Ka-band broadband filtering packaging antenna based on through-glass vias (TGVs)*

Zhen FANG,Jihua ZHANG,Libin GAO,Hongwei CHEN,Wenlei LI,Tianpeng LIANG,Xudong CAI,Xingzhou CAI,Weicong JIA,Huan GUO,Yong LI

1School of Integrated Circuit Science and Engineering,University of Electronic Science and Technology of China,Chengdu 610054,China

2State Key Laboratory of Electronic Thin Films and Integrated Devices,University of Electronic Science and Technology of China,Chengdu 610054,China

3Chengdu Micro-Technology Co.,Ltd.,Chengdu 611731,China

Abstract: This work presents a novel design of Ka-band (33 GHz) filtering packaging antenna (FPA) that features broadband and great filtering response,and is based on glass packaging material and through-glass via (TGV) technologies.Compared to traditional packaging materials (printed circuit board,low temperature co-fired ceramic,Si,etc.),TGVs are more suitable for miniaturization (millimeter-wave three-dimensional (3D) packaging devices) and have superior microwave performance.Glass substrate can realize 3D high-density interconnection through bonding technology,while the coefficient of thermal expansion (CTE) matches that of silicon.Furthermore,the stacking of glass substrate enables high-density interconnections and is compatible with micro-electro-mechanical system technology.The proposed antenna radiation patch is composed of a patch antenna and a bandpass filter (BPF) whose reflection coefficients are almost complementary.The BPF unit has three pairs of λg/4 slots (defect microstrip structure,DMS) and two λg/2 U-shaped slots (defect ground structure,DGS).The proposed antenna achieves large bandwidth and high radiation efficiency,which may be related to the stacking of glass substrate and TGV feed.In addition,the introduction of four radiation nulls can effectively improve the suppression level in the stopband.To demonstrate the performance of the proposed design,a 33-GHz broadband filtering antenna is optimized,debugged,and measured.The antenna could achieve |S11|

Key words: Filtering packaging antenna (FPA);Through-glass vias (TGVs);3D packaging devices;Laser bonding

1 Introduction

With the booming growth of smart phone technol‐ogy,high-performance computing,artificial intelligence,and other emerging fields,millimeter-wave antennas are becoming increasingly prevalent in communication systems (Zhang XY et al.,2015,2017;Hu PF et al.,2016,2019;Hwang et al.,2017;Li WX et al.,2017;El-Halwagy et al.,2018;Jin et al.,2018;Li JF et al.,2018,2021;Shah et al.,2018;Wu et al.,2018;Zhang BH and Xue,2018;Cao et al.,2020;He et al.,2020;Hu KZ et al.,2020;Liu et al.,2020;Watanabe et al.,2020;Xia et al.,2020;Yao et al.,2020;Chen et al.,2021;Shao and Zhang,2021;Fang et al.,2022;Hu HT et al.,2022;Su et al.,2022;Li WL et al.,2023).Microstrip antennas are widely used in millimeterwave antenna design due to their low profile,simple manufacturing process,and easy integration (Li WX et al.,2017;He et al.,2020;Chen et al.,2021;Shao and Zhang,2021;Fang et al.,2022;Hu HT et al.,2022;Su et al.,2022).Meanwhile,various new applications demand higher requirements for advanced packaging (Shah et al.,2018;Chen et al.,2021;Fang et al.,2022;Hu HT et al.,2022).Fig.1a shows the radar plots for three different packaging antenna technologies.Packag‐ing antenna typically uses printed circuit boards (PCBs);however,the dimension cannot be made small enough due to process constraints,and the performance of the antenna is affected by the large interconnections between the device and PCBs (Su et al.,2022).Impor‐tantly,the dimension of device package is often overengineered to match the fabrication error (>40 μm) (Su et al.,2022).Recently,through-silicon via (TSV) has become a popular technology for packaging antennas.It has a precise microelectronic process and low manu‐facturing process error,which can meet the application needs of smaller interconnection length and shorter electrical delay (Watanabe et al.,2020;Xia et al.,2020;Yao et al.,2020).Nonetheless,silicon is a semicon‐ductor material and produces intolerable signal loss at high frequencies.When the transmission line trans‐mits through the signal,the signal and the substrate material produce a strong electromagnetic coupling effect,and the eddy current phenomenon occurs in the substrate,resulting in poor signal integrity (Watanabe et al.,2020;Xia et al.,2020;Yao et al.,2020;Chen et al.,2021).Through-glass vias (TGVs) have been widely investigated due to their ability to from finepitch line and their coefficient of thermal expansion (CTE) matching that of silicon (Watanabe et al.,2020;Xia et al.,2020).Besides,they present low signal loss tangent at high frequencies (0.0025 at 33 GHz),adjust‐able dielectric constant (Dk) that can vary from 3.78 to 8 ppm/K,and manufacturability of ultra-thin process‐ing (CTE and Dk can be tailored depending on the materials used for integrated circuits (ICs) and PCBs) (Watanabe et al.,2020;Xia et al.,2020;Su et al.,2022).Meanwhile,TGVs can be prepared by laserinduced wet etching at low temperature to reduce the surface wave effect.The fabrication error of TGVs and redistribution layer (RDL) is low (<10 μm),and the thickness of glass substrate can be controlled between 50 μm and 2.5 mm to match the application require‐ments (Watanabe et al.,2020;Xia et al.,2020).Many researchers have carried out TGV-related research,such as glass-based integrated waveguide,filters,and radio frequency (RF) module (Watanabe et al.,2020;Xia et al.,2020).Fang et al.(2022) studied the properties of glass materials and made progress in reducing micro‐wave loss tangent,which can well address the shortage in the low-loss glass material supply chain (Watanabe et al.,2020;Xia et al.,2020).

