Integration of multiple functions is for the first time achieved within a single patch element. Firstly, out of phase equal power division and bandpass filter characteristics are combined within a patch element. The novelty of the proposed structure is to use simple asymmetric cross slots in the patch element to achieve this integration. A simplified equivalent circuit model to describe operation of this patch element is proposed. Coplanar waveguide/microstrip broadside coupling is then investigated to enhance the performance of the patch balanced filter and eliminate narrow coupling gaps and microstrip lines. Subsequently, transition between microstrip and coplanar waveguide is then added to the patch element by using certain electromagnetic coupling methods for higher level integration without introducing additional loss. Different patch elements operating at 2.4 GHz are developed to validate the feasibility of the proposed structures. The circuits were designed, fabricated and measured. The measured results agree quite well with the simulation, exhibiting small amplitude and phase imbalance at the output ports throughout the desired passband, and good rejection levels elsewhere.
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