The contribution of this paper is to propose a novel rat-race hybrid coupler of arbitrary coupling coefficient. Traditionally, the rat-race hybrid couplers are built by various loop-alike transmission-lines of multiple quarter-wavelength, and in this paper, we approach the coupler design by using a circular substrate integrated waveguide (SIW) cavity (SIWC). The employed SIWC supports two mutually orthogonal degenerate modes, and cavity field is formed by the two modes in an arbitrary weighting ratio which defines the proposed rat-race coupler's coupling coefficient. The cavity is excited by a microstrip combined coupling slot with the microstrip along a specifically chosen direction. The energy of each degenerate mode can be solely extracted by an associated subminiature version A (SMA) whose position is carefully determined. The isolation between the coupling slots is assured by their perpendicular layout, and the isolation between the SMA probes is obtained by the orthogonality of the two degenerate modes. Experiments are conducted on the 3- and 10-dB coupling coefficient samples to verify this novel rat-race coupler design. The measurements agree well with the simulations, and circuit's good performance is observed in terms of coupling precision, isolations, and small phase imbalances.

This paper presents an ultra-wideband coplanar waveguide (CPW)-to-asymmetric coplanar stripline (ACPS) transition based on aluminum nitride (AlN) substrate. The concepts of designing CPW, ACPS, and CPW-to-ACPS transition are explained. In order to suppress parasitic modes, vias going through AlN substrate are added along the ground traces. The signal trace is tapered out and chamfered to reduce the reflection caused by the termination of ground trace. The CPW-to-ACPS transition is designed, fabricated, and measured in a back-to-back configuration. The fabricated CPW-to-ACPS transition can provide a bandwidth of 165 GHz with an associated insertion loss of 3 dB.

A modified compact Y-junction substrate-integrated waveguide (SIW) four-way power divider (PD)/combiner is proposed in this paper. The proposed approach is based on the traditional Y-junction waveguide. By using direct transition structure from SIW to half-mode SIW, four-way PD that provides equal power split to all four output ports is achieved. The even- and odd-mode equivalent circuits are given to analyze and design the PD. The measured results validate the proposed design methodology and show good agreement with the simulation results. The measured 17 dB return loss bandwidth and 1.2 dB insertion loss bandwidth of this four-way PD are both about 2.5 GHz.

In this paper, a self-actuated frequency-selective radome is presented and applied to a microstrip antenna. The radome acts as a self-triggered switchable screen to achieve adaptive electromagnetic protection in the L band. A prototype of the radome is fabricated to measure its transmission performance. The switchable characteristic is verified by a high-power radiation experiment carried out in a waveguide system. Besides, the antenna is placed under the radome to realize integration analysis, and the radiation performance of the composite antenna radome is measured in the anechoic chamber.

In this paper, a novel class of balun bandpass filters is presented on slot-line resonator (SLR) toward intrinsic balanced performance in amplitude and phase. The proposed balun filter consists of three inductive-coupled SLRs in the middle, one single-ended unbalanced port, and one balanced port with two terminals. According to the distinct field conversion from the slotline to the microstrip feeding line, good balanced performance in amplitude, and phase performance can be intrinsically realized over a wide frequency range. To validate the proposed technique, a prototype third-order balun filter is designed, fabricated, and measured. Both the simulated and measured results have demonstrated that the proposed balun filter can not only achieve good frequency selectivity but also exhibit intrinsic balanced performance in amplitude and phase.

This paper presents a substrate-integrated waveguide (SIW) mixed electric and magnetic coupling structure implemented on a single-layer substrate to create finite transmission zeros (TZs), which can be used to design microwave filters with higher frequency selectivity. Mixed coupling is realized by three slot-lines on the top metal plane combined with an iris-window between two adjacent SIW cavities. The electric and magnetic coupling can be separately controlled by adjusting the dimensions of the slot-lines and the width of the iris-window, and a controllable TZ below or above the passband can be produced. Furthermore, a detailed analysis of the mixed coupling structure is presented. To demonstrate the validity of the proposed structure, third- and fourth-order cross-coupled generalized Chebyshev bandpass filters are designed and fabricated using the standard printed circuit board process. The experimental results are in good agreement with the simulation results. The filters exhibit simple structure and good frequency selectivity.

In this paper, a triple-wideband bandpass filter (BPF) with controllable bandwidths based on two multi-mode stub-loaded resonators (MMSLRs) and a triple-mode resonator is presented. The MMSLR is loaded with two identical folded open-ended stubs and a T-shaped stub. Each passband of the tri-band BPF is formed by four resonant modes, which provide sufficient bandwidths to meet various application requirement. By adjusting the lengths of open-ended stubs, three passband bandwidths can be controlled individually. The center frequencies of the triple-wideband BPF are allocated at 2.7, 3.67, and 5.44 GHz, with the 3 dB fractional bandwidths (FBWs) of 20.1, 14.7, and 26.3%. Among the three passbands, the highest one covers the 5 G WiFi band (5.15–5.85 GHz). The measured results of the proposed filter exhibit excellent agreement with simulated results.

