Wideband Broadside-Coupled Line Baluns Enabled by Multimaterial Additive Manufacturing

The manuscript reports on a comprehensive design methodology for the realization of wideband Marchand baluns (MBs) alongside a unique integration concept using multimaterial inkjet printing. An optimization method determining the maximum achievable fractional bandwidth (FBW) is proposed for the first time. Several transmission line (TL)-based integration concepts are analyzed using 2-D and 3-D electromagnetic (EM) simulations to maximize FBW, while considering the process capabilities of a multimaterial, multilayer inkjet printing process which is used in this work for the realization of MBs for first time. A miniaturization scheme using spiral TLs and slanted vias is also explored for size compactness. To validate this approach, several coupled-line test structures and MBs were designed, manufactured, and tested in resistively terminated and back-to-back configurations. They include: 1) a straight MB with a footprint of
$0.033\times 0.241\times 0.028~\lambda _{\mathrm {g}}^{3} $
, center frequency (
$f_{0})~4.4$
GHz, and 10 dB return loss bandwidth (BW) between 2.8 and 8 GHz (i.e., FBW of 96%). Across this BW, the power loss, phase imbalance (PI), and amplitude imbalance (AI) were measured as 1.2–3.9 dB,
$3.5~\pm ~3.5^{\circ }$
, and
$0.6~\pm ~0.3$
dB, respectively, and 2) spiral MB with a footprint of
$0.043\times 0.094\times 0.028~\lambda _{\mathrm {g}}^{3},f_{0} =4.4$
GHz, and BW between 2.35 and 6.8 GHz (i.e., FBW of 95%). The power loss, PI, and AI were measured as 0.9–3.1 dB,
$5~\pm ~2^{\circ }$
, and
$0.4~\pm ~0.4$
dB, respectively.