Magic tee

In this presentation we have covered a magic tee topic from wave guide

1. COLLEGE OF ENGINEERING , PUNE DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION MOC PRESENTATION MAGIC TEE Presented By:- Anuja Gulhane-141807002 Kanchan Itankar-141807005 Pranali Patil-141807006 Saniya Shaikh-141807008 Triveni Vyavahare-141807009 Shreyasi Kore-141807012 Under the Guidance of Dr. S. P. Mahajan

2. INTRODUCTION Wave guide magic tee is an important element in microwave and millimeter wave engineering especially in monopulse antenna systems. Field analysis on waveguide magic tee is also difficult. Sieverding and Amdt analyzed the magic tee with the full wave modal S-matrix by mode-matching. Waveguide junctions are used when power in a waveguide needs to be spilt or some extracted. The main idea behind the “Magic Tee” is to combine a TE and a TM waveguide splitter.

3. WORKING A magic tee has four ports: Port 1 - Co-linear Port 2 - Co-linear Port 3 - Sum Port Port 4 - Difference Port

4. Operation of a Magic Tee The H-plane port and E-plane ports must be matched for a magic-tee to function properly, and hence are only effective over a select range of frequencies. Case 1: When two signals of equal magnitude are fed from port 1 and 2, we get a zero at port 4 and the sum of the two signals at port 3. Case 2: When a signal is fed through port 3, it gets divided equally between port 1 & 2 and both the outputs are in phase. No output comes from port 4. Case 3: When a signal is fed through port 4, we get an output of equal magnitude but opposite phase at port 1 & 2 (the signals are 180 degrees out of phase). Output at port 3 is zero. Case 4: If a signal is fed at one of the collinear ports 1 or 2, then there appears no output at the other collinear port, as the E-arm produces a phase delay and the H-arm produces a phase advance.

5. The justification for the “magic” in the name, the two collinear ports are also matched and isolated from each other. Though the quality of the matching networks in the E-plane and H-plane ports dictate the quality of the isolation and the frequency over which the collinear ports are isolated. The electric field of the dominant mode of each port is perpendicular to the long wall of the waveguide structure, enabling orthogonal polarization of the E-plane and H-plane ports.

6. Magic Tee S-Matrix Because of H-plane tee junction S 23 = S 13 Because of plane of symmetry Because of E-plane tee junction S 24 = -S 14 Outputs at ports 1 & 2 are phase shifted by 180 with respect to port 4 ---(3)

7. Because of geometry of junctions an i/p at port 3 can not came out of port 4 ,since they are isolated and vice versa. S 34 = S 43 = 0 ---(4) From symmetric property S ij = S ji , we have S 12 = S 21 ; S 13 = S 31 ; S 23 = S 32 = S 13 ; S 34 = S 43 ; S 24 = S 42 = - S 14 ; S 41 = S 14 ----(5) If ports 3 and 4 are perfectly matched then we have S 33 = S 44 = 0 ----(6)

8. Putting above values of S parameters in matrix (1), we get, From unitary property [S][S]*=[I]

9. Multiplying we get, From eq’ n (10) and (11), we get

10. Comparing eq’n (8) and (9), we get,

11. Using eq’ n (12) and (13) in eq’ n (8), we get

12. Note:- Eq’n (15) and (16) gives that ports 1 and 2 are perfectly matched hence port 3 and port 4 will also match, then such tee is called magic tee. Putting all the values of scattering parameters, we get We have [b]=[S][a]

13. Cases Case 1. a3≠0 & a1 = a2 = a4 = 0: Putting these values in eq’n (19), we get,

14. Case 2. a4 ≠0 & a1=a2=a3= 0 Putting these values in eq’n (19), we get This gives property of E plane tee. Case 3.a1 ≠0 & a2=a3=a4= 0; Putting these values in eq’n(19), we get When power is fed into port 1, nothing comes out of port 2 even though theyare collinear ports. ii.Hence port 1 and 2 are called isolated ports. iii.No output at collinear ports hence magic.

15. Case 4. a3=a4 & a1= a2 = 0 Putting these values in eq’n (19), we get Gives additive property. Equal inputs at port 3 and 4 gives output at port 1 in phase and in equal magnitude. Case 5. a1=a2 a3=a4= Putting these values in eq’n (19), we get E qual input at ports 1 and 2 results in an output at port 3 and no output at ports 1, 2 and 4.

16. APPLICATIONS A magic tee has several applications. A few of them have been discussed here. 1.Measurement of Impedance 2.Magic Tee as a Duplexer 3.Magic Tee as a Mixer

17. Measurement of Impedance

18. It is used in the form of bridge for measuring impedance. Microwave source is connected in arm (3), and null detector in arm (4). The unknown impedance is connected in arm (2), and a standard variable known impedance in arm (1). Using the properties of Magic Tee, the power from microwave source (a3) gets equally divided into ports 1 & 2. Impedance at port 1 & 2 are not equal to characteristics Impedance Zo hence there will be reflections from arm(1) and (2). If ρ1& ρ2 are reflection coefficients from port 1 & 2, then they will enter in null detector port (4) given by:

19. For perfect balancing of the bridge (null detection) eqn (1) is equated to 0. Z1 = Z2 Thus unknown impedance is measured by adjusting standard variable impedance till bridge is balanced & both impedances become equal.

20. 2. Magic Tee as a Duplexer

21. Working The transmitter and receiver are connected at port (2) and (1). Antenna is connected at arm (4) and matched load at port (3). • During transmission half power reaches to antenna & other half to matched load where it is absorbed without reflection • During reception half power goes to receiver & other half to transmitter, which are isolated during reception & transmission.

22. 3. Magic Tee as a Mixer

23. Description E-Arm port is connected to the antenna and the H-Arm port is connected to the local oscillator. Port 2 has matched load which has no reflections and port 1 has the mixer circuit, which gets half of the signal power and half of the oscillator power to produce IF frequency. Half the local oscillator power and half of the received power from antenna goes to the mixer where they are mixed to generate the IF frequency . IF=Fin-Fo Magic Tee junction is also used as Microwave Bridge, Microwave discriminator etc

24. Advantages 1. Decoupling property of the output ports. 2. In three junction devices power division between ports depends on termination existing at the respective olp ports, but in case of magic tee all the olp ports are perfectly matched. Hence power division between the ports is independent of terminations.

25. Disadvantages When the signal is applied to any arm of a magic tee, the flow of energy in the olp arms is affected by reflections. Reflections are caused by impedance mismatching at the junctions. This reflections are the cause of the two major disadvantage of the magic tee. 1. The reflections represents the power loss 2. The maximum power a magic tee can handle is reduced.

26. Numerical 1. The collinear ports 1 and 2 of a magic tee are terminated by impedances of reflection coefficients ρ 1 =0.5 and ρ 2= 0.6 .The difference port 4 is terminated by an impedances with reflection coefficient of 0.8. If 1W power is fed at sum port 3. Calculate the power reflection at port 3 and the power divisions at the other ports. solution: The input output relations for a magic tee is given by,

27. References Microwave and Radar by M. Kulkarni Seminar on “Magic tee” by kazi md saidur - https://www.slideshare.net/KaziMdRahaman/seminar-on-magic-tee https://www.everythingrf.com/community/what-is-a-magic-tee https://www.microwaves101.com/encyclopedias/magic-tees https://blog.pasternack.com/uncategorized/magic-tee-magical/

28. THANK YOU!!!