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A 3-dB rectangular-junction directional coupler is designed using integrated substrate gap waveguide (ISGW) technology. The coupler uses the odd mode and even mode of Q-TEM to phase difference of 90°. The proposed coupler has a coupling ratio of $3.8\pm 0.5\text{dB}$ , a phase deviation within 2.5° around 90°, above 20dB isolation and return loss from 27.8GHz to 33.2GHz centered at 30GHz.

In order to achieve ultrahigh data capacity and to overcome the wireless spectrum crunch, 5G is going to adopt millimeter-wave (mmW) frequencies (30 GHz - 300 GHz). To generate high-quality mm W signals by lasers, it requires optical sources with ultra-narrow optical linewidth and low relative intensity noise (RIN). In this paper, we have developed InAs/InP quantum dot (QD) multi-wavelength lasers (MWLs) around 1550 nm with the frequency spacing from 10 GHz to 1000 GHz. Those QD MWLs have very low RIN, ultra-narrow optical linewidth, small timing jitters, compact size, low power consumption and the ability for hybrid integration with silicon substrates. As an example, we present a buried heterostructure (BH) QD dual-wavelength (DW) DFB laser as an optical beat source for mmW generation. The BH QD DW-DFB laser with the optical linewidth of 16 KHz and the RIN of -158 dB/Hz is capable of generating spectrally pure mm W signals between 46 GHz and 48 GHz. By using it, we have demonstrated a real time 24-Gbit/s (64QAM x 4Gbaud) data bandwidth wireless transmission operating at 47.2-GHz carrier over 25-km SSMF., 2021 Photonics North (PN), May 31 - June 2, 2021, Toronto, ON, Canada

This paper presents a real-time demonstration of all-optical broadband photonic wireless downlink and uplink transmissions at the K-band with data rates of 16-Gb/s and 4 to 12-Gb/s, respectively. The experimental configuration is comprised of optical fiber and RF wireless channel with a successful transmission and detection of 4 GHz 16-quadrature amplitude modulated (QAM) wireless signals at 25 GHz over 2-m of wireless distance in the downlink using photonic heterodyning of a low noise monolithic quantum dash (QD) passively mode-locked laser (MLL), whereas in the uplink, a single wavelength laser is employed together with an optical intensity modulator to transmit 4/16/64-QAM signals with 2 GHz bandwidth. For both downlink and uplink, error vector magnitude (EVM) of lower than the standard requirements of 17.5%, 12.5% and 8% is achieved for 4, 16, and 64-QAM signals, respectively., 2021 Photonics North (PN), May 31 - June 2, 2021, Toronto, ON, Canada

In this paper, based on the integrated substrate gap waveguide (ISGW), an ultra-wideband power divider using multilayer slot coupling technology is designed for 5G and satellite radar applications. The power divider used the ISGW which is composed of a via layer and a gap layer and transmitted energy from a coupling patch on transmission ridge of bottom layer through coupling slot to coupling patch on transmission ridge of top layer. This design has good isolation after adding the isolation resistor to a modified position. The simulated results show that return loss of the power divider is less than 10-dB, which the bandwidth can reach at least 15.7 GHz from 20.2GHz to 35.9 GHz. Also, the best insertion loss in a band is 3.53dB. The isolation degree is always better than 15-dB in 22.2GHz-35.4GHz.

This paper proposes a wide stopband filter based on integrated substrate gap waveguide (ISGW) technology. The ISGW wide stopband filter structure is composed of three-layer dielectric substrates. The top substrate uses metallic via-holes and metallic patches to achieve a perfect magnetic conductor (PMC) structure. It is suitable for package substrates and integrated waveguide (SIW) filters. The middle layer substrate provides a stable gap layer, and the base substrate is used to obtain the SIW filter by etching the dumbbell slot in the mental plane, i.e. the self-packaged ISGW filter. The center frequency of the filter is 10.9GHz, and the simulation results show that the return loss in the passband is better than 25dB, and the out-of-band rejection in the 12.2 GHz – 19 GHz frequency band is better than 40dB, achieving a wider stopband.

