A Variety of Active Patch Antenna with a New Design Philosophy

Microwave systems like radar, missile guidance and communication equipment which require large amplifiers to produce high power beam, wave-guides for its low loss and higher power capabilities and motors for scanning are bulky, occupy large space and are not easily routed. Most efficient replacements have been found in the active antenna array where active devices are integrated directly into the antenna platform. Whenever an active device, either a Gunn, IMPATT or a FET is integrated within a microstrip patch antenna, the assembly is commonly called active microstrip patch antenna (AMPA). AMPA serves both the purpose of radiation and power generation. In an active antenna there are two ways of integrating the Gunn diode within the patch e.g. i) direct integration of the device within the patch(AMPA-I), ii)device is connected to the patch through a microstrip transformer (AMPA-II). The central idea is obviously, to realize maximum power output from an antenna. In the first instance, position of the diode on the patch [1] is of importance whereas in the second it is related with the appropriate design of the quarter wave transformer. An antenna where the diode is placed within the patch is capable of producing high power output with spectral purity, yet suffers certain difficulties: (a) Whenever a device is integrated within the patch it affects the field equations as well as the resonant frequency.(b)When desired frequency of oscillation is high , patch dimension become comparable to the active device and is difficult to design in practice.(c) Diode has a finite dimension, which limits the placement of it in the exact location on the patch. To overcome these limitations an excellent way of integrating a two/three terminal device within the patch through a microstrip transformer is proposed in this paper. Fig 1 shows the way of placing the active device (Gunn diode) within the patch. The central idea is to obtain