it allows easy series and parallel connections to external electrical components. The microstrip line is 2.2.3.3 Microstrip and slot lines also useful for making series connections but not parallel connections because the only way through to the ground The microstrip line (Figure 2.2-5(a)) is a variant of the plane is either through or around the edge of the sub- stripline with part of the 'shield' removed. The slot line strate. This is particularly true when a short circuit is (Figure 2.2-5(b)) is also a useful line for h.f. transmission. required between the upper conductor and the ground plane; holes have to be drilled through the substrate. Microstrip also suffers from radiation losses. Neverthe- 2.2.3.4 Twin lines less, microstrip can be made easily and conveniently and it is therefore used extensively. In Figure 2.2-6, we show a sketch of a twin line carefully spaced by a polyethylene dielectric. This is used at rel- atively low frequencies. This twin cable is designed to 2.2.3.5 Coupled lines have a characteristic impedance (Zo) of approximately 300 $ and it is frequently used as a very high frequency Coupled lines are lines which are laid alongside each (VHF) cable or as a dipole antenna for FM radio receivers other in order to permit coupling between the two lines. in the FM band. The parallel wire line arrangement of One example of microstrip coupled lines is shown in the Figure 2.2-6 without a dielectric support can also be seen F1 layout box of Figure 2.2-2 where three sets of coupled mounted on poles as overhead telephone lines, overhead lines are used to couple energy from input port 1 to power lines, and sometimes as lines connecting high output port 4. power, low and medium frequency radio transmitters to their antennas. All seven transmission lines shown in Figures 2.2-3- 2.2.4 Line characteristic 2.2-6 have advantages and disadvantages. For minimum loss, you would use the waveguide, the coaxial line and impedances and physical the strip line in integrated circuits. However, the latter parameters