This paper proposes a new broadband circularly polarized (CP) antenna for 5G millimeter waves based on the integrated substrate gap waveguide (ISGW). The broadband circularly polarized antenna etches a rectangular slot on the PEC on the upper surface of the ISGW, and then adds two rectangular perturbation patches of different shapes on the rectangular slot, thereby realizing circularly polarized wave radiation. To expand the 10dB return loss bandwidth and axial ratio bandwidth of the slot circular polarization antenna based on the substrate integrated gap waveguide, a new dielectric plate is added above the ISGW, and a cross-shaped patch is added above the dielectric plate. This cross-shaped patch not only functions as a parasitic patch but also circularly polarized radiation, thereby achieving the purpose of expanding the 10dB return loss bandwidth and axial ratio bandwidth of the circularly polarized antenna.

This paper presents a novel circularly polarized (CP) filtering antenna based on integrated substrate gap waveguide (ISGW). Circularly polarized wave radiation is obtained by etching irregular slots on the ISGW transmission waveguide to form perturbation, and filtering is introduced by interdigital coupling line feed on the ISGW transmission line. The simulation results show that the CP filtering antenna has a center frequency of 31 GHz, and $\vert \mathrm{S}_{11}\vert dB from 25.5 to 36.4 GHz, i.e., a relative bandwidth of 35.06%. The 3-dB axial ratio (AR) bandwidth is 27.7-30.8 GHz, i.e., a relative axial ratio bandwidth of 10%. The antenna gain in the 3-dB AR bandwidth range is greater than 6.2 dBi, and the out-of-band suppression is above 14.4 dB.

Over recent years, the memory effect compensated digital pre-distortion (DPD) has been widely used for linearizing wideband radio frequency power amplifiers (RF-PAs). However, with the increase of memory depth, the DPD model becomes more accurate, but the computational complexity of the DPD is significantly increased. In this paper, an approach using the attention mechanism is proposed, which can be used for locating and eliminating the memory terms with a small contribution to the performance of the DPD model so that the complexity of the DPD model is significantly reduced. The attention mechanism is employed to obtain the weighted correlation coefficient matrix of the memory effect. And the memory terms in the DPD model will be retained only if the contributions are high, which are evaluated by ensemble averaging over each diagonal of the weighted correlation coefficient matrix. To verify the applicability of the approach, a three-carrier wideband code-division multiple access signals with a bandwidth of 15 MHz and a single carrier long-term evaluation signal with a bandwidth of 20 MHz are employed for testing two Doherty RF-PAs with an operating frequency of 460 and 1900 MHz. Moreover, the generalized memory polynomial model is used to verify the effectiveness of the proposed approach. The simulation and experimental results show that the modeling accuracy and the DPD linearization performance of the DPD model with and without the memory term reduction are all almost the same, which indicates the effectiveness of the proposed approach.

A bandpass filtering power divider (FPD) using integrated substrate gap waveguide (ISGW) technology is proposed, which has high selectivity and wide stopband. The filtering power divider includes three-layer substrates. The top layer substrate realizes a perfect magnetic conductor (PMC) using periodic plated vias and metallic patches. It is applied for packaging filter power divider composed of substrate integrated waveguide (SIW) and microstrip to avoid interference and losses induced by external radiation emission and internal radiation leakage. The middle layer substrate generates a gap layer. and the bottom layer substrate etch the slots on the metal plane and place a metal through hole in the middle of the metal layer to generate resonance and transmission zeros, and connect the microstrip to form a filter power divider circuit. The results show that FPD has multiple transmission zeros, the passband is 13.2 to 15.5 GHz, and an insertion loss of -4 dB. The return loss in the passband is less than -15 dB, and the isolation below is -16.5 dB.

