New design philosophy of active microstrip patch antenna

Active integrated antennas satisfy the most important specifications in the area of wireless communications. These combine the function of power generation and radiation in the same element. By far, the most popular antenna for integration is the microstrip patch antenna. Whenever a three terminal device is used, it is always placed outside the patch. But whenever a diode is used it can be positioned at an appropriate point on the patch or connected to the patch through a microstrip transformer. In the case of a high frequency patch antenna it is sometimes necessary to use the latter technique. Location of the device into the patch is of prime importance so far as the power output, radiation characteristics, and antenna efficiency are concerned. The existing idea is to design two or more transformer matching sections using conventional impedance matching technique, then to place the diode where the input impedance of the last section matches the linear conductance of the diode (/spl alpha//sub d/). To obtain the dimensions of each section i.e., the characteristics as well as their input impedance should be evaluated separately. In this paper the author has shown that the ratio (n) of characteristic impedances of the transformer sections is sufficient to design the active patch. The output power is maximised with respect to radiation conductance from which the value of n is obtained (within a appropriate limit of pass band tolerance).