Fig.1 Comparison and schematic of three primary substrate materials used for 5G millimeter-wave applications (a) and the proposed FPA connected to the power amplifier of a transmitter and the equivalent circuits (b) (FPA: filtering packaging antenna;PCB: printed circuit board;TSV: through-silicon via;TGV: through-glass via;CTE: coefficient of thermal expansion;PA: power amplifier;BPF: bandpass filter)

Recently,filtering antenna has been studied exten‐sively because it can effectively reduce the system volume and loss (Zhang XY et al.,2015,2017;Hu PF et al.,2016,2019;Jin et al.,2018;Li JF et al.,2018,2021;Wu et al.,2018;Zhang BH and Xue,2018;Hu KZ et al.,2020;Liu et al.,2020;Hu HT et al.,2022).The filtering antenna promotes the develop‐ment of packaging antenna (Zhang XY et al.,2015,2017;Hu PF et al.,2016,2019;Jin et al.,2018;Li JF et al.,2018,2021;Wu et al.,2018;Zhang BH and Xue,2018;Hu KZ et al.,2020;Liu et al.,2020).As shown in Fig.1b,the antenna and filter of a transmitter are usually connected to a power amplifier (PA).The design of filtering antenna includes the following aspects: first,the antenna feeder is used to obtain the filtering response (Hu PF et al.,2016;Zhang XY et al.,2017).It is necessary to cascade the filter circuit in the front section of feeder,which results in large size and com‐plex structure.Second,the traditional filter synthesis method is adopted,and the antenna needs to be de‐signed according to the coupling matrix theory (Wu et al.,2018;Zhang BH and Xue,2018).Finally,some parasitic elements are introduced into the patch antenna to change the current distribution (Jin et al.,2018;Li JF et al.,2018;Hu PF et al.,2019;Liu et al.,2020).Thus,the antenna can obtain filtering response and effectively expand the bandwidth,which is highly suit‐able for preparing a miniaturized antenna.However,all of the filtering antennas mentioned above work only in S-band or C-band.The vast majority of the filtering antennas are made using PCBs,which limits the minia‐turization ability and three-dimensional (3D) packaging of antennas.To the best knowledge of the authors,how‐ever,neither filtering antennas for Ka-band nor TGVbased filtering antennas have been published so far.This study is the first to integrate TGV technology into the design of filtering antennas.Of note,in a recent study,a filtering antenna was designed that works in V-band based on PCBs (Hu HT et al.,2022).An impedance bandwidth of 15% and radiation efficiency of 92% were obtained,and the out-of-band suppression also met the application requirements.However,this filtering antenna has a large volume (>0.286λ30,whereλ0is the guide wavelength),and its structure is overly complex.

