Substrate Integrated Suspended Line Research Articles

A sequentially rotated feeding circularly polarized stacked patch antenna array based on SISL

AbstractA sequentially rotated feeding circularly polarized stacked patch antenna and its array based on substrate integrated suspended line (SISL) are presented. The resonant frequencies of 5.05 and 5.35 GHz are obtained by using the cross slot on the driven patch, which can also realize circular polarization. The windmill stacked patch is introduced to generate another resonant frequency of 5.85 GHz and expand 3‐dB axial ratio (AR) bandwidth (BW). The measured 10‐dB impedance BW of 18.2% (4.98–5.98 GHz) and the 3‐dB AR BW of 3.6% (5.45–5.65 GHz) are obtained from the proposed antenna element. The measured peak gain is 9.0 dBi. A sequentially rotated feeding is used to excite the proposed 2 × 2 antenna array. The measured peak gain is 13.31 dBi. The measured 10‐dB impedance BW is 28.3% (4.80–6.38 GHz) and the 3‐dB AR BW is 8.9% (5.35–5.85 GHz).

FR‐4‐based Ka‐band SISL bandpass filters using folded half‐wavelength resonators

AbstractIn this letter, bandpass filters (BPFs) with folded short‐circuited half‐wavelength (λ/2) resonators are proposed based on the substrate integrated suspended line (SISL) platform for satellite communications. Each λ/2 resonator is folded, to achieve an overlapping structure, which not only reduces the size, but more importantly, reduces the loss. In addition, air cavity, metal shielding wall, and substrate excavation method also dramatically reduce the loss in substrates. Note that professional material term (FR‐4) material is chosen for the design, therefore, it is low‐cost and more suitable for production application. Finally, a second‐order and a fourth‐order combline BPFs are fabricated and measured to verify the design method. The insertion loss of the second‐order and the fourth‐order filters are only 0.78 and 1.19 dB at the center frequency of 29.2 GHz, respectively. The presented SISL filters using FR‐4 material demonstrate the advantages of low‐loss, low‐cost, and self‐packaging.

An SISL-Based 24-GHz FMCW Radar With Self-Packaged Six-Port Butler Matrix Receiver

A 24-GHz frequency modulated continuous wave (FMCW) radar system with self-packaged six-port Butler matrix receiver using substrate integrated suspended line (SISL) platform is proposed in this article. Since all active and passive components are integrated on the SISL platform using the standard printed circuit board (PCB) process, the proposed system is highly integrated with low cost. The system is composed of a transmitting (TX) antenna, a Butler matrix with a receiving (RX) antenna array, a single pole four throw (SP4T) switch, a low noise amplifier (LNA), and a six-port receiver. The Butler matrix and SP4T switch are implemented for beam scanning, which has the advantages of low loss and compact size. The SISL-based six-port receiver is designed for quadrature downconversion. The supporting digital signal processing algorithms are also proposed for the calculation and display of multiple targets information. The radar system has shown excellent performance in the measurement of indoor environment, including range, velocity, and direction of arrival (DOA). The proposed radar provides a new solution for a transceiver system.

A Low-Cost High-Gain Filtering Patch Antenna With Enhanced Frequency Selectivity Based on SISL for 5G Application

This letter presents a high-gain filtering antenna with multiple radiation nulls and enhanced frequency selectivity using substrate integrated suspended line (SISL) technology. The presented antenna is composed of driven patches with slots, parasitic units, stubs, and stacked patches. The first radiation null is caused simultaneously at the upper band edge when the stacked patches are introduced to produce a resonance mode. The second radiation null is produced by the slots on the driven patches at the lower band edge. Due to the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> mode of the driven patches, the third radiation null is introduced at higher frequency. Owing to the stubs and parasitic units, the fourth radiation null is caused at lower frequency. The above four radiation nulls achieve excellent filtering performance with high selectivity. The measured results indicate the outstanding performance of the filtering antenna. The passband is from 3.28 to 3.79 GHz, perfectly covering the 5G-N78 band. The peak gain reaches 11.14 dBi, and the out-of-band rejection level is 17.8 dB. In addition, this filtering patch antenna is designed based on low-cost substrate FR4.