This paper discusses some significant design issues that are faced in resonant inductive system for wireless power transfer ‘on the move’. The targeted system adopts a single AC source to power a sequence of transmitting (Tx) coils, placed along the Rx path, whose geometry is optimized to minimize the variations of coupling for every possible Rx position. To retain a constant coupling coefficient, two nearby Tx coils are series-connected and simultaneously activated, establishing a path without any theoretical bound on its length, by a suitable switching network. This work analyzes the effects of asynchronous switching times, which are rigorously accounted for and minimized by a proper design of the compensating circuit elements, minimizing both the voltage spikes and the over currents on the coils, while keeping the system at resonance. A prototype operating at 6.78 MHz is built and experimental validations are carried out to verify the feasibility of a constant coupling link without experiencing the mentioned effects, but the adopted procedure is general and independent on its size or frequency.

In this paper, theoretical/simulation study of specific absorption rate (SAR) and/or temperature distributions in a bi-layered bio-media (fat and muscle)/realistic tri-layered bio-media (skin, fat, and muscle layers) in direct contact with water-loaded metal diagonal horn (MDH) designed at 915 MHz are investigated. The effects of fat thickness on the input reflection coefficient, reflection coefficient at the interface between the MDH and the bi-layered bio-media, and the SAR distribution in the bi-layered bio-media are also studied through simulation and theoretically at 915 MHz. Further, the SAR parameters such as penetration depth and effective field size inside the bi-layered bio-media due to the MDH are evaluated theoretically and the theoretical results are compared with the corresponding simulation results. Finally, SAR and temperature distributions in tri-layered bio-media without and with embedded irregular/oval-shaped tumor are provided for demonstrating the hyperthermia performance of the MDH applicator.

Microwave and millimeter-wave reflectometry is one of the potential techniques for the diagnosis and detection of biological abnormalities, such as subcutaneous masses or cancerous tumors in human body. In this paper, a high-quality microwave sensor based on planar misrostrip resonator is designed, fabricated, and successfully tested with different kinds of biological samples. The proposed sensor has unique properties such as small size, simple fabrication, non-contact with a sample, excellent de-coupling from surroundings, and high microwave power is directly coupled into the tissue. Two experiments are performed for the detection of visible and hidden “lipoma” (fat masses), and minimum size of “lipoma” that is diagnosed by the sensor is obtained as well. In this regard, a two-dimensional image of hidden “lipomas” with amplitude contrast about 30 dB and frequency shifts contrast about 60 MHz at a λ/10 (at 13.5 GHz) stand-off distance is provided. Finally, a measurement scenario for the detection of skin cancer based on the artificial model using different layers of raw chicken with different water content is described. Results show that the proposed microscope is easy to fabricate and provide a low-cost solution for fast and accurate skin cancer detection.

This paper presents a technique to increase the bandwidth in substrate integrated waveguide (SIW) cavity-backed antennas, inspired by the design of cavity filters. The proposed structure consists of a slot antenna backed by two cavities, located one on top of the other and coupled through a slot. To demonstrate the bandwidth increase, a standard cavity-backed SIW antenna, with a rectangular slot etched in the top metal plane, has been designed, manufactured, and measured. Subsequently, a similar antenna was developed, by doubling the substrate thickness with the aim to improve the bandwidth. Finally, the new topology of two-cavity SIW antenna has been implemented and compared with the two previous ones. Simulation and experimental results show that the proposed two-cavity antenna exhibits a bandwidth twice as large as the standard SIW cavity-backed antenna.

A simple multiple-input-multiple-output (MIMO) antenna with quad-band-notched characteristics for ultra-wideband (UWB) system is proposed and tested in the article. Based on two similar radiators, the UWB-MIMO system only occupies 22 mm × 28 mm. By etching an inverted L-like meander slot, two inverted L-shaped slots, and adding a C-shaped stub beside the feeding line, four notched bands are realized (3.25–3.6, 5.05–5.48, 5.6–6, and 7.8–8.4 GHz) to suppress interference from WiMAX, lower WLAN, upper WLAN, and uplink of X-band satellite communication system. With a T-like stub extruding from the ground plane, port isolation is effectively improved. The results show that the antenna covers 3.1–10.6 GHz UWB frequency band except four rejected bands and has high isolation of better than −20 dB over most of the frequency band. Moreover, envelope correlation coefficient and good radiation patterns also prove that the introduced antenna is suitable for UWB applications.