This work presents the design and demonstration of a 33-GHz filtering antenna-in-package (AiP) module with broadband,which induces four radiating nulls to improve the suppression level in the stopband based on TGVs.The entire filtering packaging antenna (FPA) is stacked by three layers of glass substrate.The upper surface of layer 1 (radiation patch layer) is the radiation patch of the antenna,and the lower surface is the ground plane.Layer 2 is a glass transition layer introduced for signal interconnection between layer 1 and layer 3.Layer 3 is the signal feed layer,i.e.,substrate integrated waveguide (SIW) transition feeding structure layer,of the entire FPA.Electrical interconnection of this threelayer structure is achieved using laser bonding inter‐connections.The signal is transmitted to the SIW transi‐tion feeding structure layer through a waveguide coax‐ial converter,and then fed to the antenna radiation patch through TGV interconnection,thereby realizing the conversion of the wireless signal.When considering the insertion loss and the reliability of the feed con‐nection,TGV undoubtedly shows superiority in highfrequency performance (Hu HT et al.,2022).Com‐pared with the coupling feed,TGV is more stable and is less affected by the environment.Impedance control of TGVs and pads is the key to achieving impedance matching and high bandwidth of the entire FPA.Spe‐cifically,the impedance of the antenna radiation patch should be designed to be slightly lower than 50 Ω with a capacitive impedance component (Ansoft HFSS ver.11).This is because TGV usually introduces addi‐tional resistive and inductive components (Fig.1b) (Li WL et al.,2023).

2 Materials and methods

The fabrication process of the FPA of this work is shown in Fig.2.Our fabrication method enables high-density low-loss interconnections (Ka-band) and high-precision RDLs on glass substrate.Glass sub‐strate with a thickness of～650 μm and a surface rough‐ness of less than 10 nm was prepared by a solid-phase reaction method.TGVs with a diameter of 60 μm were formed on the glass substrate by laser-induced etching (step 1).The glass substrate preparation pro‐cess and the laser-induced etching were described in detail in Fang et al.(2022),which are repeated here.Through the single-side sputtering (step 2),electro‐plating (step 3),and polishing (step 4) processes,glass substrate with copper-filled TGVs was obtained,and the surface had no metal layer.Via double-side sputtering (step 5) and photolithography (step 6),metal patterns (including pads) on the surface of the glass substrate were formed (step 6).Then,the antenna radiation patch layer and the glass transition layer with copper-filled TGVs were bonded through laser inter‐connection (step 7) to achieve signal interconnection and physical support (the bonding interface was glass/Ti/Cu/Ti/glass).Finally,the laser interconnection bonding was realized between the SIW transition feeding structure layer (step 8) and the backside of layer 2 (step 9).

Fig.2 Fabrication process of the proposed FPA (FPA: filtering packaging antenna;TGV: through-glass via;RDL: redistribution layer;SIW: substrate integrated waveguide)

2.1 Magnetron sputtering (step 2)

First,a layer of an intermediate layer metal (tita‐nium) of about 100-nm thickness was sputtered on the glass surface using magnetron sputtering equipment (JGP-450 of SKY Technology Development Co.,Ltd.,Chinese Academy of Sciences,China).The sputtering conditions were as follows: the sputtering atmosphere was 60 sccm of argon,the sputtering pressure was 1 Pa,the sputtering power was 250 W,and the sputtering time was 5 min.Immediately,after the sputtering of cop‐per film layer (2 μm),the sputtering atmosphere was 60 sccm of argon,the sputtering pressure was 1 Pa,the sputtering power was 150 W,and the sputtering time was 120 min.