A tunable reflection‐type filtering phase shifter using SISL technology

This letter proposed a novel tunable reflection-type phase shifter (RTPS) with a filtering function using substrate-integrated suspended line (SISL) technology. First, a novel 3-dB branch-line coupler with a filtering function is designed by using broadside coupling lines. On this basis, the filtering RTPS is realized by combining with a series varactor network. The proposed SISL filtering RTPS can obtain a continuous phase shift range of 104° under 0–30 V DC bias control, which enables multifunctional integration of phase shifters. All circuits are implemented on the SISL platform, which has the advantages of double-sided wiring, self-packaging, and low loss.

A 77-GHz Low-Conversion-Loss Fourth-Harmonic Mixer on SISL Platform

This letter presents a 77-GHz low-conversion-loss (CL) fourth-harmonic mixer based on the substrate-integrated suspended line (SISL) platform. Based on the traditional stub-type harmonic mixing structure, we add several additional transmission lines, which will participate in the impedance matching of the diode together with stubs to reduce the CL. A 3-D electromagnetic (EM) diode model is established for accurate simulation at millimeter-wave frequency. The presented SISL mixer was fabricated by the low-cost printed circuit board (PCB) process and was self-packaged in FR4 substrates. When the local oscillator (LO) frequency is 19.45 GHz and the radio frequency (RF) is 78 GHz, the minimum CL is 12.2 dB under an LO input power of 12 dBm. This mixer is suitable for 77-GHz automotive anti-collision radar systems.

Design of Miniaturized 5G SISL BPFs With Wide Stopband Using Differential Drive Inductor Resonators

In this article, the differential inductor, widely used as an inductive element, is modified as a resonator. This differential drive inductor resonator (DDIR) can achieve miniature size and extension of second-order mode based on the different electric field distributions on different modes. The second- and fourth-order bandpass filters (BPFs) are designed and fabricated with DDIRs at the promising 5G frequency band of 700-MHz spectrum. The low-loss platform substrate integrated suspended line (SISL) is adopted. The filters are centered at 0.76 GHz/ 0.77 GHz. The footprint areas are only 0.0023 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.0052\lambda g^{2}$ </tex-math></inline-formula> without using any lumped elements or substrate with high permittivity. The second-order mode is 5.7/3.92 times the working band without introducing any extra method to broaden the stopband. To improve the rejection of stopband, a T-shaped coupling structure is first proposed on SISL to get the desired location of zeros by weakening the electric coupling and enhancing the magnetic coupling. The comparable version of second- and fourth-order BPFs with T-shaped coupling structure are designed and fabricated. The 20-dB roll-off rate has been decreased by 58.8% and 66.1%.

Bandwidth improvement of patch antenna and array with out‐of‐band rejection based on SISL platform for 5G applications

AbstractA low‐profile patch antenna is designed for bandwidth enhancement based on a substrate‐integrated suspended line (SISL) platform using low‐cost FR‐4 substrates. Two identical slots are cut at the patch edges for antenna miniaturization and controlling the first resonance. To achieve the bandwidth enhancement and ensure the uniformity of radiation patterns of the proposed design, two pairs of symmetrical slots are etched out on a rectangular patch. Thus, the second resonance is introduced, leading to significant bandwidth enhancement from 5% to 10%. Besides, two radiation nulls are generated. Based on the proposed design above, the antenna array comprising two identical radiating elements for gain enhancement and out‐of‐band rejection improvement is proposed, which provides another method for further improving the filtering response. The antenna element operates from 4.69 to 5.17 GHz with a measured gain of 8.9 dBi at the broadside direction, while the array achieves a high gain of 11.3 dBi.

