TABLE OF CONTENTS Some advanced techniques for better RF performance and/or smaller size are given in this chapter. Some of these techniques were developed for SiP modules, while others were developed for printed circuit board solutions. However, all of these techniques are applicable to SiP modules.
Couplers typically employ discrete components for low-frequency operation, less than 500 MHz, and microstrip or stripline quarter wavelength transmission lines for higher-frequency operation. However, high-power base station and magnetic resonance imaging (MRI) equipment exceed the power limitations on the discrete components, and quarter wavelength couplers are large. In addition, a typical 0.25-dB insertion loss of a quarter wavelength coupler would dissipate 559W for every 10 kW of incident power. A technique in practice to circumvent these issues is a shortened microstrip coupler with an additional capacitor to provide directivity [1]. The coupler design is a standard pair of edge-coupled microstrip transmission lines with a capacitor placed at the coupled port or reverse-coupled port or both. This same technique can be applied to RF wireless modules that demand more functionality and smaller sizes [2].
The design goals for the RF SiP designer are cost, size, and performance. A quarter wavelength coupler can be purely implemented in the low-cost laminate substrate, which is the industry staple for performance. Unfortunately, it is very large for frequencies below 2 GHz, which may require more layers of laminate or a larger-size laminate to accomplish. The smallest coupler implementation is a single capacitor, but it has no directivity and is...
