http://www.hfoscillators.com/apskhanna/articles/IMS1984_FETDRO

7-’10 PARALLEL

FEEDBACK

FETDRO

DESIGN

APS

Loral 5001

Advanced

G Forbes

Blvd.

USING

3-PORT

S-PARAMETERS

Khanna

Technology

Labs.

Lanham,

MD.

20706

Abstract new approach for the design of parallel feedback FET oscillators has been presented using 3-Port S parameters.

The linear analysis accurately determines the reflection gain at any port as a function of the parameters of the dielectric resonator parallel feedback network between the other two of design ports of the FET. An example and practical realization of FETDRO is presented at 9 GHz.

A

two port connected between the other two ports.

The method of analysis presented also allows the designer to determine the preferred output port of the transistor.

The approach presented is easily expendable to Dual Gate FET applications.

Dielectric

Resonator

The dielectric resonator coupled simultaneously to two microstrip lines and its equivalent circuit is shown in At resonant frequency the S– figure 2. parameters

Introduction With the advent of the miniature high Q and temperature stable dielectric resonators, the interest in their utilization in the active and passive Microwave Integrated circuits has been fast increasing [1].

A number of interesting configurations of FET oscillators using dielectric resonators (FETDRO) have been presented in the past [2] - [4].

Some of these oscillators use dielectric resonator as a parallel feedback element between the two ports of the transistor while taking the RF output at the third port of the same (fig. la) e.g.

[2].

The feedback twoport can as well be placed between any two ports as shown in figure lb and lc.

No analytical approach has so far been presented to determine the optimum postition of the dielectric resonator or to calculate the reflection gain at any port of the transistor as a function of the parameters of the two port feedback network connected between the other two In this paper ports of the transistor. we present: i) S-parameters characterization of the dielectric resonator coupled simultaneously to two microstriplines and ii) a linear approach to calculate the reflection gain at any port of the transistor as a function of its 3-port S-parameters and the S-parameters of the

Characterization~

Lo

be

of

given

this

by

two-port

[5].

can

be

shown

“

.

81 -

52 -

-2je

1

2/~

-2jQ 81+82+1

B~+B2+l

[1 Sr

-

.e

.e

=

2=2

-2j~

-2j.9

-61-1

62

.e

81+62+1

61+62+1 —

where $land coefficients microstrip given by:

62 represent the coupling of the resonator with lines on both sides and

the are

’02

’01 61

and

=

62

= Go

Go

and 0 represents = fll = 2 ~1 ag Transistor The FET, characterized

the

electrical

length

Characterization a

three by

port its

device, 2-port

is generally S-parameters

181

0149-645 X/84/0000-CI187 $01.00 @ 1984 IEEE

19841EEEMTT-S

DIGEST

with one of its leads (generally source) grounded.

The use of three port Sparameters though introduced quite sometime ago [6] has not been often used mainly due to the complexity of the analysis involved.

The availability of desktop computers and CAD has now made their

use

practical.

S-parameters

The

eliminates

necessary

conversion

to

use the

of 3-port otherwise

and

from

Z

or

‘kkA

=

‘iiA

‘jjA

-

‘ijA

‘jiA

‘jkA

=

‘ijA

‘kiA

-

‘iiA

‘kja

‘kjA

-

‘jjA

‘kiA

‘jjB

-

‘ijB

‘jiB

A

ikA

‘B

=

and i, following

Y

to analyse the feedback effect and due to the property of 3P-S-matrix of a transistor that the sums of rows and columns is equal to 1, the systematic errors in the measurement or analysis can be determined and eventually corrected.

It may also be noted that the problen presented in this paper can be solved only by the use of 3-port S-parameters.

The FET 3P S-matrix can be directly measured or determined from the generally available 2-port S-parameters [6] .

s.

=

]iA

‘iiB j,

k can table:

be

known

from

the

parameters

I

’11A

alA

+

’12A

a2A

+

’13A

a 3A

b2A

=

’21A

alA

+

’22A

a2A

+

’23A

a3A

b3A

=

’31A

alA

+

’32A

a2A

+

’33A

a3A

blB

=

‘llB

alB

+

’12B

a2B

b2B

=

’21B

alB

+

’22B

a2B

when port 1 and 2 of the connected to port 1 and port we have:

two 2 of

alA

= blB

a2A

are three

Practical alB

= b2B

port the

= blA

a2B=

Using the reflection

above relations the modi;ied coefficient at port 3 S33 can be determined.