Channel-Continuous Triplexer With Multiple Transmission Zeros Based on Cascaded High-Pass and Low-Pass Filters

A channel-continuous triplexer (CCT) with multiple transmission zeros (TZs) is designed and processed by cascading the high-pass filter (HPF) and low-pass filter (LPF) through the matching branches. The CCT is realized based on the substrate integrated suspended line (SISL) technology. The out-of-band suppression (OBS) and roll-off rate (ROR) of CCT are improved by the TZs introduced by cross-coupling lines between the nonadjacent branches in the HPFs and high-low impedance microstrip line T junction in LPFs. The experimental results show that CCT covers 4&#x2013;7 GHz by three continuous bandwidth-identical passbands with the fractional bandwidths (FBWs) of 22.2&#x0025;, 18.1&#x0025;, and 15.3&#x0025;, respectively. The insertion loss within three passbands is less than 1.7 dB, the out-of-band rejection is more than 50 dB, and the ROR is greater than 200 dB/GHz.

A Cavity-Backed Antenna Using SISL Technology for 77 GHz Band Application

A cavity-backed antenna based on substrate-integrated suspended line (SISL) technology is proposed for 77 GHz applications. The antenna is designed to be self-packaged using six substrate layers with embedded air cavities. Two rows of metal holes surround the core circuit to form the cavity and reduce the leaked field loss. Patches are printed in G5 and G6 layer and connected by metalized holes to form the double-side SISL with part of the substrate excavation to reduce the substrate loss. Thus, the simulation efficiency of better than 93% is achieved. Because of the cavity structure, the standing wave resonant mode can be obtained and achieve broadside radiation. A predominantly TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">710</sub> aperture field is obtained by adjusting the sizes of the backing cavity. The measured result shows that the proposed antenna has a −10 dB bandwidth from 75.6 to 81 GHz, covering 77 GHz automotive radar band and the max gain is 14.4 dBi. Based on this antenna, we design a differential-fed antenna array with a max gain of 17.5 dBi at 79 GHz.

A W‐Band Broadband Self‐Packaged Compact SISL Tripler using FR4 substrate

AbstractA W‐band low‐cost and high output power tripler based on a substrate integrated suspended line (SISL) platform is presented in this paper. An accurate three‐dimensional electromagnetic model is established to characterize the high‐frequency parasitic effect of diodes, and the field‐circuit cosimulation method is employed to design the tripler. A SISL‐WR10 transition is designed and added in the output port to facilitate the test, and it also functions as a W‐band bandpass filter (BPF) to output the third harmonic, which avoids insertion loss caused by an additional BPF and makes the tripler more compact. The whole circuit of the tripler is fabricated on FR4 substrates, and it is self packaged. The measured results show that with 22 dBm input power, the tripler achieves 0–4.46 dBm output power from 75 to 106 GHz.

An FR4-Based Self-Packaged Full Ka-Band Low-Loss 1:4 Power Divider Using SISL to Air-Filled SIW T-Junction

An FR4-based full <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -band 1:4 passive power divider using substrate integrated suspended line (SISL) technology is presented in this letter and it achieves a relatively low insertion loss. A SISL to air-filled substrate integrated waveguide (SIW) T-junction with an iris structure is proposed as the first stage of the divider to obtain wideband matching, and a bandwidth of 61.7% is achieved. The power-handling capability of the power divider is studied. A back-to-back 1:4 power divider was fabricated, and the measured results agree well with the simulated ones. From 25.2 to 40 GHz, i.e., a 45.5% fractional bandwidth, the measured return loss is better than 15 dB, and the measured insertion loss is less than 1.2 dB. Moreover, the isolation performance is improved from 2.5 to 15 dB by adding three ports connected with the load resistor.

