 proposed reconfigurable unit cells on the superstrate, the beam-steering angle can be effectively enhanced from ±7° to ±17° with fewer active elements and a much simpler biasing network. The proposed antenna was fabricated to validate the feasibility. Good agreement between the simulated and measured results is achieved. Moreover, the measured realized gains are over 11 dBi with a gain variation from the boresight direction to the tilted direction <0.2 dBi.

A magnetic dipole quasi-Yagi antenna based on a dielectric resonator (DR) is proposed in this letter. The dominate TE1δ1 mode of the rectangular DR is used as a magnetic dipole which can be differentially fed by the coplanar strip line (CPS). Thanks to the DR employment, the proposed antenna has several advantages such as compact size and flexible design which means the 3-D dimensions of the DR can be easily adjusted to cater for various applications. Meanwhile, the gain of the proposed DR quasi-Yagi antenna is higher than that of traditional electric dipole counterparts. Furthermore, since the DR driver is horizontally polarized, both the metal strip and DR can be used as a director for enhancing the end-fire gain. To verify the design concept, a prototype operating at the X-band is fabricated and measured. Good agreement between the simulated and measured results can be observed.

A novel tri-beam slot antenna array based on substrate integrated waveguide (SIW) technology is proposed in this paper. The beam forming network is a 3 × 3 Butler matrix consisted of three couplers and four phase shifters. A 1.76 dB coupler is located between two 3 dB couplers, with this arrangement; the input signal can be divided into three parts with the same amplitude and certain phase differences. Two parallel slots are cut off broadside of SIW transmission line, which constitutes the basic unit of the antenna array. A 3 × 2 slot antenna array is connected with this circuit. Three beams with the directions of −30, 0 and 30° are produced when different ports are excited, respectively. The S parameters, radiation patterns, and gains are simulated and measured, which show that it can be a candidate for multi-beam wireless communication systems.

A compact ultra-wideband (UWB) monopole antenna with reconfigurable band-notch characteristics is demonstrated in this paper. It is comprised of a modified rectangular patch and a defected ground plane. The band-notch property in the WiMAX and WLAN bands is achieved by etching an open-ended slot on the radiating patch and an inverted U-shaped slot on the ground plane, respectively. To obtain the reconfigurable band-notch performance, two PIN diodes are inserted in the slots, and then the notch-band can be switched by changing the states of the PIN diodes. The antenna has a compact size of 0.47 λ1 × 0.27 λ1. The simulated and measured results indicate that the antenna can operate at a UWB mode, two single band-notch modes, and a dual band-notch mode. Moreover, stable radiation patterns are obtained.

A multi-input multi-output (MIMO) antenna is designed and discussed for multi-band applications. The constituent antennas are composed of four L-shaped elements and a ground plane. When placed beside each other to form a MIMO antenna, a T-bar shaped parasitic structure is also embedded between the antennas on the backside of the substrate to increase the inter-element isolation. The triple-band performance of the antenna is observed at 2.15–2.73 GHz, 3.1–3.9 GHz, and 5.04–6 GHz. The isolation level of more than 20 is seen over the operating frequency range. The fabricated prototype of the MIMO antenna size is very compact (20 × 40 mm), printed on the FR4 substrate. Based on simulation and experimental results, the proposed design is useful for WiMAX and WLAN applications.