H2020 MSCA ITN 2019 EID - mywave-project.eu

H2020‐MSCA‐ITN‐2019 EID

MyWave 860023

Evaluation report of first iteration antennas

Deliverable D3.2

V1

D3.2 MyWave Confidential Page 1

Document history – List of changes

Version Date Author name Scope

V0.1 2021‐03‐22 Roger Argaez R.

Yingqi Zhang

Dmitrii Kruglov

Kirill Alekseev

ESR 3 antenna design

ESR 4 anntena design



V0.2 2021‐03‐25 Adriana Briseno Edition

V1 2021‐03‐26 Adriana Briseno Final version ‐ submitted


Contents1 Introduction .......................................................................................................................................... 3

2 Description of designed antennas ........................................................................................................ 3

2.1 ESR 3: Power Amplifiers and Antenna Co‐Design Strategy for Optimised Efficiency ................... 3

2.1.1 Motivation and state‐of‐the‐art design review .................................................................... 3

2.2 ESR 4: W‐band Waveguide Antenna Elements for Wideband and Wide‐Scan Array Antenna

Applications for Beyond 5G ...................................................................................................................... 4

2.2.1 Motivation and state‐of‐art design review ........................................................................... 4

2.2.2 Proposed antenna: Ridge gap waveguide array element for 2D beam‐steering solution.... 4

2.3 ESR 7: Analogue Radio‐over‐Fiber‐fed antennas for massive deployment .................................. 6


2.4 ESR 8: 120GHz Dual‐Polarized Antenna‐on‐Chip .......................................................................... 7


2.4.2 Proposed antenna: 120 GHz in‐silicon antenna employing electromagnetic bandgap

structures to suppress the substrate waves ......................................................................................... 7

3 References .......................................................................................................................................... 10

Funded by the European Union


1 Introduction

This report aims to describe the antennas designed by the ESRs after 18 months into the project

MyWave. The following sections explain the motivation and the first antenna proposal.

2 Descriptionofdesignedantennas

2.1 ESR3:PowerAmplifiersandAntennaCo‐DesignStrategyforOptimisedEfficiency

2.1.1 Motivationandstate‐of‐the‐artdesignreview

Antennas are the front‐most RF component, which allows to transform electrical waves into

electromagnetic waves and vice versa. These are prone to capture unwanted signals from adjacent

elements. The active impedance of the antenna is the varying impedance seen at its feeding point, which

in a SISO communication might not be as relevant as in MIMO systems. Due to the large number of users,

the transmitters are expected to be integrated with several transmitters and therefore, many radiating

elements. The component that handles the largest amount of power and directs the overall performance

of the transmitter is the power amplifier. For an optimal performance, the power amplifier has a specific

complex impedance to which it is matched. But two major effects that cause this impedance to vary are

the mutual coupling and the scanning angle.

Figure 1. Mutual coupling and scanning angle effects.

In this study, the effects of the active antennas are translated into variation of the impedance connected

to the amplifier’s output‐port. This is so far independent of technology, but the parasitic effects will be

added with further information of the semiconductor.


Figure 2. Load mismatch as active antenna impedance.

In general, a square array is considered using dipole elements with λ/2 separation between each other.

The operating frequency and further requirements are no decided due to integration limitation, as for low

frequencies, the antenna size is quite large. For this project, the individual effect of the antenna is not as

relevant as the combined effect in an array, namely the active impedance seen from its feeding point.

2.2 ESR4:W‐bandWaveguideAntennaElementsforWidebandandWide‐ScanArrayAntennaApplicationsforBeyond5G

2.2.1 Motivationandstate‐of‐artdesignreview

Antenna systems for future beyond 5G applications are required to have a much higher effective radiated

power, but facing many challenges include significantly smaller antenna dimensions, tighter

manufacturing tolerances, and extra difficulties of integrating active integrated circuits (IC) (that become

comparable in size with antenna elements) and signal routing, especially in large‐scale arrays.