This paper presents a multilayer slot-coupled bandpass filter based on integrated substrate gap waveguide (ISGW). The bandpass filter consists of two ISGW unit structures that are placed back-to-back. Source-load coupling is achieved by etching double rectangular slots on the common ground of the two ISGW unit structures that can achieve better filtering performance in addition to introduction of out-of-band transmission zeros. Simulation results show that a passband of the filter from 26.6 to 28 GHz, insertion loss of lower than 0.7 dB, and return loss of better than 20 dB. Two transmission zeros on both sides of the passband improve the frequency selectivity.

In this letter, a differentially coplanar-fed antenna using integrated substrate gap waveguide (ISGW) is proposed for millimeter-wave applications, which has high gain and low cross polarization. The antenna consists of the differential power divider and radiation patch, and the power divider is deployed to excite the differential feeding antenna. The differential power divider is designed using rectangular-shaped coupling slot to achieve a stable 180° phase imbalance and 15% fractional operating bandwidth. The differentially coplanar-fed cross-shaped patch antenna has high gain and good radiation patterns. A fractional bandwidth of about 8.3% at the center frequency of 24 GHz and a peak gain of 10 dBi are obtained.

To support the multi-gigabit/s wireless connectivity and to overcome the wireless spectrum crunch, 5G is going to adopt higher frequencies from the plentiful available spectrum in the millimeter-wave range. Photonic millimeter-wave signals generation and distribution in the optical domain is of great interest owing to their high spectral purity, low system complexity, low cost, small footprint, and long transmission distance. In this paper, we experimentally demonstrate spectrally pure photonic mm-wave signal generation and data transmission around 47.2 GHz using a novel low noises monolithic dual-wavelength semiconductor InAs/InP quantum dash (QD) DFB laser as a compact optical beat source for 5G applications., 2019 International Topical Meeting on Microwave Photonics (MWP), October 7-10, 2019, Ottawa, ON, Canada

The one-sided junction photodiode has a simple epitaxial layer structure, while maintaining the characteristics of high speed and high output power. An evanescently coupled one-sided junction waveguide photodiode is studied numerically and presented. The waveguide photodiode with 20 μm active region length leads to a responsivity of 0.435 A/W with a simulated bandwidth of 45 GHz.

We have developed a novel monolithic dual-wavelength semiconductor InAs/InP quantum-dash (QD) C-band DFB laser. A record narrow optical linewidth below 30 kHz and relative intensity noise (RIN) of less than -150 dB/Hz are experimentally demonstrated for the two optical modes stemming simultaneously from a single cavity of a free running dual-wavelength semiconductor QD laser., 2019 Photonics North (PN), May 21-23, 2019, Quebec City, QC, Canada

A multilayer slot-coupler based on integrated substrate gap waveguide (ISGW) is proposed. The proposed coupler is consisted of two ISGWs, which are broadside coupled through fish bone shape slot in the common ground. Simulation shows that the proposed coupler can have either $-3\pm 1\ \text{dB}$ tight coupling from 23.07 to 28.55 GHz or $-6\pm 1\ \text{dB}$ tight coupling from 24.48 to 30.73 GHz. Moreover, the phases between through and coupled port differ by 90°. The return loss and isolation are less than −20 dB over the operating frequency band.

To support the multi-gigabit/s wireless connectivity in the future wireless access networks, photonic millimeter-wave-over fiber (MMWoF) technologies are of great interest owing to their high bandwidth, high energy efficiency, low complexity and small footprint. In this paper, we experimentally demonstrate a 1 Gbaud four-level pulse amplitude modulation (PAM4) photonic MMWoF system at 47.2 GHz based on a novel dual-wavelength quantum-dash (QD) DFB laser and optical heterodyning., 2019 Photonics North (PN), May 21-23, 2019, Quebec City, QC, Canada

