1, spiral antenna
Spiral is a slow wave structure, and the spiral antenna is actually a slow-wavefrotic monopole antenna. Due to the action of the helix, the phase speed propagating the electromagnetic wave along the helix, so the length of the antenna can be shortened.
The antenna design only needs to find the equivalent wavelength of the antenna according to the phase speed of the helix, and can be obtained according to the design method of the monopole antenna.
It is also due to the slow wave structure of the spiral, so that the Q value of the antenna is high, the bandwidth, the antenna is large, and the radiation efficiency is lowered.
The design method of multi-band spiral antennas is shown in the next section, and its design formula has not seen, but can be derived by the structure of the upright unipolar antenna.
2, PCB board spiral antenna
The PCB plate helical antenna is actually a deformable spiral antenna, which further reduces the size of the antenna using the dielectric constant of the PCB board.
3, PIFA antenna
The PIFA antenna is obtained to the extension of the Fi line antenna. The development of this antenna is - top loading - poured L Antenna - Pour F Annex - PIFA. This development process is known to know the characteristics and advantages of the antenna. It is characterized by a wide frequency bandwidth, small size, low profile.
The PIFA antenna corresponds to the parallel of a large number of IFA antennas, which is equivalent to in parallel of many linear antenna impedance, so the input impedance of the planar antenna is lower, not only broadband resonance characteristics, but also reduces size. In order to generate self-resonance, avoiding the use of a power consumption, the radiant resistor should be utilized, reduce the loss resistance, so that the antenna system maintains a sufficiently high efficiency.
The main points of its design:
When the circumference of the flat panel unit is about half a wavelength, resonance is generated.
Design experience:
In the experiment, we found that the horizontal length L1 of the antenna can be roughly adjusted in the range of the antenna center (selected a height H); the width L2 of the antenna can adjust the bandwidth of the antenna, which makes the bandwidth performance becomes different.
The PIFA antenna relative band width has a limit value, about 16%.
The height H of the antenna adjusts the bandwidth and efficiency of the antenna. The larger h, the wider bandwidth, the higher the efficiency, but the increase in H is not only increased by weight but also destroy the characteristics of the antenna. The airfoil position of the antenna also affects the center frequency and bandwidth. Generally, the farther the foil is left, the greater the center frequency, in order to increase the antenna input impedance, the feeder point is not too close.
4, microtic patch antenna
A, Characteristics and Design of Microstrip Unit Antenna
The microstrip antenna is miniaturized, integrated line antenna protagonist, is known from the advantages of low outline, printing process, facilitating and circuit integration, but there are defects with narrow and low efficiency. The microstrip tablet antenna is developed in all-round development of a variety of different design objectives with flexibility in its three-dimensional structure. It is used separately in the mobile phone antenna, which is also widely used as a unit of various array antennas, which are both diverse in engineering design, and more is more common to the electromagnetic field numerical analysis as a typical example. Applying photon crystal structures (PBG) in microstrip tableting antennas to improve microstrip patch antenna performance is the current hotspot.
The design of the microstrip patch cell antenna is very simple, not explained here, the following mainly discusses the method of miniaturization technology, multi-frequency implementation, and broadband implementation.
B, microfilt technology
Miniaturization is achieved by the coupling capacitance between the feeder and the short path. The resonant frequency of the antenna mainly depends on the thickness and position of the short-circuit probe, and the antenna size can be reduced by 50%. shortcoming:
1) The impedance match is seriously dependent on the distance between the position of the short-circuit probe and the feed point.
2) Variety
3) Hes' cross-polarization level is higher
The resonant frequency of the antenna is inversely proportional to the dielectric constant. The main problem with high dielectric constant media is to excite the strong surface waves, the surface loss is large, and the gain is reduced, and the efficiency is lowered.
The bandwidth is narrow, but the PBG structure can be used to suppress surface waves and reduce mutual coupling.
When a different form of groove is opened on the surface of the patch antenna, the original surface current path is cut, and the radio wave winding side is fluteled and the path is long, and the antenna circuit is equivalent to introducing cascading inductance. The dual frequency antenna and a circularly antenna can also be generated using a patch slot. Disadvantages: When the size is particularly small, the bandwidth of the antenna becomes particularly narrow, and the gain of the antenna is also particularly low.
The size requirements of the shaped micropro-belt patch antenna are one-half of the working wavelength in the medium, and the discontinuity of the microstrip table is introduced to rely on its own switch. The area of the antenna unit can be greatly reduced. This principle is adopted by the H-shaped antenna.
It is used to increase the equivalent length of the patch by changing the distribution of current on the patch, reducing the resonant frequency. From the physical meaning, the removed two patchs are equivalent to adding appropriate inductances in the cavity of the antenna, thereby achieving miniaturization purposes.
3, microprocessing technology
The narrow frequency band characteristic of the microstrip antenna is determined by the resonant characteristics of its high Q, that is, the method of the exhibition band is achieved around the Q value of the reduced antenna.
a, using thick substrates
b, a substrate material with small dielectric constant or large dielectric loss
C, using nonlinear substrate materials, different dielectric materials
D. Additional impedance matching network The feed circuit uses broadband impedance matching (such as impedance matching circuit or using sewing coupling to antenna feed), resonance is a parallel resonant network, and the feed is generally equivalent to an inductor.
If it is a multi-frequency antenna, use an external matching circuit to extend the electrical energy of the low-band vibrator, that is, "widening the band". Matching circuits generally adopt high-pass design so that the matching circuit is transparent to high-band vibrators. Such circuitry can also reduce the minimum operating frequency of the antenna.
f, use multilayer structure, using multi-patch resonance. Passive vibrators can also be used to generate four pole responses to increase the bandwidth of the antenna. Or maintain an antenna as a diode structure, and then introduce an additional pole by the matching circuit when necessary.
In general, the effect of the first three methods is not obvious, and the fourth method needs to design a broadband matching circuit, but the circuit structure is complicated, and the production is relatively large. Therefore, we use the fifth method, which uses multi-patch coupling, so that each patch antenna is different, and each resonant bandwidth intersects, so that the overall bandwidth of the entire antenna is wide. Read more
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