Summary  7
Streszczenie  8
List of symbols  11
1. Introduction  13
2. Analysis of coupled transmission lines  19
2.1. Capacitance matrix of coupled lines  20
2.2. Even and Odd modes of symmetrical coupled lines  21
2.3. Four-port symmetrical network  23
2.4. Directional couplers  26
2.4.1. Forward-wave directional couplers  30
2.4.2. Backward-wave directional couplers  32
2.4.3. Asymmetric coupled lines  34
2.5. Summary  40
3. Improved FD method for numerical calculation of the coupled line parameters  41
3.1. FD method for coupled-line parameters calculation  42
3.2. Accelerating algorithm for FD method  46
3.3. Improved FD method with unequal mesh  49
3.4. Multiconductor coupled-line section analysis with the use of improved FD method and application examples  52
3.5. Summary  57
4. Design aspects of high-performance coupled-line circuits  58
4.1. Conditions of ideal coupled-line section realization  59
4.1.1. Analysis of influence of modal phase velocity inequality on directional coupler’s parameters  59
4.1.2. Influence of coupling coefficient inequality on directional coupler parameters  63 
4.2. Coupled-line section compensation techniques  66
4.2.1. Compensation of coupling coefficients by the choice of dielectric layers  66
4.2.2. Compensation of coupling coefficients using capacitive and inductive elements  75
4.2.3. Compensation of coupling coefficients using corrugated ground plane  97
4.2.4. Wiggly line couplers  99
4.3. Parasitic reactances within coupled-line structures  101
4.3.1. Influence of parasitic reactances of the transition regions between coupled and signal lines  102
4.3.2. Influence of parasitic reactances of the transition regions between coupled-line sections  105
4.3.3. Compensation method of parasitic reactances  107
4.4. Summary  118
5. Directional couplers designed with the use of the developed techniques and their circuit applications  120
5.1. Single-section 3-dB directional coupler designed in symmetric stripline coupled lines  121
5.2. Single-section 3-dB directional coupler in microstrip multilayer technology  122
5.3. Broadband multisection, asymmetric 3-dB directional coupler  127
5.4. Broadband multisection, symmetrical 3-dB directional coupler  128
5.5. Broadband multisection, asymmetric 8.34 dB directional coupler  130
5.6. Three-section 3-dB, symmetrical directional coupler designed in multilayer microstrip technology  135
5.7. Suspended stripline directional coupler with equalized inductive and capacitive coupling coefficients  142
5.8. Low-loss, suspended stripline directional coupler with equalized inductive and capacitive coupling coefficients  143
5.9. Low-loss multisection suspended stripline directional coupler  146
5.10. Broadband high-performance coupled-line magic-T network for direction finding systems  150
5.11. Integrated stripline multibeam antenna array fed by a compact Butler matrix  155
5.12. Summary  158
6. Final remarks  160
Appendix I  162
Appendix II  166
References  174