An ultra-wideband bandpass (UWB) filter using integrated substrate gap waveguide (ISGW) technology is proposed, which has ultra-wideband and high selectivity. The UWB ISGW bandpass filter structure consists of three layer dielectric substrates, the top substrate uses metallic via-holes and metallic patches to implement perfect magnetic conductor (PMC) structure, which is suitable for packaging substrate integrated waveguide (SIW) filters to avoid external interference and loss caused by radiation and internal radiation leakage, the middle layer substrate provides a stable gap layer, and the base substrate is used to obtain a SIW filter by etching the slots in the metal plane and placing metallic via-holes in the middle of the layer, i.e. a self-packaged UWB ISGW filter. The proposed filter was fabricated and tested at a center frequency of 17.5 GHz as an example. The measurements show that the filter has a passband from 14.4 to 20.7 GHz, i.e. This filter has a fractional bandwidth (FBW) of 36%, and an insertion loss of 0.91 dB. More importantly, thanks to ISGW, two transmission zeros are obtained at 12.9 and 22.1 GHz to improve high selectivity.

This work reviews fundamentals of integrated substrate gap waveguide (ISGW) in structure and operation principle. The most important aspect of ISGW is that not only circuit functions such as antennas, filters, and power dividers can be designed and implemented, but also inherent self-packaging function of the circuit is obtained. Compared with substrate integrated waveguide (SIW), ISGW introduces less transmission loss, and additional design freedoms that may result in better performance of a circuit. Moreover, examples of ISGW based antennas, filters and power couplers are given to show advantages of ISGW. It is believed that ISGW has high potential for 5G integrated microwave and millimeter-wave circuits.

In this paper, an integrated substrate gap waveguide ISGW) bandpass filter is proposed. The filter consists of three layers of dielectric substrates, base layer, middle layer and top layer. The base layer is used to obtain substrate an integrated waveguide (SIW) filter, the middle layer is a substrate gap layer which is used for a gap layer between the top and base layer, and the top layer is used to obtain perfect magnetic conductor (PMC) layer. An ISGW filter is designed to validate the concept. The filter has a fractional bandwidth of 32.2% and two transmission zeros at 14 and 22.8 GHz, and wide passband, wide stopband and high selectivity of the passband are achieved.

In this paper, we propose a high capacity multiple-input-multiple-output (MIMO) enabled all-optical analog-millimeter-wave-over-fiber (A-MMWoF) mobile fronthaul architecture employing mode division multiplexing (MDM) along with wavelength division multiplexing (WDM) for 5G and beyond of wireless networks. The proposed design is flexible and scalable for achieving high capacity, high speed and low latency fronthaul links., 2019 Photonics North (PN), May 21-23, 2019, Quebec City, QC, Canada

With the growing demand for cloud radio access networks, mobile fronthaul networks must stay adaptable, efficient and cost-effective. To simplify fronthaul transmission systems, 1-bit delta-sigma modulation (DSM) radio over fiber (RoF) transmission has been considered promising, in which 1-bit DSM technique is used to simplify remote radio units. Moreover, carrier aggregation is a key technique for increasing fronthaul transmission capacity. This work demonstrates, for the first time, concurrent dual-band 1-bit envelope DSM 64-QAM 20-MHz LTE signals transmitted over RoF system. It is shown that carrier aggregation combined with 1-bit delta-sigma modulation is a possible promising technique for high-capacity fronthaul transmission

A broadband aperture circularly polarized (CP) antenna based on substrate integrated gap waveguide (SIGW) for millimeter applications is presented. An inclined aperture is etched on the metal layer of the SIGW and excited by transmission microstrip line of SIGW. The mechanism of CP radiation is analyzed briefly in the paper. The simulated results show impedance bandwidth from 24.8 to 31.7 GHz (24.4%) and 3-dB axial ratio bandwidth from 27.3 to 28.8 GHz (5.3%). The design is validated.

