Design and validation of miniaturize Rat Race Coupler based microstrip Balun

Miniaturized Twelve-Stubbed Microstrip Balun With Twelfth Higher Order Harmonic Suppression and Improved Bandwidths

“…Several planar balun designs have been reported [2][3][4][5][6][7][8][9][10][11]. Marchand balun [2], using coupled lines, is difficult to realize and further requires compensation to match the even-and odd-mode phase velocities.…”

“…The balun based on Wilkinson topology [3] requires a very large area and additional circuitry. In contrast, the branch-line balun (BLB) design [4][5][6][7][8][9][10][11], based on modified rat race coupler, entirely composed of transmission line sections, is simple and easy to implement, hence being the choice in wide attempts like dual-band operation [4,5] and bandwidth enhancement [6,7]. However, the circuit size of BLB is large due to the transmission line topology composed of half-wavelength lines; moreover, BLB exhibits harmonic responses, which interfere with other circuitries in system level.…”

“…However, the circuit size of BLB is large due to the transmission line topology composed of half-wavelength lines; moreover, BLB exhibits harmonic responses, which interfere with other circuitries in system level. Addressing this, several methods were proposed in [8][9][10][11]. Transmission line equivalent shunt open-stub units with single and two stubs were presented in [8][9][10] for simultaneous size and harmonic reduction, while an inter digital capacitor like structure (resembling two stub unit) is presented in [11] only for miniaturization.…”

“…Transmission line equivalent shunt open-stub units with single and two stubs were presented in [8][9][10] for simultaneous size and harmonic reduction, while an inter digital capacitor like structure (resembling two stub unit) is presented in [11] only for miniaturization. However, the total size of the balun is large in [8] as the stubs were placed outside, while the amplitude imbalance is huge (0.9 dB) at operating frequency in [11]. Though a good size reduction was achieved in [9][10][11], the harmonic suppression was not wide, limited up to fourth [9] and sixth [10].…”

“…However, the total size of the balun is large in [8] as the stubs were placed outside, while the amplitude imbalance is huge (0.9 dB) at operating frequency in [11]. Though a good size reduction was achieved in [9][10][11], the harmonic suppression was not wide, limited up to fourth [9] and sixth [10]. These were achieved at the expense of reduced balun bandwidths, which were not addressed in [8][9][10][11].…”