TH2G-4

A K-Band Low-Complexity Modular

Scalable Wide-Scan Phased Array

F. Akbar and A. Mortazawi

Department of Electrical Engineering and Computer Science

University of Michigan, Ann Arbor, MI, USA

TH2G-4

Outline

• Introduction and Motivation

• Phased Array’s Operation Principle

• Phased Array’s Circuit Diagrams

• Simulation and Measurement Results

• Conclusion

TH2G-4 3

Introduction

A phased array is an ensemble of antennas capable of beamforming and steering

by adjusting the relative phase and magnitude of the signals received or transmitted

by the antenna elements.

Δ𝜙 = inter-element

phase difference

2𝜋𝑓

𝑐𝑑 sin 𝜃 = Δ𝜙

Antenna

Elements

Phase

Shifters

Spacing (𝑑)

𝜽

Input𝜃 = scan angle

TH2G-4 4

Phased Array Applications

In Radars

Increase cross-range resolution

Reduce required transmit power

Enhance SNR

In Communication Systems

Alleviate multipath fading

Mitigate co-channel interference

Reduce required transmit power

Enhance SNR

TH2G-4 5

Motivation

Reducing the

Complexity

Circuit size

of phased arrays in the interest of their widespread use in commercial

communication and radar systems such as:

5G communications

Automotive radars for ADAS and autonomous vehicles

TH2G-4 6

Conventional Phased Array ArchitecturesRF-Phase-Shifting

IF-Phase-Shifting Digital-Phase-Shifting

LO-Phase-ShiftingPhased arrays typically

employ one phase shifter per

each array element.

In general, phase shifters

along with their control

circuitry contribute significantly

to complexity, size, and cost of

phased arrays.

A modular scalable phased

array with a significantly

reduced number of phase

shifters and control circuitry is

presented.

RF Power Combiner

LNA

Phase

Shifter

LO

IF

IF Power Combiner

LO Power Divider

LNA

Mixer

LO

IF

Phase

Shifter

IF Power Combiner

LO Power Divider

Phase

Shifter

LNA

Mixer

LO

IF

LO Power Divider

Beam Forming

LNA

Mixer

LO

IF

A/D A/D A/D A/D

D/A

TH2G-4 7

𝜃𝑖 = tan−1sin 𝜙

𝑎𝑖𝑏𝑖

+ 𝑐𝑜𝑠 𝜙𝑖 = 1,2, … , 𝑛

The number of phase shifters is reduced by integrating the phase-shifting

function into the sub-array’s feed network through vector summation.

An n-element subarray employing a single phase shifter

𝑒𝑖 = 𝑎𝑖 + 𝑏𝑖 𝑐𝑜𝑠 𝜑 2 + 𝑏𝑖 𝑠𝑖𝑛 𝜑 2

en

en-1

e2

𝝓

𝜽𝒏

e1

A

B

Phased Array’s Operation Principle

bn b1bn-1

en en-1

an an-1 a1

e1ϕ

B

AInput

Feed Network

TH2G-4 8

A Low-Complexity Modular Scalable Phased Array

Multiple subarrays can be connected to form a larger array with a narrower beamwidth.

Independent control of 𝜙1 and 𝜙2 enables a correct phase progression between the

subarrays.

By using phase shifters with tunable amplitude, gain can be maintained over the scan

range.

An n-element subarray module employing two phase shifters𝝓 = 𝝓𝟏 −𝝓𝟐

en

en-1

e2

e1 Phase Shifters with Tunable Amplitude

Structure of a modular scalable phased array formed by connecting multiple n-element subarray modules

bn b1bn-1

en en-1

an an-1 a1

e1

B

AInput

Feed Network

ϕ 2

ϕ 1

bn b1bn-1

en

an an-1 a1

ϕ 1

ϕ 2

en-1 e1Subarray Subarray Subarray

Input

TH2G-4 9

A Wide-Scan Low-Complexity Phased Array Module

Simplified schematic of the proposed eight-element wide-scan phased array module with four phase shifters

The 8-element phased array module employing two 4-element subarrays is

designed for ~±15° of scan range.֞Avg. of ~±45° inter-element phase difference

Utilizing a quadrature signal generator along with quadrant selector switches at

each antenna port ֜ ±90° of scan range

Four-Element Subarray

Feed Network

b4

a4

Input

S in

𝒆𝒋𝜱𝟏𝑹 S in

S in a3

b3

a2

b2

a1

b1

Switched

Quad.

Gen.

e1Re2Re3Re4R

b4

a4a3

b3

a2

b2

a1

b1

e1L e2L e3L e4L

𝜱𝟏𝑹

Switched

Quad.

Gen.

Switched

Quad.

Gen.

Switched

Quad.

Gen.

𝜱𝟐𝑹 𝒆𝒋𝜱𝟐𝑹 S in

Switched

Quad.