A Low-Cost Dual-Band Multimode High-Gain Stacked-Patch Antenna Based on SISL for 5G Applications

A dual-band multimode high-gain stacked-patch antenna based on substrate integrated suspended line (SISL) is proposed for 5G applications. The proposed antenna comprises five low-cost FR4 dielectric substrate layers and ten metal layers with embedded air cavities. The driven patch generates TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> mode, and the other two modes are generated by etching the U-slot and horizontal slot on the driven patch to achieve dual-band. The stacked patch with the U-slot can suppress the radiation pattern split of TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> mode, improve the antenna gain in the high-frequency band, and generate radiation null to increase the out-of-band gain-suppression level. To verify this principle, the antenna is fabricated and measured. The measured results show good agreement with the simulated ones and the proposed antenna operates at 3.21–3.66 and 4.75–5.40 GHz, which can cover the 5G communication band. The antenna has high efficiency. The maximum gains in the two bands are 9.12 and 8.65 dBi, respectively.

FR4-Based Low Phase Noise SISL VCO Using Tunable Weakly Coupled Resonators

In this letter, a voltage-controlled oscillator (VCO) with low cost, wide-tuning range, and low phase noise is proposed based on substrate integrated suspended line (SISL) technology. Benefiting from the weak coupling between half-wavelength resonators, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> value can be improved, so as to reduce the phase noise of the VCO. By introducing a varactor in the high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> resonator, a wide-tuning range is achieved. All the used boards choose FR4 material with very low cost. The designed SISL VCO has a tuning range of 380 MHz and has a phase noise of −122.81 dBc/Hz at a 1-MHz offset relative to the 5.88-GHz carrier. Compared with the existing board-level VCOs, this design features a wide-tuning range and low phase noise based on a low-cost platform.

A Dual-Band and Dual-State Doherty Power Amplifier Using Metal-Integrated and Substrate-Integrated Suspended Line Technology

In this article, a novel design method of dual-band and dual-state (DBDS) Doherty power amplifier (DPA) is proposed. Considering the actual parasitic parameters, the DPA can be designed by using the impedance transformation of saturation and back-off points at dual frequency bands of DBDS as well as second harmonic matching. The DBDS DPA for dual-band (DB) 5G application, i.e., 3.4 and 4.9 GHz band are designed and implemented, for the first time, by using metal-integrated and substrate-integrated suspended line (MI-SISL) technology, which has advantages of high performance and self-packaging. The fabricated DBDS DPA achieves the measured 44 and 43.2 dBm saturated power at 3.4 and 4.9 GHz bands, respectively. For the 3.4 and 4.9 GHz bands, the measured drain efficiency (DE) is 70.7% and 70.4% at peak power levels and 38% and 42% at a 6-dB output back-off, respectively. When driven by a 20- and 100-MHz modulated signal with 6-dB peak-to-average power ratio (PAPR), the adjacent channel leakage ratio is better than −27 dBc at operating frequencies. The average output power of 38 and 37 dBm with an average efficiency of 37.9% and 40.9% is achieved at 3.4 and 4.9 GHz, respectively.

A Low-Cost Differentially Fed Dual-Mode Filtering MIMO Antenna With Enhanced Isolation Based on SISL Platform

A low-cost differentially-fed dual-mode multiple-input- multiple-output (MIMO) antenna is proposed for enhanced isolation and filtering response based on the substrate-integrated suspended line (SISL) platform. Stacked patches are placed above the driven patches to realize dual-mode performance and filtering response in the upper band. The stacked patches are widened and notched to enhance the isolation and the filtering response in the lower band. Eight metal stripes are set at both sides of the feed lines to enhance the frequency selectivity further. Compared with the conventional MIMO antenna based on patch elements, the isolation is enhanced by 7.6 dB, and the out-of-band suppression with 17.6 dB is achieved. To verify the design, a prototype is fabricated and measured. In a operating band of 4.8-4.96 GHz, maximum gain of 8.3 dBi, and isolation of 31.3 dB are realized. The filtering response is achieved by three broadside radiation nulls at 4.36 GHz, 4.62 GHz, and 5.08 GHz.