In this paper., a seventh-order filter using substrate integrated gap waveguide (SIGW) technology., i.e. SIGW filter., is proposed for the first time., which has high selectivity and wide stopband. The SIGW filter includes three-layer substrates. The top layer substrate realizes a perfect magnetic conductor (PMC) using periodic plated vias and metallic patches. It is applied for packaging substrate integrated waveguide (SIW) filter to avoid interference and losses induced by external radiation emission and internal radiation leakage. The middle layer substrate generates a gap layer. In the base/bottom layer, cascaded resonators of the SIW filters are formed by properly etching slots on the metal plane and placing plated vias in the middle of this layer. The higher-order modes of TE 103 and TE104 are suppressed using slots designed in the base layer at the third-order cavity, which leads to wide stopband. Moreover, the effect of the SIGW-based PMC structure on bandwidth and transmission zeroes is studied. The measured results demonstrate that the proposed SIGW filters perform well in the both passband and stopband.

This paper proposed a wideband 3dB coupler based on substrate integrated gap waveguide. The proposed coupler takes the branch-line coupler as the prototype and the simulations have done. According to the simulation results, the proposed coupler achieved the equal power division and the isolation are all above 20dB from 23.59GHz to 29GHz. Moreover, the phases between through port and coupled port differ 90 deg and the losses for both the through port and isolated port are about 1dB. In addition, the comparison of the couplers with different tilt angle coupling lines has been done. And with the simulation results, when the tilt angle equals 0, the bandwidth of isolation above 20dB is about 3 times of the tilt angles equaling $\pi/4,4\pi/25$ and $\pi/6$ .

In this paper, a six order bandpass SIW filter is presented which can realize efficiently by using the technology of electric and magnetic couplings. It is made up of a layer substrate. The six order SIW filter is a narrow bandpass microwave filter through electric coupling and magnetic coupling of SIW resonators or cavities. The cascaded resonators of the filter are formed by properly etching the slots on the top metal plane of a SIW cavity. The slots create the electric coupling. The magnetic coupling is formed by period metallic vias in the middle of a SIW cavity. Furthermore, the electric and magnetic couplings achieves two transmission zero points. The electric coupling have influence on the upper transmission zero point, and magnetic coupling have influence on the lower transmission zero point. It is demonstrated that the SIW filter has a bandwidth of 1.5 GHz at a center frequency of 15 GHz. The measured results have a good agreement with the simulated results.

A new low-loss quasi-transverse electromagnetic (TEM) microstrip line, called as a self-packaged microstrip line, is proposed for microwave and millimeter-wave applications. It is fully based on the low-cost PCB process, but without the issues of radiation and surface waves by using a top layer perfect magnetic conductor (PMC) substrate. The self-packaged microstrip line consists of three layer substrates: a bottom layer to place the metal strip, a top layer to build the PMC shielding with the periodic plated vias, and a middle layer to separate the PMC layer from the metal strip and base ground plane. The ground plane works as an ideal PEC creating a PEC-PMC structure. It is evident that, within the band of interest, the space radiation, surface waves, and cavity resonances appearing in the standard microstrip line (without/with a bulky metallic shielding box) can be efficiently suppressed by the top-layer PMC shielding when a proper gap height is implemented [1]-[4]. As a result, a thicker bottom layer substrate can be applied in the packaged microstrip line to reduce the conductor losses; and no issues of interference or crosstalk will arise between the adjacent circuits/components [5], [6]. Therefore, this self-packaged microstrip line is very helpful to improve the microstrip circuit performance, such as the gain, bandwidth and radiation efficiency of the microstrip antenna, and the passband/stopband characteristics and compactness of the microstrip filter, in particular at high frequencies, due to the reduced attenuation and the absence of surface waves (and/or radiation) [7]-[9]. Indeed, the suppression of the surface waves in the substrate can also be realized by electromagnetic bandgap (EBG) or defect ground structure (DGS), because of the high-impedance surface [10], [11]. However, an additional metal shielding that surrounds a microstrip-EBG/DGS circuit is still required to prevent the space radiation. Otherwise, significant radiation will increase the insertion loss and additionally cause the unwanted RF interference among the adjacent circuit elements. Moreover, such packaging is very complicated, since a recessed region is required in the metal bearing carrier under the defected ground slots, and the resonance frequency of the DGS depends on the dimensions of this region [12], [13]. So, it can be seen that the proposed novel self-packaged microstrip line perfectly merges both the merits of suppressing the radiation in space and the surface waves in the substrate, which makes it very attractive for the high cost-effective circuit design in both performance improvement and size reduction.

