1. Paper review
Yun-tae Park
Antennas & RF Devices Lab.

2. Contents
Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
- IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 16, 2017
Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
- IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 15, 2016
Antennas & RF Devices Lab.

3. Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
I. Introduction
The millimeter-wave communication is regarded as one of the most potential solutions for the exponentially expanding wireless data traffic in the future, due to the wide usable spectrum in the millimeter waveband.
However, the radio waves suffer large path-loss and limited scattering in the millimeter waveband.
massive multiple-input multiple-output (MIMO) technique & beamforming technique
An antenna array with large element spacing will introduce high sidelobes and then cause multiuser interference.
the requirement of the antenna element spacing in the beamforming system is around half-wavelength
Figure 1. Millimeter-wave communication system model for
the multiuser MIMO beamforming.
Figure 2. Effects of the element spacing in the radiation pattern
(1×8 H-plane array arranged in horizontal direction).
Antennas & RF Devices Lab.

4. Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
I. Introduction
A broadband printed-dipole antenna for use in 5G application is proposed.
- use an integrated balun as the feed structure to enable broadband operation
- the printed-dipole is angled at 45° to reduce the antenna size
- insert a microstrip stub between the two printed-dipole antennas to achieve a low mutual coupling
Antennas & RF Devices Lab.

5. Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
II. Single Element
The antenna was composed of a 50-Ω microstrip-line feed,
a truncated ground plane, an integrated balun, and a printed dipole.
The dipole was fed by a slot line with a characteristic impedance of 116 Ω.
To achieve the impedance matching over a broad frequency range, the balun acts as a microstrip-to-slot-line transformer, which consists of a folded microstripline connected to the feedline and a rectangular slot etched on the ground plane.
Impedance matching was realized by adjusting the folded line and rectangular slot.
Figure 3. (a) Geometry of the printed-dipole antenna.
Antennas & RF Devices Lab.

6. Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
II. Single Element
The printed dipole was angled to achieve a compact size,
as well as to realize a wide pattern in the E-plane.
To fit the jig and SMA connector, we extended the ground plane of the fabricated antenna.
Figure 3. (a) Geometry of the printed-dipole antenna.
Figure 3. (b) A photograph of the fabricated sample including aluminum jig and SMA connector.
Antennas & RF Devices Lab.

7. Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
II. Single Element
As shown in Fig. 4(a), the measured impedance bandwidth for 𝑆 11 <−10 dB was 36.2% ( GHz), whereas the simulated value was 40% ( GHz).
In addition, the antenna yielded a small gain variation.
Within the operational bandwidth, the measured gain was dBi, while the simulated value was dBi.
Figure 4. The simulation and measurement results of the single element : (a) 𝑆 11 and gain values; (b) normalized 32-GHz radiation pattern.
Antennas & RF Devices Lab.

8. Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
II. Single Element
Fig. 4(b) shows the 32-GHz radiation patterns of the antenna.
The measurement results agreed with the simulations, and the two resulted in a symmetric profile in both the
E- and H-planes.
At 32 GHz, the antenna yielded half-power beamwidths (HPBWs) of 66° and 152° in the E- and H-planes,
respectively.
Within the operational bandwidth, the measurements yielded HPBWs of 60°-70° and 150°-160° in the
E- and H-planes, respectively.
Figure 4. The simulation and measurement results of the single element : (a) 𝑆 11 and gain values; (b) normalized 32-GHz radiation pattern.
Antennas & RF Devices Lab.

9. Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
III. Antenna Arrays - Mutual Coupling
For designing antenna arrays, the tradeoff between low mutual coupling and close spacing has attracted considerable attention from researchers.
To obtain a low mutual coupling for close spacing, we inserted a microstrip stub between the two printed-dipole antennas with a 4.8-mm center-to-center spacing ( λ at GHz).
The mutual coupling characteristic is based on the LC resonance of the stub structure.
The inductive and capacitive components can be controlled via adjustments to the stub length; consequently, the operating frequency can be determined by measuring 𝐿 𝑛 .
We chose 𝐿 𝑛 =1mm for the final design to obtain a low mutual coupling of <−20 dB
across the operational bandwidth.
Figure 5. (a) Geometry of the two printed-dipole antenna with a stub and a center-to-
center of 4.8 mm and (b) simulated mutual coupling ( 𝑆 21 ) for different
lengths of the stub ( 𝐿 𝑛 ).
Antennas & RF Devices Lab.

10. Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
III. Antenna Arrays - Scanning Performance
We implemented an 8-element array with the printed dipole antennas and a 4.8-mm center-to-center spacing between adjacent elements, as shown in Fig. 6(a).
The arrays were fed by eight ports with the same magnitude, while the scanning was achieved by the phase control at each port.
Due to the lower mutual coupling between adjacent elements, the array with stubs yielded a wider scanning angle, higher gain, and a lower sidelobe level as compared to the array without the stub.
At the higher frequencies,
due to the mutual coupling of <−15 dB for both configurations [see Fig. 5(b)], their scanning performance is
similar.
Figure 6. (a) Geometry of an 8-element linear array with the proposed antenna, a center-to-center spacing of 4.8 mm, and stubs. Scanning performance in E-plane of the array (b) without and (c) with stubs at 28 and 32 GHz.
Antennas & RF Devices Lab.

11. Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
III. Antenna Arrays - Scanning Performance
Stub (O)
Stub (X)
28 GHz
Scan angle
75°
60°
SLL
<−10 dB
<−5 dB
Gain
dBi
dBi
32 GHz
50°
<−13 dB
<−9.5 dB
dBi
dBi
Figure 6. (a) Geometry of an 8-element linear array with the proposed antenna, a center-to-center spacing of 4.8 mm, and stubs. Scanning performance in E-plane of the array (b) without and (c) with stubs at 28 and 32 GHz.
Antennas & RF Devices Lab.

12. Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
III. Antenna Arrays - Eight-Element Array Measurements
To verify the scanning performance, we fabricated and measured the 8-element arrays with stubs for different fixed scanning angles.
Fig. 7(a) shows a fabricated sample of the array with the 0° scanning angle.
Both simulation and measurement resulted in an 𝑆 11 <−10 dB at GHz and a small gain variation;
at GHz, the measured gain was dBi as compared to the simulated value of dBi.
Figure 7. (a) Fabricated sample of the 8-element array with 0°-scanning and its results: (b) 𝑆 11 and gain values; (c) normalized 32-GHz radiation pattern.
Antennas & RF Devices Lab.

13. Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
III. Antenna Arrays - Eight-Element Array Measurements
Fig. 8(a) shows a fabricated sample of the 8-element linear array with a fixed scan angle for a 4.8-mm center-to-center spacing and a microstrip stub between adjacent elements.
As opposed to the array without scanning, this array employed fixed microstrip-line delays in the feed to achieve a 45° scan angle at 28 GHz (40° scan angle at 32 GHz).
At 28 GHz, the measurements resulted in an HPBW of 19°, a gain of 10.0 dBi, and an SLL of <−14 dB.
At 32 GHz, the measurements resulted in a 3-dB beamwidth of 15°, a gain of 10.3 dBi, and an SLL of <−13 dB.
Figure 8. (a) Fabricated sample of the 8-element array with fixed scanning; its (b) 𝑆 11 values and (c) E-plane radiation patterns at 28 and 32 GHz.
Antennas & RF Devices Lab.

14. Broadband Printed-Dipole Antenna and Its Arrays for 5G Applications
IV. Conclusion
A broadband printed-dipole antenna with advantages including compact size, broad impedance-matching bandwidth, wide radiation pattern, small gain variation, and high radiation efficiency is proposed.
To achieve low mutual coupling for a close center-to-center spacing, we inserted a microstrip stub between the two printed angled-dipole antennas.
- the array resulted in a wider scanning angle, higher gain, and a lower sidelobe level in the low
frequency region.
The proposed antennas are good candidates for mobile terminals and base stations in 5G wireless cellular networks, as well as other millimeter-wave wireless communication systems.
Antennas & RF Devices Lab.