2.2 Electroplated copper-filled TGVs and polishing (steps 3 and 4)

The glass substrate after single-side sputtering of titanium or copper was transferred to an electroplating tank with electroplating solution with the current of 0.1 A/cm2,and taken out after 72 h of electroplating.The formulation of the plating solution was as follows: the main contents were 67.4 g/L copper sulfate solu‐tion and 157 g/L sulfuric acid solution.The additives were inhibitor,leveler,and accelerator at 10,12,and 0.8 ml/L,respectively.After being taken out,it was ground by a polishing machine for 2 h to obtain a bright glass substrate with copper-filled TGVs.Then,a copper-filled TGV glass substrate covered with tita‐nium and copper films was obtained by magnetron sputtering.

2.3 Photolithography (step 6,RDL formation)

The patterning of the surface metal of the antenna radiation patch layer and the SIW transition feeding structure layer was obtained by photolithography.The pattern on the specific mask plate was copied to the photosensitive glass by the photolithography machine (URE-2000B,Institute of Optoelectronics Technology,Chinese Academy of Sciences,China).Meanwhile,alignment marks needed to be designed in advance.The parameters of the photolithography were as follows: first,we used a spin coater to evenly cover the sur‐face of the copper film with the photoresist (AZ4620),which was then left to dry.After an exposure time dura‐tion of 15 s,it was transferred to the developer to remove the excess photoresist.Then,the glass sub‐strate was soaked in nitric acid solution for 2 s and taken out immediately to remove excess copper films.Sub‐sequently,it was transferred to a hydrogen peroxide solution at 90 ℃ for 10 s and taken out to remove the excess titanium films.

2.4 Laser interconnection bonding (step 7,metal–glass bonding)

The radiation patch layer was connected to the SIW transition feeding structure layer by a glass tran‐sition layer bonding process with many pads.In the process of photolithography,we designed the size (radius of 50 μm) and position of the pad on the mask in advance.Only metal patterns and pads were left on the glass substrate through photolithography.The SIW transition feeding structure layer and the glass transi‐tion layer were aligned and pressed (the applied pres‐sure was 1 MPa) using a bonding interconnection align‐ment machine,fixed by a specific model,and finally placed on a laser bonding machine to achieve bonding between metal and glass (the energy of the laser was 3 W).Similarly,the bonded SIW transition feeding structure layer and glass transition layer were bonded to the antenna radiation patch layer.

3 Results

3.1 Radiation patch layer design

Fig.3 illustrates the configuration of the proposed antenna radiation patch layer,which consists of twoλg/2 defect ground structures (DGSs) and three pairs ofλg/4 defect microstrip structures (DMSs).The glass sub‐strate has a relative permittivity of 4.8 and dielectric loss tangent of 0.0025 at 33 GHz.The thickness of the glass substrate is 0.56 mm.Meanwhile,the input impedance of the antenna can be changed by varying the position of the TGV feed to match the impedance of the 50-Ω RF circuit.A pair of slots are etched on the ground plane to change the electric field distribution on the ground.In addition,a circle is etched around the TGV signal to prevent the signal from being transmitted to the ground.

Fig.3 Geometry of the proposed filtering packaging antenna: (a) exploded view;(b) top view;(c) bottom view;(d) side view

The distance from the TGV to the center can be approximated according to the characteristic imped‐ance calculation of the coaxial line in Eq.(1):

whereRrepresents the distance from the outer con‐ductor to the center,Z0represents the characteristic impedance,is the dielectric constant of the glass substrate,andrrepresents the radius of the inner con‐ductor.According to the process,whenris 30 μm,theRcalculated is about 150 μm.The radiation nulls are designed according to the frequencyfnull.Three pairs of slots are etched on the radiation patch,resulting in three radiation nulls on both sides of the passband (DMS).The radiation nulls (null 1,null 3,and null 4) are produced by comparing the length of the corre‐sponding slotsL.These slots operate at quarter wave‐length resonance,so the radiation null frequency can be evaluated aswherecrepresents the speed of light.Null 2 is caused by etching two U-shaped slots in the ground plane (DGS).The region between the central resonator and the slotted patches is above the two U-shaped slots.The final optimized size is shown in Table 1.