In this paper, a new all-fiber mode converter was proposed, which can achieve LP 01 to LP 02 mode conversion and vice versa. The proposed mode converter is based on a tapered core and four bipyramids combined structure with annular distribution; the tapered core is used to excite the high-order modes while the bipyramids combined structure curb the undesired high-order modes and make the LP02 dominate. A analysis shows that conversion efficiency of 89% and extinction ratio of12dB over the whole C-band; and the performance of the mode converter is not sensitive to minor changes in structural parameters. The proposed mode converter also can achieve LP 02 back to LP 01 .

This paper proposes a novel multi-stub ultra-wide band planar monopole antenna. The radiation patch of the antenna is composed of a pair of back-to-back E-shape-like stub elements. The E-shape-like stub element is the extension of the E-shape stub element, adding two semi-circle elements at the back of the E-shape stub element and extending the top of the E-shape stub element with an inverted L-shape element with a “suspending hammer” element. Two semi-circle slots etched on the rectangular ground which is extended make the ground with two step-like structures to realize ultra-wideband. The antenna is printed on a substrate of the dielectric constant 4.6. The experiment results show that the bandwidth of the antenna is 3.2GHz–18.7GHz for S11 of less than −10dB.

In this paper, a new-version microstrip line is proposed, named packaged microstrip line. It is comprised of three dielectric substrates. This novel microstrip line is no longer suffering from the issues of radiation losses, surface waves, or cavity resonances that exist in the standard microstrip line without or with a metallic shielding box. Instead of the packaging way based on the standard air gap waveguide technology, this novel packaged microstrip line has the following merits: greatly reduced weight and size, easy manufacturing, constant gap height and more flexibility in design. We present how to adopt a proper dielectric substrate for each layer of the packaged microstrip line considering both stopband and line losses, and how to design the line width for a given characteristic impedance. One prototype of this proposed novel packaged microstrip lines is fabricated and tested, showing a good agreement with the simulated results.

In this paper, a novel comprehensive transmitter architecture has been proposed, which enables the concurrent transmission of two separate frequency bands by carrier aggregation. For different frequencies, the proposed transmitter can simultaneously employ 1-bit Low-pass and Band-pass delta-sigma modulators structures, or employ hybrid structures. Carrier frequencies are equal to oversampling frequencies of modulators. Besides, signals on two carriers are not interfered with each other to ensure transmission dual-band signal. Performance analysis is simulated by using Matlab/Simulink. The simulation results achieve high signal-to-noise radio and show the effectiveness of the proposed architecture.

A small CPW fed triple band-notched (Ultra Wide Band) UWB antenna is presented. The proposed antenna consists of a shovel-shaped radiating patch with three C-shaped slots, a feed line and a modified ground plane. By etching three C-shaped slots with variable dimensions on the radiating patch, frequency band-stop performance is generated and we can control its band-notched frequency and bandwidth through modifying the dimensions of C-shaped slot. The proposed antenna has a very compact size of 14×22×1.6mm3. Simulated VSWR shows that the proposed antenna could operate from 2.88 to 10.67 GHz with VSWR less than 2, except 3.20 to 3.97GHz, 5.26 to 5.75GHz and 7.57 to 8.37 GHz.

To miniaturize the conventional air gap waveguide (GW), a substrate integrated gap waveguide (SIGW) is proposed. Moreover, SIGW makes up the defects in the microstrip-ridge air GW, such as inconstant gap height, holes in strip, as well as strip electroless nickel immersion gold (ENIG) coating. To verify the proposed SIGW, a prototype was designed and manufactured using the multi-layer printed circuit board (PCB) technology. It contains a very simple transition between SIGW and microstrip lines for measurements. Further, the experimental results show that the measured performance agrees well with the simulated.