Study of effective permittivity and loss reduction of SISL using ring resonator

AbstractA ring resonator used to study the effective permittivity and the loss of substrate integrated suspended line (SISL) is presented in this article. The effective permittivity is obtained by calculating resonant frequency and the relative value of loss is calculated by comparing unloaded quality factor (Q factor). For the four cases of uniform ring resonators, their S‐parameter, effective permittivity, unloaded Q factors are simulated, measured and investigated. The effect caused by the height of air cavity, the material of dielectric substrate, dielectric loss tangent is also investigated. Finally, the calculated results indicate that the effective permittivity of SISL structure at operating frequency is very closed to 1, which manifests that within a certain substrate‐material range the relative permittivity of substrate has little influence on SISL platform that is instructive for SISL circuits design. And the use of metalized via‐hole connection with dielectric removal can reduce the circuit loss dramatically.

Dual‐mode wideband slotted patch antenna using characteristic mode analysis and low‐cost SISL technology

AbstractA dual‐mode wideband slotted patch antenna using characteristic mode analysis (CMA) on substrate integrated suspended line (SISL) platform is presented. The proposed antenna combines the fundamental mode (TM01) and a higher‐order mode (TM21) of a rectangular patch to enhance antenna bandwidth. First, detailed studies into the modal significance, far‐field pattern, and current distribution on the potential radiating patch with the assistance of the CMA. The split radiation pattern of the TM21 mode is reshaped into a single directive pattern through slot‐loading techniques on the rectangular patch. The TM21 shifts close to the fundamental mode with similar polarization currents at the short‐edge length of the patch. Full‐wave simulations are performed to verify the CMA report by exciting the TM01 and TM21 modes. The proposed antenna is fabricated and tested. The experimental results agree well with the simulations and show a −10 dB bandwidth of 3.30–3.65 GHz. An average gain and efficiency of more than 7.0 dBi and 86% are accomplished in measurement over the operation band of the ongoing 5G communication. Besides, the antenna exhibits a compact size, low cost, and self‐package characteristics.

A substrate integrated suspended line gain‐enhanced patch antenna with high‐order mode suppression by feeding structure design using characteristic mode analysis

AbstractA substrate integrated suspended line (SISL) gain‐enhanced patch antenna is proposed. Enhanced gain is obtained by a long patch. To suppress the high‐order mode in the anticipated band, a feeding structure is designed with the assistance of characteristic mode analysis. The proposed SISL antenna with the proposed feeding structure suppresses higher‐order modes, achieves good impedance matching and stable broadside gain across the operating frequency band. The antenna has the potential to satisfy wireless local area network (WLAN) application. Measured results show that the 10‐dB impedance bandwidth for the proposed antenna is 18.6% from 4.93 to 5.94 GHz with an average gain of 8.34 dBi. The measured results show great agreement with simulated results.

Design of novel compact SISL filters with multiple TZs based on patch resonators

AbstractThis letter presents two compact filters using patch resonators based on the substrate integrated suspended line (SISL) technology platform. First, a bandpass filter (BPF) with multiple coupling schemes is designed by using a shorted‐stub‐loaded patch resonator. Two shorted stepped‐impedance resonators are working together to form the third‐order BPF. A 98.18% size reduction is achieved, and five transmission zeros (TZs) are produced by introduced mixed electric and magnetic coupling, cross‐coupling, and source to load coupling. Then, the SISL dual‐band bandpass filter (DBBPF) with six TZs is designed by using an improved slotted patch resonator. By adopting the patterned suspended substrate structure, the implemented DBBPF, featured with self‐packaging, achieves a fractional bandwidth of 52% and 10%, centered at 0.95 and 3.25 GHz with insertion losses of 0.57 and 2.89 dB, respectively.