Design of millimetre wave diplexers with relaxed fabrication tolerances

Abstract

A novel millimetre wave waveguide diplexer topology that can be fabricated using relaxed fabrication tolerances is presented. This is achieved by using a highpass filter/hybrid coupler topology in addition to a low order capacitive iris bandpass filter. By targeting the most sensitive centre resonators in the bandpass filter and increasing their length to full wavelength, the sensitivity to fabrication errors associated with changes to the resonator length can be reduced without the introduction of spurious responses close to the passband. The main benefit of this topology is that only one bandpass filter is required to realise the final diplexing response. This is advantageous when tolerance is considered as it is found that resonating structures associated with bandpass filters contribute to tolerance effects. In addition to this, the authors find that the choice of iris discontinuity used to realise the impedance inverters in the bandpass filter can help to relax fabrication tolerances. By subjecting the proposed circuit to a tolerance analysis, simulated results suggest that the circuit can be fabricated with relaxed fabrication tolerances. These discussions are verified with the fabrication of a Kaband waveguide diplexer, where the measured and simulated scattering parameters are in very good agreement.

High-Performance Compact Diplexers for Ku/K-Band Satellite Applications

“…The in-band frequency response of the novel band-pass filters proposed in this paper is not based on coupled resonant structures as it happens in [17], [18] or in transmission lines of different characteristic impedances as it occurs in [20]. Instead, the passband characteristic has been realized by combining a reduced loss low-pass waveguide filter designed following the technique described in [6] and a high-pass configuration based on the cut-off effect [20].…”

“…designing the filters to have sufficient margin to fulfill the frequency specifications at the cost of increasing the filter length, have been proposed in the literature [16]. In [17], the length of the resonating structures was enlarged to improve the tolerance issues. However, the latter implies that the overall size of the filter (and consequently the diplexer) increases as well and, besides, spurious resonances could appear below the passbands, which does not occur for half-wavelength resonators [18].…”

Millimetre wave SIW diplexer circuits with relaxed fabrication tolerances

“…To demonstrate the translation process, a bandpass filter, highpass filter and hybrid coupler are designed using the method in [6] for use with RT 5880, which has a dielectric constant of 2.2 and a height 1.574 mm. Simulated results are shown in Figs.…”

“…A recent circuit topology proposed by the authors has shown that the fabrication tolerance of millimetre wave diplexer circuits can be relaxed by using a hybrid coupler/highpass filter topology in addition to a bandpass filter with full wavelength centre resonators [5,6]. The main advantage of this topology is that the number of resonators in the diplexer circuit is halved when compared with other diplexers with a similar fractional bandwidth which relaxes the circuit sensitivity to fabrication errors.…”

“…Simulated results of a bandpass filter, highpass filter and hybrid coupler are shown to demonstrate the translation process. In Section 3, the design of a Ka-band SIW diplexer based on the topology proposed in [5,6] is presented. To investigate the circuits handling of fabrication errors, simulated results of a tolerance analysis are discussed in Section 4 where changes to the via position, via diameter and dielectric constant of the substrate are considered.…”