The b3A/a3 genera ?’ ~zed r~lation of reflection at any port can be ~;:~;;i~;~ ‘kk ‘;k

=

‘kkA

‘iiBsikAskiA AB AkkA

where

+

-

SiiB

‘ij SiiA

A’=s

=

Frequency: Efficiency:

+

+ S, IIB

jkA

A +

+ ‘jiBsikAskj ‘jiB

‘jkA

+s.

. ]lB

+

‘“ L]A

‘ikA

A

‘jj~sj~skj~+

+ ‘jjB

A ikA

B

‘jjA

j

k

I

Realization:

Using a half micron dielectric resonator feedback oscillator the drain as output results were obtained:

b2A

Qext:

BsjkAskiA

i

~

Figure 3 represents the generalized form of the parallel feedback FET oscillator configuration.

The three-port network “A” represents the FET and the two port network “B” represents the feedback network for example a dielectric resonator coupled simultaneously to two microstrip lines.

The relations for the three port and two port can be presented as: =

at

For simplicity the port number for the two-port is the same as the connecting port of the three port.

Using the above relation and knowing the S-parameters of the FET and dielectric resonator feedback network the reflection coefficient at all the three ports of the E’ET can be determined as a function of 0 and 6 of the network and the preferred output port can be easily determined to achieve the maximum reflection gain.

As an example the ‘reflection coefficient at the drain port of a half micron FET as a function of feedback network parameters between gate and source at 9GHZ is presented in figure 4.

This can be used to determine the feedback parameters to maximize the reflection gain S~2.

The matching circuit at the drain port can be determined to realize the oscillation condition by using the well known empirical relations or the load pull measurement technique.

A damping resistance is generally required at one of the FET ports (Fig.lC) in order to avoid spurious oscillations.

This converts the two port resonator to a three port one and redistributes the Sparameters.

W2!zY

blA

Reflection Coefficient

At

9010 18 1700

FET at was port

RF

MHz 2

and a Thomson CSF 9GHz a parallel realized.

With following

Pushinq: FM

Noise:

Power:

12dBm

260KHz’vDS 90 dBC/Hz @ 10 KHz

References:

+1

1.)

J.K. “Application Microwave Vol 29, 182

and C.L. Ren, Plourde of Dielectric Resonators in lEEE Tran~ ItTT components,” NO ~, pp 754-769 August 1981.

OUTPUT MATCHING “RCU’T

(a)

// $--=2

(b) /q-o f

‘\j~f5:”;”

h

,,

0

“4I

+l+A/4”[

,0

+v~--”

I

!

(c)

~%4-3A/4+ Ficr.

Configurations for feedback FETDRO.

1.

parallel

(c) 2. Dielectric Fig. simultaneously

to

Resonator coupled two microstriplines.

12

a

n“

--1

I

: 0 . ..*

‘$-@ A

V

,1

3 PORT

160°

< mm

< no It

150

Fig. 4. Reflect~~n Drain as a function parameters 6 & !3

S;3

Fig.

3

Two-port network

as a parallel to a three-port.

feedback

2.)

O. Ishihara etal, “A highly stabilized GaAs FET oscillator usinq dielectric resonator feedback circuit IEEE Trans.

MTT; vol 28, 9-14 GHz,” August 1980.

“Efficient 3.)

APS Khanna etal, Three Port X-band FET oscillator two dielectric resonators,” Proc -S 1982 Dallas, PP. 277-279.

4.)

G.D.

Alley

and

H.

Wang,

“An

Low

noise microwave NTT vol 27 Dec.

a in No.

8

noise

using IEEE

MTT

Synthesizer,” 1979 pp.

at

IEEE 969-974

Trans.

“Scattering Matrix 5.)

B.A. Galwas, Description of Microwave Resonators,” MTT VO1.31 No. 8 pp.

669-670 Trans.

August 1983.

6.)

G.E. Bodway, characterization khx~e–po=t

ultra-low

coefficient of feedback (6=6,=62)

Microwave

183

“circuit design of transistor

sca+tic?ring

Journal

vol.

parameters,” 11 No.5

by

IEEE

and means

May

1968

of