Highly miniaturized wideband 3‐dB branch‐line hybrid with second harmonic‐suppression

Abstract

In this article, a highly miniaturized second harmonic suppressed 3‐dB branch‐line hybrid (BLH) with wideband performance is developed by employing a novel transmission‐line architecture (TLA). The proposed architecture consists of a coupled‐line, a series microstrip‐line and two open‐ended stubs. The even‐odd mode technique is used to formulate the required design equations. In order to reduce the size of the BLH, the internal areas between the branches are properly utilized for accommodating the proposed TLA structures with parameter values calculated using the derived formulas. To demonstrate this technique, a wideband three‐section BLH operating at 0.9 GHz is designed and fabricated. The measurement results show the proposed technique reduces the total circuit‐area of the BLH by 90.24% compared to the traditional three‐section hybrid while maintaining a fractional bandwidth greater than 53%. In addition, the second harmonic is eliminated utilizing the spurious response produced by the open‐ended stubs.

Wideband Highly-Selective Bandpass Filtering Branch-Line Coupler

“…A number of techniques have been developed to achieve larger bandwidth, harmonic suppression, arbitrary power division, compact size, multiband operation, and filtering response . For example, bandwidth enhancement can be obtained by attaching impedance transformers to each port of the single-section BLC [1][2][3], utilization of two-section/three branch-line topologies [4][5][6][7][8][9][10], but also three-section/four branch-line topologies [11][12][13][14][15][16][17][18].…”

“…The conventional 90-degree lines used for BLC design are unable to realize transmission zeros (TZs), which could be employed to suppress the harmonics. To implement the suppression, various equivalent circuits of 90-degree lines, such as L-shaped and open-ended stub [1], multiple πshaped [3], open stub [7], unequal-length open stub [14, and coupled-line and open stub [16], [18], have been suggested. It should also be emphasized that wideband BLC topologies reported in [2], [4]- [6], [8][9][10][11][12][13], [15], [17], and [19], are not suitable to suppress the harmonics.…”