Miniaturisation of planar microwave circuits by using resonant-type left-handed transmission lines

It is demonstrated that planar microwave circuits and components such as impedance inverters or power dividers, among others, can be compacted by using artificial left-handed transmission lines in their designs. Key to this size reduction is the possibility to control the electrical characteristics of these lines (namely electrical length and image impedance) over wide margins by means of a single cell structure. It consists of a microstrip line section with a series capacitive gap etched in the conductor strip and loaded with a complementary split rings resonator etched in the ground plane. A recently reported model of the artificial line is used as a first step in the design of the desired devices. To demonstrate the viability of the approach, several prototype device examples are provided, that is a 90 degrees impedance inverter and several power dividers with different topologies. A 50% size reduction (as compared to conventional devices) has been achieved by implementing the devices in conventional low loss microwave substrates, but further levels of miniaturisation can be obtained if the devices are fabricated on advanced technologies such as low temperature co-fired ceramic or multi chip module-deposited, among others.