Adjustable metamaterial phase shifter based on active device

[0020] In order to make the present invention more comprehensible, preferred embodiments are described below in detail with accompanying drawings.

[0021] The phased array system (applicable to radar, communication and other systems) is based on the ability to phase shift microwave and millimeter wave signals so as to achieve antenna beam scanning. The basic idea of ​​using metamaterial elements to realize a phased array system is: first, according to the requirements of phased array antenna beam scanning, the amplitude and phase modulation parameters of the antenna radiating element are allocated; then the microstrip line embedded with the metamaterial configuration is used to optimize the super Material voltage tuning parameters to achieve the requirements of phased array antennas, the basic block diagram is as follows figure 1 As shown, figure 1 Where n represents the number of phased array radiating elements, k 0 Represents the amplitude weighting coefficient of the radiating element, d c Indicates the distance between radiating elements, and θ represents the feed phase difference between adjacent radiating elements. figure 1 The structure shown includes a phase shifter implemented with multiple metamaterial units.

[0022] The metamaterial structure can realize the positive refractive index (PRI) and negative refractive index (NRI) of the metamaterial transmission line. This metamaterial transmission line can be used to construct a high-frequency phase shifter, and this structure can be constructed with positive and negative directions Wideband compact phase shifter.

[0023] figure 2 It is a phase shifter unit realized by metamaterials. It consists of a microstrip line equipped with a series capacitor and a parallel inductor. This is equivalent to cascading the PRI line and the NRI line, which causes the phase shift of the compensated propagation signal. Using periodic analysis, it can be shown that the phase shift value of the unit cell can be given by equation (1):

[0024]

[0025] Where θ TL Is the phase lag caused by a section of the microstrip line, and its value can be expressed as:

[0026] θ TL = Β TL d/2.

[0027] Where β π Represents the phase velocity of the wave, and d represents the length of the transmission line.

[0028] In order to maintain the characteristic impedance Z of the metamaterial transmission line 0 Matching, we will enter the reflection coefficient (S 11 ) Is equal to zero, and the relationship between inductance, capacitance and phase shift in frequency can be obtained:

[0029]

[0030] To simplify the calculation, assuming that the signal propagates in the microstrip line with a small phase shift, which is approximately zero, the matching condition (the above formula) can be approximated as:

[0031]

[0032] The same result can be obtained by studying the stop band of the periodic structure and finding the conditions to eliminate the stop band near the zero phase shift region. Under this matching condition, the phase can be approximated as:

[0033]

[0034] This means that both positive and negative phase shifts can be realized by a single cell, without having to undergo a complete phase rotation like traditional low-pass or high-pass. In addition, the amount of phase shift can be achieved by adjusting and changing the value of the loaded elements (L and C), but to keep the transmission line matching, the two elements must be adjusted at the same time to satisfy formula (3).

[0035] If the series capacitance is only in C=(C max +C min The inductance value selected at )/2 to match the phase shifter changes, which will cause the phase tuning range Δφ C Smaller, given by:

[0036]

[0037] Where: r=C max /C min , If both L and C are tuned to meet the matching conditions, the phase tuning range Δφ C-L Expressed as:

[0038]

[0039] It can be seen from the above formula that changing the values ​​of L and C to achieve matching can achieve different phase shifts.

[0040] image 3 The designed metamaterial phase shifter unit based on active adjustable device is shown. The adjustable capacitor is realized by a varactor diode, in which the reverse voltage of the varactor diode controls its capacitance. On the other hand, use active circuits to implement electronic tunable inductors; most of the implementations of active inductors are based on the gyrator-C architecture, such as image 3 Shown. Common equivalent inductance through L=C/g m1 g m2 Approximately, by adjusting the transconductance g m1 And g m2 So as to realize the adjustment of the inductance value.

[0041] Both the varactor diode and the active inductor must achieve a sufficient quality factor (Q) at the design frequency, which sets the upper limit of the operating speed of the phase shifter. The operating frequency of active inductors is up to several G or more than tens of G Hz, which can be realized by using 0.1μ InGaAs/InP High Electron Mobility Transistor (HEMT). The active tunable metamaterial shifter realized by the above method can be applied to the microwave or millimeter wave frequency band and has a wide range of application prospects.