ABSTRACT
Active electrodes are part of the circuits which are no longer made of lumped elements (self inductances, capacitors, resistors, transformers, etc.). They are instead distributed, being of resonant cavity or waveguide type. They are usually completely shielded, so that they do not radiate. They are connected to external sources and loads by means of coaxial cables and waveguides which also do not radiate. All stray capitances and inductances are reduced to a minimum and become part of the microwave circuit. These circuits show some improved qualities compared with
their low frequency, lumped element counterparts. They have no radiation, lower losses (intrinsic Qs of the order of 10,000 are common at S-band, whereas they seldom reach 1000 for lumped element circuits at low frequencies) and constant geometry resulting in constant rf properties. In fact, these advantages are such that, for high power transmitters, the tendency is now to replace lumped element circuits at as low a frequency as possible (30MHz) by cavity-type resonators integrated with the tetrode. This trend is limited only by the bulk of the resonators which becomes considerable at low frequencies.
