Analysis of Different Techniques for Microwave Amplifiers Shreyasi S, Kushal S, Jagan Chandar BE Student, DEPT of Telecommunication, RV College of Engineering, Bangalore INDIA BE Student, DEPT of Telecommunication, RV College of Engineering, Bangalore INDIA BE Student, DEPT of Telecommunication, RV College of Engineering, Bangalore INDIA I. Abstract This paper describes different types of matching circuits for microwave amplifiers at input and output side at 1GHz. This paper compares the results of all possible combinations of T, L and π type matching circuits. The designed circuit is simulated with Advanced Design System (ADS) software. T- L matching configuration gives better results than L-L, L-T, T-T, π-l, L-π, π-t, T-π, and π-π circuits. Forward gain and stability factor for T-L match are 16.755 db and 0.917 is observed which is better than other configurations. Keywords-Advanced Design System (ADS), T, π, L matching networks, Low Noise Amplifiers (LNA), Scattering (S) Parameter II. Introduction An amplifier is the most common electrical element in any system. The requirements for amplification are as varied as the systems where they are used. The key to successful microwave amplifier design is impedance matching. In any high-frequency amplifier design, improper impedance matching will degrade stability and reduce circuit efficiency. At microwave frequencies, this consideration is even more critical, since the transistor s bond-wire inductance and base-to-collector capacitance become significant elements in input/output impedance network design. In selecting a suitable transistor, therefore, it should be kept in mind that the input and output impedances are critical along with power output, gain and efficiency. The main role in any impedance matching scheme is to force a load impedance to look like the complex conjugate of the source impedance, and maximum power transfer to the load. When a source termination is matched to a load with passive lossless two-port network, the source is conjugate matched to the input of the network, and also the load is conjugate matched to the output of the network. The matching process becomes more difficult when real parts of the terminations are unequal, or when they have complex impedances. III. Literature Survey Recently lumped matching networks for matching a microwave amplifier have been studied by many researchers. A symbolic approach and an optimization algorithm for the optimal design of Low Noise Amplifiers (LNAs) through S-parameters have been discussed in [1]. This paper gives the idea of computing automatically the symbolic expression of S parameters using Coates diagraph technique. A new technique has been employed for improving the stability of the Low Noise Amplifier. A RLC series circuit has been employed to make the Low noise amplifier stable. The simulation results of all possible combinations of L type matching circuits are done. Each circuit is simulated for, with ISSN: 2231-5381 http://www.ijettjournal.org Page 625
and without stabilizing circuit and feedback circuit. Under stability condition, forward gain and noise figure of L type network are calculated. In paper [2], in this paper, the design of impedancematching networks by distributed network synthesis is presented to achieve high-efficiency characteristics of microwave and millimetre-wave amplifiers. The transfer function for distributed network structures with an arbitrary electrical length is derived by the Chebyshev approximation. The values of network elements synthesized to match the load impedance are tabulated in terms of the minimum insertion loss (MIL) and ripple parameters. To validate the performance of matching circuits by the network synthesis, the results are applied to the design of an octave-band microwave transistor amplifier. In paper [3], Impedance matching for microwave amplifiers have been investigated extensively using different methods such as stub matching for broadband applications. In the present communication broadband impedance matching technique has been developed by combining the amplifier module with series microstrip transmission lines with optimum characteristic impedance and electrical length. Resistive loading are used at both the source and load terminals to ensure unconditional stability. Different variable parameters like resistance values, characteristics impedance and length of the transmission line are used to design the amplifier. The analysis of the design circuit has been carried out using multiplication of transmission matrices. This unique method hitherto unpublished can be used as a broad band technique for designing microwave amplifiers. IV. Networks Connecting two circuits together via a coupling device or network in such a way that the maximum transfer of energy occurs between two circuits is called matching. Impedance matching is a very important concept in RF/microwave frequencies because it allows maximum power transfer to occur from source to load and signal-to-noise ratio to be improved due to an increase in the signal level. These are the primary reasons to employ tuning in practically all RF/microwave active circuit design. Ideally, the matching network is lossless to prevent further loss of power to