To date, most reported designs of high‐gain, high‐ efficiency W‐/D‐band array antennas are for fixed‐beam

applications; other 2D beam‐steering solutions that are based on AoC (Antenna‐On‐Chip) and SiP (System‐

In‐Package) implementations, as realized today at 60 GHz bands, have limited potential to simultaneously

achieve the required wideband and wide‐angle beam‐steering performance with high radiation efficiency.

2.2.2 Proposedantenna:Ridgegapwaveguidearrayelementfor2Dbeam‐steeringsolution

We propose a novel array element design based on an open‐ended ridge gap waveguide (RGW) [1],

depicted in Figure 3. The main advantage of the RGW design is its intrinsically contactless structure, which

thereby allows for low‐cost manufacturing, especially at high millimeter wave frequencies. A single ridge

is adopted inside the WG structure to lower the cut‐off frequency of its fundamental mode, thus providing


a wideband low‐dispersive operation [2] with element size of 0.5 λ × 0.6 λ . The nail structure covered

by the metal plate forms the 2D electromagnetic bandgap structure, thus blocking millimeter‐wave

leakage from the RGW to adjacent H‐plane array elements. The RGW input will be connected to the

beamforming network (not shown) of an array antenna that comprises a power distribution system and

phase‐shifting circuitry.

The WG elements are arranged in a triangular array grid (see Figure 2) that has been chosen to relax the

requirements on the array inter‐element spacing in the H‐plane [3]. This allows for > 0.5 λ inter‐element‐

spacing for grating lobe‐free wide‐angle beam steering. The increased H‐plane spacing is also beneficial

for lowering the WG cut‐off frequency and increasing the available physical space for active electronics

integration behind the array aperture. To overcome the mutual coupling effects among the waveguide

array antennas, a pair of E‐plane grooves are added above the aperture as a soft surface to stop the

electromagnetic waves propagation.

Figure 3. Perspective view of the proposed open‐ended ridge gap waveguide (RGW) array antenna element.

Figure 4. The triangular array grid of the infinite array model.

To characterize the array antenna element beam‐steering performance in large finite array configurations,

we have employed a full‐wave simulation model of the array unit cell. This unit cell model has sidewall

periodic boundary conditions and Floquet port above the element aperture. The analysis was performed

in the Ansys HFSS environment with the simulation setup as shown in Figure 4. The central design

frequency is f = 95 GHz. All the considered element designs have been optimized to maximize the


impedance matching bandwidth for the broadside radiation. The magnitude of the active reflection

coefficient (Γ) for the beam steering in the E‐ and H‐planes is shown in Figure 5. The black dashed line

indicates the grating lobe‐free border in the E‐plane, where no grating lobes can exist in the H‐plane inside

the studied frequency‐scan angle range. As seen, the impedance matching degrades when both the

scanning angle and bandwidth increase. The maximum scan angle is 45° and 33° for the 10% and 20%

bandwidth requirements in the E‐plane; and 40°, 39° for 10%, 20% BW requirements in the H‐plane. This

promising beam‐steering capability, along with possible contactless RGW interface towards active

electronics, makes this RGW array element a suitable candidate for future 100+GHz electronically scanned

array antennas.

Figure 5. Active reflection coefficient (in dB) for RGW element.

2.3 ESR7:AnalogueRadio‐over‐Fiber‐fedantennasformassivedeployment


LNA – Antenna co‐design assumes that both of these devices will be designed in such kind of way to

improve the noise performance for the whole system. LNA optimal input impedance creates the specific

condition for the input antenna impedance. Common source LNA configuration has pretty low optimal

input impedance. In this case, the easiest solution for the antenna design becomes a rectangular patch

antenna.

This type of antennas allows to change input impedance in a wide range of variations and keep good

radiation parameters. The feed position of a patch antenna excited in its fundamental mode is typically

located in the center of the patch width direction and somewhere along the patch resonant length

direction. The exact position along the resonant length is determined by the electromagnetic field

distribution in the patch. Looking at the current (magnetic field) and voltage (electric field) variation along

with the patch (Figure 6), the current has a maximum at the center and a minimum near the left and right

edges, while the electric field is zero in the center and maximum near the left and minimum near the right

edges.