A compact and planar broadband circularly polarized (CP) eighth-mode substrate integrated waveguide (EMSIW) antenna is proposed in this paper. An isosceles right triangular waveguide with one electric sidewall (located on one of its catheti) and two magnetic sidewalls (located on the other two edges of the triangle) is presented to investigate the characteristics of the EMSIW. The closed-form mode solutions of the electromagnetic field components and the cut-off frequencies are derived for all propagating modes in this triangular waveguide. The simulated electromagnetic field distribution is consistent with the analytical results. The resonant frequencies of the EMSIW cavity are then determined. A CP antenna consisting of four EMSIW elements is designed, fabricated, and measured. The measured 3-dB axial ratio bandwidth of the antenna is 21.6% from 4.72 to 5.86 GHz. Within this frequency range, the measured reflection coefficient is below −10 dB, and the measured peak gain in circular polarization at broadside is 6.89 dBic at 5.1 GHz.

A novel shape penta-band microstrip patch antenna is presented in this paper. The proposed antenna shows five operating frequencies and can be used for various wireless applications, i.e. 2.58 GHz for non-direct line of sight, wireless Internet service providers, and compatible with Navini Networks; 3.17 and 3.42 GHz for WiMAX; 4 GHz for C-band application such as weather radar systems; and 5.3 GHz for higher WLAN. Very small frequency ratios of the values 1.2286, 1.078, 1.169, and 1.325 are achieved between two consecutive resonant frequencies. Antenna design techniques for achieving five bands are presented and discussed step by step. The analysis is done by Ansoft HFSS v.15, and results are verified with experimental results of fabricated prototypes.

A compact coplanar waveguide (CPW)-fed circular polarization (CP)-antenna for new generation applications with dual bands filtering performance along with CP feature based on unit-cell semi-fractal is proposed in this paper. The CP-antenna privileges from semi-fractal radiator causes to have a miniaturized size. The stopped bands are designed to suppress the interference with present WLAN and ITU-R satellite systems. These properties are obtained by embedding semi-fractal unit-cell patterns stubs at the radiator and applying two rectangular-shaped slits inside CPW ground plane and a pair of grounded L-shaped strips. By introducing the first step of semi-fractal strips, and the mirrored defected ground surface structures, dual-band rejection functionality at WLAN (5–6 GHz) and ITU-R (7.725–8.5 GHz) are practically obtained. Besides that, semi-fractal strips results to two orthogonal modes stimulation on the radiator and CP attribute are obtained at WiMAX (3.1–3.7 GHz). CP-antenna presents omni-directional radiation H-plane patterns over the applicational frequency band. The CP-antennas size is 25 mm × 25 mm and fabricated on commercially available FR4-epoxy substrate with 1 mm thickness. Measured results illustrate that the proposed ultimate CP-antenna with miniaturized structure, efficient impedance tuning characteristics, and adequate radiation performances is the best choice for new generation of wireless communications.

This paper presents a new technique for the enhancement of axial ratio (AR) bandwidth of a circularly polarized dielectric resonator antenna with a single feeding. To enhance the AR bandwidth, adjacent 3-dB AR passbands are merged by inserting the notches and conductive coating in the dielectric resonator. The dimensions of the notches and conductive coating are selected in such manner that impedance bandwidth remains approximately unchanged. The antenna provides the measured AR and impedance bandwidths of 55.22% and 66.45%, respectively.

This paper presents a hexa-band frequency reconfigurable planar antenna, printed on a 1.6 mm thicker FR 4 substrate and backed by a truncated ground plane. The given antenna operates in four different frequency modes, depending on the state of the two lumped element switches. The proposed antenna works at six frequencies, 2.10, 2.40, 3.35, 3.50, 5.28, and 5.97 GHz. These frequency bands are dedicated to useful wireless applications, including 3G Advanced (2.10 GHz), Wireless Fidelity (Wi-Fi) (2.40 GHz), WiMAX (3.35 GHz), WiMAX (3.5 GHz), WLAN (5.28 GHz) and fixed-satellite and mobile satellite services (5.97 GHz). Satisfactory gain of 1.96, 2.20, 2.671, 2.81, 3.80, and 3.88 dBi, efficiency of 92.5, 94.5, 94.56, 95.0, 93.8, and 97.0% and bandwidth of 332, 485, 1020, 1080, 512, and 465 MHz has been obtained at 2.10, 2.40, 3.35, 3.50, 5.28, and 5.97 GHz, respectively. The modeling and simulations are conducted in CST MWS (2014). The simulated reflection coefficient and radiation pattern are validated in antenna measurement facility. In addition, the specific absorption rate of the antenna on a flat section of human body is also studied. The antenna is compact, low profile, and vastly suitable for multi-band wireless devices.