T/R Lens Amplifier Antenna Arrays for X-band and Ka-band

Antennas integrated with active circuitry are usually referred to as active antenna arrays. The integration can be done at different levels, depending on the goal and application. For example, a low-noise amplifier (LNA) is often integrated directly with the antenna for reduced loss and therefore decreased noise figure. Another example is the integration of power amplifiers with antenna arrays to achieve spatial power combining. The focus of this paper is the integration of bidirectional amplifiers with each element in an antenna array, for transmit-receive (T/R) applications. The schematic of the architecture is shown in Figure 1. Each element of a directional antenna array is connected to a power amplifier (PA) and LNA. The elements can be fed with a corporate feed network, but such a network is typically lossy and complex for a large number of elements. Figure 1 shows an array with a free-space feed. In this architecture, all elements are fed in phase from a feed placed at a focal point in the near field. This is accomplished by delay lines of varying length between the input (feed-side) antenna and output antenna. An array designed in this way is a planar microwave lens with gain. The lens is fed from a point (or multiple points) along a focal surface, and the output radiated wave is a collimated beam defined by the output antenna array. These active arrays are appropriately referred to as quasi-optical. (A review of quasi-optical active components developed to date can be found in [1]). In transmission, the advantage of the architecture from Figure 1 is that the radiated power from the array is obtained by combining the individual amplifier output powers [2,3,4,5]. This allows for lower cost and lower power individual elements, and graceful degradation. In