15. Antennas & RF Devices Lab.
Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
I. Introduction
Employing higher frequencies for the networks results in an increase in free-space path loss. Moreover, different link scenarios suggest different premises, outdoor-to-indoor links in dense urban areas are relatively difficult to establish considering the high reflectivity and attenuating properties of various building materials at mmWave frequencies.
The phased array solution introduces the beamsteering function and enables the system to achieve a good link when incoming signals are coming from different angles. The steering range will however still be limited, and results suggest that there is a necessity and desire for larger scanning freedom of the receiving antennas in the mobile terminal.
Figure 1. System model of presumed outdoor 5G cellular
networks. Beamsteering is applied in the
mobile station.
Antennas & RF Devices Lab.

16. Antennas & RF Devices Lab.
Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
I. Introduction
As a comparison, 3G/4G mobile antennas exhibit good coverage relative to the required gain due to the rather low power level requirements.
The directive beam from a mmWave cellular antenna array however, as illustrated in Fig. 2, introduces the challenge of achieving both a strong signal path and simultaneously obtaining a spherical coverage.
This letter presents a characterization method for analyzing the performance of phased array antennas in cellular handsets, not only according to classical standards, but according to their achievable total scan pattern and its respective coverage for a given threshold of received gain.
Figure 2. Array pattern of a 4×1 notch array, design
description in Section III.
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17. Antennas & RF Devices Lab.
Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
II. Array Performance Analysis
The total scan pattern is obtained from all array patterns corresponding to the electronically steered beam at different phase shifts by extracting the best achievable gain at every angular distribution point (𝜃,∅), as illustrated in Fig. 3.
The effective coverage of the mobile terminal phased array is then retrieved from its total scan pattern with respect to a set value of received gain ( 𝐺 𝑚𝑖𝑛 ).
All signals below the threshold are considered too weak to establish a link.
Thus, the coverage efficiency ( 𝜂 𝑐 ) is defined such as
(1)
Polarization mismatch can be included in 𝜂 𝑐 , thus accounting for the antenna performance in a cross-polarized scenario, and the multiple-input-multiple-output (MIMO) scenario of scanning with different polarized arrays.
Figure 3. Conceptual model of the total scan pattern of a
mobile terminal phased array.
Antennas & RF Devices Lab.

18. Antennas & RF Devices Lab.
Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
III. Single-Element Design and Performance
For illustration purposes, two different antenna designs are considered
- an aperture-coupled rectangular patch
- a quarter-wavelength notch
Potential designs need to be cheap to manufacture and integrated on a very limited space in the smartphone,
among many other limitations.
Thus, the antenna types are selected due to their small size, in terms of half a wavelength in the substrate,
which enables array implementation at the desired operating frequency.
Antennas & RF Devices Lab.

19. Antennas & RF Devices Lab.
Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
III. Single-Element Design and Performance - Quarter-Wavelength Notch Antenna
The quarter-wavelength notch is a novel antenna designed for mmWave usage in the mobile terminal.
It is a two-layer structure with a resonant slot of length 𝐿 𝑛 , approximately a quarter-wavelength in the substrate ( 𝜆 𝜀 4 ), and width 𝑊 𝑛 ( 𝑊 𝑛 ≪ 𝐿 𝑛 ) cut in the ground plane.
The slot is fed through a microstrip line, where a mitered bend is utilized in order to achieve a 𝜆 𝜀 4 stub.
To suppress induced surface waves and achieve a wider single-element beam with a controlled pattern, parasitic notches of the same lengths are cut on each side of the resonant notch with a periodicity 𝑑= 𝜆 𝜀 4 .
Thus, the unit cell of the array is 𝜆 𝜀 2 wide and consists of one fed notch and one passive notch.
Figure 4. Topologies of the single-element antennas.
- Notch antenna ( ℎ 1 =0.305𝑚𝑚)
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20. Antennas & RF Devices Lab.
Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
III. Single-Element Design and Performance - Aperture-Coupled Patch Antenna
The microstrip patch antenna is a conventional antenna type that is inexpensive and easy to fabricate.
The length 𝐿 𝑝 is approximately 𝜆 𝜀 2 , and the width 𝑊 𝑝 ~1.5 𝐿 𝑝 , allowing for compact array configurations in the case model.
The aperture-coupling is employed by cutting a slot in the ground plane and feeding the patch using a microstrip on the opposite side of the ground.
This feeding approach contributes to isolation of the radiating patch from other intended components and suppression of spurious radiation.
Figure 4. Topologies of the single-element antennas.
- Aperture-coupled patch antenna
( ℎ 1 =0.305𝑚𝑚, ℎ 2 =0.508𝑚𝑚)
Antennas & RF Devices Lab.

