Synthesis of Filtering Terminal Antennas Based on N-Port Networks

In this communication, a method for synthesizing filtering antennas with isotropic high band rejection levels is proposed for terminal applications based on N-port networks and characteristic modes (CMs). Besides the roll-off of the reflection coefficients, the filtering behavior is achieved in radiation efficiency as well, which further enhances the filtering performances. A uniplanar pixel antenna is first utilized to demonstrate the method due to its strong reconfigurability and clear modal behaviors. Reactive loads between the pixels are optimized, which lead to different CMs of the structure. By establishing and solving the multiobjective functions, a uniplanar filtering antenna is successfully obtained, providing flat gains within the passband and high band rejections within the stop bands. As a typical terminal device, a filtering handset antenna is then investigated and synthesized. With the aid of the reactive loads, the filtering features are well integrated into the handset, with the antenna fully conformal to the platform. The filtering responses of the proposed antennas were validated experimentally with the measured results agreeing well with the simulated ones. The proposed method provides an additional dimension to improve the filtering responses of the antennas, which is practical for terminal applications.