Wideband Transition Research Articles

W-Band High-Gain TE-Mode Slot Antenna Array With Gap Waveguide Feeding Network

In this letter, a high-order-mode substrate integrated cavity (SIC) excited $2 \times 2$ -slot antenna subarray for wideband and high-gain W-band array application is presented. This antenna subarray is designed by using two low-cost double-side printed circuit broads (PCBs). The transmission loss caused by divider can be reduced by using the high-order-mode substrate integrated cavity to excite the slot antenna subarray. Furthermore, such use reduces processing difficulty and fabrication cost. The bandwidth and gain of the proposed antenna are also improved. To validate our design, an $8 \times 8$ antenna array with $4 \times 4$ SIC subarrays has been fabricated and measured. To reduce the loss further, the microstrip-based ridge gap waveguide (GWG) technology is applied to feed the SIC subarrays. Furthermore, for measurement purposes, a wideband transition structure between rectangular waveguide (RWG) and GWG is designed. Measured results show that an $8 \times 8$ slot array with the transition achieves a maximum boresight gain of 25.3 dBi and an impedance matching bandwidth of 82-102 GHz with a boresight gain above 24.5 dBi. In addition, the measured aperture efficiency is 64%.

Low-Profile Log-Periodic Monopole Array

This paper presents a low-profile log-periodic monopole array antenna with end-fire radiation and vertical polarization. It consists of 15 monopole elements and a conductor-backed coplanar strip line as the feeding line. The monopoles are of the same height but loaded with top hats of different sizes to achieve the required resonant frequencies. A wideband transition from coaxial line to conductor-backed coplanar strip line is designed for the antenna feed. A prototype is fabricated and tested. Measured results show that an impedance bandwidth from 1.5 to 6.8 GHz (4.53:1) for $\text{VSWR { and a gain better than 4.5 dBi over the same operating frequency band are obtained while the antenna has a very low profile of only $0.047\;\lambda_L$ ( ${{{\lambda}}_L}$ is the free-space wavelength at the lowest operating frequency).

Wideband Excitation Technology of <formula formulatype="inline"><tex Notation="TeX">${\rm TE}_{20}$</tex></formula> Mode Substrate Integrated Waveguide (SIW) and Its Applications

The higher order mode substrate integrated waveguide (SIW) has advantages in the applications, which are: 1) simplifying the structure with reduced fabrication cost and 2) enhancing the stability of performance by relaxed fabrication tolerance. In this paper, two wideband ${\rm TE}_{20}$ mode excitation structures are presented and investigated for the SIW. A slot along the mid line in the longitudinal direction of the SIW is employed to convert the electromagnetic field pattern between slotline and the ${\rm TE}_{20}$ mode SIW. The second structure is based on the slot aperture coupling and can realize wideband direct transition between the ${\rm TE}_{20}$ mode SIW and microstrip line. Both transitions have a simple and compact structure, as well as broadband characteristics. The wideband transition performance is demonstrated in this paper. As application examples of the transitions, two broadband substrate integrated baluns are presented and fabricated based on the ${\rm TE}_{20}$ mode excitation structures and ${\rm TE}_{20}$ mode characteristics. The 180 $^{\circ}$ out-of-phase and equal magnitude of the balun outputs in a wide frequency range can be achieved inherently. The balun based on the slotline excitation has a fractional bandwidth of 50.2%, from 7.3 to 12.2 GHz, with measured return loss, amplitude imbalance, and phase imbalance better than 10 and 0.45 dB and 3.8 $^{\circ}$ . The balun based on the aperture coupling excitation shows a fractional bandwidth of 50.3%, from 7 to 11.7 GHz, with measured return loss, insertion loss, amplitude imbalance, and phase imbalance better than 10, 1, and 0.27 dB and 2.4 $^{\circ}$ , respectively. Both baluns not only show good performance, but also demonstrate the existence of the ${\rm TE}_{20}$ mode in the SIW.