21. Antennas & RF Devices Lab.
Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
IV. Single-Element Simulations and Measurements
The arrays are 4×1 configurations with element spacing slightly less than half a free-space wavelength (10 mm at 15 GHz).
Thus, the total size of any array is around 40 mm, and schemes with two subarrays can be implemented in the phone case model within a limited area.
Simulated and measured normalized radiation patterns for the corresponding configurations can be seen in Fig. 5 with defined cross-sectional cuts.
Both the notch and the patch exhibit a wide main beam in both planes, suggesting that a large phased array scan is feasible. Simulated absolute gain is around 4.4 dBi for all notch elements,
and 5.2 dBi for all patch elements.
Figure 5. Simulated and measured two-dimensional radiation patterns of the (a), (b) single-element notch antenna and (c), (d) single-element patch antenna.
The single elements were embedded in a 4×1 array in the phone case model, with pattern orientation as in (e).
Antennas & RF Devices Lab.

22. Notch array > Patch array
Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
V. Coverage Performance of Phased Arrays
A continuous phase shift was assumed as to illustrate electrically steered beams.
Notch array
Patch array
Max absolute gain
9.9 dBi
10.4 dBi
Max coupling
< -16 dB
< - 16 dB
Radiation efficiency
87 %
85 %
Coverage efficiency
Notch array > Patch array
For the notch array, it is held above 50% for 𝐺 𝑚𝑖𝑛 ≤4.5 dBi.
Figure 6. Total scan patterns for different array configurations.
(left) Notch array. (right) Patch array.
Figure 7. Coverage efficiency 𝜂 𝑐 as a function of minimum
received gain 𝐺 𝑚𝑖𝑛 for different array configurations.
Antennas & RF Devices Lab.

23. Antennas & RF Devices Lab.
Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
V. Coverage Performance of Phased Arrays
Subarray schemes can be employed, where each respective beam is separately steered using its corresponding phase shift, to achieve pattern diversity and enhanced 𝜂 𝑐 .
With dual boresight in alternate directions, the schemes can be evaluated according to their improved performance.
Three schemes were tested :
two perpendicular aligned notch arrays
two parallel but opposite directed notch arrays
a notch and patch array perpendicularly mounted
In a good signal range, all three settings have high 𝜂 𝑐 , and it can be seen by comparing to Fig. 7 that the coverage has been significantly enhanced in all cases.
Specifically, the opposite directed notch alignment achieves
𝜂 𝑐 ≥95% for 𝐺 𝑚𝑖𝑛 ≤5 dBi.
Figure 8. Coverage efficiency 𝜂 𝑐 as a function of minimum
received gain 𝐺 𝑚𝑖𝑛 for different subarray configurations.
Antennas & RF Devices Lab.

24. Antennas & RF Devices Lab.
Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
VI. Conclusion
This letter proposes an approach of analyzing performance of utilized phased array antennas in the mobile terminal for 5G cellular networks.
The performance of the phased array antenna is quantified in its total scan pattern and a related quantity, the coverage efficiency.
The method can be directly applied as a form of evaluation for array configurations targeting the specific area of application.
It is flexible with respect to its preconditions, i.e., testing more advanced network models still allow for the performance analysis to be applied.
This can leverage good insight in how the 5G cellular antenna designs should be further developed.
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25. Thank you for your attention
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