[IJET-V1I2P6] Authors :Sarat K Kotamraju, K.Ch.Sri Kavya, A.Gnandeep Reddy, G.Naveen Kumar, K.Nandini Priyanka, P.V.Santosh

International Journal of Engineering and Techniques - Volume 1 Issue 2, Mar - Apr 2015

ISSN: 2395-1303 http://www.ijetjournal.org Page 32

Design and Modeling of a Ku-Band Power Amplifier using GaN-

HEMT Technology for Defense and Aerospace Applications

Sarat K Kotamraju1, K.Ch.Sri Kavya

2, A.Gnandeep Reddy

3, G.Naveen Kumar

3, K.Nandini Priyanka

3,

P.V.Santosh3

1Professor, Department of ECE, K L University, Guntur Dt., A.P., India

2Associate Professor, Department of ECE, K L University, Guntur Dt., A.P., India 3Students, B.Tech, Department of ECE, K L University, Guntur Dt., A.P., India

Introduction:

The power Amplifier is one of the key components

in a wireless Transmitter system to amplify the low

power RF Signal to the required power level at the

antenna [1] and the Maximum output power of a

transmitter is determined by a power amplifier. To

provide the better and sufficient quality of service

for high user capacity, one needs a highly linear and

highly efficient power Amplifiers. These high

efficiency and high output power amplifiers are

desirable for defense and aerospace applications.

The power amplifiers are generally classified as

Trans conductance and switch mode power

amplifiers. The Trans conductance power amplifiers

operate the transistor as a dependent current source.

While the switch mode power amplifiers operates

the transistor like a switch.

The trans conductance or the biasing class power

amplifiers includes class A, class AB, class B and

class C where the particular amplifier class is

defined by its DC bias condition and the conduction

angle analysis. Among the above mentioned biasing

class power amplifiers the class A power amplifiers\

is the most linear amplifier but its power added

efficiency is 50% The switching mode PA’s

include class D, class E and class F. They are

strongly non linear amplifiers which have a

maximum efficiency of 100% Due to the “on” and

“off” conditions in the switching mode power

amplifiers the voltage and current wave form and do

not overlap resulting which power dissipation will

be zero and the theoretical efficiency can reach

100% easily [2]

In this paper the RF Power GaN-HEMT device

model CG40010F manufactured by Cree is used

with an operating frequency of 15GHz.The

balanced amplifier configuration is used in this

paper.

GaN-HEMT Technology:

Variety of power amplifiers are available in the

market like SiC (Silicon Carbide), GaAs Hetero

junction Bipolar Transistors (HBT’s), Si-LDMOS

(Lateral diffused MOS), GaAs MESFET’s. Of all

the various semiconductor materials and device

RESEARCH ARTICLE OPEN ACCESS

Abstract:

This paper reports on the design of an ultra wideband power amplifier using 0.25um GaN- HEMT

Technology device obtained from the Triquint Semiconductor. There is huge interest in transistors based on

Gallium Nitride in recent years due to its high breakdown voltage and its capability to operate in High frequency

applications. The load pull analysis is carried out to obtain both the required source and load impedances. The

power amplifier with over 10W output power and 42% power added efficiency in the frequency range of 3-5GHz

is presented in this paper. The PA is designed using a computer aided design tool called Advanced System Design

(ADS).ADS provide two different simulation opportunities. These are referred as schematic simulation and

electromagnetic simulation called Momentum. Schematic Simulations are performed on the proposed PA in this

paper. Keywords:- GaN-HEMT Technology, Load pull analysis, Advanced system design(ADS)



technologies the GaN-HEMTs are most promising

for defense and aerospace applications due to its

high breakdown voltage of nearly 3.2ev and high

frequency of operation.[3] and In addition to this

GaN devices have some superior properties such as

high electron mobility(2DEG) (~1500Cm2/Vs) and

high electron density(~1x1013

cm-2

)[5] When

compared to Si and GaAs devices GaN based

transistors offer high input and output impedances

with high output power density (>10x)[4].

The Comparative analysis of the GaN

properties with the other device technologies or

materials are summarized as shown in the table 1

below [5]. Characteristic

Feature

AlGaAs/

InGaAs

Sic InAlAs/

InGaAs

AlGaN/

GaN

Electron

Mobility at

300K

8500 700 5400 1500-

2200

Critical

Breakdown

field(V/cm)

0.4 3 0.5 3

Band gap(Ev) 1.42 3.3 1.35 3.5

Peak electron

Velocity

1.3 2.0 1.0 1.3

Table 1: Comparative analysis of the Device technologies

Balanced Amplifier Configuration:

The Balanced Amplifier Configuration is often used

in the Microwave Amplifiers. It was introduced by

Eisele, et al. [6] .Generally the Balanced amplifier

has two identical single ended Amplifiers (A1, A2)

that are connected in parallel by two 3-DB

quadrature couplers(900 Hybrid Couplers).These

couplers are operated as a power splitter and as a

power combiner at the input and the output

respectively. Both the input and the output matching

of the complete balanced amplifier structure do not

depend totally on the Individual amplifying cells as

long as both the cells are identical. This unique

property of balanced amplifiers has made it more

suitable for designing Power Amplifiers [7], Low

Noise Amplifiers [8] and the Broadband Amplifiers

[9].

