Compact Low-Loss Integration of High-$Q$ 3-D Filters With Highly Efficient Antennas

Abstract

A novel synthesis technique to integrate high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> 3-D filters with highly efficient slot antennas is presented in this paper. This technique allows for compact integration of 3-D filters and antennas with very high antenna efficiency and significantly reduced form factor of integrated RF front ends. Prototype four-pole Chebyshev cavity filters integrated with slot antennas are demonstrated at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -band using both coaxial and coplanar waveguide feeding. The center frequency and fractional bandwidth of the filter/antenna system with coaxial feeding are 9.96 GHz and 6.0%, respectively. Due to the high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factor (~850) of the cavity resonator, the efficiency of this filter/antenna system is measured to be 89%, compared with the measured <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> of -0.5 dB (89%) for an identical filter. This means a near 100% efficient slot antenna is achieved within this integrated filter/antenna system. The measured impedance matching, efficiency, gain, and radiation pattern closely agree with simulation results. Equivalent-circuit models of the integrated filter/antenna system are developed and verified with full-wave simulations. This technique can be applied for filter/antenna integration in all microwave, millimeter-wave, and submillimeter-wave frequency regions.