Table 1 Parameters of the filtering packaging antenna

3.2 SIW transition feeding structure

In an actual microwave circuit system,the pro‐posed filtering antenna is controlled by RF chips embe?dded in the middle layer (transmitting signals through TGVs).However,an SIW transition feeding structure is used for the convenience of measuring the far-field radiation performance,as shown in Fig.4a.The signal is transmitted to the SIW using a waveguide coaxial converter (26.5?40 GHz,HD-320WCAK).The radia‐tion patch layer provides electrical interconnection to the SIW transition feeding structure layer by a glass transition layer formed by laser bonding process us‐ing a pad and a TGV.Fig.4c illustrates the configura‐tion of the proposed SIW transition feeding structure layer,where the SIW has been deliberately designed to work in an ultra-wide frequency band,making sure that the cutoff frequency is lower than the passband frequency of the proposed antenna.The ?10-dB imped‐ance bandwidth ranges from 25 to over 45 GHz,while the insertion loss in the antenna passband is below 0.6 dB.The final optimized size of the SIW transition feeding structure is shown in Table 2.

Table 2 Parameters of the substrate integrated waveguide transition feeding structure

Fig.4 Geometry of the proposed filtering packaging antenna (FPA) with substrate integrated waveguide (SIW) transition feeding structure: (a) exploded view;(b) side view;(c) SIW transition feeding structure

3.3 Operation principle

3.3.1 Resonant point

To intuitively illustrate the amplitude module,Fig.5a depicts the simulated E-field distributions on the SIW transition feeding structure.Since the SIW structure can transmit only TEn0(n>0) mode and the radiation patch is fed by SIW,we can reveal the mechanism of antenna resonant points as long as we analyze the transmission mode in SIW.As shown in Fig.5b,only the TE10mode flows into the antenna through the SIW transition,and a higher mode can‐not be transmitted.Hence,the resonant points in the antenna passband are generated by the TE10mode.Fur‐thermore,as shown in Fig.5c,the current distribu‐tions of the TE10mode are symmetrical along thexaxis at 31.2 and 35 GHz.This is because only the TE10mode flows into the antenna through the SIW transition,and the currents of the TE10mode distributed along thexaxis of the radiation patch are cut off by the slots.

Fig.5 Operation principle of the resonant point in the passband: (a) E-field distributions on the substrate integrated waveguide (SIW);(b) simulated performance of the SIW transition feeding structure;(c) simulated current distributions on the radiation patch at the resonant point

3.3.2 Four radiation nulls

To gain some insights into the radiation nulls of the proposed FPA,the simulated current distributions at null 1 (25.6 GHz),null 2 (27.2 GHz),null 3 (38 GHz),null 4 (42.1 GHz),and the central frequency (33 GHz) are compared in Figs.6?8.For symmetry and visibility,only the partial current distribution of the radiation patch is given.With reference to Fig.6,the strong flows of patch currents in opposite currents are observed at the edges of the patch.The destructive superposition of the radiation field from the opposite current gives rise to null 1.However,there is a strong flow of patch currents in the same direction at the central frequency (33 GHz),in which the radiated fields are construc‐tively superimposed.Similarly,because the radiation patch radiates upward,it is partly generated by ground reflection,as shown in Fig.7.At 27.2 GHz,the electro‐magnetic wave radiated by the main body is in the opposite phase to the electromagnetic wave reflected from the ground,which also produces a destructive superimposed radiation field that is responsible for null 2.As shown in Fig.8,null 3 and null 4 are also caused by the same principle.

