Miniaturized Dual-Mode Circular Patch Bandpass Filters With Wide Harmonic Separation

Two slots oriented orthogonal to each other are cut on a circular patch resonator. The slots bring down the fundamental resonance frequency of the patch. The second higher order mode, however, remains unaffected. This effectively miniaturizes the patch by 57.8% at the same time increases the harmonic separation by 2.51 times. By adding two more slots parallel to and on both the sides of each arm of the crossed slot, fundamental frequency can be further brought down resulting in a filter which is 87.4% smaller compared to a circular patch. The second passband appears at a frequency which is 4.66 times that of the first passband center frequency.