LTCC-packaged Branch-line Coupler Using Capacitance Improved Capacitor for VHF-band Applications

A compact branch-line coupler is proposed with capacitance improved capacitor (CIC) using low-temperature co-fired ceramic (LTCC) packaged technology. The proposed CIC is constructed for higher capacitance without any size increment by further separated horizontal finger pads on VIC. The area of the coupler is only 10.3 * 9.4 * 1 [mm.sup.3], which is equivalent to 0.0041 * 0.0035 * 0.0004[lambda][g.sup.3]. The application frequency band covers maritime and aircraft navigation in the very high frequency (VHF)-band. The measured in-band [S.sub.11], [S.sub.21], [S.sub.31], and [S.sub.41] are better than -15, -4.1, -2.2, and -18 dB from 47 to 67 MHz, respectively. And the measured phase difference between the coupled and through ports is within 90 [+ or -] 0.2[degrees], which presents an excellent linear characteristic.