8/12/2019 4.Design and Analysis of Four Hole Coupled Microstrip Directional Coupler

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DESIGN AND ANALYSIS OF FOUR HOLE COUPLED

MICROSTRIP DIRECTIONAL COUPLER

Ravi Kumar*, Member IEEE, Narendra Singh,

*Corresponding Author

Jaypee Institute of Engineering & Technology, Guna-473226, INDIAE-Mail: ravi.kumar6@gmail.com, narendra.singh@jiet.ac.in

ABSTRACT- The present work describes the

design of a four hole coupled MultilayeredMicrostrip directional coupler. The multi-layered

four hole directional coupler consist of two

layers one with Ground plane layer. This four

hole directional coupler is used to greatly extendthe coupling up to -10dB. The Proposed

directional coupler has been designed and

analyzed using IE3D software. Variation of the performance of the coupler with frequency has

also been investigated.

INTRODUCTION:

Directional couplers are passive microwavecomponent used for power division or power

combining. Directional couplers are essential

elements in microwave circuits and they are

commonly used in balanced amplifiers, balanced

mixers, phase shifters etc. In the recent decades,Engineers developed various RF or Microwave

modules with high performance, light-weightand compact size. The modules have widespread

application in telecommunications, radar andinformation systems. Lightweight and compact

size RF or Microwave circuits are especiallycritical in hand held, airborne and satellite

communication systems. [1].

Commonly used directional coupler

used in Microstrip substrate are coupled

Microstrip directional coupler [2], bi-levelcouplers [3], Re-entrant mode directional

couplers [3] etc.

In this paper, a four hole directionalcoupler using coupled Microstrip configuration

to improve the coupling at higher frequency

range is proposed. Here the hole means the

aperture in the middle layer of the directionalcoupler on the basis of the conventional

directional coupler. These apertures are made to

form a coupling between port 1 and port 2 or 3

and vice versa. The simulation of the proposed

structure has been carried out using IE3Dsoftware [5]. The coupling of 10dB at the center

frequency of 10GHz using four hole microstripdirectional coupler is proposed in this paper.

THEORY

The circuit layout of a multilayered microstrip

four hole directional coupler is shown in Fig.1.The coupling coefficient C and directivity of the

coupler D in dB can be designed using following

equations

C = -20 Log | E3/E0 | = -20 Log k – 20 Log ∑=

N

n

nnba

0

2 (1)

D= - 20 Log |E4/E3| = -C – 20 Log k – 20 Log(S) (2)

Where,

S= |∑=

N

n

nnba0

2e-j β (nπ / β

0 )| (3)

Where Eo is the input electric field at port 1, E3

and E4 are electric field at port 3 and port 4, β isthe propagation constant of the dual layer

multiaperture coupling structure, βo is the

propagation constant at the center frequency, k isa constant to be determined, and an and bn are the

width and length of the nth aperture, respectively.

Assuming that N is an even number( an odd

number of apertures) and the coupler is

symmetrical (a0 x b0= a Nxb N, a1xb1 = a N-1xb N-1,a2xb2= a N-2xb N-2,……), couplers with different

responses will be achieved by equating S to

different N degree polynomials, respectively

|)cos(sec|)2cos(22/

0

2θ θ θ m N n

N

n

n P K n N baS =−= ∑=

(4)

Where K and θm are constant to be determinedand polynomial P N(secθm cosθ) may be

binomial(maximum flat), or chebyshev polynomial, etc. Multiaperture, dual layer

Microstrip directional couplers with different

coupling coefficients can be designed with theabove method and small-hole coupling theory.

Here a directional coupler has been designed for

four apertures in middle layer of the designed

multilayered microstrip directional coupler.

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PROPOSED GEOMETRY:

Figure 1(a) and 1(b) shows the Top view and theside view of the proposed directional coupler.

The dimensions of four apertures of Microstrip

directional coupler with different couplingcoefficient and constant k have been calculated

using equation (4) and the approach proposed[6]. Matching transformers of λ g/4 length have

been used for the Impedance matching purpose.The coupler has been simulated by IE3D

simulation software for microwave circuit

design. The middle line is grounded with the

ground plane placed at zero height. The fourdifferent holes are made in this grounded

Microstrip line at the length of λ g/4. The

Microstrip transmission line has been taken of

50Ω whose width has been found 4.4mm. The

effective permittivity of 2.1361 has been taken inconsideration. The dielectric constant of 2.55 of

silica material has been taken in consideration.The calculated guided wavelength has been

found 20.52mm. The width has been calculated

for the Microstrip is 1.5875 and the distance between Ground plane and Microstrip plane has

been taken 1mm.

By using the approach [6], thedimensions of external apertures i.e.r 02 and

internal apertures r 01 with the distance of λg/4i.e. 5.131mm for matching purpose have been

given as follow:

Dimension of apertures for four hole coupler

r 01 = 0.293mmr 02 = 0.464mm

Here these apertures have been made to get the

coupling between port 1 and port 2 or 3 and viceversa, based on the new approach that has been

followed by equation (4) as above.

ACKNOWLEDGEMENT

The authors thankfully acknowledge the support provided by and the authorities of Jaypee

Institute of Engineering & Technology, Guna,

INDIA.

REFERENCES

[1] Pozar D.M., “Microwave Engineering”, Second

edition, Wiley, 1998.

[2] Kitlinski M., “Coupled Microstrip Lines withThree Layer Substrate”, 40. Internationaleswissenschafliches colloquium, Ilmenau 1995,

Band 2,PP.302-307.

[3] Buntschuh C., “High Directivity Microstrip

Couplers Using Dielectric Overlays”,1975, IEEEMTT-S International Microwave SymposiumDigest,pp 125-127.

[4] IE3D software release 8 & developed by m/sZealand software Inc.

[5] “IE3D users Manual”, Zeland Softwares,USA.

[6] Altman J.L., “Microwave Circuits”, D.Van Nostrand Company,Inc.,1964.

[7] Janiczak B., “Compact Hybrid-Mode Approach

to Design of Bimode High-Directivity MicrostripDirectional Couplers in MIC Proximity”,Mikrowellen Magazine,vol.13,No 3, 1987.

[8] Collin Robert E., “Foundation For Microwave

Engineering, Second Edition, Mc Graw Hill,Inc.,1992.

[9] Chun Dong Wan, Design of Directional Couplerusing three layer Microstrip Structure, IEEEProceedings,2001.

RESULTS & DISCUSSION:

The proposed structure have been simulated

experimentally using IE3D software[5] wherethe desired results have been found. Figure 2

shows variation of the coupling with frequency

where it shows that -10.37dB has been found atthe center frequency of 10GHz that is nearly -10dB for which all the components have been

calculated theoretically. Figure 3 shows the

variation of Isolation with frequency where the

Isolation -35.68dB has been found between the

port 1 and port 4 of the four hole multilayeredMicrostrip directional coupler. The simulated

and measured result shows that designed coupler

has good performance over a tight coupling.

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Λg/4

Figure 1(a). Cross Sectional view of Four hole Coupled Microstrip Directional Coupler

Figure 1(b). Side View of Four Hole Coupled Microstrip Directional Coupler

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Figure 2. Variation of Coupling with Frequency

Figure 3. Variation of Isolation with Frequency