Fig.6 Simulated current distributions on the radiation patches at radiation null frequency fnull 1 25.6 GHz (a) and central frequency 33 GHz (b)

Fig.7 Simulated current distributions on the radiation patches at radiation null frequency fnull 2 27.2 GHz (a) and central frequency 33 GHz (b)

Fig.8 Simulated current distributions on the radiation patches at radiation null frequency fnull 3 38 GHz (a) and radiation null frequency fnull 4 42.1 GHz (b)

3.4 S-parameter analysis of TGVs

In this part,S-parameters of TGV (diameter of 65 μm,height of 1.68 mm) and PCB (Rogers 5880) via (diameter of 65 μm,height of 1.68 mm) are extracted and compared.As shown in Fig.9,the simulation model seeks to realize the interconnection of three layers of substrate by microstrip line and vias.In ad‐dition,the diameter of the grounding shield column is 200 μm to ensure the smooth impedance transi‐tion of the signal transmission via and reduce signal distortion (Li WL et al.,2023).Li WL et al.(2023) proposed seven shielding patterns to realize the high isolation capability and diversified application of glass interposer,and discussed the influence of the ground‐ing shield column around the signal via on the trans‐mission characteristics.Compared with the single microstrip line,theS-parameter of the vias was ex‐tracted.Figs.9a and 9b present the PCB via simulation model and the TGV simulation model,respectively.The comparison in Fig.9c reveals that there is little difference in the low frequency band (<10 GHz),and that the advantages of TGV are not obvious.However,in the high frequency band (10?40 GHz),the insertion loss of TGV is much smaller,and the maximum is 0.3 dB at 33 GHz.The lower insertion loss in the high frequency band can effectively increase the radi‐ation efficiency of the antenna.This establishes TGV as one of the best options for antenna radiation materials in the high frequency band.

Fig.9 S-parameter analysis: (a) printed circuit board (PCB,Rogers 5880) via simulation model;(b) through-glass via (TGV) simulation model;(c) S-parameters of the TGV and via

3.5 Measurement and simulation results

In this work,the reflection coefficient |S11| was measured by an Agilent Technologies N5234A PNA-L network analyzer (10 MHz?43.5 GHz).The radiation performance was quantified in an indoor far-field mea‐surement chamber.The far-field radiation performance of the proposed antenna can be determined according to the excitation power provided by the signal source and the power measured by the spectrum analyzer,com‐bined with the gain of the standard gain horn (SGH).

Fig.10 illustrates that the proposed antenna was fab‐ricated using TGV and micro-electro-mechanical sys‐tem (MEMS) technology.Two substrates (50.8 mm×50.8 mm×0.56 mm) with copper-filled TGVs and sur‐face metal patterns were first fabricated separately,and then the SIW transition layer (5-μm thick copper) and the radiation patch were connected through an intermediate glass transition layer (50.8 mm×50.8 mm×0.56 mm) using a laser bonding technique under appro‐priate temperature and pressure conditions.The specific process is shown in Fig.2.The final prototype was coated with copper resistant oxidant to achieve high reliability.Fig.10g illustrates the proposed FPA fab‐ricated prototypes (50.8 mm×50.8 mm×1.689 mm),which were measured in an indoor far-field chamber.

Fig.10 Fabricated prototypes of the proposed filtering packaging antenna (FPA): (a) diagram of the radiation patch layer of copper-filled through-glass vias (TGVs);(b) the fabricated prototypes of the radiation patch layer (top view,bottom view,and side view of TGVs);(c) diagram of the substrate integrated waveguide (SIW) transition feeding layer of copper-filled TGVs;(d) the fabricated prototypes of SIW transition feeding layer;(e) side view of interconnection bonding;(f) final prototype;(g) radiation performance measured in an indoor far-field chamber