Figure 6: Patch antenna current and voltage distributions.

By properly choosing the feeding point and antenna geometry, it is possible to provide antenna input

impedance that will be equal to the optimal LNA impedance for the noise matching. An important thing

that affects the design of the antenna, is the final configuration it is mean that antenna should be

integrated into the package and simulations of this final configuration inseparable task. In other words,

antenna design combines two more big topics: IC – antenna interconnection and packaging solution.

2.4 ESR8:120GHzDual‐PolarizedAntenna‐on‐Chip


In this work, the antenna‐on‐chip (AoC) concept was chosen [4] as it might provide valuable advantages

when the frequency of operation is above 100GHz. The size of the radiating element of an antenna goes

below 1mm at these frequencies, and it becomes feasible to consider placing it on the IC. This approach

provides great integration capabilities since the antennas can be matched directly to the amplifiers and

are fabricated in the same technological process. A generalized model of a SiGe BiCMOS [5] IC chip was

used, which represents a similar technology of the ESR’s secondment host – NXP Semiconductors.

2.4.2 Proposedantenna:120GHz in‐siliconantennaemployingelectromagneticbandgapstructurestosuppressthesubstratewaves

Silicon on‐chip antennas often exhibit very poor performance (η < 30%). Two main reasons for that

are the high permittivity and the low resistivity (high losses) of thick bulk Si substrates. Due to the former,

most of the radiation is sucked into the substrate [6], or coupled to the substrate waves [7] which

introduce harmful interference and undesired re‐radiation. The latter means that the radiation trapped

in the substrate dissipates quickly.


Figure 7. Illustration of the substrate waves problem in Si (from [4]).

To address these issues, it is proposed to grind down the silicon chip to 100m and to use a gap

waveguide‐like electromagnetic bandgap (EBG) structure [8] to attenuate the substrate waves.

Figure 8. Cross‐section of the proposed antenna element (a). The EBG structure is formed between the metallization in the top PCB and ground plane in the IC dioxide layer (blue) (b). Antenna feeds – differentially excited field probes (c).

The antenna element (Figure 8a) consists of a silicon IC connected to the Bottom PCB – via e.g. flip‐chip

technology – which serves to enhance the radiation performance of the antenna by introducing the

optimal distance to the ground plane. Metal layers and vias in the Bottom PCB prevent the EM radiation

from travelling through the PCB. The top PCB is placed on top of the IC. A grid of vias in the top PCB is

designed to form an artificial magnetic conductor (AMC) surface. When such an AMC surface is placed at

a proper distance parallel to the perfect electric conductor (PEC) surface, no EM mode can propagate

between those two [8]. Thus, the two PCB that the silicon chip is sandwiched between act both as an EBG

structure (Figure 8b) and as a radiation‐enhancing cavity. Four field probes are patterned in the IC metal

layers that can excite the antenna in one of two desired linear polarizations (Figure 8c).

Below are the simulated results of the proposed antenna that was designed for 120 GHz center frequency.

A CST Microwave Studio model with 12+ million mesh cells was simulated using the time‐domain solver.

Silicon substrate is 100m thick, has permittivity ε = 12.9, and conductivity σ = 2 S/m (similar to [9]). The

PCBs have the permittivity ε = 3 and tanδ = 0.002 ([10] was used as a reference). All metal layers have

conductivity 2.5x107 S/m. The bottom PCB is 389m thick and has three metal layers evenly spaced 133m

from each other. The top PCB is 558m thick and has three metal layers spaced at (counting from the


bottom) 257, 174 and 117m. The vias in both PCBs has 100m diameter and are spaced 380m from

each other.

Figure 9. A dispersion diagram of the EBG structure used in the proposed design.

