Compact RF Crossover Utilizing Orthogonal Fields for Low Loss and Improved Isolation Bandwidth

This work introduces a compact ultra-wideband microstrip line based RF crossover. By utilizing the orthogonal fields of two perpendicular microstrip lines, the crossover achieves significantly enhanced isolation performance. A twolayer prototype is fabricated on a 20-mil and 10-mil thick RO4003C substrate with a dielectric constant of 3.55, occupying a rectangular area of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$8 \times 5 \text{mm}^{2}$</tex>. The presented crossover topology is applicable for higher frequency due to its microstrip line based geometry, which is verified with simulation of 10 GHz structure. Measured performance shows an insertion loss below 0.4 dB for both ports, a return loss better than 16 dB, and isolation exceeding 23 dB across the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.1 - 5 \text{GHz}$</tex> frequency range. This design also offers promising performance over 0.1 - 8 GHz with 0.6 dB insertion loss, 13 dB return loss and 16 dB isolation.