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This paper deals with the design of a microstrip series power divider for circularly polarized sequential rotational antenna array. The theoretical description of the design is firstly proposed, comprising the cases of nonuniform weighted antenna arrays. A more flexible open octagon shape instead of the classical open ring is suggested, highlighting benefits in the case of nonuniform power distribution. A design example of an ultra-high frequency (UHF) band

Circularly polarized (CP) patch antennas have gained considerable interest due to their main advantage of being insensitive to depolarization [

The design of a single CP antenna intrinsically has narrow impedance and axial ratio (AR) bandwidth. However, many applications demand good performance for both impedance and AR over a wide frequency bandwidth. Sequential rotation (SR) technique has been extensively used to improve impedance and AR performances in array design. The mechanism of SR technique has been theoretically and experimentally analyzed [

It has been proved in [

In [

Other feeding structures are also suggested in [

In this paper, the theoretical design of a series power divider for the generic output power distribution case is presented. To the best of the authors’ knowledge, a theoretical analysis of the series power divider with generic output power distribution is not present in the literature. A more flexible open octagon shape instead of the classical open ring implementation is proposed. This modification provides better results because of the flexibility to realize different quarter wave transformer lengths, which better address the case of different quarter wave transformer characteristic impedance. Simulation results are presented to confirm these benefits. Finally, the design of an ultra-high frequency (UHF) band

This paper is organized as follows. The design of a microstrip series power divider is theoretically treated in Section

An equivalent circuit of the series power divider is depicted in Figure

Equivalent circuit of the series power divider.

Furthermore, in order to guarantee impedance matching at each intersection of the series divider, the following

Finally, the first quarter wave impedance transformer is only used to match the source impedance to the series divider input impedance, and then

Equations in (

From the above equations, a design procedure can be summarized:

After defining the power coefficients

From (

The adapted lines lengths

A common microstrip implementation of the series divider has an open ring shape [

The microstrip branches widths

The radius

The output phase contributions

The first branch length

Open ring and open octagon implementations of the series power divider.

It should be noted that, according to [

Thus, a different implementation of the series power divider is suggested in this work. The open ring is replaced with an open octagon, where the lengths of the three 45 deg edges are individually adjusted through the parameters

The microstrip branches widths

The radius

The branch lengths

The output line lengths

The first branch length

It should be noted that the open octagon implementation introduces some new degrees of freedom; this is the reason why the radius

Let us now consider the implementation of a nonuniform series divider for UHF applications. The microstrip divider is designed on a glass reinforced hydrocarbon and ceramic dielectric named S7136, with dielectric constant

Nonuniform series divider design results.

Parameter | Open ring | Open octagon |
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Nonuniform series divider

Nonuniform series divider power coefficient and phase mean errors for both open ring and open octagon implementations.

In this case, the open ring implementation cannot be optimized to have three 90 deg phase differences; this affects the input return loss performance, whose minimum does not correspond to the 90 deg phase difference error minimization situation (as shown in Figure

In this section, the design of UHF band

Amplitude and phase feeding values for the antenna elements.

Antenna | Amplitude | Phase [deg] |
---|---|---|

1 | | |

2 | | |

3 | | |

4 | | |

5 | | |

6 | | |

7 | | |

8 | | |

9 | | |

10 | | |

11 | | |

12 | | |

13 | | |

14 | | |

15 | | |

16 | | |

Design parameters (measurement unit is mm).

Parameter | | | | | |
---|---|---|---|---|---|

| 29.5 | 25.5 | 25.5 | 25.5 | 25.5 |

| 6.93 | 2.13 | 2.13 | 2.13 | 2.13 |

| 9.04 | 1.32 | 1.69 | 1.32 | 1.69 |

| 5.11 | 5.79 | 8.83 | 5.79 | 8.83 |

| 1.46 | 5.09 | 6.02 | 5.09 | 6.02 |

| 20.3 | 0.7 | 1.4 | 0.7 | 1.4 |

| 18.4 | 5.2 | 6.5 | 4.8 | 6.5 |

| 14.5 | 5.3 | 5.5 | 5.0 | 5.5 |

| 45.4 | 52.0 | 52.5 | 52.9 | 53.4 |

| 18.5 | n.a. | n.a. | n.a. | n.a. |

| 10.0 | n.a. | n.a. | n.a. | n.a. |

| 31.0 | n.a. | n.a. | n.a. | n.a. |

| 25.0 | n.a. | n.a. | n.a. | n.a. |

The single antenna element was

Theoretical design, simulated performance, and measurement results are compared in Figures

Broadside gain of the

AR of the

H plane AR as function of elevation angle at 922.5 MHz.

V plane AR as function of elevation angle at 922.5 MHz.

H plane radiation pattern at 922.5 MHz.

V plane radiation pattern at 922.5 MHz.

In this paper, the theoretical design of a generic microstrip series power divider is presented. The description is focused on the design of the series divider for CP SR antenna array. Particularly, the generic case of unequal output power and unequal output impedance is treated, which allows for designing nonuniform weighted antenna array. A more flexible open octagon shape instead of the classical open ring is suggested, highlighting benefits in the case of nonuniform power distribution. This modification provides better results because of the flexibility to realize different quarter wave transformer lengths, which better address the case of different quarter wave transformer characteristic impedance. A design example of UHF band

The authors declare that there is no conflict of interests regarding the publication of this paper.

Authors acknowledge that part of the work herein presented was funded by National Natural Science Foundation of China under Project Contract no. 6137104, Guangdong Provincial Science and Technology Planning Program of China (Industrial High-Tech Field) under Project Contract no. 2016A010101036, and Sichuan Provincial Science and Technology Planning Program of China (Technology Supporting Plan) under Project Contracts no. 2016GZ0061.