A 94 GHz Monopulse Duplexing Horn Antenna for a 3-D Tracking Radar

New observables of the cosmic microwave background

“…For the high order mode, due to the presence of a null in the boresight direction, the amount of cross-polarisation is more difficult to define. In [25] the simulations show overall good cross-polar performance. The main issue however is that the retrieval of the required orthogonal polarisations for the high order mode may require a complex network of waveguide components, with potential accommodation issues for a space born experiments, maybe less of a concern for ground based systems.…”

“…It is also important to emphasize that the observables defined in Eq. ( 25) are orthogonal when assuming statistical independence of the coefficients a ′ l,m (25) T ,1 = Table 1 Estimated magnitude of the temperature signal which can be expected when using the proposed observables, including the existing one (δT 11 ) as well as the newly proposed (δT 21 and δT 31 ) as a function of the half-power beamwidth. The estimates do not take into account efficiency or implementation losses which will reduce the actual magnitudes, which is unimportant for a comparative analysis Half-power beamwith h [degrees] δT 11 [μK] δT which follows immediately from the fact that their linear combinations involve coefficients a ′ l,m with different azimuthal index.…”

“…The detection of pure high order modes which can be used for monopulse autotracking is widely described in literature. Examples are provided in [23], related to a corrugated horn feed for ground applications operating at 8 -8.5 GHz, where HE21 is extracted, in [24] (30-50 GHz, extraction of the mode TE21) and in [25] (94 GHz with extraction of TM01), the latter reference revealing the technological difficulty of increasing the operating frequency towards the THz range for such devices. 4 The extraction of higher order modes, like HE31, is not addressed in monopulse autotracking literature, due to the fact that the correlation of such mode with the fundamental leads to information which cannot be obviously interpreted (apart from the use proposed within this paper).…”

“…The extraction of a high order mode is the fruit of resonant behaviours within the feed system, which are only effective within a narrow bandwidth around a given centre frequency, especially if the phase relation between fundamental and high order mode has to be preserved [30]. When looking at available literature, like the quoted [23] and [25], one could estimate the available bandwidth as few percent of the centre frequency.…”

“…2), with proper discrimination. The retrieval of both orthogonal polarisations is feasible for the dominant mode as well as for the higher order modes, as exemplified in [23] and [25], with cross-polar discrimination between 25 and 30 dB over the supported frequency range for the dominant mode. For the high order mode, due to the presence of a null in the boresight direction, the amount of cross-polarisation is more difficult to define.…”