the load. It acts as an intermediate circuit between the two non-identical impedances in such a way that the source sees a perfect match while the multiple reflections existing between the load and matching network will be unseen by the source. Several types of matching network are available, however factors likes complexity, bandwidth, implementation and adjustability need to be considered in the matching network selection. In this paper, L, T matching and π matching circuits and its all possible combinations are discussed. V. Parameters for comparison of different matching circuits A. S-Parameters The network representation of a two port network at high RF/microwave frequencies is called Scattering Parameters. In view of linearity of the electromagnetic field equations and the linearity displayed by most microwave components and networks, the scattered waves are linearly related to the incident wave amplitude. The matrix describing this linear relationship is called a scattering matrix or [s]. This linear relationship is expressed in terms of a ratio of two phasors that are complex numbers with magnitude of the ratio less than or equal to 1. Each specific element of [S] matrix is defined below: S 11 - Input reflection coefficient S 12 - Reverse transmission coefficient S 21 - Forward transmission coefficient S 22 - Output reflection coefficient ISSN: 2231-5381 http://www.ijettjournal.org Page 626
B. Stability In a two-port network, oscillations are possible if the magnitude of either the input or output reflection coefficient is greater than unity, which is equivalent to presenting a negative resistance at the port. This instability is characterized by either input or output reflection coefficient greater than 1, which or a unilateral device implies s 11 >1 or s 22 >1. The requirements for stability are defined by circles, called stability circles. The radius and centre of the output and input stability circles are derived from the S parameters. The concept of instability with varying input or output matching conditions is significant, as an amplifier is desired to be unconditionally stable under all expected conditions of source and load impedances. Alternatively, stability is also verified if the following conditions are met: VI. MATCHING CIRCUIT CONFIGURATIONS A. CASE 1: L Type Input and L Type Output In Figure 2, the L type matching is used at the input as well as on the output side. K=1- s 11 2 - s 22 2-2 / 2(s 12 *s 21 ) ---- (1) Figure.2 L Type Input and L Type Output And =s 11 *s 22 s 12 *s 21 where >1 --- (2) Figure.3 S 11, S 22, S 12, S 21, and stability factor for L-L Figure.1 Input stability circles 2, the results are shown in Figure 3. The stability and forward gain are as 0.917 and 16.219dB. The output reflection coefficient is 13.945 db, reverse transmission coefficient is - 18.428 db, and input reflection coefficient is -11.892 db. Since the stability circuit is not introduced, stability factor is less than 1. ISSN: 2231-5381 http://www.ijettjournal.org Page 627
B. CASE 2: L Type Input and T Type Output In Figure 4, the L type matching is used at the input and on the output side the T type matching is used. C. CASE 3: T Type Input and L Type Output In Figure 6, the T type matching is used at the input and on the output side the L type matching is used. Figure.4 L Type Input and T Type Output Figure.6 T Type Input and L Type Output Figure.7 S11, S22, S12, S21, and stability factor for T-L Figure.5 S 11, S 22, S 12, S 21, and stability factor for L-T 4, the results are shown in Figure 5. The stability and forward gain are as 0.917 and 16.283 db.the output reflection coefficient is -15.875 db, reverse transmission coefficient is 18.365 db, and input reflection coefficient is -9.999 db. Since the stability circuit is not introduced, stability factor is less than 1 6, the results are shown in Figure 7. The stability and forward gain are as 0.917 and 16.043 db.the output reflection coefficient is -11.094 db, reverse transmission coefficient is 18.605 db, and input reflection coefficient is -12.176 db. Since the stability circuit is not introduced, stability factor is less than 1 ISSN: 2231-5381 http://www.ijettjournal.org Page 628
D. CASE 4: T Type Input and T Type Output In Figure 8, the T type matching is used at the input and on the output side the T type matching is used. E. CASE 5: L Type Input and π Type Output In Figure 10, the L type matching is used at the input and on the output side the π type matching is used. Figure.8 T Type Input and T Type Output Figure.10 L Type Input and π Type Output Figure.9 S11, S 22, S 12, S 21, and stability factor for T-T 8, the results are shown in Figure 9. The stability and forward gain are as 0.917 and -18.957 db.the output reflection coefficient is -5.115 db, reverse transmission coefficient is 15.690 db, and input reflection coefficient is -13.157 db. Since the stability circuit is not introduced, stability factor is less than 1 Figure.11 S 11, S 22, S 12, S 21, and stability factor for L-π 10, the results are shown in Figure 11. The stability and forward gain are as 0.917 and 15.440 db.the output reflection coefficient is -6.976 db, reverse transmission coefficient is -19.208 db, and input reflection coefficient is 21.682 db. Since the stability circuit is not introduced, stability factor is less than 1 ISSN: 2231-5381 http://www.ijettjournal.org Page 629
