A New Class of Miniaturized Balanced Couplers: Low-Loss Design for Wireless Network and RF Scavenging Systems

A new class of miniaturized balanced 0° microstrip filtering couplers is presented, characterized by an ultra-compact footprint of only 0.006 λg² achieved through a unique configuration of coupled thin microstrip lines integrated with solid stubs. The proposed design exhibits a built-in filtering response with balanced output magnitudes and phase (0° phase difference) across its passband, while maintaining exceptionally low group delays (0.84 ns at S₂₁ and 0.83 ns at S₃₁). Operating at 1.2 GHz, the coupler achieves outstanding performance metrics, including a return loss of 31.1 dB, an insertion loss of 3.11 dB, and a coupling factor of 2.98 dB. These metrics surpass those of prior coupler designs by concurrently achieving extreme miniaturization, low loss, and minimal group delay in a single device. Close agreement between full-wave electromagnetic simulations and measurements from a fabricated prototype validates the design’s effectiveness and underscores its suitability for wireless network and RF energy scavenging systems, where extreme compactness, low loss, and phase coherence are critical.