Fig.11 illustrates that compared to the Ref_antenna (a traditional rectangular patch),the proposed FPA has enhanced bandwidth and filtering characteristics.Fur‐thermore,it has four radiation nulls for the band-edge,which improves the suppression level in the stop‐band.The measurement results show that the imped‐ance is matched from 29.4 to 36.4 GHz,with the mea‐surement out-of-band suppression being higher than 16.51 and 16.82 dB for the lower and upper stopbands,respectively (Fig.11a).The measurement peak realized gain is～6.5 dBi.Fig.11b illustrates the measurement and simulation results of radiation efficiency for the proposed antenna.The measurement radiation effi‐ciency is less than 90%,which may cause ohmic loss in the FPA prototype.Fig.11c illustrates the measure‐ment and simulation radiation patterns at the central frequency (33 GHz).The maximum co-polar field is found in the boresight direction (θ=0°).The mea‐surement radiation patterns of E-plane and H-plane have a large deviation from the simulation results,which is caused by experimental imperfections including assembly errors.According to the measurement data,the application requirements of the system are met.

Fig.11 Measurement and simulation results of reflection coefficient and antenna gain (θ=0°) (a),radiation efficiency (b),and radiation patterns at 33 GHz (c)

4 Discussion

The proposed filtering antenna has been quantita‐tively compared with some fabricated packaging anten‐nas (Table 3) and filtering antennas (Table 4).As shown in Table 3,compared with PCB-packaged antennas,glass-packaged antennas exhibit obvious advantagesin the millimeter-wave frequency band.These include mainly low-loss transmission,high-density integra‐tion,and a more precise manufacturing process.In addition,although silicon package (TSV) has a higher integration level than TGV,the intolerable transmis‐sion loss at high frequency has become the main fac‐tor limiting its development.As an enhancement to the glass-packaged antenna type,this work introduces a three-layer glass stack structure to achieve signal interconnection by laser metal–glass bonding tech‐nology.The 3D integrated packaging of the antenna is realized,which effectively reduces the insertion loss of the signal during the transmission process and lowers the process cost,as shown in Table 4.Since the pro‐posed antenna adopts SIW combined with TGV feed,it undoubtedly shows superiority in high-frequency performance when considering the insertion loss and reliability of feed connection.The filtering antenna is also the AiP type because the manufacturing process entails the fusion of TGV technology and MEMS tech‐nology.The antenna structure requires only three glass substrates,which reduces the complexity and cost of fabrication.In addition,the proposed antenna intro‐duces four radiation nulls in the stopband,and obtains a sufficient level of out-of-band signal suppression.As a whole,the FPA is particularly suitable for millimeterwave communication systems.

Table 3 Comparison with packaging antennas

Table 4 Comparison with filtering antennas

5 Conclusions

The innovation of this work in the research of glass 3D packaging antennas is a novel laser intercon‐nection bonding scheme to realize a low-cost,highdensity 3D interconnected structure.By combining the glass packaging antenna and the filtering antenna design,this work achieves high-performance 3D stack miniaturization and filter response in the Ka-band.In addition,the introduction of four radiation nulls can effectively improve the suppression level in the stop‐band.Overall,this work presents an FPA with three layers of glass bonding interconnection and assembly,which is particularly suitable for millimeter-wave receiv‐ing or transmitting circuit systems.

Contributors

Zhen FANG and Jihua ZHANG designed the research.Zhen FANG,Hongwei CHEN,and Libin GAO processed the data.Zhen FANG drafted the paper.Wenlei LI and Tianpeng LIANG helped organize the paper.Zhen FANG,Xudong CAI,Xingzhou CAI,Weicong JIA,Huan GUO,and Yong LI helped complete the antenna prototype preparation,assembly,and testing.Jihua ZHANG and Zhen FANG revised and finalized the paper.

Compliance with ethics guidelines

Zhen FANG,Jihua ZHANG,Libin GAO,Hongwei CHEN,Wenlei LI,Tianpeng LIANG,Xudong CAI,Xingzhou CAI,Weicong JIA,Huan GUO,and Yong LI declare that they have no conflict of interest.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.