Gen.

Switched

Quad.

Gen.

Switched

Quad.

Gen.

Switched

Quad.

Gen.

𝒆𝒋𝜱𝟏𝑳 S in

𝜱𝟏𝑳

S in

S in𝜱𝟐𝑳 𝒆𝒋𝜱𝟐𝑳 S in

TH2G-4 10

Reduced number of

phase shifters and their

associated control

signals by a factor of two

Detailed block diagram of the K-Band wide-scan integrated phased array

K-Band Wide-Scan Integrated Phased Array

Input

Divider

Vector

Modulator

Phase Shifter

Feed

Network

D2S

Amp1Channel 1Quad. Gen. Network

+ Switches

Single-ended to

Differential Signal

Converter

Differential to

Single-ended

Signal Converter

4-Element Subarray

S2D

D2S Channel 2

D2S Channel 3

D2S Channel 4

Subarray Core

D2S Channel 5

S2D

D2S Channel 6

D2S Channel 7

D2S Channel 8

Amp1

Amp1

Amp1

Amp1

Amp1

Amp1

Amp1

Amp2

Amp2

Amp2

Amp2

Amp2

Amp2

Amp2

Amp2

For Wide-Scan

Applications

Feed

Network

Quad. Gen. Network

+ Switches

Quad. Gen. Network

+ Switches

Quad. Gen. Network

+ Switches

Quad. Gen. Network

+ Switches

Quad. Gen. Network

+ Switches

Quad. Gen. Network

+ Switches

Quad. Gen. Network

+ Switches

Applications in automotive

radars and 5G technology

TH2G-4 11

Active feed network with polarity selector switches

Phased Array’s Circuit Diagrams

Design parameters’ optimum

values (normalized to the

value of 𝑏1):

|𝑎1|=|𝑏4|=7

|𝑎2|=|𝑏3|=8

|𝑎3|=|𝑏2|=5

|𝑎4|=|𝑏1|=1

The transistors in the current

distribution network are sized

such that their drain current

ratios are equal to the design

parameters’ optimum values.

VbiasVbias

M1M2

Gm-Cell

RBRB

CCCC

Vbias Vbias

M4 M3

Gm-Cell

RB RB

CC CC

VB

42 µm

0.18 µm

M6 M5

VB

48 µm

0.18 µm

M7M8

VB

30 µm

0.18 µm

M10 M9

VB

M11M12

VB

6 µm

0.18 µm

M14 M13

VB

30 µm

0.18 µm

M15M16

VB

48 µm

0.18 µm

M18 M17

VB

42 µm

0.18 µm

M19M20

Vector

Summation

Unequal Current

Distribution Network

𝑽𝒊𝒏,𝝋𝟏

+

𝑽𝒊𝒏,𝝋𝟏

−

𝑽𝒊𝒏,𝝋𝟐

+

𝒊𝝋𝟏+

𝒊𝝋𝟏−

𝒊𝝋𝟐+

𝒊𝝋𝟐−

𝒊𝟏,𝝋𝟏

+

𝒊𝟏,𝝋𝟏

−

𝒊𝟐,𝝋𝟏

+

𝒊𝟐,𝝋𝟏

−

𝒊𝟑,𝝋𝟏

+

𝒊𝟑,𝝋𝟏

−

𝒊𝟒,𝝋𝟏

+

𝒊𝟒,𝝋𝟏

−

𝒊𝟒,𝝋𝟐

−

𝒊𝟒,𝝋𝟐

+

𝒊𝟑,𝝋𝟐

−

𝒊𝟑,𝝋𝟐

+

𝒊𝟐,𝝋𝟐

−

𝒊𝟐,𝝋𝟐

+

𝒊𝟏,𝝋𝟐

−

𝒊𝟏,𝝋𝟐

+

MS1MS2MS3MS4

LP

CH1 CH1

V1

V1V1MS1MS2MS3MS4

LP

CH2 CH2

V2

V2V2MS1 MS2 MS3 MS4

LP

CH4CH4

V4

V4 V4 MS1 MS2 MS3 MS4

LP

CH3CH3

V3

V3 V3

6 µm

0.18 µm

Polarity Selector Switches

𝒊𝒆𝟏+

𝒊𝒆𝟏−

𝒊𝒆𝟐+ 𝒊𝒆𝟐

− 𝒊𝒆𝟑− 𝒊𝒆𝟑

+ 𝒊𝒆𝟒− 𝒊𝒆𝟒

+

𝑽𝒊𝒏,𝝋𝟐

−

Feed Network

b4

a4 a3

b3

a2

b2

a1

b1

e1e2e3e4

𝜱𝟏

𝜱𝟐

TH2G-4 12

Phased Array’s Circuit Diagrams (Cont’d)

Vector modulator phase shifter Quadrature generation network with I/Q selector switches

