A 3-dB Quadrature Coupler Using Broadside Striplines for FM Power Amplifiers

A 3-dB quadrature coupler is an important component for FM power amplifiers to realize high power output. Conventional couplers are realized by using tightly quarter-wavelength transmission lines. An FM Frequency range is low frequency that increases the physical size of conventional couplers which may be unsuitable to fabricate. This paper presents the 3-dB quadrature coupler using broadside striplines for FM power amplifiers. The broadside-coupled striplines technique can reduce the physical size of 3-dB quadrature couplers which are suitable for FM power amplifiers. The proposed coupler uses low-cost FR-4 printed circuit boards (PCB) with 0.8 mm substrate thickness to implement. An overall dimension of the proposed coupler is 75x85 mm. Experimental results show that return losses of all ports are lower than -15 dB. Coupling coefficients of the coupled port and the directed port are -3.4 dB and -3.3 dB respectively. Relative phase differences between two output ports are 90, pm 2
^o
. The proposed coupler is simple, low cost and small size that can be used in FM power amplifiers.