Figure 10. Simulated antenna Gain (IEEE) of the proposed design. The E‐plane (a) and H‐plane (b) cuts at 114, 120 and 126 GHz. Gain in broadside direction is ≈ 5dBi in this frequency range.

To investigate the effect of the EBG structure, we simulated a two‐element array with and without the

top PCB, see Figure 11 below. Note the improved S11‐bandwidth (≈114‐128 GHz) and the reduced inter‐

element coupling (S21 < ‐20dB).

Figure 11. Two‐element array S‐parameters without (a) and with (b) the top PCB.


In the 112‐125 GHz frequency range the antenna has the radiation efficiency of >70% and the S11

matching better than ‐10dB at the same time.

Figure 12. Radiation efficiency of the proposed antenna.

The proposed antenna element will be further investigated to determine its thermal properties and for

the possibility to use it for large arrays.

3 References

[1] A. U. Zaman and P.‐S. Kidal, Gap Waveguide in Handbook of Antenna Technologies. New York, NY:

Springer Science + Business Media Singapore, 2015, p. 464.

[2] Rong and K. A. Zaki, “Characteristics of generalized rectangular and circular ridge waveguides,” IEEE

Trans. Microw. Theory Tech., vol. 48, no. 2, pp. 258–265, 2000.

[3] K. Bhattacharyya, Phased array antennas: Floquet analysis, synthesis, BFNs and active array systems.

John Wiley & Sons, 2006, vol.179.

[4] R. Karim, A. Iftikhar, B. Ijaz, and I. Ben Mabrouk, “The Potentials, Challenges, and Future Directions of

On‐Chip‐Antennas for Emerging Wireless Applications—A Comprehensive Survey,” IEEE Access, vol. 7,

pp. 173897–173934, 2019, DOI: 10.1109/ACCESS.2019.2957073.

[5] H. Rücker and B. Heinemann, “High‐performance SiGe HBTs for next generation BiCMOS technology,”

Semicond. Sci. Technol., vol. 33, no. 11, p. 114003, Nov. 2018, DOI: 10.1088/1361‐6641/aade64.

[6] R. W. Ziolkowski, “Custom‐Designed Electrically Small Huygens Dipole Antennas Achieve Efficient,

Directive Emissions Into Air When Mounted on a High Permittivity Block,” IEEE Access, vol. 7, pp.

163365–163383, 2019, DOI: 10.1109/ACCESS.2019.2952112.


[7] A. Babakhani, X. Guan, A. Komijani, A. Natarajan, and A. Hajimiri, “A 77‐GHz Phased‐Array Transceiver

With On‐Chip Antennas in Silicon: Receiver and Antennas,” IEEE Journal of Solid‐State Circuits, vol. 41,

no. 12, pp. 2795–2806, Dec. 2006, DOI: 10.1109/JSSC.2006.884811.

[8] P.‐S. Kildal, E. Alfonso, A. Valero‐Nogueira, and E. Rajo‐Iglesias, “Local Metamaterial‐Based Waveguides

in Gaps Between Parallel Metal Plates,” IEEE Antennas and Wireless Propagation Letters, vol. 8, pp.

84–87, 2009, DOI: 10.1109/LAWP.2008.2011147.

[9] H. J. Ng, R. Wang, and D. Kissinger, “On‐Chip Antennas in SiGe BiCMOS Technology: Challenges, State

of the Art and Future Directions,” in 2018 Asia‐Pacific Microwave Conference (APMC), Nov. 2018, pp.

621–623, DOI: 10.23919/APMC.2018.8617626.

[10] “PCB‐Material‐Selection‐for‐RF‐Microwave‐and‐Millimeter‐wave‐Designs‐1.pdf.” Accessed: Mar.

22, 2021. [Online]. Available: https://www.isola‐group.com/wp‐content/uploads/PCB‐Material‐

Selection‐for‐RF‐Microwave‐and‐Millimeter‐wave‐Designs‐1.pdf.

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H2020 MSCA ITN 2019 EID - mywave-project.eu