RF Front-End Passive Circuit Implementation Including Antenna for ZigBee Applications

This paper presents a front-end passive circuit module for ZigBee applications using low-temperature co-fired ceramic technology. The front-end part consists of an antenna, a bandpass filter, a switch, and two baluns. In antenna design, the solenoid shape is employed for reducing the size of the antenna, resulting in an overall size of ${\hbox {9}}\times {\hbox {16.4}}\times {\hbox {1.82}}\ {\hbox {mm}}^{3}$ and a gain of $-$1.4 dBi. As for the filter, two types of filters are suggested. First, the lumped-type filter employing a high-$Q$ spiral inductor has more than 20-dB attenuation at both stopbands, very near to the passband. Secondly, the semilumped-type filter adopting an edge coupled line and a loading capacitor provides a group delay of below 5 ns and is adequate for the full module structure due to the structure flexibility. A balun is evaluated using lumped components instead of a transmission line and, thus, it provides an insertion loss of only 0.3 dB and a phase difference of 180 $^{\circ}$ between balanced signals. Based on these components, an RF front-end module including attaching pads for an RF integrated circuit (IC) and baseband IC is implemented. In case of using the lumped-type filter, the insertion loss of the front-end module is 6.5 dB, and the group delay is below 7 ns. In case of adopting the semilumped-type filter, the insertion loss is 6.2 dB, and the group delay is below 4 ns. The overall size of the former and latter is ${\hbox {25.14}}\times {\hbox {28.5}}\times {\hbox {0.68}}\ {\hbox {mm}}^{3}$ and ${\hbox {25.66}}\times {\hbox {25.58}}\times {\hbox {1.17}}\ {\hbox {mm}}^{3}$, respectively.