Design And Analysis of Hybrid Coupler

Design And Analysis of Hybrid Coupler

Swati Shelar

Department of Electronics Government College of Engineering Aurangabad

Nilima Kolhare

Department of Electronics Government College of Engineering Aurangabad

Abstract The proposed work is to design the 90 hybrid coupler that can operate with an arbitrary frequency 1.5GHZ to 3GHZ. The paper describes the two different design of hybrid coupler : firstly by using lumped element and secondly by using microstrip line. The system is designed for constant parameters like centre frequency 1.9GHZ, uses FR4 substrate with dielectric constant 4.6 and h is 1.6mm. All the results have been observed by using ADS (Advance Design System) software. The results of hybrid coupler are well satisfied by using above two elements. The size of the hybrid coupler is reduced; due to these it can be used in applications such as MMIC where size is important criteria. Measured result shows 18.2% bandwidth for given frequency. The measured results are in well agreement with simulation and demonstration of its performance.

Keywords Lumped element, Microstrip line, ADS software

1. INTRODUCTION

   Power divider and power couplers are used for power combination or power combining which are passive microwave components. Have a fixed division ratio, used to divide signals for a given phase difference and division ratio [1][2] . Hybrid coupler is 4 port passive circuits, which splits the incident power signal into 2 output ports with 3db attenuation i.e. 50%of i.e. power get lost. They are electrically and mechanically symmetrical. Ideal couplers are perfectly matched with all ports .a common application[3] for hybrid coupler is for splitting the signal at the input ,equally with two output signals .Depending on the signal spilt ratio of a hybrid

   ,most applications needs equal splitting of the input signals between two same circuits.in addition with this it also use for combining signals. The quadrature (90 degree) is a special case of directional coupler, with coupling factor 3dB and phase difference between output is either 90 degree i.e. quadrature hybrid 180 degree i.e., magic T or rat race hybrid.

   In this paper hybrid coupler design is based on lumped element i.e. R, L, C and transmission line. (CPW, stripling, microstrip) design given is by using microstrip line, with centre frequency of 1.9 GHZ. Lumped component design is promising because it provides low insertion loss, wider bandwidth and smaller size circuit, which is very better fit for monolithic microwave integrated circuit MMIC.

   Advance Design System (ADS) by Agilent technologies is used as simulation tool in this paper [4][10].

   There are so many advantages for choosing microstrip line because of low cost, its suitable for manufacturing in large quantities they are outstanding with its volume and weight as

   compare to waveguide.it containing whole circuit ion a substrate, suitable for insertion of MIC. Couplers having different applications [8][9] like microwave phase shifter, driver circuit protection and in phase/quadrature modulation/demodulation. Hybrid used to combine two power amplifiers.as shown in figure 2, its used for combining the output from two lower power amplifier to achieve greater output power. From the combination that is possible from either of the individual power amplifier.

   Characteristics of the coupler Substrate dielectric constant Er.=4.6 Centre frequency =1.9GHZ Bandwidth=18.6%

   Height of substrate=1.6mm tanD=0.0019

   Figure1 Types of power divider and directional

   Figure2 Hybrid used to combine two power amplifier

2. DESIGN APPROACH

   Given coupler consist of two pairs of transmission lines with characteristic impedances of 50 and 35.5 . at low frequency its physical size is large which can be reduce as proposed in [6][7].

   1. Using Lumped Element

      The one technology for 90 degree coupler is using lumped components. Its useful because connecting wires are assumed to be ideal and each element is considered to be independent. The initial step in the design is to synthesize the nominal values of inductor I and capacitor C based on design. Lumped element design is as shown in figure 3

      The equations used for synthesizing the element value based on 1.9GHZ frequency and characteristic impedance 50 and 2.

      Figure 3 Lumped equivalent circuit for hybrid coupler

   2. Microstrip Line

      Each transmission line is designed by using the principle of lambda quarter transformer for perfect matching between the ports. Lines are designed with 2 characteristics impedance

      50 & For extracting even and odd impedance even and odd analysis is used, which is based on two principles: symmetry of circuit and superposition

      Figure 4.a. Even mode symmetry

      Figure 4.b. Odd mode symmetry

3. ANALYTICAL MODEL

   The designs of microstrip line for determine its length, width, height by assuming an infinitesimal TL thickness.

   Figure5 new design approaches for hybrid coupler

   1. Impedance calculation

      For calculation of the impedance two formulas are given

      1. for

      2. for

   2. Calcuation of W,H,D of Microstrip Line

      Calculated: W1=2.9103mm L2=16.635mm W2=4.8193mm L2=16.2822mm

      Where phase is constant and d is the distance.

   3. S parameter calculation For even and odd mode

      Figure 6.schematic of the hybrid coupler with transmission line (Microstripline)

      Figure 7.layout for hybrid coupler a. microstip line

      Figure8 3dB attenuation of two output ports

4. RESULTS

   Figure9 phase difference between two ports

   Figure10 90 degree phase difference between two ports

   Figure11 3dB attenuation between different ports.

   A. TableI.

   RESULT ANALYSIS

   SR.NO	Parameters	Calculated (dB)	Simulated( dB)
   1	Return loss	11.52	15.882
   2	Insertion loss	4.131	3.614
   3	Coupling factor	3.358	2.911

5. CONCLUSION

   In this paper hybrid coupler with compact sized is designed and simulated.3dB attenuation and phase difference is observed from the s parameter graphs. Further improvement can be possible by using better fabrication technique. Hybrid coupler by using microstrip line is fabricated with FR substrate. Simulation is done in ADS software. we can believe that given coupler can plays different applications i.e. in MMIC and MIC circuit where compact size is required the proposed coupler can also be implemented by using different technologies like CPW, strip line etc.

   REFERENCES

   1. S. Y. Zheng, S. H. Yeung, W. S. Chan, K. F. Man, and K. S. Tang, Design of broadband hybrid coupler with tight coupling using jumping gene evolutionary algorithm, IEEE Trans. Ind. Electron., vol. 56, no. 8, pp. 29872991, Aug. 2009.

   2. J.-L. Li and B.-Z. Wang, Novel design of Wilkinson power divider with arbitrary power division ratios, IEEE Trans. Ind. Electron., vol. 58, no. 6,pp. 25412546, Jun. 2011

   3. Veljko Napijalo, Member, IEEE, and Brian KearnsMultilayer 180 Coupled Line Hybrid Coupler IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 56, NO. 11,

      NOVEMBER 2008

   4. Advance design system2002 circuit components distriultaed components by agilent technology

   5. Prof. Tzong-Lin Wu Microwave Filter Design Chp4. Transmission Lines and Components Department of Electrical Engineering National Taiwan University.

   6. D. M. Pozar, Microwave Engineering. Norwell, MA: Artech House,1990

   7. R. Ludwig and P. Bretchko, RF Circuit Design. : Prentice Hall, 2000.

   8. J. Wang, J. Ni, Y. X. Guo, and D. Fang, Miniaturized microstrip Wilkinson power divider with harmonic suppression, IEEE Microw. Wireless Compon. Lett., vol. 19, no. 7, pp. 440442, Jul. 2009.

   9. Y. Chun and J. Hong, Compact wideband branch-line hybrids, IEEE Trans. Microw. Theory Tech., vol. 54, no. 2, pp. 704709, Feb. 2006.

   10. [Online]. Available: http://www.home.agilent.com/