Single- and Dual-Band LTCC Filtering Switch With High Isolation Based on Coupling Control

This paper presents a novel method for designing single- and dual-band filtering switches based on coupling control. First, the ON- and OFF-state coupling matrices are analyzed to achieve bandpass responses and high isolation, respectively. Then, they are used to guide the low temperature cofired ceramic circuit realization. The ON- and OFF-states are enabled by controlling the PIN diodes in the filter feeding structures. In the ON-state, the circuit is equivalent to a bandpass filter without signals passing through the PIN diodes, which avoids additional loss introduced by the PIN diodes. For the OFF-state isolation, it is realized by controlling the coupling of the filtering circuit, which is different from that of conventional switches by turning off transistors or diodes to obtain isolation. Thus, isolation is considerably enhanced. For demonstration, a single-band filtering switch is implemented with a compact size of 0.050 λg × 0.048 λg × 0.023 λg . Furthermore, a dual-band one of the same dimension is realized with controllable passband frequencies and bandwidths in the ON-state as well as high isolation in OFF-state. The presented filtering switches feature compact size, low ON-state insertion loss, high OFF-state isolation, and high reliability, which are suitable for industrial applications.

I. Introduction

In INDUSTRIAL and consumer electronics applications, various passive and active radio frequency (RF) circuits are needed [1]–[7] , such as the filters [1]– [3], power dividers [4], couplers [5] , [6], oscillators [7], etc. To form RF front-ends, different components are cascaded, which may exist interstage mismatching and cause performance degradation. Instead, codesign of multiple components can solve this problem [8] –[10].