This paper presents a simple method to realize a circular polarizer by inserting a dielectric septum in the middle of the cylindrical waveguide. Since fixing slots are built to precisely locate the septum, dual-compensation slots are made in the orthogonal plane to balance the effects of the fixing slots. The measured axial ratio is smaller than 0.5 dB and the phase difference is flat in the frequency range from 60 to 62.25 GHz. In addition, the return losses are better than 13 dB for both and polarizations in the same frequency range. This design has the added advantage that poor phase differences resulting from fabrication error or an inaccurate dielectric constant can easily be improved by adjusting the length of the inserted dielectric septum.
Naked oat (Avena nuda L.) was originated from China, where there soil nitrogen (N) is low availability. The responses of chlorophyll (Chl) fluorescence parameters and leaf gas exchange to N application were analysed in this study. After the N application rate ranged from 60 to 120 kg hm-2 , variable fluorescence (Fv), maximal fluorescence (Fm), maximal photochemical efficiency (Fv/Fm), quantum yield (ΦPSII) of the photosynthetic system II (PSII), electron transport rate (ETR) and photochemical quenching coefficient (qP) increased with N application level, however, non-photochemical quenching coefficient (qN) decreased. Moreover, there was no difference in initial fluorescence (Fo) with further more N enhancement. Maximum net photosynthetic rate (Pmax), apparent dark respiration rate (Rd) and light saturation point (LSP) were improved with 40-56 kg N ha-1 as basal fertilizer and 24-40 kg N ha-1 as top dressing fertilizer applied at jointing stage. Initial quantum yield (α) was decreased with 24 kg N ha-1 as basal fertilizer and 56 kg N ha-1 as top dressing fertilizer. Flag-leaf net photosynthetic rate (Pn) was significantly enhanced at the jointing and heading stages with 40-56 kg N ha-1 as basal fertilizer; in addition, increased at grain filling stage of naked oat with 40-56 kg N ha-1 as top dressing fertilizer. 90 kg N ha-1 (50-70% as basal fertilizer and 30-50% as top dressing fertilizer) application is recommended to alleviate photodamage of photosystem and improve the photosynthetic rate in naked oat.
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