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

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 0.6 ±0.2 dB ( 0.3 ±0.1 dB for the transition) from 27 to 40 GHz. Finally, two elementary circuits, namely, the T-junction and 90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> hybrid coupler based on the air-filled SIW, are also demonstrated.

New Wideband Transition From Microstrip Line to Substrate Integrated Waveguide

A new wideband transition from microstrip line to substrate integrated waveguide (SIW) is introduced. Unlike most transitions that show reduced return loss over significant parts of a regular waveguide band, the presented configuration achieves return losses better than 30 dB in standard waveguide frequency bands from X to E. The new aspect of this transition is the addition of two vias to the widely used microstrip taper transition. Moreover, the influence of the substrate height is demonstrated. The results in each frequency band are compared with the data for the regular microstrip taper alone. A design formula for the placement of the vias and taper dimensions is presented and demonstrated to provide excellent results. The structures are simulated and optimized with CST Microwave Studio. Measurements performed on a Ku-band back-to-back prototype transition demonstrate a minimum return loss of 26.05 dB and maximum insertion loss of 0.821 dB over the entire Ku-band, thus validating the design approach.

A Ultra Wideband Low Loss CBCPW-to-Microstrip Transition With Multiple Via Holes

A wideband (0 to 26.5 GHz) transition from conductor backed coplanar waveguide (CBCPW) to microstrip line has been developed. Field and impedance transformation have been used in the design; also, via holes were placed on the side ground planes of the CBCPW to suppress the parallel plate resonant mode thereby reducing radiation loss. A back-to-back transition board has been fabricated and tested. The test result shows good agreement with simulation. Under test, the back-to-back design insertion loss is less than 2 dB and the return loss is less than 15 dB from 0 to 26.5 GHz.

A Semi-Analytical Solution of a Tapered Half-Mode Substrate-Integrated Waveguide With Application to Rapid Antenna Optimization

A semi-analytical solution for the input reflections, inner field distribution and radiated fields for a wideband traveling-wave antenna based on a tapered half-mode substrate-integrated waveguide (HMSIW) is proposed in this paper. The analysis validates the operation mechanism for this type of traveling-wave antenna which exhibits omni-directional radiation properties with horizontal polarization (“magnetic dipole”). The derived expressions allows the design and efficient optimization of different antennas towards fulfilling various predefined specifications of reflection coefficient and operating bandwidth. The antenna utilizes a wideband transition from coaxial cable to a HMSIW, which is also considered in the model to provide highly accurate semi-analytical results. Utilizing the proposed method, three antennas of different specifications have been optimized, manufactured and tested. The analysis, simulation and measurement results show good correspondences, which verifies the design process and demonstrates the versatility of the concept.

Novel Empty Substrate Integrated Waveguide for High-Performance Microwave Integrated Circuits

Over the last years, a great number of substrate integrated circuits has been developed. These new circuits are a compromise between the advantages of classical waveguide technologies, such as high quality factor and low losses, and the advantages of planar circuits, such as low cost and easy compact integration. Although their quality factor and losses are better than for planar circuits, these characteristics are worse than in the case of waveguides, mainly due to the presence of the dielectric substrate. In order to improve the performance of the integrated circuits, a new methodology for manufacturing empty waveguides, without a dielectric substrate, but at the same time completely integrated in a planar substrate, is proposed in this work. A wideband transition with return losses greater than 20 dB in the whole bandwith of the waveguide allows the integration of the empty waveguide into the planar substrate so that the waveguide can be directly accessed with a microstrip line. Therefore, a microwave circuit integrated in a planar substrate, but at the same time with a very high quality factor (measured quality factor is 4.5 times higher than for the same filter in the substrate integrated waveguide), and very low losses is successfully achieved.

A W-Band Low-Loss and Wideband LTCC Transition From Waveguide to Microstrip

A broadband transition structure from rectangular waveguide (RWG) to microstrip line (MSL) is presented for the realization of the low-loss packaging module using Low-temperature co-fired ceramic (LTCC) technology at W-band. In this transition, a cavity structure is buried in LTCC layers, which provides the wide bandwidth, and a laminated waveguide (LWG) transition is designed, which provides the low-loss performance, as it reduces the radiation loss of conventional direct transition between RWG and MSL. The design procedure is also given. The measured results show that the insertion loss of better than 0.7 dB from 86 to 97 GHz can be achieved.

