A novel balanced‐to‐unbalanced (BTU) power divider with negative group delay (NGD) characteristics is proposed. The λ/4 open‐ and short‐circuited coupled lines with resistors are used to realize the NGD characteristics and enhance the common‐mode suppression in the meantime. The complete design equations and procedures are presented. A BTU NGD power divider with the center frequency of f0 = 1.0 GHz is designed and fabricated to verify the proposed structure. The measured differential‐mode to single‐ended group delay at center frequency is −2.06 ns with an NGD bandwidth of 40 MHz. The measured differential‐mode return loss at f0 is 25.7 dB with a 12.5‐dB bandwidth of about 58% from 0.7 to 1.272 GHz, in which the insertion loss is less than 7.8 dB. The measured common‐mode to single‐ended suppression at f0 is 37.3 dB with a 15‐dB bandwidth of about 22.7% from 0.869 to 1.092 GHz.
A compact feeding network with radiation contribution is proposed in designing microstrip patch array antenna (MPAA) for X-band marine radar applications. The 1-to-4 feeding network consists of two circular-sector patch balun, which can radiate electromagnetic wave with the same polarization of the patch array for enhancing the gain and suppressing the cross polarization. The feeding line in the series-fed patch subarray is modified as the step-impedance microstrip line to decrease the side-lobe level (SLL). To verify the method, a 28-element 9.41-GHz MPAA with the proposed radiated feeding network is designed and fabricated. Measured results show that the impedance bandwidth is 183 MHz with a peak gain of 21.3 dBi. The SLL is 27.8 and 21.4 dB in the E-and H-planes, respectively. The cross polarization is effectively reduced, which is lower than the copolarization of about 57 dB. K E Y W O R D S cross-polarization suppression, gain enhancement, patch array antenna,
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