VDD

Vbias

SWI SWISWQ

Vbias

VDD

vo vo+

vin+vin

I/Q Selector

Switches

Quadrature

Generation

Network

RC

SWI SWQ

CC

RBRB

M1

CC

M2

M3M4M5M6M7M8M9M10

𝒊𝑸−

𝒊𝑰−

𝒊𝑰

𝒊𝑸

VDD

VB2

VB1

VB2

vin

VDD VBI VDDVBQ VBI VDDVBQVDD

vin

vo vo+

MB

M1M2M3M4

CC RBCCRB

R C

M5M6M7M8M9M10M11M12

LP

+

TH2G-4 13

130-nm CMOS Phased Array

The chip is mounted on a four-layer PCB comprising of a 10 mil Rogers RO3006

substrate on top of a 4 mil prepreg connected to a 16 mil FR4 substrate.

The input and output GSG pads are wirebonded to 50-Ohm grounded coplanar

waveguide (GCPW) lines on the top layer of the PCB.

Die photo of the eight-element CMOS phased array Top view of the phased array chip mounted on a four-layer PCB

TH2G-4 14

Simulated and Measured Array Factor at 24 GHz

Simulation Measurement

Scan range: ±90°

SLL < -10 dB

Array factor variation over the scan

range < 1.1 dB

Scan range: ±90°

SLL < -9.75 dB

Array factor variation over the scan

range < 2 dB

TH2G-4 15

Measured Phased Array’s Power Gain and

Input/Output Power 1-dB Compression Point

Phased array’s power gain at each scan angle varies less than 3 dB over the range

23.2‒24.4 GHz.

1-dB compression point of the phased array’s output power is larger than 4.3 dBm

within 23.2‒24.4 GHz.

TH2G-4 16

Simulated and Measured Reflection Coefficients

Simulation

Measurement

Within 23.2‒24.4 GHz:

Simulated input reflection coefficient < -15.7 dB

Simulated output reflection coefficient < -14.7 dB

Measured input reflection coefficient < -14.3 dB

Measured output reflection coefficient < -11 dB

TH2G-4 17

Comparison with Integrated Phased Arrays

This Work [1] [2] [3] [4]

130-nm CMOS SiGe BiCMOS 130-nm SiGe BiCMOS 180-nm CMOS 65-nm CMOS

23.2-24.4(1) 28.4-29.4(2) 27.2-28.7 (3-dB BW) 15-18 28

8 TX 4 TRX 32 TRX 8 TX 4 TRX

> -5.1(3) (at 24 GHz) 10.5 (at 28-29 GHz) 13.5 (at 28 GHz) 13 (at 17 GHz) 15.7

85 200 319 (at Psat) 528 300(4)

1.683.954 2.54.7 10.515.8 38.5 34

Process

Reference

Frequency (GHz)

Number of Channels

OP1dB/Channel (dBm)

PDC/Channel (mW)

Area (mm2)

(1)3-dB BW of phased array’s power gain. (2)3-dB EIRP BW. (3)Excluding the PCB loss. (4)At Pout/Ch. of 11 dBm.

[1] K. Kibaroglu et al., “A quad-core 28-32 GHz transmit/receive 5G phased-array IC with flip-chip packaging in SiGe BiCMOS,” IEEE MTT-S Int. Microw. Symp. Dig.,

Honololu, HI, USA, June 2017, pp. 1892‒1894.

[2] B. Sadhu et al., “A 28GHz 32-element phased-array transceiver IC with concurrent dual polarized beams and 1.4 degree beam-steering resolution for 5G

communication,” IEEE International Solid-State Circuits Conference (ISSCC), San Francisco, CA, 2017, pp. 128‒129.

[3] D. Chen et al., “A Ku-Band 8-element phased-array transmitter with built-in-self-test capability,” IEEE/MTT-S International Microwave Symposium - IMS,

Philadelphia, PA, 2018, pp. 610‒612.

[4] J. Pang et al., “A 28-GHz CMOS phased-array transceiver based on LO phase-shifting architecture with gain invariant phase tuning for 5G new radio,” IEEE J.

Solid-State Circuits, vol. 54, no. 5, pp. 1228‒1242, May 2019.

The phased array in this work has the smallest chip area mainly due to its smaller

number of phase shifters (by a factor of 2) as compared to the conventional designs.

TH2G-4 18

Conclusion

A new architecture for modular scalable phased arrays with a reduced number of

phase shifters and control signals has been presented.

An 8-element wide-scan phased array has been designed based on the

described approach and fabricated using 130-nm CMOS process.

In the presented wide-scan phased array operating at K-band, the number of

phase shifters and their associated control signals are reduced by a factor of two

as compared to conventional phased arrays using one phase shifter per each

radiating element.

The presented phased array is a promising candidate for applications in 5G

technology and automotive radars for advanced driver assistant systems (ADAS)

and autonomous vehicles.