Design of a Proposed Class AB Power Amplifier:

No

Yes

Figure 1: Power Amplifier design flow

Design specifications

(Output power, Gain, Efficiency

,PAE)

Active device selection

Stability analysis

Load-pull for determining

optimum source and load

impedances

Harmonic matching &

Biasing network

synthesis

Final PA

characterization

Met design

specification

s

Efficient and desired amplifier

designed



Load Pull Investigation:

The fundamental source-pull /load-pull simulation

is used to find the optimum source and load

impedances that can maximize the efficiency of the

transistor across the band. The Load pull

simulations in this paper are carried out using ADS,

HB1 Tone_Load pull design guide with a large

signal model of a transistor obtained from Cree. The

Load Pull analysis will be performed first and later

source Pull analysis will be carried out.

The matching networks provide transformation

from source and load impedance to the standard

50ohm termination. These values are required to

provide desired gain, power added efficiency and

the output power.

Gain Stage:

The first stage of the power amplifier is the Gain

stage which is designed to provide most of the RF

Gain and to drive the second stage (Power Stage).

The different impedance values for input and output

matching networks is obtained for different input

power levels at the desired frequency

In this paper in the output matching network the

radial stub is used for achieving wider bandwidths.

By the proper design of matching networks using

the radial stub the 12Db Gain is achieved only at the

gain stage.

Figure 2: Final Schematic with a Branch Line Coupler

The Branch line coupler is used at the power stage

which is composed of two parallel arranged

identical amplifiers. The reason behind using this

approach is to achieve 3Db more power at the

output when compared to the single power stage

amplifier circuit. This approach is referred as a

Balanced Amplifier topology. Here the input power

to the power stage is divided by the means of the

above 3Db branch line coupler, amplified and then

combined by a second coupler.

Schematic Simulation Results: The Schematic and the electromagnetic simulations

called Momentum can be performed on the

designed Power amplifier using ADS. The

schematic simulations are performed and presented

in this paper. Generally every stage in the power

amplifier which includes biasing network, Input and

output matching networks at gain stage and a 3DB

Branch line coupler at the power stage are designed

to produce the desired output power, gain and the

efficiency.

The simulation performance of the proposed power

amplifier is tabulated as follows

Frequency Input

Power,

Pin

Output

Power,

Pout

Gain

(Gain

Stage)

Gain

(Power

Stage)

Final

Gain

15GHz

24dBm

43dBm

10.34

8.92

19.26

Table 2: Schematic Simulation Results

Monte-Carlo Simulation Results: Monte-Carlo method is used to investigate the

affects of circuit component tolerances or the

manufacturing tolerances in a lumped element or

the distributed transmission line components.

In this paper 50 iterations were performed with

varying input power from 20dBm to 30dBm.

The performance of the designed power amplifier is

very sensitive to the component tolerances. Where

the variations degrade the gain from 19dBm to

13dBm. Which is less than 6dBm when compared

to the schematic simulation results.



Conclusion:

The highly efficient two stage Ku-Band power

amplifier has been demonstrated in this paper. A

Peak power added efficiency of 40% is obtained at

15GHz frequency. The practical design issues are

also discussed with reference to Monte Carlo

simulation analysis. The tuning of harmonic

components was discarded in this work during the

design. By terminating the harmonic components up

to second fundamental frequency an increased PAE

can be achieved.

References:

[1]A.Rasmi,A.Marzuki,A.I.AbdRahim,M.R.Yahya,

A.F.A.Mat,”A 3.5GHz Medium power Amplifier

using 0.15um GaAs PHEMT for WiMAX

Applications”, Asia Pacific Microwave Conference,

pp.277-280,December 2009.

[2]F.H.Rabb, “class:f power amplifiers with

maximum flat wavesforms,” IEEE transcations on

microwave theory and techniques,vol.45,no.11 nov

1997, pp..2007-2012

[3] Shinichi Hoshi,Hideyuki okita,Yoshiaki

Morino,Masanori Itoh,”Gallium Nitride High

Electron Mobility Transistor(GaN-HEMT)

Technology for High Gain and Highly Efficient

Power Amplifiers” Oki Technical Review October

2007/Issue 211 Volume 74,No.3.

[4] U.K.Mishra,L.Shen ,T.E.Kazior,Y.F.Wu, “GaN

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[5] U.Misra, P.Parikh and Y.F.Wu “ AlGaN/GaN

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90,pp.1022-1031,June 2002.

[6]Eisele,K.M., R.S.Engelbrecht and K.Kurokawa,

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wideband microwave applications”, IEEE Int. Solid

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[7] L.Wu, et al, “A Broadband High

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Amplifier “, European Microwave Conference,

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[8] Mandeep J.S., Abdullah,H., and Ram N., “ A

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[9] chao-Hsiung Tseng and Chih-Lin Chang,”

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271.

[10] Ruchi,Sanjay Kumar Tomar, Meena

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Vol.5,Issue 4,Oct-Dec 2014.