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Both water activity and glass transition concepts were used for stability evaluation of jujube powder in this study. The water sorption behaviour at 25, 35 and 45 °C and the relationship between water content (X w), glass transition temperature (T g) and water activity (a w) were investigated for jujube powder with and without the maltodextrin addition. Moisture sorption isotherms of different jujube powders were of type III and BET model was the best for fitting the experimental data. The equilibrium moisture content of jujube powder containing 20% maltodextrin at a given a w was lower than that of pure jujube powder. However, temperature had no significant effect on the moisture sorption of jujube powders. Values of T g of different jujube powders were obtained using differential scanning calorimetry and the glass transition line was fitted to the Gordon-Taylor model. A depression in T g with increasing water content was observed. State diagrams of different jujube powders were established based on the moisture sorption isotherm and the glass transition curve. Results showed that jujube powders with and without maltodextrin addition were stable at 25 °C when the water content was lower than 0.0673 and 0.0566 g/g solid, respectively.

In order to solve the problem of the stability of the UWB omnidirectional radiation antenna, a three-dimensional bipolar antenna is proposed, which is composed of metal frame with Klopfenstein curve boundary. The antenna is fed with a 50 Ω coaxial line and the reflection coefficient |S 11

In order to reduce the minimum antenna measurement distance, the aperture reduction is needed. While the aperture reduction will cause the gain of the antenna reduced. The method of loading the elongated dielectric rod on the rectangular waveguide can remarkably improve the gain of the antenna without increasing the antenna aperture. A simulation study was carried out on the antenna with a dielectric rod loading covering 18–36 GHz. The dielectric rod is loaded on waveguide WR42 fed by the parallel coaxial. The CST simulation results show that the reflection coefficient of the antenna is lower than −10 dB in the frequency range of 18–36 GHz, the gain is stability in 10–16 dBi, and high efficiency is reached at high frequency, which is 95%.

In order to reduce the profile of the ultrawideband directional antenna, a disc-shaped combined dipole used as a feed is proposed, and a rectangular metal plate with right angle bend is used as a reflector. The disc-shaped dipole is used as a director. Through CST Microwave Studio modeling and simulation, ultimately achieved operating in 0.7-2.4 GHz, with a gain of more than 4 dBi ultra-wideband directional antenna. The ratio of the profile dimension to the wavelength of the minimum operating frequency is 0.15, and the front-to-back ratio is more than 6.5 dB. The simulation results show that the antenna can be regarded as a combined antenna of electric dipole and magnetic dipole.

In order to improve the gain of the aperture antenna based on integrated waveguide technology, the slender dielectric rods are designed to be planar and loaded on the SIW port, which is fed by a microstrip line. Finally, a high-gain printed antenna unit operating in the Ka-band is formed. The simulation results of CST Microwave Studio show that the reflection coefficient of the antenna in the frequency range of 33–37GHz is lower than −10dB, the gain is between 11–15dBi, and the antenna aperture is only 1.6mm × 30mm, which shows that The antenna has the effect of small aperture and high gain. More importantly, this type of antenna can form a miniaturized array to further increase the gain because of its simple feeding.