F. CASE 6: π Type Input and L Type Output In Figure 12, the π type matching is used at the input and on the output side the L type matching is used. G. CASE 7: π Type Input and T Type Output In Figure 14, the π type matching is used at the input and on the output side the T type matching is used. Figure.14 π Type Input and T Type Output Figure.12 π Type Input and L Type Output Figure.15 S11, S22, S12, S21, and stability factor for π-t Figure.13 S 11, S 22, S 12, S 21, and stability factor for π-l 12, the results are shown in Figure 13. The stability and forward gain are as 0.917 and 16.280 db. The output reflection coefficient is -10.823 db, reverse transmission coefficient is -18.368 db, and input reflection coefficient is - 13.428 db. Since the stability circuit is not introduced, stability factor is less than 1 14, the results are shown in Figure 15. The stability and forward gain are as 0.917 and 14.755 db.the output reflection coefficient is -10.438 db, reverse transmission coefficient is -17.893 db, and input reflection coefficient is - 18.397 db. Since the stability circuit is not introduced, stability factor is less than 1. H. CASE 8: T Type Input and π Type Output In Figure 16, the T type matching is used at the input and on the output side the π type matching is used. ISSN: 2231-5381 http://www.ijettjournal.org Page 630
Figure.16 T Type Input and π Type Output Figure.18 π Type Input and π Type Output Figure.17 S11, S 22, S 12, S 21, and stability factor for T-π Figure.19 S11, S 22, S 12, S 21, and stability factor for π-π 16, the results are shown in Figure 17. The stability and forward gain are as 0.917 and 15.161 db.the output reflection coefficient is 9.012 db, reverse transmission coefficient is -19.486 db, and input reflection coefficient is - 13.539 db. Since the stability circuit is not introduced, stability factor is less than 1. I. CASE 9: π Type Input and π Type Output In Figure 18, the π type matching is used at the input and on the output side the π type matching is used. 18, the results are shown in Figure 19. The stability and forward gain are as 0.917 and 14.487 db.the output reflection coefficient is 3.672 db, reverse transmission coefficient is -20.160 db, and input reflection coefficient is - 13.344 db. Since the stability circuit is not introduced, stability factor is less than 1. VII. SIMULATION RESULTS In this paper, combination of different input and output matching networks have been developed for a microwave Amplifier circuit at 1 GHz range and simulated using ADS software. The results are shown in Table 1. ISSN: 2231-5381 http://www.ijettjournal.org Page 631
VIII. CONCLUSION The simulation results of all possible combinations of L, T and π type matching circuits are shown in Table 1 for without stabilizing circuit (SC). From Table 1 the π type input matching with T type output matching gives better results without much degradation in terms of forward gain, and stability point of view. It gives gain as 16.755 db and stability as 0.917. Other parameters like output reflection coefficient (S 22 ) = 10.438 db, input reflection coefficient (S 11 ) = -18.397 db and reverse transmission coefficient (S 12 ) = -17.893 db are also comparatively better than other matching sections. Since stability circuit has not been included, the stability factor is less than 1. REFERENCES [1] D. Senthilkumar, Dr.Uday Pandit knot, Prof. Santosh Jagtap / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.403-408 [2] Microwave and optical technology letters, Volume 27, issue 2, 25 august 2000 [3] S K Khah, Pallavi Singh, Sweta Rabra, Tapas Chakarvarty IEEE01/2007; DOI:10.1109/AEMC.2007.4638055 In proceeding of: Applied Electromagnetics Conference, 2007. AEMC 2007. IEEE [4] Philip H. Smith: A Brief Biography by Randy Rhea, Noble Publishing 1995. Parameters [5] Chris Bowick, RF Circuit Design, Newnes imprint of Butterworth Heinemann, 1982, Ch. 4-5. analysed LL LT TL TT Lπ π L [6] Joseph F. White, High Frequency Techniques / An Introduction to RF and Microwave Engineering, John Wiley & Sons 2004. [7] Randy Rhea, Yin-Yang of : Part 2- Practical Techniques, High Frequency Electronics, April 2006. [8] J. F. White, High Frequency Techniques / An Introduction to RF and Microwave Engineering, JohnWiley & Sons 2004, pp. 70-71. [9] Agilent Technologies, Advanced Design System. [10] B. Becciolini, Impedance Networks Applied To R-F Power Transistors, Motorola AN-721, Motorola Inc., 1974. T πt Tπ π π S11-11.892-9.999-12.176-13.157-21.68-13.428 S12-18.428-18.365-18.605 15.690-19.208-18.368 - -18.397-13.539-13.344 - -17.893-19.486-20.160 S21 16.219 16.283 16.093-18.957 15.440 16.280 S22-13.945-15.875-11.094-5.115-6.976-10.823 Stability Factor.917.917.917.917.917.917 H 16.755 15.161 14.487 - -10.438-9.012-3.672 0.917.917 0.917 Table I Comparative Results of microwave amplifier Circuit (without Stabilizing circuit) using different matching techniques. [11] Agilent Technologies, win-smith 2.0, Noble Publishing 1998. [12] linsmith, John Coppens, 1999-2008, www.jcoppens.com/soft/linsmith. ISSN: 2231-5381 http://www.ijettjournal.org Page 632