An active quasi-circulator using gallium nitride (GaN) high electron mobility transistors technology is presented. By using two common-gate and one commonsource transistors, two self-interference signal paths from transmitting (Tx)-port to receiving (Rx)-port are constructed. Due to the features of out-of-phase and equal magnitude for the two-path signals, sufficient Tx-Rx isolation can be realized through cancellation of the twopath signals at the Rx-port. One prototype working at 27-29 GHz was designed and fabricated for demonstration. The measured results indicate maximum isolation of 44 dB at 28.2 GHz and the 30 dB isolation bandwidth of 300 MHz. The measured insertion losses of Tx-path and Rx-path are less than 4.5 and 3.6 dB within the operating frequency. Due to the high power density of the GaN devices, the measured IP1dB of the quasi-circulator is better than 18 dBm.
A wideband antenna based on substrate‐integrated suspended line (SISL) platform is presented for the fifth generation (5G) communication applications. The antenna is composed of two dipoles and differentially driven by coupled slot between dipole arms to achieve symmetrical radiation pattern on both E and H plane. Combining with the multilayer feature of the SISL, a metallic cavity under the dipole is formed to improve the antenna bandwidth and radiation performance. To verify the proposed antenna, one prototype was fabricated using the conventional printed circuit board process and a balun structure was designed to provide the differential excitation. The measured results indicate that the proposed dipole antenna with differential feeding network achieves a large −10 dB impedance bandwidth of 58% from 24.5 to 44.5 GHz and a peak gain of 8.2 dBi. The proposed antenna is a promising candidate for 5G communications due to its advantages of wideband, high gain, low cost, and convenient integration with differential active circuits.
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