Millimeter-Wave Broadband Transition of Substrate Integrated Waveguide on High-to-Low Dielectric Constant Substrates

For emerging millimeter-wave wireless applications at W- and E-bands, active components including LNA and power amplifier are preferably fabricated or surface-mounted on the materials of a high dielectric constant (such as CMOS and MHMIC). On the other hand, antennas or radiating elements should be developed on relatively low-dielectric constant substrates for the enhancement of gain and bandwidth. Therefore, the development of a wideband transition from high-to-low dielectric constant substrates becomes necessary because the use of wire bonding schemes brings up packaging, interconnects, and manufacturing problems at millimeter-wave frequencies. This paper presents a novel integrated wideband transition of substrate integrated waveguide (SIW) on high-to-low dielectric constant substrates. The transition is made of a single-layer structure, which consists of a tapered high-dielectric constant substrate that connects two SIWs. Because of the waveguide-based structure of the transition, it has a self-shielded configuration, and its interference is minimum. Simulated and measured results show that the bandwidth of the proposed transition covers almost the entire W- and E-bands with low insertion loss.

A Novel Wideband Transition between Waveguide and SIW

Based on a linearly tapered antipodal finline, a novel low-loss wideband transition between waveguide and substrate integrated waveguide (SIW) is discussed. Results show that a low insertion loss (1.2-2.1dB) and a return loss better than 15dB across the entire Ka-band are obtained for a back-to-back transition structure.

A novel compact microstrip lowpass filter with wide rejection band and sharp transition band using diamond-shaped resonator

In this paper, a novel compact microstrip lowpass filter (LPF) using diamond-shaped resonator with wide rejection and sharp transition band is presented. The proposed filter has −3 dB cut off frequency at 2.6 GHz. The maximum insertion loss is only 0.1 dB in the passband and the rejection band extends from 2.89 to 20.84 GHz with the attenuation level better than −21 dB. The transition band is only 0.288 GHz, from 2.606 to 2.894 GHz with corresponding attenuation levels of −3 and −20 dB, respectively. The filter size is 12.4 × 11.5 mm2. The proposed filter is fabricated and tested, where the measurement results are in good agreement with the simulation results. The proposed LPF has compact size, simple structure, wide rejection band, and low insertion loss, where all of these characteristics are essential for LPF in the modern communication circuits.

Design and study of enhanced wideband transition between coplanar waveguide and broadside coupled stripline

Enhanced wideband transition between coplanar waveguide (CPW) and broadside coupled stripline (BCS) with arbitrary characteristic impedance ratio is developed on a basis of an improved tightly coupling, via-hole-free structure. The E-field of CPW gradually changes to that of BCS within a wide bandwidth with ratio up to 10.4:1. Parametric studies of the transition are carried out and four different back-to-back prototypes are simulated, fabricated and measured. It is shown that maximum operation bandwidth from 1.16 to 12.01 GHz for return loss higher than 10 dB and average insertion loss of 1.41 dB can be obtained.

A Series Slot Array Antenna for 45$^{\circ}$-Inclined Linear Polarization With SIW Technology

The design method for a standing-wave series slot array antenna with 45°-inclined linear polarization in the Ka-band is presented. The proposed 16 × 8 planar slot array antenna consisted of arrays with alternating reactance slot pairs that could achieve impedance matching and uniform field ex- citation, simultaneously. Furthermore, the grating lobes were effectively suppressed with the help of these radiating units due to the one-half guided wavelength slot spacing. An equivalent circuit analysis was done to evaluate the input impedances of the radiating and feeding lines with the impedance recursive formulas as well as the mode voltages of the radiating slot elements. In addition, a wideband transition with a 30.13% bandwidth under the criteria of less than VSWR 1.5:1 was presented to provide the necessary power with the minimal reflection and to prevent the distortion of the radiation patterns. The proposed planar slot array antenna occupied an aperture area of 57.4× 51.6 mm. The measured bandwidth, gain, and efficiency were 990 MHz (2.88%), 24.3 dBi, and 53.7%, respectively. Furthermore, the side lobe levels (SLLs) were verified for each cutting plane with -13.57 dB and -13.17 dB, respectively. The proposed antenna structure was achieved with a substrate integrated waveguide (SIW) with the low costs and lightweight features.

