Nowadays, there has been growing demand for miniaturized, multi-frequency, and multi-polarization RF and microwave devices for ground, air and space-based applications such as communications and sensing which can embed sophisticated functionalities. An inevitable step toward this purpose is the integration of several separate functional devices into a single RF system for dual band dual polarized (DBDP)/multi-band multi-polarized (MBMP) synthetic aperture radars (SAR). Shared aperture antenna (SAA) is a high-tech approach for SAR systems in order to combine several antennas inside a common physical aperture.

“Airborne/Spaceborne systems need to be payload friendly” this statement actually leads the trend of today’s shared aperture antenna (SAA) technology. At the end of year 1995 Axness et al., (1996) had laid the initial foundation for SAA technology. The initial success of synthetic aperture radars (SAR) suitable for sensor and communication systems, military platforms (ships and aircrafts) payloads, radiometers and shuttle imaging radars, ultra/very small aperture terminals (USAT's/VSATs), high-speed internet access and multimedia services, automotive communications (intelligent transport system), mm-wave wireless communications and navigation satellite systems.

In the last two decades, the evolution of SAR has the major significant interest in multi-band antenna design. Specifically, because of size reduction in payload requirements, compact, dual band dual polarized (DBDP) and multi-band multipolarized (MBMP) antennas for airborne and spaceborne platforms is currently receiving a lot of attention. However, designing an MBMP antenna is not an easy task, as this type of antenna is subjected to very tough radar specifications. Compact structure, light weight, flexibility, robustness, and low profile are some of the key considerations for design of MBMP antennas.

The SAA design methodologies can be proposed for ground, airborne synthetic aperture radars and spaceborne applications and have their own way of using them based on the parameters. Further, these designs can be implemented with large frequency ratios along with frequency reconfigurability by introducing active components. Some of these are outlined in the following task:

• SAA can be designed with integrated feeding network. Minimizing the loss and complexity by incorporating integrated feeding network in SAA technology.
• Introducing active modules like digital attenuator and digital phase shifter for achieving multiple beams in both elevation and azimuth angles.
• Differential feeding network and pair-wise opposite-phase feeding concept for improving low cross polarization and high isolation.
• Investigation of new techniques to reduce the size and enhancing bandwidth of SAA.
• The effect of material properties on shared aperture antenna performance such as gain, efficiency, radiation patterns, bandwidth etc. can be studied.

• With the help of different miniaturizing techniques MTM’s, FSS can be used to minimize the aperture of SAA.

• As per this exhaustive study I found that main beam tapering concept can be implemented for getting optimized SAA.

• Under source free condition coupling can be analyzed even the frequency range between the bands is too high.
• SAA can be designed in Nano fabrication level using graphene material, low temperature co-fired ceramic (LTCC) substrates in future. It will have the advantages of direct integration with mm-wave radar applications.