An air-filled substrate integrated waveguide (SIW) made of a multilayer printed circuit board process is proposed in this paper. It is of particular interest for millimeter-wave applications that generally require low cost and low-loss performance and excellent power-handling capability. This three-layered air-filled SIW allows for substantial loss reduction and power-handling capability enhancement. The top and bottom layers may make use of a low-cost standard substrate such as FR-4 on which baseband or digital circuits can be implemented so to obtain a very compact, high-performance, low-cost, and self-packaged millimeter-wave integrated system. Over Ka-band (U-band), it is shown that the air-filled SIW compared to its dielectric-filled counterparts based on Rogers substrates RT/Duroid 5880 and also 6002 reduces losses by a mean value of 0.068 dB/cm (0.098 dB/cm) and 0.104 dB/cm (0.152 dB/cm), increases average power-handling capability by 8 dB (6 dB) and 7.5 dB (5.7 dB), and quality factor by 2.7 (2.8) and 3.6 (3.8) times, respectively. The peak power-handling capability of the proposed structure is also studied. A wideband transition is presented to facilitate interconnects of the proposed air-filled SIW with dielectric-filled SIW. Design steps of this transition are detailed and its bandwidth limitation due to fabrication tolerances is theoretically examined and established. For validation purposes, a back-to-back transition operating over the Ka-band is fabricated. It achieves a return loss of better than 15 dB and an insertion loss of ${\hbox{0.6}} \pm {\hbox{0.2 dB}}$ ( ${\hbox{0.3}} \pm {\hbox{0.1}}~{\hbox{dB}}$ for the transition) from 27 to 40 GHz. Finally, two elementary circuits, namely, the T-junction and 90 $^{\circ}$ hybrid coupler based on the air-filled SIW, are also demonstrated.

Air-Filled Substrate Integrated Waveguide for Low-Loss and High Power-Handling Millimeter-Wave Substrate Integrated Circuits

In this work, a mm-Wave vertically-polarized electric dipole array solution for 5G wireless devices is presented. The dipole is fabricated using vias in a standard PCB process to fit at the phone or tablet edges featuring wideband operation with broad half-power beamwidth in the elevation plane (HPBWELEV), high gain and high front-to-back radiation ratio (F/B). For enhanced gain, parasitic-vias are added in front of the dipole as directors. To improve HPBW without sacrificing gain, the directors are implemented as V-shaped bisection parasitic-vias. A via-fence surrounds the dipole structure to suppress back radiation and enhance F/B. The dipole is connected to a parallel-strip line (PS) which is interfaced to the main SIW feed through a novel SIW-to-PS transition. Thorough investigation, optimization, and parametric study are provided for each design parameter of the proposed structure. A single dipole, $2\times 1$ , and $4\times 1$ arrays were designed and fabricated showing close agreement between the simulated and measured results. The single-dipole operates over 7.23-GHz bandwidth with stable radiation performance. The $4\times 1$ array achieves HPBWELEV of 133.1°, F/B of 36.6-dB, cross-polarization less than −39.6-dB and 12.61-dBi gain with 95.8% radiation efficiency. The low cost, compactness, and good performance of the proposed dipole make it a competing candidate for the future 5G mobile devices transceivers.

Investigation of Wideband Substrate-Integrated Vertically-Polarized Electric Dipole Antenna and Arrays for mm-Wave 5G Mobile Devices

This work introduces, for the first time, a millimeter-wave imaging system with a “synthetic” ultra-wide imaging bandwidth of 98 GHz to provide the ultra-high resolutions required for early-stage skin cancer detection. The proposed approach consists of splitting the required ultra-wide imaging bandwidth into four sub-bands, and assigning each sub-band to a separate imaging element, i.e., an antenna radiator. Each of the sub-band antennas transmits and receives signals only at its corresponding sub-band. The captured signals are then combined and processed to form the image of the target. For each sub-band, a Vivaldi tapered slot antenna fed with a combination of substrate-integrated waveguide and coplanar waveguide is designed and microfabricated. Design techniques are also provided for the four similarly-shaped sub-band antennas for achieving excellent impedance matches ( $S_{11}$ < –10 dB) and nearly constant gains of 10 dBi over the entire 12–110 GHz bandwidth. The design procedure is validated by comparing the simulated results with measurements performed on the fabricated prototypes. Excellent agreements are obtained between simulations and measurements. Finally, the feasibility of detecting early-stage skin tumors in three dimensions is experimentally verified by employing the sub-band antennas in a synthetic ultra-wideband imaging system with a bandwidth of 98 GHz. Two separate setups, each comprising a dispersive skin-mimicking phantom as well as two dispersive spherical tumors, are constructed for imaging experiments. Lateral and axial resolutions of 200 μm are confirmed, and a successful reconstruction of the spherical tumors is achieved in both cases.