Wide band via-less transition from FG-CBCPW to microstrip

A novel wideband transition from finite ground-conductor backed-CPW (FG-CB-CPW) to microstrip has been demonstrated in 8–23 GHz band. Proposed transition provides a very low-loss alterative to microstrip/coplanar lines at higher frequencies. Simulated results are detailed for both alumina and silicon substrates. Simulated results are validated on alumina substrate providing more than 100% bandwidth with maximum insertion loss of around 1.5 dB in the targeted frequency range. Comparison of the results along with design procedures is detailed in this article.

Wideband coplanar waveguide to edges-even broadside-coupled stripline transition

A wideband transition between a coplanar waveguide (CPW) and an edges-even broadside-coupled stripline (EEBCS) is proposed. The simple transition is composed of a linear tapered line on the top layer and an electromagnetically-coupled Y-shaped stub on the bottom layer. A back-to-back, 50 Ω CPW to 100 Ω EEBCS transition is simulated, fabricated and measured. It is reported that a maximum insertion loss of 2.4 dB, a return loss better than −10 dB and average group delay of about 0.5 ns are obtained from 1.1 to 11.2 GHz for the transition.

Design of Millimeter Wave Wideband Transition From Double-ridge Waveguide to Coaxial Line

In this paper, an improved design method of millimeter wave wideband transition from double-ridge waveguide to coaxial line is introduced. The proposed design is based on the mode conversion theories and impedance matching techniques. The characteristics of the transition in microwave frequencies are analyzed and simulated by full-wave analysis software. According to the simulated results, a couple of transitions are fabricated. The predicted superduper performances have been confirmed experimentally in a wide frequency range of 18 ~ 40 GHz.

Wideband coplanar stripline to double-sided parallel-strip line transition

A novel wideband transition between the coplanar stripline and the double-sided parallel-strip line is presented. The simple transition consists of two tapered lines, one located on the top layer and one tapered line on the bottom layer. Through the proposed transition, horizontally distributed electric fields of the coplanar stripline become rotated by 90° to match the vertically distributed fields of the double-sided parallel-strip line. Simulated and measured results of a back-to-back transition show good agreement.

DEVELOPMENT OF A NOVEL UWB VIVALDI ANTENNA ARRAY USING SIW TECHNOLOGY

A compact Vivaldi antenna array printed on thick substrate and fed by a Substrate Integrated Waveguides (SIW) structure has been developed. The antenna array utilizes a compact SIW binary divider to significantly minimize the feed structure insertion losses. The low-loss SIW binary divider has a common novel Grounded Coplanar Waveguide (GCPW) feed to provide a wideband transition to the SIW and to sustain a good input match while preventing higher order modes excitation. The antenna array was designed, fabricated, and thoroughly investigated. Detailed simulations of the antenna and its feed, in addition to its relevant measurements, will be presented in this paper.

Method for widening the reject-band in low-pass/band-pass filters by employing coupled C-shaped defected ground structure

Two new compact defected ground structure low-pass filters with broad stop-band and low insertion loss in the pass band are presented. The structures of these new microstrip low-pass filters are simple as they are composed of a pair of DGS-slots and an openstub. One filter is realised through the multi-layer method, and the second filter by cascading. With these configurations, two LPF with compact size, wide reject band and sharp transition from pass to stop-band are realised. The design formulas are derived by using an equivalent circuit model of coupled DGS resonators. Demonstration filters are designed, fabricated and tested. The experimental results show good agreement with theoretical results and demonstrate that the required characteristics of LPF could be simply obtained through the proposed methods. Finally a simple gap-method will be used in order to transform the LPF to BPF.