Coupled‐line directional coupler with tunable power division ratio and operating frequency

Abstract

This study presents a novel planar coupled‐line directional coupler with tunable both power division ratio and operating frequency, which is achieved using microstrip technology for the first time. Its tunability of the operating frequency and the power division ratio, or coupling ratio, can be independently controlled by the bias voltages. Moreover, it can simultaneously maintain perfect port match and isolation. On the basis of the even–odd mode analysis method, both the closed‐form analytical equations and parameter discussions are provided to facilitate the practical design. An experimental prototype of the tunable coupler is simulated, fabricated, and measured to demonstrate how it works. The measured results indicate that power division ratio can vary from 0.35 (9 dB) to 0.71 (3 dB) when operating frequency ranges from 0.55 to 1.48 GHz (91.63%) while power division ratio varies from 0.35 (9 dB) to 1 (0 dB) when operating frequency is fixed at 1 GHz, which validated the reliability of the proposed model.

Trans‐directional coupler with adjustable coupling coefficients and reconfigurable responses

“…The relative bandwidths under the criterions of return loss >20 dB, isolation >20 dB and amplitude imbalance <1 dB are also listed in Table 2. It can be found that the bandwidth of return loss >20 dB for the couplers in [14][15][16][17][18][19][20] are more than 2, 9, 10, 3.8, 9, 3, and 8%, respectively. While the bandwidth for the proposed coupler is more than 14.3%.…”

“…While the bandwidth for the proposed coupler is more than 14.3%. The bandwidth of isolation >20 dB for the couplers in [15][16][17][18][19][20] are more than 22.5, 7.5, 1.1, 9, 4, and 10% respectively. While the bandwidth for the proposed coupler is more than 10.6%.…”

“…While the bandwidth for the proposed coupler is more than 10.6%. The output ports power distributions of the couplers in [14][15][16][17][18][19][20] are all unbalanced. From the column of amplitude imbalance, it can be observed that the relative bandwidth (amplitude imbalance <1 dB) of the proposed TRD coupler is wider than the others under different coupling coefficients.…”

“…With the recent advent of multi-standard frontends in modern telecommunication systems, directional couplers are required to be frequency adjustable [8][9][10][11][12][13], coupling coefficient adjustable [14][15][16][17][18][19][20], and phase adjustable. A coupler with adjustable coupling coefficient is useful in the amplitude weighting control of antenna arrays to reconfigure the radiation pattern of a multi-beam antenna with no substantial increase in loss.…”

“…The size of the coupler is as same as that of a traditional branch line coupler. Recently, coupling adjustable COD coupler with better isolation and port match is presented [19]. However, the bandwidths under the criterion of return loss >20 dB and isolation >20 are narrow, and the extra insertion loss is large.…”