Synthetic Ultra-High-Resolution Millimeter-Wave Imaging for Skin Cancer Detection

A substrate integrated waveguide (SIW) H -plane filtering horn antenna with embedded metallized via-hole arrays is proposed in this letter. The SIW H -plane filtering horn originates from a simple SIW H -plane horn with very narrow bandwidth and no frequency selectivity performance. To significantly increase bandwidth, two metal strips are printed on both sides of the substrate near the radiating aperture of the horn antenna. Critically, four rows of inductive metallized via holes are embedded into the flare region of the horn antenna, forming three coupled resonant cavities to achieve filtering function without any increase of the antenna dimension. The proposed SIW H -plane filtering horn antenna achieves good frequency selectivity, which satisfies the increasing demand of the miniaturization and integration of multifunctional devices. An optimized prototype is manufactured and measured to verify the design feasibility. The results show that the filtering performance is successfully realized with high level of integration.

Substrate Integrated Waveguide Filtering Horn Antenna Facilitated by Embedded Via-Hole Arrays

In this paper, a wideband $2 \times 2$ multilayer substrate integrated waveguide (SIW)-based cavity-backed slot array is proposed. The array element is constructed by stacking five layers of SIW cavity-backed slots and has a wide impedance bandwidth from 18 to 30 GHz. Two different feed networks based on probe coupling and slot coupling are introduced to maintain the wideband characteristic of the proposed element when employed in an array. Two $2 \times 2$ arrays fed by the proposed feed networks are designed, fabricated, and tested. The measured results show that both the arrays employing probe coupling and slot coupling feed networks have a wide impedance bandwidth over 30%. Within the obtained operation bands, good radiation performance is achieved. Moreover, advantages and disadvantages of the proposed two feed networks are discussed.

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A Wideband Multilayer Substrate Integrated Waveguide Cavity-Backed Slot Antenna Array

In this paper, a novel ultra-wideband GCPW to SIW transition is developed. The transition integrates the coupling slot and impedance transformer into one tapered coupling slot to achieve an ultra wide bandwidth. The tapered coupling slot converts the arbitrary impedance of the SIW to the GCPW port impedance. The vias were strategically located to suppress unwanted modes across the transition as well. The fabricated transition demonstrated over 10 GHz bandwidth with less than 0.4 dB insertion loss at X-band. Theoretical and experimental results are presented and compared with previously designed transitions.

Development of an ultra wide band GCPW to SIW transition

A compact antipodal Vivaldi antenna array fed by a waveguide feed network is optimized to significantly reduce feed loss and achieve a wide band performance. It is implemented using SIW technology, and has eight antipodal Vivaldi antenna elements. The feed network utilizes a novel low-loss wide band GCPW transition to get a good input match and prevent the excitation of higher order modes. The array demonstrated a broadband performance from 8 to 12 GHz, a 12 dB gain, 13° BW, and −14dB SLL at the center frequency of 10 GHz and occupies only 10cm×5.7cm.

Ultra-wide band vivaldi antenna array using low loss SIW power divider and GCPW wide band transition

Dielectric rod antennas of circular cross-sections have been numerically investigated. Various structures of finite-length rods are compared as functions of their different physical parameters, such as the rods' diameter, length, dielectric constant, multi-layer and finally the effect of corrugation. The far-field radiation pattern characteristics of these various antennas are presented as well. Results indicate that the operating bandwidth of these antennas can be extended by utilising either a core with a high dielectric constant and a cladding layer with a lower dielectric constant or equivalently a corrugated rod of the high dielectric constant material. The simulation of the various types of rod antennas have been compared with the measurement and very good agreement has been achieved.

Design guidelines for multi-layer dielectric rod antennas fed by Vivaldi antennas

Ultra wideband components have been developed using SIW technology. The various components including a GCPW transition with less than 0.4dB insertion loss are developed. In addition to, T and Y-junctions are optimized with relatively wide bandwidth of greater than 63% and 40% respectively that have less than 0.6 dB insertion loss. The developed transition was utilized to design an X-band 8 way power divider that demonstrated excellent performance over a 5 GHz bandwidth with less than ±4o and ±0.9 dB phase and amplitude imbalance, respectively. The developed SIW power divider has a low profile and is particularly suitable for circuits' integration.

R. Ali Sadeghzadeh

Papers

Development of an ultra wide band GCPW to SIW transition

Ultra-wide band vivaldi antenna array using low loss SIW power divider and GCPW wide band transition

Design guidelines for multi-layer dielectric rod antennas fed by Vivaldi antennas

A new compact wide band 8-way SIW power divider at X-band