Patent EA-000368-B1 (EA)
Title: High impedance ratio wideband transformer circuit
Inventor: REYNOLDS ROBERT L
IPC: H03H7/42
Filed: 1996-09-09
Abstract: 1. A high impedance ratio wideband transformer circuit comprising: transmission line transformer means having a first port and a second port, said transmission line transformer means including first and second transmission line transformers connected in series so that the impedance ratio of said first transmission line transformer is multiplied by an impedance ratio of said second transmission line transformer to reduce the length of said secondary windings of said transmission line transformers thereby increasing the range of frequency, a first reactive impedance connected between said first and second transmission line transformers, and a second reactive impedance connected at said first port with the values of said first and second reactive impedances being selected to optimise an impedance match from said first port to said second port for a selected turns ratio of said transmission line transformer means and a desired transformation ratio and frequency response to provide transformation ratios of above about 4 : 1 over a range of frequencies of about 5 MHz to 1.2 MHz, said first transformer having a first winding connected to a low impedance port and having a second winding inductively coupled to said first winding, said second transformer having a first winding and a second winding inductively coupled to said second transformer first winding, said second transformer second winding connected to a high impedance port, said first reactive impedance being connected between said first transformer second winding and said second transformer second winding, said second reactive impedance being connected between said low impedance port and ground. 2. A transformer circuit as set forth in Claim 1 wherein each of said first and second transformers are autotransformers, said first winding of said first transformer being a primary winding and said second winding of said first transformer being a secondary winding, said first winding of said second transformer being a primary winding and said second winding of said second transformer being a secondary winding. 3. A transformer circuit as set forth in Claim 2 wherein each of said first and second transformers are autotransformers each having a miniature ferrite core with a pair of spaced apertures and first and second windings wound through said apertures on said core. 4. A transformer circuit as set forth in Claim 3 wherein said windings include a twisted pair wound on said core forming 2.0 turns for said first transformer and 2.5 turns for said second transformer. 5. A transformer circuit as set forth in Claim 3 wherein said windings include a twisted pair wound on said core forming 2.0 turns for said first transformer and 2.5 turns for said second transformer. 6. A transformer circuit as set forth in Claim 3 wherein said windings include a twisted pair wound on said core forming 1.5 turns for said first transformer and 2.5 turns for said second transformer. 7. A transformer circuit as set forth in Claim 2 wherein said first and second transformers each have a core resistance of about 32 ohms per turn squared. 8. A transformer circuit as set forth in Claim 2 wherein said primary winding of said first transformer has about 5 turns, and said secondary winding of said first transformer has about 7.5 turns, said primary winding of said second transformer has about 4 turns and said secondary winding of said second transformer has about 6.5 turns. 9. A transformer circuit as set forth in Claim 1 wherein said first reactive impedance is an inductor. 10. A transformer circuit as set forth in Claim 1 wherein said first reactive impedance is an inductor, said inductor is a single strand enamel coated magnet wire wound on a phenolic torrid core. 11. A transformer circuit as set forth in Claim 1 wherein said first reactive impedance is an inductor of about 2.7 nanohenries. 12. A transformer circuit as set forth in Claim 1 wherein said second reactive impedance is a capacitor having a value of about 1 picofarad. 13. A transformer circuit as set forth in Claim 2 wherein said primary winding of said first transformer has about 4.5 turns, and said secondary winding of said first transformer has about 6.5 turns, said primary winding of said second transformer has about 3.0 turns and said secondary winding of said second transformer has about 5.5 turns. 14. A transformer circuit as set forth in Claim 2 wherein said primary winding of said first transformer has about 4.5 turns, and said secondary winding of said first transformer has about 6.0 turns, said primary winding of said second transformer has about 2.5 turns and said secondary winding of said second transformer has about 5.0 turns 15. A transformer circuit as set forth in Claim 1 including a balun connected to said high impedance port to provide a balanced output. 16. A transformer circuit as set forth in Claim 15 wherein said balun has a 1:1 ratio. 17. A transformer circuit as set forth in Claim 8 wherein there is provided about a 1:9 impedance ratio at a bandwidth of about 5 MHz to 1.2 GHz. 18. A transformer circuit as set forth in Claim 13 wherein there is provided about a 1:12 impedance ratio at a bandwidth of about 10 MHz to 1000 MHz. 19. A transformer circuit as set forth in Claim 14 wherein there is provided about a 1:16 impedance ratio and a bandwidth of about 10 MHz to 600 MHz.